STUDIES ON REVERSE OSMOSIS REJECT AND
179
STUDIES ON REVERSE OSMOSIS REJECT AND RECLAMATION OF RESOURCES BY NON-THERMAL EVAPORATION METHODS THESIS Submitted to the Pondicherry University in partial fulfillment of the requirements for the Award of the Degree of DOCTOR OF PHILOSOPHY IN CIVIL ENGINEERING BY S. VIRAPAN DEPARTMENT OF CIVIL ENGINEERING PONDICHERRY ENGINEERING COLLEGE PUDUCHERRY – 605 014 INDIA MAY 2016
Transcript of STUDIES ON REVERSE OSMOSIS REJECT AND
STUDIES ON REVERSE OSMOSIS REJECT AND
RECLAMATION OF RESOURCES BY
NON-THERMAL EVAPORATION METHODS
THESIS
Submitted to the Pondicherry University in partial fulfillment
of the requirements for the Award of the Degree of
DOCTOR OF PHILOSOPHY
IN
CIVIL ENGINEERING
BY
S. VIRAPAN
DEPARTMENT OF CIVIL ENGINEERING
PONDICHERRY ENGINEERING COLLEGE
PUDUCHERRY – 605 014
INDIA
MAY 2016
i
DECLARATION
I hereby declare that the thesis titled “STUDIES ON REVERSE OSMOSIS
REJECT AND RECLAMATION OF RESOURCES BY NON-THERMAL
EVAPORATION METHODS” submitted to the Pondicherry University for the award
of the Degree of DOCTOR OF PHILOSOPHY in Civil Engineering, is a record of the
original research work done by me under the guidance and supervision of
Dr. R. SARAVANANE, Professor, Department of Civil Engineering, Pondicherry
Engineering College, and that the work has not been submitted either in whole or in part
for any other Degree / Diploma / Certificate or any other title by any University /
Institution before.
(S. VIRAPAN)
Place: Puducherry -14
Date : 25-04–2016
ii
CERTIFICATE
This is to certify that Mr. S VIRAPAN has single-handedly carried out the work
embodied in this Thesis “STUDIES ON REVERSE OSMOSIS REJECT AND
RECLAMATION OF RESOURCES BY NON-THERMAL EVAPORATION
METHODS”, being submitted for the award of the Degree of DOCTOR OF
PHILOSOPHY in Civil Engineering of the Pondicherry University. He has complied
with all the relevant academic and administrative regulations of the University and that
this Thesis embodies a bonafide record of an independent work done by him, under my
supervision. This work is original and has not been submitted for the award of any other
Degree / Diploma / Certificate of this or any other University.
(Dr. R. SARAVANANE)
Research Guide / Thesis Supervisor
Place: Pondicherry -14
Date : 25-04-2016
iii
ACKNOWLEDGEMENT
I would like to express my deep and sincere gratitude to my Research Guide,
Dr. R. Saravanane, Professor, Department of Civil Engineering, Pondicherry Engineering
College (PEC), Pondicherry, India, for his excellent guidance and whole hearted involvement
during my research work. His understanding, encouragement and personal guidance have all
contributed to the present form of the Thesis.
I am deeply grateful to Dr. M.S. Pandian, Professor and Head, Department of Earth Science,
Pondicherry University, Pondicherry, and a member of the Doctoral Committee, for his
constructive comments, and support throughout the period of this work.
I specially thank Dr. M.A Sivasankaran, Professor, Department of Civil Engineering, PEC,
Pondicherry, and a member of the Doctoral Committee, for his constant involvement in making
my research work more significant by providing constructive suggestions during the entire period
of research work, as well as during the preparation of this Thesis.
It is a great pleasure to convey my special thanks to Dr. T. Sundararajan, Principal, PEC,
Pondicherry, for providing necessary help, facilities and constant encouragement for the
successful completion of the research work.
I am also thankful to Dr. D. Govindarajulu, (Retired) Principal, PEC, Pondicherry,
Dr. G. Gerald Moses, Professor and Head of Civil Engineering, Dr. S. Kothandaraman,
Professor of Civil Engineering Department, Dr. S. Sivamurthy Reddy, Professor of Civil
Engineering, Dr. V. L.Narasimha, Professor of Civil Engineering for their moral support and
encouragement during the period of this research work.
I remain grateful to Dr. V. Murugaiyan, Professor, Department of Civil Engineering, PEC,
Pondicherry for his spontaneous support at all times.
iv
It is my pleasure and duty to thank all the Faculty members, supporting staff of Civil Engineering
Department, Library staff PEC, Pondicherry, for their help in the Literature review and web
Research and acquiring data.
It gives me immense pleasure to thank my office top management Mr. S.N Subrahmanyan,
Deputy Managing Director and President, Larsen and Toubro Construction, Mr. M V Satish,
Mr. K Kannan, Mr. Niranjan Simha and my Colleagues Chennai for their encouragement,
motivation in formulating the discussions and successful completion of my research work.
My grateful appreciations to Dr S Sundaramoorthy, former Technical Expert to Urban
Sanitation Sub-committee of Lok Sabha and Dr. S Saktheeswaran, Member, National Project
Management Unit, Swachh Bharat Mission, Government Of India and co-coordinator for
Tamilnadu state for their motivation, spontaneous responses and sharing the national outlook.
I extend my special thanks to the managements and staff of M/s Suntex Processing Mills,
Chennai and Jaipur Integrated Textile Park, Rajasthan for giving me permission for carrying
out research study and also extending their lab for testing purpose.
I record my appreciation to my wife Mrs. R Sudha, my daughter Ms. V Yogalakshmi, son
Mr. V Surendran Bala and Parents for patiently putting up with my thesis efforts throughout
the period of completion of project.
Finally, I owe my deepest gratitude to the Almighty who provided me with all the required help,
strength and perseverance to carry on with the work, even, when the going got tough. To Him
this is reverentially dedicated.
S. Virapan
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ABSTRACT
Zero liquid discharge (ZLD) of industrial wastewaters has become the order of the day in the war
against pollution and resurrection of contaminated environment. The reverse osmosis (RO) has
come to stay as the technology of choice in recovering the water as a useable resource in ZLD
practice. But the fact remains that the RO rejects (ROR) are typically concentrated in their
dissolved solids (TDS) and its ingress into the environment endangers the aquatic sources almost
irretrievably in terms of sustainable practices and costs of remediation. Literature survey of
studies spread across India varying from food processing, pulp and paper, pharmaceuticals,
textiles, tanneries, electroplating etc brings forth the position that none of these are able to
maintain a concordant ZLD and its observance is more in breach than concordant compliance.
A day may be reached where such a sink will reach a stage where even the RO technology will
be inadequate due to the higher and higher concentrated ions in the waters. This may even
forebode a desertification. Set in this background, there is a need to study, evaluate and validate
sustainable nature based evaporation systems especially for the many small scale industries who
cannot afford a thermal evaporator in the first place. The ZLD project in the common effluent
treatment plants (CETPs) of Tiruppur India, once the world’s capital in knitwear exports is the
glaring example. Launched with public money and great expectations way back in 2005 under a
court directive for a total of 100 million liters daily (MLD) of textile wastewaters it is now
curtailed to only about 30 % and the production as well because a sustainable technology for
ROR eludes and the aquatic environment is already irretrievably demolished as in Photoplate-1.
Similar is the fate of the Palar River in India for over 130 km where many tannery CETPs are
also suffering the same fate. The drinking water schemes originally provided with this river as the
source have also been curtailed or wound up due to salt ingression. The real difficulty in the
induced thermal evaporation systems & recourse to steam boilers, thermal evaporators, spalled
calendria tubes, odour strippers etc which are high cost installations as hereunder and beyond the
technical and economic sustainability. Arising from this situation, this thesis demonstrates the
sustainability and viability of nature based net evaporator systems in two identified wastewater
streams one for textile spent dye bath with salt concentration at about 1.5 times of seawater
and the other for ROR from a textile common effluent treatment plant (CETP).
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The study validates a design for these newer systems by a scientific application of phase transfer
in natural falling film wetted surfaces and minimizes electrical energy.
The Schematic of the validated evaporator is shown in photoplate-1. The high TDS wastewater is
pumped up from the receiving sump and is diffused on top of the falling film evaporator nettings
and undergoes a three phase mass transfer in its trickling down on the faces of the nettings. The
concentration in the sump keeps increasing to a value where the facility is switched to the spare
which has undergone maintenance and the one taken out is put through maintenance when the
salt is solar dried in-situ and carted away to designated landfill. During rainy periods temporary
sheeting is put over the evaporator using interim adhoc support dismountable frames.
The novel features of the validated system are found to be as under:
1. Eliminates steam generators as induced thermal evaporative operation
2. Eliminates complicated mechanical and electrical infrastructure
3. Eliminates metal scaling and corrosion problems
4. Eliminates dependence on specialist trained high-skill operators
5. Eliminates dependence of vendors for equipment repairs and renewals
6. Eliminates back up high energy diesel generator sets
7. Eliminates need to keep the set-up “warm” even during “no-Reject” periods
8. Eliminates O&M costs as close to about INR 200 / kiloliter of R O Rejects
9. Eliminates random specifications as there is no BIS code of practice
10. Completely nature based system with phase transfer
11. Permits switch-on and switch-off as and when needed
12. System uses only an ordinary centrifugal foot mounted pump set
13. The nettings are readily available off the shelf green-house nettings
14. Efficiency can be maximized using spray nozzles for application on nettings
15. Rainy days also bring about evaporation and does not need shut down
16. Temporary roofing using tarpaulins over truss work protects from direct rainfall
17. O&M cost is a maximum of INR of only about Rs 15 / kiloliter of RO Rejects
18. System can be fabricated by locally available masons and fabricators
19. Permits preventive maintenance by removing and re-erecting the nettings easily
20. Above all can be locally designed, built and operated even in remote locations
21. A mathematical model for evaporation index has been developed for this evaporator.
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The Tragedy at Tiruppur. From left- The impoundment once upon a time, the polluting
discharge into one of the water courses, the stagnant pollution in summer month, the
concentrated water spread, the withered trees.
Existing RO Reject handling equipments. From left-Steam boilers and chimney, multiple effect
evaporators, spalled callendrias, mechanical vapour compressors, odour strippers
Receiving Sump with
forward mixing
Net Evaporator as wind aided falling film
evaporation and bottom slurry solar-dried in
summer as in-situ- (In standby for maintenance)
Net Evaporator as wind aided falling film
evaporation and bottom slurry solar-dried in
summer as in-situ- (In active operation)
in operation
Sec
ure
Lan
dfi
ll Pumped Recirculation
Pumped Recirculation
Schematic of the Developed, Demonstrated and Design Validated Alternative System
Photoplate-1. Figurative Depiction of the Existing Challenged Systems, the Schematic of the
now Developed and Design Validated Sustainable System with its Figurative Depictions
The Validated Installations of Nature Based Evaporators in this study. The RO Reject
installation is at left and spent dye bath installation is at right.
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TABLE OF CONTENTS
Page No.
Declaration i
Certificate ii
Acknowledgement iii
Abstract v
Table of Contents viii
List of Tables xiv
List of Figures xvi
List of Abbreviations xx
CHAPTER 1 INTRODUCTION
1.1 General 1
1.2 Specific Technologies in Vougue for ROR 1
1.3 The Indian Scenario 5
1.3.1 The Tiruppur Merry Go Around 6
1.3.2 The River Palar Deterioration 7
1.4 Challenges of Design of ROR Thermal Evaporator 7
1.5 Need for the Study 8
1.6 Objective of the Study 9
1.7 Organisation of the Thesis 10
CHAPTER 2 LITERATURE REVIEW
2.1 Desalination Technologies and Applications 15
2.2 Thermal Processes 17
2.3 Multiple-Effect Distillation 17
2.4 Multi-Stage Flash Distillation 18
2.5 Vapour Compression 19
2.6 Membrane Processes 20
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2.6.1 Basic Principle of Osmosis 21
2.6.2 Reverse Osmosis 22
2.6.2.1 Basic Principle of RO 22
2.6.3 Electrodialysis 24
2.7 The Preferences for RO 25
2.8 Reject from RO 28
2.9 Possibilities for Processing of ROR 28
2.10 Salt Ingress into Environment by ROR 30
2.11 The Limitations in the Water Act of India 30
2.12 State Of Discharge of ROR in to the Sea in Israel 30
2.13 The Red Tide Blooms in the Gulf Of Oman 31
2.14 Characterization of Pollutants from ROR 31
2.15 ZLD in Industrial Wastewater Management 31
2. 16 Closure of Textile Dyeing Industries in a Textile Town 32
2.17 The Madras Fertilizers and Refineries Experiences 32
2.18 The Experiences of GMR, New Delhi and Mumbai Airports 33
2.19 The Bangalore Indirect Water Augmentation 33
2.20 Major Issues in Sewage ROR 33
2.21 RO Reject Reuse for Salt Recovery in Tanneries 34
2.22 Evaporation of ROR and soak liquor in tanneries 35
2.23 Solar pans and spray ponds for evaporating ROR 35
2.23.1 Integrated Systems with Spray Ponds and
Salt Recovery from ROR 36
2.23.2 The Heat Sink Spray System 36
2.24 Direct Spray Nozzle Systems for RO Rejects 37
2.25 Rotary Atomized Spray Evaporators 38
2.26 The Mixed Oxidant Technology 38
2.27 The German Gladierwerkwoodstack 39
2.28 The Packed Bed Falling Film Technology 40
2.29 The Wind Assisted Intensified Evaporation Technology 41
2.30 Generation of Mixed Oxidants from ROR 43
x
2.31 Thermal Evaporation of RO Rejects 44
2.31.1 Thermal Vapour Compression 44
2.32 Calendria Problems 45
2.33 The Hadwaco Evaporator 45
2.34 The Elusiveness of Evaporator Issues in ROR 46
2.35 The Infirmities in Adopting Thermal Evaporators 46
2.35.1 Heterogonous Characteristics of ROR 46
2.36 Fouling of RO Membranes 47
2.37 Membrane Fouling Categories 48
2.38 Control Over Fouling of Membranes 49
2.39 Removal of Silica, Ca & Mg to Control Scaling 50
2.40 Silica Removal by Precipitation 50
2.40.1 Silica Removal by E Cells 51
2.41 Precipitation of Heavy Metals 52
2.42 Removal of Ca and Mg 53
2.43 Validating RO Feed Quality For Ionic Balance 53
2.44 Arriving At A Monomolecular Nacl in ROR 53
2.44.1 Driving the Cations to Monovalent NaCl 53
2.45 Classification of Membranes 54
2.45.1 Physical Morphology 54
2.46 Membrane Geometry 54
2.47 Membrane Characteristics 55
2.48 MF Membrane Operation Modes 56
2.49 RO Membrane Process 56
2.50 Characteristics of ROR 57
2.51 Studies on RO Management Techniques 59
2.51.1 Existing ROR Minimization & Management Methods 59
2.51.2 Surface Water Discharge 59
2.51.3 Sewer Discharge 59
2.51.4 Deep Well Injection 59
2.51.5 Evaporation Ponds 60
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2.51.6 Land Application 60
2.52 ZLD and near ZLD 60
2.53 Emerging ROR Minimization & Management Methods 61
2.53.1 Two-Phase Reverse Osmosis with Intermediate
Chemical Precipitation 62
2.53.2 Two-Phase Reverse Osmosis with Intermediate
Biological Reduction 62
2.53.3 RO with Softening Pretreatment and High pH Operation 63
2.53.4 Two-Pass Nano filtration 64
2.53.5 Seeded Slurry Precipitation and Recycle 65
2.53.6 Membrane Distillation 65
2.53.7 Capacitive Deionization 67
2.53.8 Dewvaporation 67
2.53.9 Forward Osmosis 68
2.53.10 Overview 70
2.54 RO for Separation of Organic Pollutants 71
2.55 RO Treatment of Industrial Wastewater 74
2.55.1 Electroplating and Metal-Finishing Process Wastewaters 74
2.56 Pulp and paper processing wastewaters 76
2.57 Food processing wastewaters 77
2.58 Radioactive processing wastewaters 78
2.59 RO Treatment of other wastewaters 78
2.60 RO Treatment of contaminated waters 79
2.60.1 Leachates 79
2.60.2 Contaminated Drinking Water 80
2.60.3 Municipal Wastewater 81
2.61 Unconventional Recent Efforts 82
2.61.1 Net Evaporator for Textile Spent Dye bath 82
2.61.2 Net Evaporator for ROR from a Textile CETP in ZLD Mode 82
2.62 Case study of thermal evaporators for ROR 83
2.63 Observations from literature review 85
xii
CHAPTER 3 EXPERIMENTAL SETUP AND METHODOLOGY
3.1 The Magnitude of the ROR Problem 89
3.2 Studies on Net Evaporator for Textile Dye Bath 89
3.2.1 The Method of Testing 92
3.2.2 Results of Testing of the Evaporator 93
3.2.3 Observations 98
3.2.3.1 Dye Bath Evaporated in Excess of Daily
Added Volume 98
3.2.3.2 Dual Use Potential for both Chlorides and Sulphates 98
3.2.3.3 Evaporation Index (EI) 98
3.2.3.4 Packing Density 98
3.2.3.5 Cost Considerations in O&M 98
3.2.3.6 Pointer 98
3.3 Studies on Net Evaporator for ROR of Textile CETP 99
3.3.1 The Method of Testing 99
3.3.2 The Results 100
3.3.3 Observations 101
3.4 Comparison of Attributes of the Two Systems 101
3.5 Variables to be evaluated in the system 102
3.6 Approach for testing and interpretation of results 104
3.7 The Experimental Pilot Plant 105
3.8 The Testing Protocol 109
3.9 The Methodology 109
CHAPTER 4 RESULTS AND DISCUSSIONS
4.1 The Approach 110
4.2 The Results of the Textile CETP ROR Net Evaporator 110
4.2.1 Time of Occurrence and the Resulting TDS 111
4.3 The Results of the Spent Dye Bath Net Evaporator 114
4.4 The Choice of Samples for Testing 116
4.5 The Experimental Pilot Test Results 117
4.6 Pilot testing Results for other dye baths and RORs 127
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CHAPTER 5 SUMMARY AND CONCLUSIONS
5.1 Genesis 129
5.2 The Study 129
5.3 Findings of the Study 130
5.4 Significance of the Findings 130
5.5 Specific Advantages of the Findings 131
5.6 Salient Conclusions 132
REFERENCES 133
APPENDIX A 148
APPENDIX B 151
LIST OF PUBLICATIONS 154
VITAE 156
xiv
LIST OF TABLES
Sl
No. Titles Page
1.1 Overview of investigations carried out on the RO reject study 14
2.1 Installed desalination capacity 16
2.2 Advantages and Disadvantages of Desalination Technologies 26
2.3 Applications of Reverse Osmosis 27
2.4 Overview Of Reuse, Further Treatment, and Discharge of ROR 29
2.5 Comparison of ceramic and polymeric membrane properties 55
2.6 Characteristics of ROR 58
2.7 Detail of products from treatment of reject brine 61
2.8 Electrical Power Consumption in ZLD Encompassing the Thermal 84
2.9 Operation and Maintenance (O&M) Cost in INR / cum of Feed 84
2.10 Split up of Costs per Kl for Each Section 84
3.1 TDS in feed, RO permeate and ROR in selected user categories 90
3.2 Observations on the net evaporator system for six consecutive days 93
3.3 Results of test of net evaporator for textile spent dye bath 94
3.4 Inferred findings from results of net evaporator for textile spent dye bath 99
3.5 Results observed during the on-field study on batch operation 100
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3.6 Attributes and performances of the two net evaporator systems 101
4.1 Continuous hours of run and TDS in the circulation sump for dye bath 110
4.2 Typical mean sunshine hours at Jaipur for the study month 111
4.3 Continuous hours of run and EC in the circulation sump for ROS 114
4.4 Results of tests on textile black spent dye bath on pilot net evaporator 118
4.5 The cause-effect relationship of the pilot test results for flux of 0.19 122
4.6 The cause-effect relationship of the pilot test results for flux of 0.26 123
4.7 The cause-effect relationship of the pilot test results for flux of 0.44 124
4.8 Effect of flux on evaporation index in the pilot testing 126
4.9 Gist of results of other samples put through pilot experiments 127
xvi
LIST OF FIGURES
Sl
No. Title Page
1.1 Illustration of steps to achieve ZLD or near ZLD of ROR 3
1.2 Depiction of forces acting on infrastructure assets and their impacts 9
2.1 Industrial desalination processes 17
2.2 Multi-effect evaporator desalination process 18
2.3 Multi-stage flash desalination process 19
2.4 Single stage mechanical vapor compression desalination process 20
2.5 Schematic of Simplified Osmosis 21
2.6 Block diagram of reverse osmosis operations 22
2.7 Simple Reverse Osmosis 23
2.8 Schematic diagram of electro dialysis desalination process. 25
2.9 The Salt Recovery from RO Rejects In Tanneries 34
2.10 Distribution Channel and Flat Plate Collector 35
2.11 The Sprinkler 35
2.12 Oriented Spray Cooling System of M/S CBA 37
2.13 The recirculating pump, the piping and nozzles in a spry pond 37
2.14 The spray pond in operation with uncontained wind age 37
2.15 Rotary atomized spray evaporators 38
xvii
2.16 Mixed Oxidants Technology and resulting end products 39
2.17 The German Gladierwerk Woodstack 40
2.18 Non Clogging Pall rings for sulphate salts crystallization 40
2.19 Recovery of crystalline sulphates from salt solutions by WAIV system 41
2.20 Performance Indicators of the WAIV system 42
2.21 The schematic of the MIOX System 43
2.22 Products of Multi-Oxidants from the MIOX system 43
2.23 Schematic of thermal vapour compression 44
2.24 Internal scaling and spalling in calendria tubes of thermal evaporators 45
2.25 Schematic of the multiple vapor compressor 45
2.26 The Hadwaco evaporator with hanging Drapes 46
2.27 Mechanisms of physico-chemical fouling in RO membranes 47
2.28 Integral occurrences of reversible and irreversible fouling 48
2.29 Schematic diagram for In-line coagulation/ultra filtration process 50
2.30 pH values of least solubility of metals in aqueous solution 52
2.31 Spiral wound RO membrane module 57
2.32 The netting drapes and distribution pipings at the textile net evaporator 82
2.33 Bird’s eye View of the CETP and the WAIV inspired system for ROR 83
xviii
2.34 Mechanical vapour recompressor installation 83
2.35 Falling film and forced circulation evaporator installation 83
2.36 Range of TDS in identified industrial wastewater segment 87
2.37 Range of TDS in identified domestic and public water segment 87
3.1 The author amidst the textile net evaporator and in the laboratory 89
3.2 Schematic of the net evaporation system operating sequence 92
3.3 View of the Net Evaporator at textile ZLD CETP at Jaipur India 99
3.4 Variation of evaporation index with arising TDS in the net evaporator 100
3.5 Simplified schematic of evaporation from water bodies 102
3.6 The experimental pilot plant for testing under various ranges of RORs 106
3.7 The drape nettings and distributor grid of the experimental pilot plant 107
3.8 The testing protocols with coloured spent dye baths and high TDS ROR 108
4.1 Buildup of TDS in circulation sump in the 24 hr mode 112
4.2 TDS buildup gradient with time of occurrence and arising TDS 113
4.3 Variation of monthly average solar radiation in kwhr/sqm/day at Jaipur 113
4.4 Variation of wind speed in m / sec at Jaipur 114
4.5 Buildup of EC with rising EC for the textile spent dye bath net
evaporator 115
4.6 Typical Chennai solar insolation 116
xix
4.7 Typical structure of the reactive group of modern dyes 119
4.8 Fluxmass Vs fluid depth in sump for a flux of 0.19 lpm/min/sqm 122
4.9 Fluxmass Vs fluid depth in sump for a flux of 0.26 lpm/min/sqm 123
4.10 Fluxmass Vs Fluid Depth in sump for a flux of 0.44 lpm/min/sqm 124
4.11 Variation of applied flux and resulting percent evaporation 125
4.12 The perfect distribution in the pilot plant and inadequacies in prototypes 126
xx
LIST OF ABBREVIATIONS
AWWA American Water Works Association
BAT Best Available Technology
BOD Biochemical Oxygen Demand
BWRO Brackish Water Reverse Osmosis
CA Cellulose Acetate
CBA Chuck Bowman Associates
CDI Capacitive Deionization
CDT Capacitive Deionization Technology
CETP Common Effluent Treatment Plant
CLRI Central Leather Research Institute
COD Chemical oxygen demand
CSMP Continuous System Modelling Programme
CTE Consent to Establish
CTO Consent to Operate
CUM/HR Cubic meter per hour
DAF Dissolved Air Floatation
DC Direct Current
DEG C Degree Centigrade
DOC Direct Osmotic Concentration
DWI Drinking Water Inspectorate
ED Electro Dialysis
EDM Electro Dialysis metathesis
EDR Electro Dialysis Reversal
EDTA Ethylenediaminetetraacetic Acid
EI Evaporation Index
ETP Effluent Treatment Plant
FO Forward Osmosis
GPCB Gujarat Pollution Control Board
GTZ German Agency for Technical Co-operation
xxi
HERO High Efficiency Reverse Osmosis
IDA International Desalination Association
IL&FS Infrastructure Leasing & Financial Services
LERIG Leather Research Industry Get together
MD Membrane Distillation
MED Multiple Effect Distillation
MEDRC Middle East Desalination Research Center
MEE Multiple Effect Evaporator
MF Micro Filtration
MGD Millions Gallons Day
MIOX Mixed Oxidants
MLD Million Litres Daily
MSF Multi Stage Flash
MVC Mechanical Vapour Compression
MVR Mechanical Vapor Recompression
NF Nano Filtration
NOM Natural Organic Matters
NPDES National Pollutant Discharge Elimination System
O&M Operation and Maintenance
OSCS Oriented Spray Cooling System
PA Polyamide
PCBs Pollution Control Boards
pH Potential Hydrogen
PIL Public Interest Litigation
RO Reverse Osmosis
ROR Reverse Osmosis Rejects
RSETM Rear screen Enclosure
SLL Superficial Lipid Layer
SP Salt Passage
STP Sewage Treatment Plant
SWRO Sea Water Reverse Osmosis
xxii
TDS Total Dissolved Solids
THM Trihalomethanes
THMFP Trihalomethanes Formation Potential
TOC Total Organic Carbon
UF Ultra Filtration
UNIDO United Nations Industrial Development Organization
VC Vapour Compression
WAIV Wind Assisted Intensive Evaporation
ZLD Zero Liquid Discharge
1
CHAPTER - 1
INTRODUCTION
1.1 GENERAL
In the present scenario, the availability of readily useable fresh water sources for potable
needs is fast shrinking especially in the Asia-Pacific, Latin American. Middle East and
some coastal settings of European Union. It is reported that over a billion people are
without it and approximately 2.3 billion people live in these regions with such water
shortages (Services, 2006). In order to meet these shortages exploitation of ground water
and seawaters is resorted to with of course the need for desalination mainly by Reverse
Osmosis (R O) technology. (Greenlee et al., 2009; Peñate and Garcia, 2012). The major
challenges are the relatively high electrical power needs and environmentally compliant
disposal of the R O rejects (ROR) with concentrated salts. The power needs are usually
met up by appropriate Government policies. However, the later challenge chokes the
inland RO plants (Oren et al., 2010). Similar is the story for inland water based industries
like tanneries and textiles which are challenged by restricted extraction of ground water
and also the disposal of ROR and these are unable to grow.
The disposal options for ROR are (i) surface water discharge (ii) deep well injection
(iii) evaporation ponds and (iv) land application (AWWA, 2004) and each is site specific
based on the quantity and concentration of the dissolved solids (TDS). With regard to
disposal through surface water, the options available are (i) discharge to rivers, (ii) bays,
(iii) tidal lakes, (iv) brackish canals or oceans. Blending of high TDS and low TDS ROR
are attempted but not always successful. Deep-well injection and evaporation ponds are
restricted to desert areas for small flows of ROR and regions having a relatively warm,
dry climate with high evaporation rates, level terrain and low land costs (AWWA, 2004;
Oren et al., 2010) and does not help habitations and industries.
1.2 SPECIFIC TECHNOLOGIES IN VOUGUE FOR ROR
In order to reduce the volume of ROR several zero liquid discharge (ZLD) technologies
have been and are continued to be developed. But then, the smaller the volume, the TDS
becomes higher and this poses the challenge in technology.
2
Van der Bruggen et al.(2003) reviewed different system configurations for reuse,
treatment and discharge of concentrate including treatment of concentrate from Nano
filtration (NF) and RO processes. Pérez-González et al., (2012) reviewed various types of
concentrate volume minimization approaches limited to treatment of ROR in municipal
and wastewater treatment with limited focus on system configurations.
For ROR from municipal wastewater treatment plants, in addition to TDS, the total
organic carbon (TOC) concentrations are also found to be high (>30 mg/L) (Lee, 2009).
It was found that the salt content (chloride and sulfate) and silica concentrations are lower
in ROR from municipal wastewater compared to ROR from groundwater treatment plants
(Lee, 2009). It was interesting to note that the ROR from industrial wastewaters contain
TOC of even up to 60 mg/L and silica up to 250 mg/L. (Subramani et al., 2011).
The selection of the best available technology (BAT) for further treatment of ROR
concentrate to achieve a true ZLD thus depends on several parameters and technologies
as presented in Fig. 1.
It seems to achieve a near ZLD with membrane-based and thermal-based technologies or
a combination of both (Pérez-González et al., 2012). It is essential to know the
pretreatment requirements to employ a particular technology.
For the case of membrane or thermal technology, the pre-requirements are (i) the removal
of scale forming ions and organics, (ii) the conditioning of the water to prevent fouling
and (iii) foaming (Perez et al.2012).
It appears that membrane-based technologies or thermal-based technologies will have to
be preferred, but then, the pre-treatment and conditioning technologies are again a
compounding challenge with their own quota of uncertainties and complexities.
3
Fig. 1.1 Illustration of steps to achieve ZLD or near ZLD of ROR
Membrane-based technologies are based on mechanism of separation as pressure driven
membranes and electric potential driven membranes (Greenlee, 2009).
In the pressure driven membranes, scaling precursors (Calcium, Barium and Silica) are
typically removed from the first stage ROR as precipitated sludge solids using chemical
precipitation techniques followed by a second stage ROR system (Bond and Veerapaneni,
2007; Tarquin, 2005; Gabelich, 2007; Gabelich, 2010).
4
It is also found that this type of treatment results in an overall feed water recovery greater
than 95% and a near ZLD is achievable when the final concentrate from the secondary
ROR is further treated with thermal technologies (Sethi, 2009). Numerous methods are
available for the removal of scaling precursors from the primary ROR such as
o Intermediate chemical softening
o Pellet reactors
o Electrocoagulation
o Intermediate biological reduction
o High efficiency RO
o Advanced reject recovery of water
o Seeded slurry precipitation and recycle
o Disc tube filtration
o Oxidation-based technologies
In the electrical potential-driven membranes technologies as Electro Dialysis (ED),
Electro Dialysis reversal (EDR) and Electro Dialysis metathesis (EDM) are in practice.
These use an electrical potential to attract the ions through ion-exchange membranes that
are virtually impermeable to water and desalination occurs by the movement of anions
and cations, without the water molecules, across the membrane (Malmrose et al., 2004).
Thermal-based technologies are also employed for ROR and are termed as mechanical
evaporators to vaporize and condense the water component and resulting in salts as a wet
sludge. (Lozier et al., 2007). These are vertical tube falling film brine concentrator
followed by a forced-circulation crystallizer (Lozier et al., 2007). These are known to be
energy intensive (Greenlee, 2009), maximizing the heat energy imparted to ROR by
multi-effect and vapor recompression systems, which consume relatively lesser energy.
A combination of membrane-based and thermal-based system is found to yield good
results in a hybrid configuration up to 99% feed water recovery and usually the outfit is a
combination of the following.
5
Multi-effect distillation and mechanical vapor compression
Brine concentrators and crystallizers
Wind-aided intensified evaporation
Spray dryers
In the recent past, several emerging technologies such as (i) Forward osmosis
(ii) Membrane distillation (iii) Thermo ionic processes and (iv) Eutectic freeze
crystallization are also being attempted but are yet to be perfected even for freshwater.
1.3 THE INDIAN SCENARIO
Historically, the Indian pollution control boards (PCBs) used to permit discharge
industrial wastewaters into inland surface waters or land for irrigation if the TDS is less
than 2100 mg/L and other parameters are met. However, this was recast to ZLD
subsequently. Invariably, the useable TDS of water in industry at the point of drawal is
itself more than the desired TDS of 500 mg/L and here itself starts the challenge of RO
rejects. This situation compounds further in the eventual wastewater and the TDS is
ranges from 5000 to even as high as even 15,000. This has necessitated a treatment for
the removal of (a) the organic pollutants and (b) the TDS as a second step. It is the
challenges of (b) that are now ending up into disposal of the rejects containing much
higher TDS. A literature survey of case studies spread across food processing to pulp and
paper to pharmaceutical to textiles, tanneries, electroplating industries as presented in
Table 1-1 and brings forth the position that none of these are able to maintain a
concordant ZLD and its observance in more in breach than practice.
The technology promulgated by PCBs is thermal evaporation and secure landfill of solid
residue which is prohibitively costly in capital and Operation and Maintenance (O&M).
In all reality, its practice the compliance by industries continues more in intermittent
breach than concordant compliance. The compulsion to go in for boilers, crystallizers etc
are impractical for small and medium scale industries in which they have neither the
human resources nor the money power.
6
All these point to the need for a simpler system. Besides, a sound theoretical design basis
is defied in these processes because of the dynamic change in mass balance throughout
the operation leading to the development of such sophisticated programmes like the
continuous system modelling programme (CSMP) which is non-viable in many industries
and is inherently a deterrent which of late has brought about migration of the well to do
segment of industrialists migrating out to nearby Asian countries where there TDS
limitation in discharge is not enforced due to abundance of water ways draining to sea.
The Infrastructure Leasing & Financial Services Limited, India (IL&FS), Washington
University and the Gujarat Pollution Control Board (GPCB) recently organized a two-day
series of talks on ZLD for industry representatives, policy makers, consultants and
regulators. The secretary of GPCB observed that "If an industry applies a combination of
ZLD technologies, both thermal and electrical, cost of ZLD can be brought down
significantly. In the second phase of the programme, we will be taking this challenge to
our engineering colleges, where students will be encouraged to pursue such research,"
He further observed that though there are RO, multiple effect evaporators, crystallization,
solvent stripping are available, still a cheaper alternative can be engineered and tailor-
made for industries producing a given type of product and specific concentration of salts.
1.3.1 THE TIRUPPUR MERRY GO AROUND
In the textile knitwear manufacturing city of Tiruppur, India, the ZLD project in their
CETPs discharging a total of nearly 100 million liters daily (MLD) of textile wastewaters
with constantly varying colour, TDS and flow was propelled by a judicial directive and
launched with great expectations way back in 2005. Evan after 11 years, there is no such
thing as a ZLD happening and the net result is these CETPs have been barred from
exceeding 30 % of their original sanctioned production. This is a classical case of idle
infrastructure and inappropriate use of taxpayers’ money as the CETPs were set up using
the said taxpayers’ money. The first part of biological and chemical treatment is
streamlined but the RO per se and rejects in particular which are yet to find the reality.
7
Initially the CETPs proposed purification of the RO rejects by precipitating the Calcium
and Magnesium /thereby obtaining a relatively concentrated solution of Sodium, which is
practically the dye bath, and thereby, this recovered water could be filtered out and taken
back to the member industries and reused as salt solution. The only residue is Ca and Mg
salts and this could be disposed at a secure landfill. The surplus salt solution if any was
proposed to be put through spray ponds considering the dry climate of Tiruppur. But
then, the PCB flatly rejected all these and insisted that a thermal evaporator alone should
be used. All the same, while transacting the order for this evaporator, the insistence by
the vendor had been that the member industries must use Sodium Sulphate and not
Sodium Chloride and the members of CETPs inadvertently conceded to this demand,
without anticipating the implications this would have on their production economics. But
even now, most members continue to use Sodium Chloride and the result is conflicts
between the evaporator vendor and the CETPs on the issue of the said evaporators not
fully meeting the promised levels of performance. The Sodium sulphate can be
crystallized by lowering the temperature of RO rejects with a chiller than raising the
temperature by steam and putting into evaporators. The net result is the compulsion to
discharge as and when the RO rejects build up to quantities which cannot be dealt within
the evaporators as of now, and the equipment as installed and commissioned is running
into contentious issues. It is all a merry go round with no end in sight.
1.3.2 THE RIVER PALAR DETERIORATION
Similar is the fate of the Palar river course for over 130 km in south India. There are
many tannery CETPs along this reach which are also suffering the same fate. The
drinking water schemes originally provided with this river as the source have also been
curtailed or wound up.
1.4 CHALLENGES OF DESIGN OF ROR THERMAL EVAPORATOR
This encompasses variables as the viscosity, rugosity, temperature, TDS, gases, heat
transfer co-efficient of the heat exchanger surfaces and the non-steady state of their inter-
alia equilibria. The TDS in the feed gets increased with vaporization and whatever mass
transfer kinetics are to be applied incurs a dynamic change.
8
This defies a theoretically verifiable design equation further compounded by variable and
intermittent flow rates. If these evaporator systems are to be operated in a batch mode,
that at least will permit a design basis but in actual practice, the multiple effect
vaporization evaporators which uses the waste heat of the upstream vapour is the
preferred choice in the field and hence, the batch operation gets ruled out. Perhaps the
fairly comprehensive design approach and material specifications are contained in the
design manual compiled by the Middle East Desalination Research Center (MEDRC) at
Oman but that again is for a fairly steady state system of seawater RO and clearly is not
applicable to the wastewater systems of the present context. It is logical not to pursue this
approach because whatever is developed for a given wastewater will not be applicable to
the other system due to inherent changes of the parameters listed out ante.
1.5 NEED FOR THE STUDY
There are alternative systems which have been in use on an ad-hoc basis. These are spray
ponds and wind aided falling film drapes using fabrics suspended into the ambient. These
have not been evaluated for their scientific performance kinetics and efficiencies vis a vis
sizes and number of the drapes. Considering the status of the present problem of thermal
systems and the compliance to ZLD being observed more in its intermittent breach, there
is a compelling need to at least establish the technicalities of these ad-hoc systems. The
spray ponds are not environment friendly due to wind age carryover of the applied
wastewater sprays to downwind leeward habitations.
This leaves the falling film drapes as the only worthwhile process for sustainable use in
the wastewater systems. In actual practice, the pollution control legislation in India has a
procedure of Consent to Establish (CTE) and Consent to Operate (CTO) and Application
for Altered Discharge (AAD). The CTE is at the project formulation stage and requires
the applicant industry to detail the proposed facility of wastewater ZLD in all its physical
dimensions, electrical power etc. The CTE is at the commissioning stage to be confirmed
by the industry that the infrastructure as per the CTO has indeed been installed on the
ground. If for some reason, the facility or its components get altered during installation,
then the AAD has to be applied prior to CTO stating the need for and changes made.
9
The classical quandary is the design details are not clear even at the CTE stage itself for
these thermal evaporator systems, much less at the AAD and CTO stages. Intertwined are
the stakeholders who have a right to know what goes on and exercise the same by way of
public interest litigations (PIL). The predicament of the stakeholders is akin to the famous
management model as in Fig. 1.2 which depicts the non-stable state of the infrastructure.
It may be seen that the creation of and sustaining the infrastructure for these evaporation
systems is squeezed from all directions by the lesser public acceptance, the higher legal
and performance requirements as people may contest in the court of law and the limiting
factor being the budget as the industry cannot go on experimenting. Hence, there is an
imminent need to experiment upon and validate an affordable dynamic system..
1.6 OBJECTIVE OF THE STUDY
The Objective of the study were:
To identify a prospective candidate technology for easier replication locally
To study the performance within the known boundary conditions
To bring out a design algorithm with variables
Fig.1.2 Depiction of forces acting on infrastructure assets and their impacts
Source: Ype C. Wijnia
10
1.7 ORGANISATION OF THE THESIS
Chapter 1 herein is Introduction; Chapter 2 is Literature Review; Chapter-3 is the
Experimental setup and Methodology; Chapter-4 is the Results and Discussions;
Chapter-5 is the Summary and Conclusions.
11
Table 1.1 Overview of investigations carried out on the RO reject study
Sl.
No Overview of Investigator
Type of Water
Waste
water
Sea
water
Saline / Brackish
water Industrial Water
Reject
Water
1 Sourirajan (1970)
2 Anderson et al. (1972)
3 Edwards and Schubert (1974)
4 Duvel and Helfgott (1975)
5 Chian et al. (1975)
6 Chian et al. (1975)
7 Fang and Chian (1976)
8 McNulty et al. (1977)
9 Chian and De Walle (1977)
10 Tsuge and Mori (1977)
11 Johnston and Lim (1978)
12 Spatz (1979) Nickel Plating
13 Glimenius (1980) Paper & Pulp Waste
14 Olsen (1980) Paper &Pulp Waste
15 Nusbaum and Riedinger (1980)
16 Sorg et al. (1980)
17 Shuckrow et al. (1981)
18 Kurihara et al. (1981)
19 Koyama et al. (1982)
20 Odegaard and Koottatep (1982)
21 Stenstrom et al. (1982)
22 Robison (1983)
23 Paulson and Spatz (1983) Paper & Pulp Waste
24 Simpson and Groves (1983) Paper & Pulp Waste
25 Terril and Neufeld (1983) blast-furnace scrubber
26 Slater et al. (1983)
12
Sl.
No Overview of Investigator
Type of Water
Waste
water
Sea
water
Saline / Brackish
water Industrial Water
Reject
Water
27 Regunathan et al. (1983)
28 Koyama et al. (1984)
29 Lynch et al. (1984)
30 Sorg and Love (1984)
31 Sourirajan& Matsuura (1985)
32 Imasu (1985) plating shops waste water
33 Thorsen (1985)
34 Jönsson and Wimmerstedt (1985) Paper & Pulp Waste
35 Hart and Squires (1985) Paper & Pulp Waste
36 Hart and Squires (1985)
37 Gekas et al. (1985)
39 Siler and Bhattacharyya (1985)
40 Rickabaugh et al. (1986)
41 Dorica et al. (1986) Paper & Pulp Waste
42 Sinisgalli and McNutt (1986)
43 Eisenberg and Middlebrooks (1986)
44 Bhattacharyya et al. (1987)
45 Davis et al. (1987)
46 Slater et al. (1987)
47 Ebra et al. (1987)
48 McCray and Ray (1987)
49 McArdle et al. (1987)
50 Baier et al. (1987)
51 Fronk (1987)
52 Taylor et al. (1987)
53 Bhattacharyya and Madadi (1988)
54 Canepa et al. (1988) Olive mill Waste
55 Anonymous (1988) Olive mill Waste
13
Sl.
No Overview of Investigator
Type of Water
Waste
water
Sea
water
Saline / Brackish
water Industrial Water
Reject
Water
56 Pusch et al. (1989)
57 Mohr et al. (1989)
58 Hsiue et al. (1989)
59 Williams et al. (1990)
60 Rautenbach and Gröschl (1990)
61 Chu et al.(1990)
62 Krug and Attard (1990) Oily Waste
63 Davis et al. (1990)
64 Kinman and Nutini (1990)
65 Cheng et al. (1991)
66 Ekengren et al. (1991) Paper & Pulp Waste
67 Stürken et al. (1991)
68 Peters (1991)
69 Bhattacharyya and Kothari (1991)
70 Lepore and Ahlert (1991)
71 Clair et al. (1991)
72 Suzuki and Minami. (1991)
73 Bhattacharyya and Williams. (1992)
74 Prabhakar et al. (1992)
75 Tan and Sudak (1992)
76 Drioli et al. (1999)
77 Masaru Kurihara et al. (2001)
78 Karabelas et al. (2001) Fertilizer waste
79 Marcucci et al. (2001) Textile effluents
80 You et al. (2001) Semiconductor industry
81 Tang, Chen (2002) Textile waste
82 Wong, et al. (2002) Paper &Pulp Waste
83 Qin et al. (2003)
14
Sl.
No Overview of Investigator
Type of Water
Waste
water
Sea
water
Saline / Brackish
water Industrial Water
Reject
Water
84 Castelblanque, Salimbeni (2004)
85 Suthanthararajan et al. (2004) Textile Waste
86 Mark Nicholson and Keith Minnich (2004)
87 Suksaroj et al. (2005) Textile Effluent
88 Pizzichini et al. (2005) Paper & Pulp Waste
89 Claudio Russo (2007)
90 Riziero Martinetti et al. (2009)
15
CHAPTER 2
LITERATURE REVIEW
2.1 DESALINATION TECHNOLOGIES AND APPLICATIONS
Almost all of the potable water required in the world today is supplied by surface water
and groundwater resources. Higher demands for potable water has led to excessive use
and thus lowered the levels of surface water and ground water availability in many areas.
Increasing population particularly in coastal regions in different countries around the
world has lowered the ground water table due to excessive pumping of ground water
causing saline intrusion in countries such as Vietnam, Bangladesh, India and Florida state
(US). Erratic weather patterns linked to global climatic changes seems to have affected
rainfall volume and pattern causing drought conditions in some parts of the world such as
Australia. The extreme shortage of potable water has made countries rethink their potable
water supply policies; for example, U SA and Australia are both considering alternatives
of potable water supply. A method exploited in many arid countries is desalination of
seawater. Seawater is freely available and exists close to coastal lands where around 39%
of the world’s population resides. Thus, seawater desalination is an attractive and logical
option as a source of public water supply.
Many countries in the Middle East, North Africa and Central Asia rely almost entirely on
desalination for their potable water needs. Indeed, it is proven technology and has helped
alleviate freshwater scarcity in the Middle East for more than 20 years. Despite the high
energy demands, capital costs and environmental concerns, desalination appears to be a
savior for low rainfall occurring countries such as Australia. Although the negative
impacts have been reported at existing plants, equally positive aspects exist in that
desalination aids and maintains industry, agricultural production, and helps preserve
existing natural water resources. The pumping of seawater causes not only coning but
also lowers close by seawater levels thus helping restrict saline intrusion into coastal
aquifers. However, environmental concerns such as emission of pollutants into the
atmosphere, noise, and pollution caused by discharge of concentrates are important
considerations and should be investigated before the desalination option is undertaken.
16
The widely applied technologies are multi-stage flash (MSF), multi-effect distillation
(MED), mechanical vapour compression (MVC) which are thermal methods involving
evaporation of the salt water which is condensed as potable grade water and leaves
behind the salt as concentrated brine. This method is mostly employed where fossil fuels
are cheaply or readily available such as in the Middle East but evaporative methods but
that is not the case elsewhere and hence RO is mostly the technology of choice.
The other lesser used ones are ED and NF. The ED is a method for desalination of sea
water or saltish waters using a main electrochemical generator that has an anode
compartment through which seawater is fed causing the formation in the solution of
chlorates and perchlorates; the removal of the latter being effected by a potassium salt
such as potassium bicarbonate. This is an electro-membrane process in which the ions are
transported through a membrane from one solution to another under the influence of an
electrical potential. The NF allows diffusion of organic compounds, and rejects some
salts with low pressures being applied and is a process normally used for mildly salt
tasting water, or as a water softening technique. The NF is a form of filtration that uses
membranes to separate different fluids or ions. NF is typically referred to as ‘‘loose’’ RO
due to its larger membrane pore structure when compared to the membranes used in RO,
and allows more salt passage through the membrane. The 1998 International Desalination
Association (IDA) directory of worldwide desalting plants showed a combined installed
desalination capacity of 22.7million m3/day as in Table 2-1.
Table 2.1 Installed desalination capacity
Sl
No.
Desalination
Method
Abbre-
viation
Inmstalled
Capacity Typical Parameters
1 Multistage
Flash MSF 44%
4000-6000 cum/day produce operating
at top brine temp. 90 to 110 deg C
2 Reverse
Osmosis RO 42% 70 to 90 % recovery
3 Electro-
dialysis ED 6% 70 to 90 % recovery
4 Multi-effect
Distillation MED 4%
2000-20000 cum/day produce operating
at lower temp.than MSF at 70 deg C
5 Vapour
Compression VC 4%
500-20000 cum/day produce operating
at temp. as low as 90 deg C
17
It showed the RO as an emerging technology at that time, but has overtaken the thermal
ever since. The further sub divisions are in Fig. 2.1 which are recounted hereunder..
Fig. 2.1 Industrial desalination processes (Maurel, 2006)
2.2 THERMAL PROCESSES
This method mimics the hydrological cycle in that salty water is heated producing water
vapor that in turn condensed to form fresh water free of salts. The fresh water is
mineralized to make it suitable for human consumption. The important factors to be
considered for this method of desalination are the proper temperature relative to its
ambient pressure and enough energy for vaporization for energy minimization and the
control of scale formation. The energy needed for vaporization is reduced usually by the
use of multiple boiling points in successive vessels, each operating at a lower temperature
and pressure, where the scale forming is controlled by controlling the top temperature of
the process or by the addition of antiscalants to the seawater. The known thermal
methods are the multi-stage flash process (MSF), multi effect distillation (MED) process
and the vapor compression (VC) distillation process.
2.3 MULTIPLE-EFFECT DISTILLATION
The multiple-effect distillation (MED) process is the oldest desalination method and is
very efficient thermodynamically. The MED process takes place in a series of
evaporators called effects, and uses the principle of reducing the ambient pressure in the
various effects. This process permits the seawater feed to undergo multiple boiling
without supplying additional heat after the first effect.
18
The seawater enters the first effect and is raised to the boiling point after being preheated
in tubes. The seawater is sprayed onto the surface of evaporator tubes to promote rapid
evaporation. The tubes are heated by externally supplied steam from a normally dual
purpose power plant. The stream is condensed on the opposite side of the tubes, and the
steam condensate is recycled to the power plant for its boiler feed water. The MED
plant’s steam economy is proportional to the number of effects and is limited by the total
temperature range available and the minimum allowable temperature difference between
the next effects. Only a portion of the seawater applied to the tubes in the first effect is
evaporated. The remaining feed water is fed to the second effect, where it is again applied
to a tube bundle. These tubes are in turn heated by the vapors created in the first effect.
This vapor is condensed to fresh water while giving up heat to evaporate a portion of the
remaining seawater feed in the next effect. This is repeated at a successively lower
pressure and temperature. A schematic diagram is shown in Fig. 2.2.
Fig. 2.2 Schematic of multi-effect evaporator desalination process.
2.4 MULTI-STAGE FLASH DISTILLATION (MFS)
In flash distillation, the water is heated under pressure, which prevents it from vaporizing
while being heated. It then passes into a separate chamber held at lower pressure, which
allows it to vaporize, but well away from heating pipes, thus preventing scaling.
19
Like MED, practical flash-distillation systems have compartments and each compartment
is called stage, hence the term Multi-Stage Flash (MSF). When first introduced in the
1960’s, MSF offered slightly lower energy efficiency than MED, but this was outweighed
by scaling considerations and MSF became the industry standard. The desalinated water
produced by the MSF process contains typically 2-10 ppm dissolved solids. Therefore, it
is remineralized through the potabilization (or post- treatment) process. The schematic is
shown in Fig. 2.3
Fig. 2.3 Schematic of multi-stage flash desalination process.
2.5 VAPOUR COMPRESSION
Compressing water vapour raises its temperature, which allows it to be used at a heat
source for the same tank of water that produced it. This allows heat recycling in a single
effect distillation process. In Thermal Vapour Compression, the compressor is driven by
steam, and such systems are popular for medium-scale desalination because they are
simple, in comparison to MSF. In Mechanical Vapour Compression, the compressor is
driven by a diesel engine or electric motor. The water produced by the process is very
pure with almost no salts, where the feed water quality has almost negligible effect on
energy consumption (Nicos, 2001). Thermal processes are the primary desalination
technologies used virtually throughout the Middle East because these technologies can
produce high purity water from seawater and because of lower fuel costs in the region.
The schematic of the vapour compression process is shown in Fig. 2.4
20
Fig. 2.4 Schematic of single stage mechanical vapor compression desalination process
2.6 MEMBRANE PROCESSES
Membranes have the ability to differentiate and selectively separate salts and water.
Using this ability but differently in each case, three membrane desalination processes
have been developed for desalting water: Electro dialysis (ED), reverse osmosis (RO) and
nano filtration (NF). The RO represents the fastest growing segment of the desalination
market (Blank et al., 2007). Membrane technologies can be used for desalination of both
seawater and brackish water, but they are more commonly used to desalinate brackish
water because energy consumption is proportional to the salt content in the source water.
Compared to thermal distillation processes, membrane technologies generally have lower
capital costs and require less energy, contributing to lower operating costs. In fact, the
most important progress in the area of membrane systems is the reduction of membrane
cost by factor of approximately 10 over the last 30 years with seawater intake and pre-
treatment alone as expensive items of a membrane system (Khawaji et al., 2008).
21
2.6.1 Basic Principle of Osmosis
Osmosis is a principle of physics according to which, if two saline solutions with
different concentrations are separated by a semi-permeable membrane, which is
permeable to water but impermeable to salt, water will spontaneously pass from the lesser
concentrated solution to the other because of its low chemical potential. When pure water
is in contact with both sides of an ideal semi-permeable membrane at equal pressure and
temperature, there will be no net flow across the membrane because of the chemical
potential is equal on both sides. According to the Second Law of Thermodynamics, if salt
is added into one side of the membrane, the chemical potential of the salt is reduced, and
osmotic flow will take place from pure water side across the membrane to the side with
salt until the chemical potential on both side of the membrane is equalized. If the
membrane were permeable instead of semi-permeable, salt would migrate to the fresh
water side until equilibrium is restored. However, the salt does not pass through the semi-
permeable membrane; only fresh water can move to achieve equilibrium. The fresh water
is doing all the work to reach equilibrium, so the fresh water side will eventually be
depleted in an effort to reduce the relative saltiness of the salty side. Equilibrium occurs
when the hydrostatic pressure difference resulting from the volume changes on both
sides, is equal to the osmotic pressure difference of the two solutions as in Fig. 2.5 where
the osmotic pressure is a solution property proportional only to the salt concentration.
Fig. 2.5 Schematic of Simplified Osmosis
22
2.6.2 Reverse Osmosis
In the reverse osmosis (RO) process, the osmotic pressure is overcome by applying
external pressure higher than the osmotic pressure on the feed water as in Fig. 2.6.
Fig. 2.6 Block diagram of reverse osmosis operations
Thus, water flows in the reverse direction to the natural flow across the membrane,
leaving the dissolved salts behind with an increase in salt concentration. No heating or
phase change is necessary. The major energy required for desalting is for pressurizing the
seawater feed. A typical large seawater RO plant (SWRO) has four components as intake,
pre-treatment, RO and product water conditioning.
2.6.2.1 Basic Principle of RO
Reverse Osmosis is the reverse process of spontaneous osmosis. The osmosis process can
be reverted by adding external pressure on the salty side so that some of the fresh water
molecules on the salty side will end up on the fresh water side. The problem is that the
osmotic pressure tends to force water to the more saline side, which is opposite of the
desired outcome. To overcome this tendency, the osmotic pressure can be overcome by
the applied pressure, forcing water from the saline side to the less saline side. Reverse
osmosis is schematically presented in Figure 2.7.
23
Fig. 2.7 Simple Reverse Osmosis
Increasingly, water scarcity will challenge human populations. Lack of water hinders
economic development, devastates human health, leads to environmental degradation,
and foments political instability. At present, approximately 50% of the water is being
used by households, and the other 50% for industrial and agricultural activities. However,
with an increasing population, there will be pressure for industries to reclaim and reuse
some of its wastewater, or face the prospect of being shut down. This is due to the
combine pressures of increasing water and wastewater costs and increasing regulatory
requirements of discharged wastewater (Pagga and Taeger, 1994).
A number of research agendas have been developed to address the water problem.
Ultimately, a number of parallel approaches will be necessary to limit the effects of water
shortages including improving the efficiency of water use, implementing technologies
and policies to encourage water conservation and reuse (James E. Miller 2003).
24
To solve or alleviate the global water scarcity problem, tremendous effort has been put
forth to identify novel methods of purifying wastewater or seawater at lower expenditure
with less energy consumption. (Bond and Veerapaneni, 2008 ;Khawaji, et al., 2008 ;
Asano, et al., 2007.) Membrane technology has become increasingly attractive for the
treatment and recycling of wastewater (Nicolaisen 2002).
In the recent years, several factors have led to the development of membrane separation
technology. The most important ones are the necessity of fresh water production for
drinking, domestic, agricultural, landscape or industrial uses, the requirement of higher
performance level methods for waste water reclamation and reuse applications, as well as
lower regulatory maximum allowed levels of contaminants. Membrane processes are
often chosen in water treatment technology since these applications achieve high
removals of constituents such as dissolved solids, organic carbon, inorganic ions, and
regulated and unregulated organic compounds. Reverse osmosis (RO) and nanofiltration
(NF) membrane processes are used around the world for potable and ultrapure water
production, chemical process separations, as well as desalination of seawater (salinity
around 35 g/l) and brackish water (less salty than the seawater). Moreover, lately there
has been a growing interest in the integration of such membrane technologies for
municipal and industrial water treatment, since they have been recommended as suitable
for cost‐effective desalination and removal of a wide range of low‐molecular‐weight
trace organic constituents (Aboyurayan and Khaled, 2003; Al-Enezi and Fawazi, 2003).
Organic compounds of particular interest include endocrine disruptors, human and animal
antibiotics, disinfection by‐products, insecticides and herbicides, and various
pharmaceutical drugs. Many of these compounds have been detected in natural
ecosystems at bioactive concentrations (Kolpin et al., 2002; Baronti et al., 2000).
2.6.3 Electrodialysis
Electrodialysis also uses membranes, but unlike RO, the salt ions are deliberately carried
through the membranes, leaving behind the freshwater. Two types of membranes are
required: one that lets anions through but not cations, and the other that does the opposite.
These membranes are stacked alternately and held apart by spacers.
25
The saltwater is fed into the spacer layers on one side of the stack, and a DC voltage is
applied to the stack as a whole. The salt ions are attracted through one membrane or the
other depending on their polarity, and by the time the water comes out from other side of
the stack, it is alternately freshwater and concentrates in separate compartment.
Reversing the polarity of the applied voltage reverses the freshwater and concentrate
compartments, and this can be done periodically (several times per hour) in order to
reduce fouling, and it is termed Electrodialysis Reversal. Electrodialysis was
commercialized during the 1960’s and is widely used today for desalinating brackish
water. The energy consumption depends on the TDS of feed water and hence it is rarely
used for seawater desalination. The schematic is shown in Fig. 2.8
Fig. 2.8 Schematic diagram of electrodialysis desalination process.
2.7 The Preferences for RO
This is now increasingly used in different applications (Drioli, and Fontananova, 2004;
G. Pearce, 2007), due to the high and stable quality of the water produced and the
relatively lower cost. Several advantages of the RO process that make it particularly
attractive for dilute aqueous wastewater treatment include: simple to design and operate,
low maintenance requirements, modular in nature, both inorganic and organic pollutants
can be removed simultaneously, recovery/recycle of ROR with no effect on the material
being recovered, lesser energy and lesser volumes of ROR which is attractive.
26
Many authors have endorsed the aforesaid views. Cartwright, 1985; Sinisgalli and
McNutt, 1986; Cartwright, 1990; McCray et al., 1990; Cartwright, 1991; Williams et al.,
1992). The advantages of R O and inherent disadvantages are in Table 2.2
Table 2.2 Advantages and Disadvantages of Desalination Technologies
Method of
Desalination Advantages Disadvantages
Multi-effect
desalination
(MED)
1. High production capacity
2. Low capital cost
3. High purity of permeate
4.Energy independent of salinity
5. Minimal skilled operator
1. Unfailing power availability
2. Long construction period
3.Difficult to control quality
4. Low conversion in seawater
5. Large footprint
Reverse
osmosis
(RO)
1. Suitable for sea / brackish water
2. Flexibility in water quantity
3. Lower power requirement
4. Flexibility in site location
5. Flexibility in operation
1. Requires high quality feed
2. High capital costs
3. High pressure requirements
4. Long construction time
5. Vendor dependency
Vapor
compression
(VC)
1. High water quality (20 ppm)
2. High operational load
3. Short construction period
4. O&M flexibility
1. High operational costs
2. High energy consumption
3. Lack of water quality
4. Material corrosion
Electrodialysis
(ED)
1. Low operating and capital costs
2. Flexible energy source
3. High conversion ratio (80%)
4. Low energy consumption
5.Low space requirements
1. only brackish water capability
2. Requires pretreatment
3. Low production capacity
4. Purity based on feed quality
5. Vendor dependency
Multi-stage
flash
1. Flexibility in salinity of feed
2.High purity production
3. High production capacity
4. Low skill requirement
5. Co-generation of electricity
1. Labor intensive
2. Low conversion ratio
3. High operating costs
4.Long construction time
5. No potential for improvement
However, the product water salinity tends to be higher for membrane desalination (< 500
ppm TDS) than that produced by thermal technologies (< 25 ppm ), but when making use
of a second RO pass the same quality can be obtained. Most of the applications of RO are
in desalination of brackish and seawater to produce potable water, but there are also
applications in food and diary industries, pharmaceutical and cosmetics production, water
softening, ultra-water production for electronic industries, as well as treatment of
municipal and industrial wastewater and agricultural drainage water. The lists of RO
applications along with selected references are presented in Table 2.3.
27
Table 2.3 Applications of Reverse Osmosis
Application Species Removed Reference
Sea water Various salt species Williams et al (1992)
Electroplating & Metal
finishing water
Nickel Spatz (1979)
Nickel, chromium, gold Imasu (1985)
Various metals Davis et al (1987)
Cadmium Slater et al (1987)
Spent sulphite liquor
components
Glimenius (1980); Olsen
(1980);Paulson &Spatz (1983)
Pulp and Paper Processing
Effluent
Wash water components Hart & Squires (1985);
Chemical compounds Dorica et al (1986);
Simpson & Groves (1983)
Bleach Plant Effluent Meat processing
COD
Hart & Squires (1985);
Gekas et al (1985)
Food Processing Effluent
Olive mills COD, TDS Canepa et al (1988);
Anonymous (1988)
Various contaminants Mohr et al (1989)
Radionuclides Ebra et al (1987)
Radioactive Processing
Effluent
Uranium conversion Hsiue et al (1989)
Various uranium species Chu et al (1990);
Uranium nitrate Prabhakar et al (1992)
Blastfurnace Scrubber TDS Terril& Neufeld (1983)
Coal Mining Drainage TDS Hart & Squires (1985)
Fuel Processing
Wastewater
TDS, COD,
Organics
Bhattacharyya et al (1984)
McCray & Ray (1987)
Ammonium Nitrate Ammonium nitrate Davis et al (1990)
Textile effluent Color, TDS, organics Slater et al (1987)
Leachates TOC, TDS, COD,
Alkalinity, NH3
Chian & DeWalle (1977)
Slater et al (1983)
Kinman &Nutini (1990)
Drinking water
Agricultural chemicals Johnston & Lim (1978)
Regunathan et al (1983)
Humic, fulvic materials Nusbaum &Riedinger (1980)
Odegaard & Koottatep (1982)
Various contaminants,
color
Sorg et al (1980),
Sorg& love (1984)
Taylor et al (1987)
Tan &Sudak (1992)
Municipal waste
TDS, organic waste
Cruver (1976);
Fang &Chian (1976)
Tsuge& Mori (1977)
TDS, TOC Stenstrom et al (1982)
TDS, TOC, fecal coliform Suzuki & Minami (1991)
28
2.8 Reject from RO
The characteristics of rejects from RO (ROR) depend on the feed water characteristics,
the pretreatment, the membrane process used, the recovery, and the additional chemicals
used (Pontius et al., 1996). A parameter frequently used to describe the rejection
characteristics of a membrane is the desalting degree. The desalting degree of a
membrane is commonly reported as the percent rejection of electrolytes such as sodium
Chloride, magnesium sulfate and other electrolytes. The desalting degree can be useful
parameter in estimating the rejection of some compounds. This parameter is needed to be
considered during membrane selection. Many researchers have used this parameter to
determine the effect of preparation condition on NF membranes performance (Yang et
al., 2007). Some investigators used the membrane permeation tests and the sequence of
salt rejection to evaluate the membrane charge (Krieg et al. 2004, Schaep et al. 2001,
Wang et al., 2005). The transport of salt across a membrane is commonly expressed as
salt passage or salt rejection. Salt passage is defined as the ratio of concentration of salt
on the permeate side of the membrane relative to the average feed concentration. The
equation describing salt passage is given by:
SP = Cp/Co x 100%
Where, SP is the percentage salt passage,
Cp is the permeate salt concentration and
Co is the average feed salt concentration.
The equation describing salt rejection is given by:
R = 100% - SP
Where R is the percentage salt rejection.
2.9 POSSIBILITIES FOR PROCESSING OF ROR
Because the composition of the ROR depends on the application and the further
environmental fate of the residue which are extremely unpredictable, a large variation in
possibilities for reuse, further treatment, or discharge exists. Cost factors and legal
aspects also play an important role (see Supporting Information). An overview of these is
presented as a relative comparison in Table 2.4 hereunder.
29
Table 2.4 Overview Of Reuse, Further Treatment, and Discharge of ROR
Category Process Reference
Reuse
as a desired product
(e.g., concentrated food products)
as fertilizer, for soil improvement,
as fuel for production of salts and other
minerals
Van der Bruggen& Van de
casteele, (2002)
Ahmed et al., (2001)
Further
Treatment
concentration by water removal:
- thermal (e.g., evaporation,
distillation)
- other (e.g., electrodialysis,
settling)
removal of specific compounds:
- activated sludge
- oxidation processes:
(electro)chemical,
Photo oxidation,
adsorption/ion exchange
Balanosky et al., (1999)
Van Hege et al., (2002)
Incineration rotating kiln furnace (hazardous waste)
grate furnace (nonhazardous waste) Kohli et al., (1985)
Discharge in
Surface
water
direct discharge
indirect discharge via sewage system Malaxos& Morin, (1990);
Del Bene et al., (1994);
Hoepner, (1999)
Discharge in
Ground
water
application on the land: irrigation
evaporation deep injection in the soil Muniz.&Skehan, (1990);
Riley (1997)
Landfilling
as solid waste after pretreatment
with additional treatment (e.g.,
stabilization/solidification)
without additional treatment
as liquid waste
Peters (a) (1998);
Peters (b) (1998)
30
2.10 SALT INGRESS INTO ENVIRONMENT BY ROR
Even the seagulls have such a semi permeable membrane in their throat by which they
can take in seawater with salts, separate the drinkable water with minimum salts and the
concentrate back into the sea. The sea water desalination plants discharge such rejects
back into the sea and this being volume wise a miniscule of the volume of the sea itself,
there will be progressive increase of the average salt content of the sea.
However, the issue becomes one of serious environmental concerns when it applies to
desalination plants inland whether these are meant for brackish water sources to be
desalinated for public use or for industrial effluents because it adds to the salt content and
renders the resultant environment as a whole than its pre-discharge state or impregnates
the environment with salts and this is an environmental damage. The recent 100 MLD of
permeate SWRO plant of Chennai, follows the same ocean disposal.
2.11 THE LIMITATIONS IN THE WATER ACT OF INDIA
Though the Indian Water Prevention and Control of Pollution Act permits the public
authority to lay down, modify or annul, in consultation with the State Government
concerned, the standards for a stream or well, provided that different standards may be
laid down for the same stream or well or for different streams or wells, having regard to
the quality of water, flow characteristics of the stream or well and the nature of the use of
the water in such stream or well or streams or wells, still when it comes to specifying the
discharge limits for dissolved solids, it is consistently maintained at 2100 mg/l. Recently,
this has been further tightened to the effect that no discharge of liquids are allowed and
what is familiarly known as zero liquid discharge (ZLD) has been mandated by almost all
state pollution control administrations.
2.12 STATE OF DISCHARGE of ROR IN TO THE SEA IN ISRAEL
Even though practiced routinely in almost all SWRO plants, the posthumous effect on
seawater over a period of time has somehow been evading a conclusive statement as
stated by Iris Safari and AlonZask of Ministry of Environmental Protection, Israel after
reviewing the status in respect of six SWRO plants on their coastline of sizes 82 MLD of
Product water to 270 MLD of product water totaling 827 MLD of product water.
31
Their apprehensions are stated as (a) It is important to realize that there is still very little
information on the impact of desalination discharge on the marine environment and (b) It
is mostly emphasized while dealing with the largest RO operated desalination plants.
They proceed to state that for all these reasons, decision makers must take the
precautionary principle in their environmental policy, meaning mainly applying Best
Available Technology (BAT) for the protection of the marine.
2.13 THE RED TIDE BLOOMS IN THE GULF OF OMAN
A problem that has been encountered in the SWRO is the red algae, or red tides which
result from seasonal upwelling from the sea floor and brings nutrients such as nitrates and
phosphates to the water's surface, which allows formerly low populations of the single-
celled organisms to multiply that cause red tides an event in which estuarine or marine
algae accumulate rapidly in the water column, or "bloom" and forces the intakes of
SWRO plants to opt for Dissolved Air Floatation (DAF) to float the algae as pretreatment
and the trapped algae if discharged back to the sea, promotes more denser growths and
incapacitate almost all other uses of the seawater due to dead fish whose gills have been
choked by these algae. Such a phenomenon has been encountered in the SWRO is the red
algae, or red tide blooms, which hit the UAE’s east coast for eight months from August
2008 incapacitating these plants and is stated to be overcome in Abu Dhabi's second
desalination plant on the Gulf of Oman coast by dissolved air flotation (DAF) a technique
which has been used successfully elsewhere in the world and which meant that rather
than washing sand filters every day, only one wash will be required every 38 hours. In
turn this has its effect on consistency of RO reject management technology.
2.14 CHARACTERIZATION OF POLLUTANTS FROM ROR
Hopner (1999) has observed that although desalination of seawater offers a range of
human health, socio-economic, and environmental benefits by providing a seemingly
unlimited, constant supply of high quality drinking water without impairing natural
freshwater ecosystems, concerns are raised due to potential negative impacts mainly
attributed to the concentrate and chemical discharges, which may impair coastal water
quality and marine life, air emissions attributed to the energy demand of the processes.
32
2.15 ZLD IN INDUSTRIAL WASTEWATER MANAGEMENT
In terms of industrial wastewaters, the requirement of ZLD implies here again the
generation of RO rejects which pose their own problems depending on the nature of the
industry and the type of treatment processes followed. Though the volumes of these are
not significant as compared to those from SWRO plants, the issue is equally important in
that assortments of chemicals are the fallout from these industrial projects.
2. 16 CLOSURE OF TEXTILE DYEING INDUSTRIES IN A TEXTILE TOWN
Recently, there is the case of textile CETPs in Tiruppur city of India where there are 20
CETPs with a total design capacity of close to 100 MLD and where ZLD plants were
installed and commissioned over the past few years by implementing a treatment process
of removals of colour, BOD, COD etc and followed by RO and the rejects put through a
thermal evaporator. The evaporator is having problems almost continuously and the net
result is all these CETPs were left with no option than to discharge their RO rejects with
TDS concentrations in the range of 50,000 to 60,000 mg/l in the local river course and
which prompted strong resistance locally which has resulted in a total closure of textile
dyeing and bleaching The direction of the High court to industry to set right the whole
ZLD scheme before reopening appears a real challenge to be met.
2.17 THE MADRAS FERTILIZERS AND REFINERIES EXPERIENCES
The earliest in Asia is the plants of Madras Fertilizers Limited at Chennai in 1992 where
a plant of 17.5 MLD received the secondary treated biological effluent of the nearby
Chennai city sewage treatment plant at Kodungaiyur and further treated it with chemical
methods followed by RO membranes and was approved for disposal of the RO rejects
into the adjoining Bay of Bengal. In practice however, the marine outfall that was
constructed was wrenched out at the shore by the fisher folk who have a large presence at
this location as a commercial operation of fishery industry and till date the RO rejects are
meandering in the backwaters. The same is the case with Madras Refineries at Chennai
who also met the same fate in 1992 for their 12.5 MLD plant.
33
2.18 THE EXPERIENCES OF GMR, NEW DELHI AND MUMBAI AIRPORTS
The GMR Vasavi Power Plant, the New Delhi and Mumbai International Airports have
overcome water shortages by treating a larger quantity of sewage up to the beginning of
the RO plant and bypassing the excess of requirement for RO and eventually blending
such a bypass with TDS of about 1,200 mg/l with the ROR to attain a blended discharge
with TDS of less than 2,100 mg/l to qualify for discharge into city sewers or water ways,
but then, the cost may come in the way when the eventual use is not for industries.
2.19 THE BANGALORE INDIRECT WATER AUGMENTATION
The city of Bangalore is the first in India to conceive and propose a project to emulate the
Singapore Newater project by advanced treatment of city sewage and experimenting
initially with storing the advanced treated water in one of the city freshwater reservoirs
with a detention time of over two years before eventually being drawn and again treated
before blending the city water supply as a means of getting over a looming water famine
by way of the city exhausting its fresh water resources by 2015 and the city left in the
lurch thereafter. In this case, the RO rejects are proposed to be treated by Lime Soda
process to precipitate out its Ca and Mg which are the main ingredients of TDS and
thereafter storing the sludge in abandoned stone quarries and discharging the Lime Soda
treated waters with low TDS into the city’s fresh water courses. The project is under a
series of public consultations before it can be brought up for implementation.
2.20 MAJOR ISSUES IN SEWAGE ROR
Even though more than 150 installations worldwide have been reported wherein sewage
is reused for various purposes along with UF / MF / RO membranes, the report is silent
on the fate of the RO rejects and it is presumed that the same goes back to the raw
sewage source at a point which is not hydraulically cascading to the said STP/ETP.
Nadav (1999) reported successful use of SWRO rejects for commercial salt in Israel by
blending 80 % SWRO reject and 20 % Brackish Water RO (BWRO) reject for10 MLD
and the salt was claimed as the highest quality within the most severe standards and
lucrative for Arabian gulf countries where strong solar radiation, low precipitation, low
cost desert land, short and easy transportation to ports command over Asian markets.
34
A problem that has been initially encountered and since got over is stated as the brine at a
flow rate of about 250 cum / hr entered to a pipe and flowed along a distance of about 7
km from the upper ponds where sparingly soluble salts are deposited to the lower ponds
and scale started to accumulate in the pipeline which was solved by blending the same
solution with 2 % seawater before its entry into the pipeline thus separating the solution
from the saturation point and the pipeline is stated as clean from any precipitation.
2.21 RO REJECT REUSE FOR SALT RECOVERY IN TANNERIES
In respect of tanneries, it was reported on two variations of recovery of resources from
RO reject with and without addition of Na2CO3 as in Fig. 2.9 When adding Na2CO3,
this precipitated CaCo3 ahead of the ponds storage and chemical recoveries and
subsequently, with addition of Lime, the resources precipitated are Na2SO4, NaCl,
Mg(OH)2 and eventually the dissolved CaCl2 is disposed in solar ponds.
Fig. 2.9 The Salt Recovery from RO Rejects In Tanneries
35
2.22 EVAPORATION OF ROR AND SOAK LIQUOR IN TANNERIES
The United Nations Industrial Development Organization (UNIDO) has conducted
extended pilot and prototype studies on tannery soak liquors which have a TDS of about
50,000 mg/l and are just about the same as RO rejects in these industries and evolved an
accelerated solar system for evaporating the water content. The technology was to use the
rooftop flat plates as a thin film continuous flow evaporating surface supplemented by
spraying through nozzles to obtain maximum area per unit volume whereby evaporation
rates of 15 mm / day was achieved compared to 5 mm / day in the case of static solar
ponds and this reduce the area needed plus usage of the existing roof shed tops and thus
getting at a resulting liquor with maximized salt content and the solar pan area and the
images are shown below Fig. 2.10 and Fig. 2.11.
2.23 SOLAR PANS AND SPRAY PONDS FOR EVAPORATING ROR
There have been historically ground level solar pans for evaporating out the soak liquor
and was also adapted for ROR in due course, but then, fears of ground water and subsoil
impregnation by TDS compelled upgrades of the technology for ROR. The spray ponds
and spray nozzles erected on gabled roof tops as above took shape as above mainly
arising from the demonstration projects carried out by United Nations Industrial
Development Organization (UNIDO). Though these were effective in situ remedies, the
foot print area needed for the industrial wastewaters was not available on the rooftops and
hence, this technology is now standing relegated to small scale industries.
Fig. 2.10. Distribution Channel and Flat
Plate Collector
Fig. 2.11 The Sprinkler
36
2.23.1 Integrated Systems with Spray Ponds and Salt Recovery from ROR
Aquasonics International claims to have patented a system whereby the spray results in
water vapour which can be collected, cooled and water recovered and the salt contained
in a thick slurry whereby nearly 95 % of water can be recovered for reuse and is called as
RSE™ technology is based on a patented method of producing very small droplets of
saltwater that are rapidly evaporated in a heated air stream. The evaporation results in
water vapor and precipitated salt particles. The salt particles are collected in a slurry or
dried form and the water vapor is condensed, resulting in potable water. The process is
environmentally friendly, in that it returns no concentrated brine to the saltwater source.
Also, unlike reverse osmosis, RSE™ does not use membrane technology, which requires
expensive periodic maintenance. When sufficient waste heat is available, the promoters
claim that no other technology is equals the advantages of RSE™ in terms of operating
and capital costs, potable water volume recovery and recovery of solids. The
technological and economical features of the RSE method make it attractive for a variety
of applications. For example, certain wastewater applications, especially those having
high concentrations of dissolved solids, may be uniquely treated by RSE. It was claimed
that the RSE™ technology is capable of cost-effective separation of solids from various
types of waters, including wastewaters having up to 25% dissolved solids.
2.23.2 The Heat Sink Spray System
M/S Chuck Bowman Associates (CBA) states of performing ultimate heat sink spray
pond analysis to satisfy the requirements of the Nuclear Regulatory Commission (NRC)
Regulatory Guide 1.27, Ultimate Heat Sinks for Nuclear Plants and that they offer
detailed designs, thermal analysis, and procurement of their oriented Spray Cooling
System (OSCS) as in Fig. 2.12 They also claim that unlike a conventional spray pond in
which spray nozzles are arranged in a flat bed and spray upward, the OSCS nozzles are
mounted on spray trees arranged in a circle and are tilted at an angle oriented towards the
center of the circle and as a result, the water droplets drag air into the spray region while
the warm air concentrated in the center of the circle rises and both of these effects
together increase the air flow through the spray region and reduces the wet bulb
temperature of the air in the spray, promoting heat transfer and more efficient cooling.
37
2.24 DIRECT SPRAY NOZZLE SYSTEMS FOR RO REJECTS
There has also been direct spray nozzles based evaporation answers to deal with small
quantities of RO rejects by tanneries and textile industries wherein, the infrastructure is a
sump equipped with pipings and spray nozzles to merely evaporate the water content and
to concentrate the RO reject into a slurry as in Fig. 2.13 and Fig 2.14. These are ad hoc
spray ponds and still serve the purpose of getting rid of the water content.
Fig. 2.13 The recirculating pump, the
piping and nozzles in a spry pond
Fig. 2.14 The spray pond in operation
with uncontained windage
Fig. 2.12 Oriented Spray Cooling System of M/S CBA
38
2.25 ROTARY ATOMIZED SPRAY EVAPORATORS
Following up on the two phase mass transfer, the finest droplet approaching a mist can
bring about evaporation of a given fluid within the governing mechanics of thermo
dynamics. This is given effect in a rotary mist atomizer sprayer claimed to handle either a
solo liquid or blend two liquid streams and then bring about the atomizing & enabling the
misty evaporation . The system is shown in Fig.2.15.The patented atomizer in its bare
state and in its use. The flow rate is stated as 5.4 cum / day per piece costing $1,351 and
working at 5500 rpm for fluid temperatures as high as 82 deg C at 1.8 kW and at a
pressure of 172 bars. The droplet size is stated as 50 to 110 microns.
Though it is a technically sound application of thermodynamics put into practice, the high
rotary speeds can complicate the atomizer exits by reverse condensation on pressure drop
and the probability of its eventual scaling does not seem to bide well for the high TDS
wastewaters and hence this equipment may be better used for liquids needing disposal but
free of depositing such solids.
2.26 THE MIXED OXIDANT TECHNOLOGY
A system of generating mixed oxidants from brine solution has been reported whereby
the mixed oxidant products are based on a proprietary membrane-less electrolytic cell
that produces a liquid stream of very aggressive mixed-oxidants that are extremely
effective in disinfecting water as in Fig.2.16.
Fig. 2.15 Rotary atomized spray evaporators
39
Fig. 2.16 Schematic of the Mixed Oxidants Technology and resulting end products
The Anode (+) products are negative ions at pH of 3 and are Hypochlorous acid, Chlorine
Dioxide, Ozone, Chlorine, Oxygen and Hydroxyl radicals. The Cathode (-) products are
positive ions at pH of 12 and are Sodium Hypochlorite, Sodium Hydroxide and Hydrogen
The system is claimed to be of superior disinfection performance, removal of biofilms,
reduced disinfection by-product formation, reduction of taste and odor problems,
enhanced micro flocculation, simplicity and low maintenance, operator and community
safety, cost effective operations, on-demand generation of oxidants and long lasting
chlorine residual. However, pH regimens of about 3 at the anode and 12 at the cathode
may not be easy in day to day operation.
2.27 THE GERMAN GLADIERWERK WOODSTACK
It is an assembly of wood stacks with the wastewater being trickled down atop and
gaining evaporation and absorption onto the twigs and is provided with an illuminated
walkway. While it sounds theoretically strong, the moot question of ultimate disposal of
the salt impregnated twigs and their prima facie life span. It is shown in Fig. 2-17.
40
A question as to deposition of the sulphate salts when temperatures are around 240C can
be a challenge as it may “bridge” the entire wood stack. In addition, the propagation of
insects in our arid temperatures cannot be ruled out though it may not be the case in the
colder regions in Germany. However, the fact remains that it proves that evaporation
does occur even at cold temperatures as long as the fine films of wastewater are flowing.
2.28 THE PACKED BED FALLING FILM TECHNOLOGY
The same as Gradierwerk, this uses Pall rings as piloted and reported by Ligy et. al.
(2013) and is shown in Fig. 2.18.
Fig. 2.18 Non clogging Pall rings for sulphate salts crystallization
2.29 THE WIND ASSISTED INTENSIFIED EVAPORATION TECHNOLOGY
This wind assisted intensified evaporation (WAIV) system of Lesico Cleantech and Ben
Gurion University has been evolved at Israel for RO rejects. This system consists of
contiguous drapes of nettings allowing the high TDS rejects to glide down as a film on
both sides. The reject is continuously pumped up onto the drapes as sprays gliding down.
Fig. 2.17 The German Gladierwerk Woodstack
41
When the dissolved solids are in the form of sulphates, the reject water is cooled to about
22 deg C and allowed as a freefall film for the sulphate to crystallize out. The evaporation
is 13 times more than the conventional solar pan per foot print and is shown in Fig. 2.19.
`
These surfaces are cooled to near the wet bulb temperature and the temperature gradient
between the warmer wind and the cold-water surface drives heat flux to the wetted
surface. The vapour pressure gradient drives the evaporation mass transfer from the
surface. Comparison of field results to the literature show that the WAIV evaporation
behaviour qualitatively follows the meteorological evaporation correlations given for
ponds. Results of evaporating 20% NaCl brine are stated as feasible to concentrate to
collect the deposits in the container below the WAIV unit to several times their original
concentration. The unit is stable to the corrosive chemicals present and to meteorological
conditions including 60 km/ hr winds. The enhancement factor was of the order of 15-20
times based on equal footprints for WAIV and the control being a simple solar pan.
Solids that deposit on the WAIV surface were sloughed off by the wind action and
collected in the tank below the WAIV unit. Results on WAIV pilot at Sde Boker (31 sqm
evaporation area on 2 sqm footprint) using tap water gave a 17 times enhancement
compared to the pan evaporation data from the meteorological station. Results on the
enlarged pilot plant (140 sqm evaporation area 33.7 sqm wetted area / sqm footprint)
operating on desalination brines, showed an evaporation rate of 13 times as compared to
evaporation pan data. Brines were concentrated from 57,000 mg/ L to 250,000 mg/L.
Fig. 2.19 Recovery of crystalline sulphates from salt solutions by WAIV system
42
The efficiency (amount evaporated/m2 wetted area relative to pan area evaporation rate)
dropped to 35-40% as compared to 100% efficiency obtained with packing density of 15
sqm / sqm footprint. It was shown that part of this was due to the nets being too close;
only 8 cm average distance instead of an average 12 cm in the previous version and the
profile of the unit (triangular versus rectangular). There are indications that the strip
width also contributed to the lower efficiency (65 cm versus10 cm on the previous
version). Deposits on the WAIV netting from desalination brines evaporated from the
Ktziot desalination plant were almost exclusively formed from gypsum. The deposit only
formed up to an asymptotic thickness of 2 mm and did not continue to grow on the
netting. Deposits in the tray below included halite (NaCl). By increasing the flow rate
through the wetting holes every other day, the holes did not plug. Also, the netting
completely wetted within a half hour from start-up after the unit was shut down and the
nets were allowed to dry. Droplet/leak loss was 5% or less of the nominal evaporated
volume and was within 2m from the unit. The performance was presented as in Fig. 2-20.
By far the advantage of this system is the ability to contain the pollutant liquid within the
footprint of the installation without getting carried away by windage. In the case of
chlorides, it is possible to concentrate the fluid to levels even exceeding that at the “Dead
Sea” for the solar pan evaporation.
Fig. 2-20. Graph at Left is Comparison
of Conductivity of WAIV vs Control
Trough in Roof Top Concentration Run
on Desalination Plants. Graph at Top is
Cumulative Amount of Brine
Evaporation in a Concentration Run on
Desalination Brine Roof Top Unit
Fig 2.20 Performance Indicators of the WAIV system
43
2.30 GENERATION OF MIXED OXIDANTS FROM ROR
A system of generating mixed oxidants from brine solution has been reported whereby
the mixed oxidant products are based on a proprietary membrane less electrolytic cell that
produces mixed-oxidants as shown in Fig. 2-21 and the products as in Fig. 2-22.
.
Fig. 2.21 The Schematic of the MIOX System
Fig. 2.22 Products of Multi-Oxidants from the MIOX system
This system functions at pH extremes of 3 to 12 and hence is not widely adopted
A system of generating mixed oxidants from brine solution has been reported.
44
The mixed oxidant products are based on a proprietary membrane less electrolytic cell
that produces a liquid stream of very aggressive mixed-oxidants that are extremely
effective in disinfecting water. The electrolytic cell uses sodium chloride (salt), water and
electricity to generate the oxidant solution. This is collected in a tank and continuously
injected into water. The system has not picked up because the pH required for the
oxidants at anode is about 3 whereas the pH required at cathode is 12, and are difficult in
an equilibrium state, though it is claimed that the multi oxidant produced in situ is stated
as non hazardous, has a broad spectrum kill of bacteria, pathogens, virus, cysts etc, long
shelf life of 9 days as compared to 3 days in the case of Sodium Hypochlorite,
2.31 THERMAL EVAPORATION OF RO REJECTS
Thermal Evaporation has been in use to deal with RO rejects and recover water as vapour
for condensation and recovering useable water. The principle is merely evaporating the
reject waters and recovering the water vapour. Various configurations as single effect,
multiple effect, falling film, rising film, mechanical vapour compression, thermal vapour
compression are employed as already covered in the beginning of this chapter..
2.31.1 THERMAL VAPOUR COMPRESSION
Another system of the utilization of the heat of the input steam is the thermal vapour
recompression where the heat latent in the vapour generated from heating the feed is
recirculated to the reactor by using an ejector through which the primary steam is fed and
thus maximizing the heat energy is achieved in practice. A schematic diagram of is
shown in Fig 2.23.
Fig. 2.23 Schematic of thermal vapour ccompression
45
2.32 CALENDRIA PROBLEMS
The heat exchanger surfaces in evaporators are to be safeguarded from corrosion as also
spalling due to the high concentrations of chloride ions in contact with the surfaces. As
temperatures approach the boiling point, the effect of these chlorides is made more
detrimental. A typical evaporator with serial reactors and callendrias housed inside,
spalled& flared status of callendrias tubes due to corrosion and scaling of the inside of
another installation in months is shown in Fig. 2.24.
2.33 THE HADWACO EVAPORATOR
Recent trends in evaporators for RO rejects are to try out synthetic materials for the heat
exchanger surfaces like M/S Hadwaco shown in Fig. 2.25 and pictured in Fig. 2.26.
Fig. 2.24 Internal scaling and spalling in calendria tubes of thermal evaporators
Thermal Evaporator with
Recirculation of the Liquid
and separate Collection of
water vapour, its
condensation and recovery
of reusable grade water.
The reaction chamber is
made of synthetic non-heat
sensitive fabric and useful
in the absence of scale
forming agents of Ca and
requires pre-softening
Fig. 2.25 Schematic of the multiple vapor compressor
46
2.34 THE ELUSIVENESS OF EVAPORATOR ISSUES IN ROR
All the same, there have also been other installations where the raw effluents themselves
and RO rejects have been earlier permitted to be discharged into the ocean but then, given
the recent directive of ZLD being mandated by the local authorities, these ocean disposals
do not offer any escape route for future industries. Arising from this background, it
becomes necessary to appreciate and understand the position that it is necessary to
remove as much as possible these issues in the pretreatment to RO itself before we can
address the ROR technology and get over the vexatious issue of ROR in ZLD practice.
2.35 THE INFIRMITIES IN ADOPTING THERMAL EVAPORATORS
2.35.1 Heterogonous Characteristics of ROR
In a way, most of the issues that negate a sound evaporation technology can be traced to
the ions in the feed water to RO plus other physical and chemical contents which are not
given their due importance and are taken for granted in the design of RO systems. Among
the serious ones are alkalinity which can induce scaling at higher values, Alum, which
disassociates into trivalent aluminum and sulfate and the hydrated aluminum ion reacts
with the water to form a number of complex hydrated aluminum hydroxides, which then
polymerize and absorb the aluminum-based colloid carryover .
The hanging Drapes of
Polymeric Materials of fabrics
arranged in parallel modules
which can be separately raised
and lowered into the reactor.
This again is in the form of
modules and spare modules kept
ready serves to replace the
saturated fabric modules when it
comes to issues of preventive
maintenance
Fig. 2.26 The Hadwaco evaporator
47
These have alert levels for the RO designer ranging from as low as 0.1 to 1.0 mg/L as
aluminum in the feed water, Barium as barium sulfate (BaSO4) whose solubility is rather
low, bicarbonate which can cause a RO scaling problem in the back-end, Boron which is
a foulant, Iron which can cause precipitation in the back end of the RO system, naturally
occurring organic material which can be a foulant to membranes even in natural waters
with total organic carbon (TOC) at 3 mg/L, BOD at 5 mg/L, COD at 8 mg/L and colour
as related to the molecular weight of Tannin & Lignin besides of course dissolved gases
whose solubility is increased at the high osmotic pressures in the RO system are sources
of concern. Silica being a complex and somewhat unpredictable with the total
concentration being composed of “Reactive Silica” (e.g. silicates SiO4) as dissolved
silica that is slightly ionized and has not been polymerized into a long chain and
“Unreactive Silica” all compound the problems in a day to day sustainable control.
2.36 FOULING OF RO MEMBRANES
Arising from the above, the fouling membrane need to be duly understood instead of
blindly opting for RO membranes especially as eventual evaporators also are affected.
The fouling physico chemical phenomena and its mechanism is best shown in Fig. 2.27.
Fig. 2.27 Mechanisms of physico-chemical fouling in R O membranes
48
Fouling is considered as a complicated phenomenon, of which causes of fouling are
multiple and poorly understood, identified the main contributors to fouling in MF and UF
of surface water as particulate fouling/scaling, and organic fouling. Therein it is also
stated that hardly one type of fouling occurs alone, but always a combination of them.
Figure 2.28 shows the scheme for rate of fouling
2.37 MEMBRANE FOULING CATEGORIES
Fouling is classified into four categories, distinguished by their main cause, as (a)
inorganic fouling/scaling, (b) particulate fouling/scaling, (c) microbial fouling, and (d)
organic fouling. Combinations of these fouling types can also occur at the same time.
Inorganic fouling (scaling) occurs when ion concentration of inorganic precipitates and
metals exceed the saturation index and precipitate on the membrane surface and inside
the pores. Since MF and UF do not have a sufficiently narrow pore size to mechanically
sieve metals and ions from the bulk water concentration polarization of them on the
surface of the membrane does not occur. Particulate fouling is caused by organic and
inorganic suspended and colloidal particles present naturally in surface water and
electrically charged, due to the presence of charged functional groups on the surface of
the colloid itself or through the adsorption of ions from the surrounding water. Particulate
fouling was found to be the main contributor which caused the flux decline.
Fig. 2.28 Integral occurrences of reversible and irreversible fouling
49
Accumulation in the form of retained particles, colloids, macromolecules and other
matter in the feed water depositing on the membrane surface and/or within membrane
pores by constricting the pore diameter which in subsequent stage leads to flux decline.
Microbial fouling is a result of the multiplication of bacteria attached on the membrane
surfaces. Their production of extracellular polymeric substances leads to the formation of
biofilms, which protect them from biocides. The severity is said to be greatly related with
feed water conditions such as abundance of microbes, nutrient availability and such other
favourable conditions for profuse microbial growth. Organic fouling is profound with
source water containing relatively high natural organic matters (NOM) and is believed to
be the most significant factor contributed to flux decline. However organic fouling of MF
membranes is promoted by chemical bonding between cations and negatively charged
organic material. Frequently multivalent cations are mentioned e.g. chemically bind
between negatively charged membrane surface and negatively charged NOM fractions
determining extend of fouling. Calcium (Ca 2+) is mentioned as inorganic foulant.
2.38 CONTROL OVER FOULING OF MEMBRANES
The fouling can be by organic, biological, hydroxide or particulate or a combination
thereof. Biological / organic fouling are somewhat synonymous and is a result of
microbial activity and attachment on membrane surface and release of biopolymers
arising in turn from sulphate reducing and anaerobic bacteriae, algae and assimilable
organic compounds. The low concentrations of metals can also be foulants if these are
oxidized to their oxides during membrane travel at high pH especially in processes such
as the High Efficiency Reverse Osmosis (HERO) and these may deposit either alone or in
combination with organic / biological fouling. Particulate fouling can be controlled by
pretreatment through ultra filtration / microfiltration etc. Colloidal fouling is the result of
negatively charged colloidal particles surrounded by a diffuse double layer and hence the
charge sustained and settling times as 3m / million years. The control over fouling is a
combination of the above and is site specific. The advent of the ultra filtration / micro
filtration membranes are useful as these membrane pore sizes are capable of filtering out
the particulates in the sub micron range.
50
2.39 REMOVAL OF SILICA, CA & MG TO CONTROL SCALING
In the present conventional practices of pretreatment to RO membrane and its
downstream evaporation of RO rejects, the fouling and scaling control is the biggest
challenge and can be brought about a reliable method of predicting the solubility and
kinetics of scaling and to develop an approach for scaling prediction and as accurate
predictive test to determine the fouling potential of the feed water and in fact both these
are still elusive thus underscoring the need to institute a preempting method of
pretreatment which can be an umbrella to ensure against the need for this tortuous control
of scaling and fouling control. As an extension of the above, the need to remove as much
as possible the divalent Ca, Mg as also Silica and pathogens are also equally important to
ensure the basic objective of this work, being the utilization of the high TDS waters
whether it is a naturally occurring water or a RO reject more as a sustainable resource
utilization that a tortuous intricacy of pretreatment, RO membrane, reject from membrane
and thermal evaporators. Some useful literatures in this focus are further reviewed.
2.40 SILICA REMOVAL BY PRECIPITATION
The removal of Silica in pretreatment stage itself implies the use of precipitation
chemistry although calcium silicate is quite insoluble, this compound does not form
rapidly except at very high temperatures. Aluminum salts can be used to precipitate
silica, but the consequences of leaving a substantial aluminum residual in the product
water makes this process undesirable. This is seen from the studies of using Poly
Aluminium Chloride (PAC) and used an ultra filtration membrane to filter out the
precipitated silica and blend it with the precipitated water mixture as shown in Fig. 2.29.
Fig. 2.29 Schematic diagram for In-line coagulation/ultra filtration process
51
The conventional method of precipitating silica has always been co-precipitation with
magnesium. Since silica becomes part of the magnesium precipitant, some means of
adding already precipitated magnesium (magnesium oxide) for precipitating magnesium
in situ is used. In situ precipitation works much better than already precipitated
magnesium, probably due to surface area of the precipitant and proximity to a silica
molecule. The addition of soluble magnesium salts (such as MgCl2) often is desirable but
it is an increase of TDS. Even though it is less effective, MgO is more often used. The
advantage of MgO is that it adds little or no TDS to the water. Temperature and pH also
have important effects on silica removal by precipitation.
The precipitation mechanism occurs faster and more completely at high temperatures.
The pH must be high enough to cause magnesium to precipitate but not so high as to
make the precipitant resoluble. The dosage is 1 mg/l of SiO2 removal for each 1 mg/l of
Mg removed if it is in-situ and 1 mg/l of SiO2 removal for 10 mg/l of Mg removed if
removed by adding MgO in ex situ. RO systems also can be used to reduce silica
concentration. Although cellulose acetate and early thin-film composite materials only
provided moderate silica rejection, newer materials reject silica quite well. The
mechanism of removal probably is by hyper-filtration, but also is related to degree of
ionization since silica is more completely removed at a high pH. Since silica is
concentrated by the membrane in the reject stream, silica solubility can be an important
consideration. RO systems currently are unable to achieve as complete removal of
reactive silica as ion exchange, but are far better at removing non-reactive silica.
2.40.1 Silica Removal by E Cells
These E cells are electro dialysis stacks where the water-flow channels are filled with ion
exchange resin. The mechanism of removal probably is that the resin first exchanges for
various ions (including silica), slowing them down, and then allowing them to be pulled
through the membranes. Since silica is weakly ionized, a higher current density is needed
for a high percentage of silica removal. The E Cell process currently is more expensive
than RO for bulk removal of ions and suffers the same inability as ion exchange to
remove non-reactive silica.
52
2.41 PRECIPITATION OF HEAVY METALS
The removal of heavy metals which also cause scaling as well as fouling of RO
membranes and also the thermal based evaporators has been postulated by many
technologies as membrane separation and precipitation as metal oxides. The membrane
technologies have not been effective in RO rejects or pretreatment to RO membranes
because of the interference to membranes from other pollutants such as suspended solids,
difficulty in attaining the required SDI and colours causing refractory organics all of
which affect the membrane performance. The more popular method is precipitation as
metal oxides at pH specific values as shown in Fig.2.30.
As the pH rises, the heavy metals present in the water are oxidized to their insoluble
metal oxides and get precipitated and do not redissolve upon neutralization be it by
acidification or carbonation. The pH limits are however temperature dependant as linked
to solubility at the temperatures on hand.
Fig. 2.30 pH values of least solubility of metals in aqueous solution
53
The removal efficiencies are reported as good even at very high concentrations as
reported especially in tackling acid mine drainage such as aluminum from 469 to 1.09
mg/l, arsenic from 4.01 to 0.0101 mg/l, copper from 2.39 to 0.0101 mg/l, iron from 653
to 0.0038 mg/l and nickel from 8.77 to 0.0389 mg/l
2.42 REMOVAL OF Ca AND Mg
For removal of divalent Ca and Mg the conventional method of Lime Soda softening is
there but it does not remove any other ions.
2.43 VALIDATING RO FEED QUALITY FOR IONIC BALANCE
More often, RO membrane manufacturers adjust the feed water cationic and anionic
concentrations to get at the ionic balance before predicting the RO membrane
performance. If the above ionic balance is not balanced, it becomes nearly impossible to
predict not only the RO membrane performance but also the RO reject and hence, the
thermal evaporator orother reuse technologies.
2.44 ARRIVING AT A MONOMOLECULAR NACL IN ROR
2.44.1 Driving the Cations to Monovalent NaCl
The reuse of RO rejects depends on getting a compound of monovalent compounds like
NaCl. This is possible by recourse to the Lime-Soda process precipitation chemistry.
It is possible to superimpose the water quality derived from the RO reject quality from
the design sheets of RO membrane and arrive at the dosages of chemicals needed before
going into the RO reject utilization exercise, but then, in the case of RO feed from treated
wastewater, it is necessary to address the issues of colour, BOD, COD, N, P, organic
substances and as interfering compounds even in small concentrations.
Specifically the phosphates need careful evaluation as these are known to form a coating
around the precipitated molecules and prevent it from settling when used as scale control
in cooling tower water quality control. Here lies the advantage of high pH Lime process.
54
2.45 CLASSIFICATION OF MEMBRANES
Other common classification than the separation mechanism of membranes in general, as
given by Mallevialle et al., (1996) is structured into physical morphology, membrane
geometry and module configuration, chemical nature, and operation conditions.
2.45.1 Physical Morphology
Flux is inverse to membrane thickness & asymmetric membranes are advantageous.
(a) The porous layer is generally an asymmetric membrane at a thin skin as the porous
substructure at a thickness of 0.1 to 1.0 mm, highly permeable to water and retains
suspended and dissolved solids at the pores of the skin, so that, once a solute enters a
pore, it will permeate with the filtrate and not be trapped in the membrane.
(b) Symmetric membranes have a constant pore size over the whole cross section of the
membrane, and have a thickness of 10 to 200 mm.
(c) Composite membranes are asymmetric membranes with a very dense top layer and
thin sub layer originate from different materials to be optimized independently.
2.46 MEMBRANE GEOMETRY
MF module geometries are Hollow Fibre Capillary, Tubular or Spiral
(a) Hollow Fibre (Capillary) Membranes consist of up to several from a diameter of <1
to 5mm with large surface area to volume ratio, simplicity of construction but the
disadvantage of high susceptibility to fouling, though can be back flushed.
(b) Tubular Membranes are characterized by a low packaging density, but good ability
to filter high turbid and viscous fluids, and are easy to clean.
(c) Spiral membranes need pre-treatment to eliminate suspended matters.
55
2.47 MEMBRANE CHARACTERISTICS
Organic Membranes are most common and show a great degree of flexibility with respect
to rejection characteristics. Their advantages are the easy processing, low cost,
availability of wide structure variations, and the possibility to realize any configuration.
Their disadvantages are reduced chemical resistance against chlorine and cleaning agents
as well as inferior stability at high temperature, high pressure, and time dependent
relaxation phenomena. Most commonly used materials are Cellulose acetate, polyamide
and polysulfone. (Mallevialle et al., 1996). Inorganic membranes are more reliable but
the downside is high cost. Materials most commonly used for ceramic membranes are
metal oxides like Aluminium Oxide, Zirconium Oxide, Titanium Oxide and Silicon
Dioxide and combinations. Surface charge is another important aspect of membranes is
their surface charge as hydrophilic or hydrophobic. Hydrophilic materials possess an
ability to form hydrogen-bonds with water. Though several studies focus on the
application of ceramic membranes in surface water treatment applications has helped
conclude on promising result for use in drinking water. The attributes, from these studies
are summarized in Table 2.5 and depict the facets.
Table 2.5 Comparison of ceramic and polymeric membrane properties
56
2.48 MF MEMBRANE OPERATION MODES
Two operation modes used in MF membrane processes are dead-end and cross-flow
In dead-end mode, all the feed water is forced to flow through the membrane so that
retained particles accumulate and form a type of cake or gel layer on the membrane
surface. The thickness of the cake layer increases with the filtered volume. In cross-flow
mode, the feed flow is parallel to the membrane surface and perpendicular to the filtrate
flow. A part of the feed water (concentrate) is recycled. These systems are more
susceptible to fouling but have lower energy consumption.
A further distinction is made into constant pressure and constant flux operation. For
constant pressure mode, where constant pressure is applied, flux decreases over filtration
time. In constant flux mode, the driving force of pressure is subsequently increased to
overcome the increasing resistance of the deposit formed on the membrane surface and
for keeping the permeate flux constant. Generally in pilot and full scale applications for
potable water treatment constant flux mode is employed. Only for lab scale applications
constant presser mode is applied. (Davis and Grant, 1992)
The choice of membrane material directly influences the separation efficiency, as the
membrane characteristics influence the solvent and solute fluxes through the permeability
coefficients. For obtaining a good efficiency, the membrane material must have high
affinity for the solvent, and low affinity for the solute. The most common reverse osmosis
membranes which attained the stage of economic application in water purification plants
are made of cellulose acetate (CA) or polyamide (PA).
2.49 RO MEMBRANE PROCESS
For most technical applications, RO membranes are used in cross flow design where
water is flowing continuously over the membrane surface. Since the permeate flow is
proportional to area of the membrane, spiral wound modules are used, obtained by rolling
stacks of membranes with separating spacer mats into cylindrical shape unit. Such a
configuration offers high surface area per unit volume.
57
The salt solution is fed axially, the water permeates the membranes and flows radial
toward the center of the cylindrical module where is collected in the permeate pipe, as
presented in Fig. 2.31.
Fig. 2.31 Spiral wound RO membrane module.
2.50 CHARACTERISTICS OF ROR
Desalination plants generate two products (clean water) and concentrate (reject or
residual stream). Proponents recognize that cost-effective and environmentally-sensitive
concentrate management can be significant obstacles in the widespread use of
desalination technologies. Proper concentrate disposal and construction methods
incorporated in the plant’s design can mitigate the concentrate’s impact on the receiving
water environments and groundwater aquifers. The following section describes
concentrate characteristics and mechanism options.
Concentrate (inter alia Reject) is the byproduct from desalination. Concentrates are
generally liquid substances that may contain up to 20% of the treated water. Brine is a
concentrate stream that contains a TDS concentration greater than 36,000 mg/L. Critical
concentrate parameters are TDS, temperature, and specific weight (density). The
concentrate may also contain low amounts of certain chemicals used during pretreatment
and post-treatment (cleaning) processes. Characteristics of the generated concentrate
depend on the type of desalination technology used. Table 2-6 shows characteristics of
concentrates from various types of desalination plants (Mickley 2001).
58
The amount of concentrate produced from a desalination plant is a factor of the
desalination process’ recovery rate (product water/feed water). Generally, membrane
plants have a higher recovery rate than distillation plants, resulting in a higher salt
amount in the concentrate.
As shown in Table 2.6, concentrate produced from seawater reverse osmosis (SWRO)
plants can have up to two times more salt concentration than the receiving water, while
the concentrate produced from a distillation process may have only a 10 percent higher
salt concentration than the receiving water. In distillation processes, the system mixes the
concentrate with once-through cooling water to dilute the salt concentration.
Table 2-6 also shows that concentrate from distillation processes is typically warmer, 10-
15°F above the ambient water temperature. Concentrate temperature from the reverse
osmosis process remains at the ambient water temperature.
Table 2.6 Characteristics of ROR
Sl
No. Process R O R O MSF / MED
1 Feed water Brackish Seawater Seawater
2 Recovery 60-85% 30-50% 15-50%
3 Temperature Ambient Ambient 10-15deg F
above ambient
4 Concentrate Blending Possible, but
not typical
Possible, but
not typical
Typical with
cooling water
Specific weight (or density) is another critical concentrate parameter. Compared to
freshwater, concentrate has a higher density due to the increased salt concentration. When
concentrate with a higher density is disposed into waters of lower salinity (lower density),
the concentrate tends to sink. In comparison, typical discharge from wastewater treatment
plants will float, because its density is normally less than the receiving water. The
tendency of the concentrate to sink when interacting with the receiving water introduces
problems for the marine environment. In some cases, plants reduce the concentrate
density by diluting it before being discharging it into receiving water.
59
2.51 STUDIES ON RO MANAGEMENT TECHNIQUES
2.51.1 Existing ROR Minimization & Management Methods
Several methods for concentrate management and disposal exist and have been
commercialized, while several are emerging. An overview of the existing methods is
presented first, followed by a description of several emerging and promising methods.
Conventional concentrate management technologies for BWRO and SWRO include
surface water discharge, sewer discharge, deep well injection, evaporation ponds, land
application, and thermal evaporation toward ZLD, or near- ZLD applications.
2.51.2 Surface Water Discharge
Surface water discharge to a receiving body is the most common concentrate disposal
practice in the U.S. This method is employed by approximately 48 percent of all desalting
facilities in the country (Mickley, 2001). Access to possible receiving bodies, such as a
river, lagoon, Ocean is required. An NPDES permit is required and permit limits may
include total suspended solids, total dissolved solids (TDS), and specific nutrients and
metals, such as arsenic. Disposal costs are low if the length of the pipeline to the
receiving body is reasonable and the concentrate meets the permit requirements.
2.51.3 Sewer Discharge
Discharge of concentrate to an excising sewage collection system is the second most
common concentrate disposal practice in the U.S. and is employed by approximately 40
percent of all desalting facilities in the country (Mickley, 2001). It requires a permit from
the local sewage agency. The permit may impose limitations to protect the sewers and
treatment plants’ infrastructure, the treatment process, and final effluent and biosolids
quality. Smaller volume discharges have limited permitting requirements.
2.51.4 Deep Well Injection
Deep well injection (DWI) or subsurface injection involves the disposal of concentrate
into a deep geological formation that will serve to isolate the concentrate permanently
from shallower aquifers that may be used as a drinking water source.
60
Regulatory considerations include the receiving aquifer’s transmitivity and TDS, and the
presence of a structurally isolating and confining layer between the receiving aquifer and
any overlying source of drinking water. DWI injection is typically economical and
employed only for larger concentrate flows (> 1 mgd) and used for large RO plants.
2.51.5 Evaporation Ponds
In this method, the concentrate is pumped into a shallow lined pond and allowed to
evaporate naturally using solar energy. Once the water has evaporated, the salt sludge is
either left in place or removed and hauled offsite for disposal. Evaporation ponds can be a
viable option in relatively warm, dry climates with high evaporation rates, level terrain,
and low land costs. They are typically economical only for smaller concentrate flows.
2.51.6 Land Application
Land application, such as spray irrigation, is a beneficial reuse of concentrate. It can be
used for lawns, parks, golf courses, or crop land. Land application depends on the
availability and cost of land, percolation rates, irrigation needs, water quality tolerance of
target vegetation to salinity, and the ability to meet groundwater quality standards.
2.52 ZLD AND NEAR ZLD
These are essentially thermal methods, such as thermal evaporators (vapor compression),
crystallizers, and spray dryers that can reduce the concentrate to slurry (near ZLD) or a
solid product for landfill disposal (ZLD).
While these methods are well established and developed, their capital and operating costs
are currently relatively high and can exceed the cost of the desalting facility itself over a
period of time especially on difficult composition of the ROR with scaling or corrosion
potentials mandating frequent downtimes and even renewals & replacements which
again mandates a perpetual dependence of the equipment manufacturer and hence this
option is typically not employed except for special situations (such as an inland
desalination facility with no sewer or surface water access) coupled with small flows and
the products from treatment of ROR in this is compiled in Table 2.7.
61
Table 2.7 Detail of products from treatment of reject brine
Product name Chemical
composition Physical form Potential application
Gypsum-
magnesium
hydroxide
CaSO4.2H2O
+ Mg(OH)2 Fine grain slurry
1.Sodic soil remediation
2.Fertiliser additive
3.Drip feed application
Magnesium
hydroxide Mg(OH)2 Fine grain slurry
1.Wastewater treatment
2.Agriculture
3.Cattle feedstock additive
4.Refractories
Sodium chloride NaCl Crystalline salt
1.Food Processing
2.Agriculture
3.Chor-alkli
Precipitated
calcium carbonate CaCO3
Fine grain
crystalline
1.Paper coating pigment
2.Filler in plastic paint
Sodium sulphate Na2SO4 Crystalline 1.Pulp and paper industries
Calcium chloride CaCl2 Concentrated
solution (35-38%)
1.Rad base stabilization
2.Sodic soil remediation
3.Dust suppression
2.53 EMERGING ROR MINIMIZATION & MANAGEMENT METHODS
A review of emerging and promising (not yet commercially significant) desalination and
concentrate management methods is presented in this section. Brief descriptions of each
key emerging technology are outlined, including key attributes and technology status.
Emerging methods that aim to enhance recovery and thus minimize concentrate include
the physical-chemical or biological treatment of primary RO concentrates, seeded slurry
processes to remove scaling compounds in a controlled fashion, dewvaporation,
membrane distillation, forward osmosis, and new methods based on softening
pretreatment and pH control, among others. Emerging ROR management technologies
may consider newer methods based on evaporation that aims to reduce the footprint
requirement of traditional evaporation ponds, reuse applications, or recovery of some sort
of useful solids as byproducts for beneficial uses.
62
2.53.1 Two-Phase Reverse Osmosis with Intermediate Chemical Precipitation
This is a physical-chemical approach to enhancing the recovery of an RO process through
treating and minimizing concentrate, using established technologies such as lime soda
softening and a second-phase RO. The approach is based on treatment of the concentrate
from a primary RO system using a physical-chemical process, followed by its subsequent
treatment in a secondary RO system. The concentrate treatment step focuses on removing
cations of concern via precipitation to reduce the scaling potential of the concentrate. The
steps involved are chemical treatment and precipitation for removing calcium,
magnesium, and other sparingly soluble salt components, followed by filtration (media
filtration or membrane filtration) for removing solids carryover from the precipitation
process. Since the secondary RO system will be operated at a higher TDS, it will require
higher pressures than the primary RO system. The combined recovery of the process is
estimated and reported to be 95 percent or greater for brackish water. This technology
includes an application of established unit processes and relatively low additional energy
requirements. Considerations include additional chemicals, production of sludge from the
chemical precipitation process, and the footprint and costs of chemical feed and storage
facilities and the secondary RO system. The approach was recently pilot tested at the
Metropolitan Water District of Southern California.
2.53.2 Two-Phase Reverse Osmosis with Intermediate Biological Reduction
This is a biological approach to enhancing the recovery of an RO process through
treatment and minimization of concentrate, using established technologies such as
biological reduction and a second-phase RO. Like the physical-chemical approach
described above, this approach is based on the treatment of the concentrate from a
primary RO system, followed by its treatment in a secondary RO system; however, the
concentrate treatment step focuses on removing anions (sulfate and carbonate, via
biological treatment followed by air stripping) to reduce the scaling potential of the
concentrate from the primary RO process. The core of the process is the biological
reactor where sulfate is biochemically reduced to sulfide. The reaction is favorable under
anaerobic conditions when a carbon source (electron donor) is present. Sulfides and
carbonates are subsequently air-stripped under acidic conditions.
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The hydrogen sulfide and other reduced sulfur species in the off-gas must be neutralized
(i.e., oxidized) prior to off gas discharge. Following this, a gravity thickener followed by
media filtration (or microfiltration) is needed to remove biological and other solids. The
filtered water is concentrated in a separate, downstream secondary RO process, or it can
be recycled back to the influent of the primary RO process. The combined recovery of the
process is estimated and reported to be 95 percent or greater for brackish water. The
technology includes an application of established unit processes and relatively low
additional energy requirements. Considerations include additional chemicals and
biological treatment, production of sludge from the solids removal process, and footprint
and costs of additional unit processes and the secondary RO system. This approach has
recently been tested at bench scale at Metropolitan Water District of Southern California.
2.53.3 RO with Softening Pretreatment and High pH Operation
This patented technology consists of the key components of a hardness and alkalinity
removal step, a degasification step to remove carbon dioxide, and caustic addition to
increase the pH of the RO feed water. It was originally developed to provide ultrapure
water to the microelectronics industry. For municipal brackish water, the process
combines a two-phase RO process with chemical pretreatment of primary RO,
intermediate ion exchange treatment of primary RO concentrate, and high pH operation
of secondary RO. The (secondary) RO step operates as a “high-efficiency” system due to
ion exchange pretreatment and high pH operation, so the system is called High Efficiency
Reverse Osmosis (HERO). The concentrate of the primary RO is treated in weakly acidic
cationic (WAC) exchange resins. The carbon dioxide from the concentrate is removed
and the pH is raised above 10 to allow operation of the secondary RO at high recoveries.
Operating the negatively charged membranes at a high pH is reported to allow better
removal of both weakly ionized anions as well as the strongly ionized species.
The solubility of silica is increased at high Ph, which allows greater recovery rates on
high silica waters. The combined recovery of the process is estimated and reported to be
greater than 90 percent for brackish water, with typical recovery of about 95 percent.
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The technology includes the application of established unit processes, negligible potential
of silica or calcium carbonate scaling or biological fouling, higher rejection of both
weakly ionized anions and strongly ionized species, and minimized cleaning.
Considerations include proprietary technology, additional chemical and ion exchange
treatment, production of sludge from the chemical treatment process, and footprint and
costs of additional unit processes and secondary RO system. This approach has been
installed at full-scale at several industrial facilities (electronics and ultrapure water
applications, and in power industry for cooling water recycling).
2.53.4 Two-Pass Nano filtration
Although NF is commonly used for softening, in this approach two passes of NF are used
in series to remove adequate amounts of salt and produce freshwater from seawater. The
first pass removes greater than 90 percent of the salinity, and the second pass removes
greater than 93 percent, resulting in a total salt reduction of about 99.5 percent.
The first NF pass operates at a pressure around 525 psi, and the second NF pass operates
at a lower pressure around 250 psi. This implies lower overall energy requirements
compared to the operating pressures of about 800 psi or higher that are typically
employed in conventional RO desalination. The presence of two passes of NF implies
two barriers to contaminants, and therefore increased reliability of water quality. It also
implies increased flexibility; for example, the second pass can be operated at a higher pH
by addition of a base, which allows better rejection of boron. The overall recovery from
the process is about 30 to 45 percent for seawater desalination, which is comparable to
conventional RO desalination. The approach is characterized by lower operating
pressures and energy costs for seawater desalination, multiple barrier technology, and use
of established unit processes. Limitations include overall recovery comparable to
conventional RO desalination.
This approach has been pilot tested by the Long Beach Water Department, California,
since October 2001. The Long Beach Water Department has applied for a patent on the
process, which is being optimized in terms of membrane selection and operation.
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2.53.5 Seeded Slurry Precipitation and Recycle
This technology uses crystals to precipitate scaling compounds in a membrane
application and is known as slurry precipitation and recycles RO (SPARRO). Seed
crystals are introduced in a tubular RO membrane such that the scaling compounds are
precipitated (on seed crystals rather than on the membrane) and removed in a controlled
fashion. The concept involves circulating a slurry of seed crystals within the RO system.
The seed crystals serve as preferential growth sites for calcium sulfate and other calcium
salts and silicates, which begin to precipitate as their solubility products are exceeded
during the concentration process within the membrane tubes. The preferred growth of
scale on the seed crystals prevents scale formation on the membrane surface. Since the
seed slurry is recirculated within the membranes, the process is confined to the use of a
membrane configuration that will not plug, such as tubular membrane systems. Gypsum
crystals are used to precipitate calcium sulfate. The water to be desalted is mixed with a
stream of recycled concentrate containing the seed crystals and fed to the RO process.
The concentrate with seed crystals is processed in a cyclone separator to separate the
crystals, and the desired seed concentration is maintained in a reactor tank by controlling
the rate of wasting the upflow and/or underflow streams from the separator. The
combined recovery of the process is reported to be greater than 90 percent. The
technology is characterized by relatively low energy costs. Considerations include
requirement of tubular RO membranes, footprint of tubular membranes, and additional
chemicals. This approach is tested at pilot scale in the East Rand Proprietary Mines, SA.
2.53.6 Membrane Distillation
The membrane distillation (MD) process consists of passing heated brackish or seawater
over a porous, hydrophobic membrane surface. The membrane allows water vapor to
penetrate the hydrophobic membrane while repelling the liquid water. The clean vapor is
subsequently carried away from the membrane and condensed as pure water, either
within the membrane package or in a separate condenser system. MD differs from other
membrane technologies in that the driving force for desalination is the difference in vapor
pressure of water across the membrane, rather than the feed pressure that forces the liquid
water through the membrane.
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The driving gradient for vapor production can be enhanced by heating the feed water,
which increases the vapor pressure and with that the penetration rate. The energy source
for feed heating and/or for a vacuum system to sweep away the vapor may be low-grade
thermal energy, such as supplied by low-pressure steam, waste heat, solar energy, or
geothermal energy. A variety of arrangements and configurations can be used to induce
the vapor through the membrane and to condense penetrant gas. Common to all concepts
is that the feed water directly contacts the membrane and the condensation is typically
achieved via the four process configurations as under:
(a) Air-Gap Membrane Distillation, the most common &versatile provides an air gap
after the membrane, followed by a cool surface for condensation to occur.
(b) Direct-Contact Membrane Distillation The cool condensing solution (pure water)
directly contacts the membrane and condenses the vapor as it passes through the
membrane. The coolant liquid flows countercurrent to the feed water and is the
simplest best suited for desalination and concentration of aqueous solutions.
(c) Sweep-Gas Membrane Distillation A sweep gas pulls the water vapor out of the
membrane gap for subsequent condensation outside of the membrane package and
is especially advantageous when volatiles need removal from an aqueous solution.
(d) Vacuum Membrane Distillation Vacuum is applied to the penetrant membrane
space to pull the water vapour out of the system. This concept is useful when
volatiles are to be flushed from aqueous solutions. The technology is characterized
with low temperature requirements (typically 60°C to 70°C); possible use of low-
grade heat (solar, industrial waste heat, or desalination waste heat may be used);
minimal pretreatment needs; and negligible scaling or precipitation concerns.
Considerations include need of waste heat to obtain better economics.
(e) MD technology is currently in the development and demonstration phase.
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2.53.7 Capacitive Deionization
During capacitive deionization (CDI), ions are adsorbed onto the surface of porous
electrodes by applying a low voltage electric field, producing deionized water. Liquid
flows between high surface electrode pairs having a potential difference of 1.3 DC
voltage. The negative electrodes attract positively charged ions such as calcium,
magnesium, and sodium. Conversely, the positive electrodes attract negatively charged
ions such as chloride, nitrate and silica. The major mechanisms related to the removal of
charged constituents during electronic water treatment are physisorption, chemisorption,
electrode position, and/or electrophoresis. Unlike ion exchange, no additional chemicals
are required for regeneration of the electro sorbent in this system. Adsorbed ions are
desorbed from the surface of the electrodes by eliminating the electric field, resulting in
the regeneration of the elecrodes. The efficiency of CDI strongly depends upon the
surface property of electrodes such as their surface area and adsorption properties. And
the technology of capacitive deionization is still in the developing stage. Bench-scale
experiments have been conducted at Colorado School of Mines using brackish
groundwater as part of a research study sponsored by Bureau of Reclamation. An
industrial CDT unit with a capacity of 1000 gpd is planned for testing by Colorado
School of Mines at a gas production well during late 2005.
2.53.8 Dewvaporation
Dewvaporation technology involves the desalination of seawater and brackish water,
suitable for small plant applications. Another potential application of dewvaporation
technology could be in the volume reduction of RO concentrates by an order of
magnitude. Dewvaporation is a specific process of humidification-dehumidification
desalination. Brackish water is evaporated by heated air, which deposits fresh water as
dew on the opposite side of a heat transfer wall. The energy needed for evaporation is
supplied by the energy released from dew formation. Heat sources can be combustible
fuel, solar or waste heat. The tower unit is built of thin plastic films to avoid corrosion
and to minimize equipment costs. Towers are relatively inexpensive since they operate at
atmospheric pressure with carrier gas such as air is brought into the bottom of the tower
on the evaporation side of a heat transfer wall at a typical wet bulb temperature of 69.8°F.
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The wall is wetted by saline feed water, which is fed into the evaporation side at the top
of the tower. As the air moves from the bottom to the top of the tower, heat is transferred
into the evaporation side through the heat transfer wall, allowing air to rise in temperature
and evaporate water from the wetting saline liquid, which coats the heat transfer wall and
as a result, the concentrated liquid leaves from the bottom of the tower, and hot saturated
air leaves the tower from the top at 189.3°F. Heat is added to this hot air by an external
heat source, increasing the air humidity and temperature to 190.2°F. This hotter saturated
air is sent back into the top of the tower on the dew formation side. The dew formation
side of the tower, being slightly hotter than the evaporation side, allows the air to cool
and transfer condensation heat from the dew formation side to the evaporation side.
Finally, pure water condensate and saturated air leave the dew formation side of the
tower at the bottom at 119.7°F. Total external heat needed is made up of the heat needed
at the top to establish a heat transfer temperature difference and the heat needed to
establish a temperature offset between the saline feed stock and the pure water
condensate. The tested recovery is reported as 82 to 85 percent for brackish water and 67
percent for seawater. The technology is characterized by elimination of scaling problems,
since the evaporation occurs at the liquid-air interface and not at the heat transfer wall.
Considerations include cost, affordability, small scale, and concentrate disposal.
Demonstration towers are in operation at Arizona State University (ASU) laboratories.
2.53.9 Forward Osmosis
In forward osmosis (FO), like RO, water transports across a semi-permeable membrane
that is impermeable to salt; however, instead of using hydraulic pressure to create the
driving force for water transport through the membrane, the FO process utilizes an
osmotic pressure gradient. A “draw” solution having a significantly higher Osmotic
pressure than the saline feed water flows along the permeate side of the membrane, and
water naturally transports across the membrane by osmosis. Osmotic driving forces in FO
can be significantly greater than hydraulic driving forces in RO, potentially leading to
higher water flux rates and recoveries. With the use of a suitable draw solution, very high
osmotic pressure driving forces can be generated to achieve high recoveries that, in
principle, can lead to salt precipitation.
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The saline feed water is fed to the FO unit, which, in principle, can incorporate spiral
wound or hollow fiber membrane modules. The feed water and draw solution flow
tangent to the membrane in a cross flow mode. Through osmosis, water transports from
the seawater across the salt rejecting membrane and into the draw solution. High osmotic
pressure gradients can lead to a high recovery given appropriate staging of the process.
To yield potable water, the diluted draw solution is sent to a separation unit, comprising a
distillation column or a membrane gas separation unit. The separated draw solution is
recycled back to the FO unit. The FO process is characterized by relatively low fouling
potential, low energy consumption, simplicity, and reliability. With the suitable draw
solution and appropriate semi-permeable membrane, the FO process can lead to salt
precipitation, i.e., zero liquid discharge. Considerations include need of appropriate draw
solution and membranes, which are the primary obstacle to a feasible FO process. An
effective draw solution solute must have very specific characteristics. It must have a high
osmotic efficiency and must also be non-toxic, since trace amounts may be present in the
product water. Chemical compatibility of the membrane is also a key concern because the
draw solution can react or degrade the membrane.
Most importantly, for processes involving the production of potable water, the draw
solute must be separated and recycled easily and economically. Previous studies have
reported that commercial RO membranes are not suitable for the FO process because of
relatively low product water fluxes attributed to severe internal concentration polarization
in the porous support and fabric layers of the RO membrane. One of the important tasks
for future research is the development of a semipermeable FO membrane having high salt
rejection and minimal internal concentration polarization to realize higher product flux.
The technology of FO is still being developed. A bench-scale FO unit has been built and
operated at Yale University laboratory supported by the Office of Naval Research. FO
also was used as pretreatment for RO in a direct osmotic concentration (DOC) system for
wastewater reclamation in space. The study was sponsored by NASA’s Ames Research
Center. The NASA DOC test unit built by Osmotek Inc. was tested at the University of
Nevada, Reno. The DOC system provided high wastewater recovery (>95 percent).
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2.53.10 OVERVIEW
The desalination technology uses segregation of the undesirable dissolved salt content to
produce treated water with the required reduced salt content. These technologies can be
grouped as (a) Thermal based, (b) Membrane based and (c) Electro dialysis based.
The thermal based technologies in simple terms vaporise the water content and condense
it to recover the water and the segregated salt is available as slurry of a mix of the various
salts originally present and hence their disposal becomes a challenge.
The electro dialysis based technology and the membrane technology retain the segregated
salts in the dissolved form itself and lends itself primarily to transporting to the desired
location of disposal such as reject disposal back into the ocean in the case of sea water
reverse osmosis (SWRO) plants or for resource recovery as the various salts originally
present by chemical precipitation techniques.
Worldwide, desalination is used on a large scale only for drinking water supplies in
coastal towns. Though applications occur for industrial needs, the volumes used here are
a miniscule as compared to SWRO. Here again, the membrane based technology is the
one used most profusely because of its user friendly day to day operational procedures
and the avoidance of high thermal installations as boilers, evaporators etc.
Though issues seem to be in place up to this stage, the challenge of dealing with the RO
rejects is the deterrent because the pollution control guidelines do not permit the
discharge into the environment except into the marine coastal area. This implies the
complexity for inland industries of RO systems.
The so called resource recovery as the various salts by sequential precipitation is not
attractive commercially in the sense that rendering these commercially saleable will
require again solutionizing and reprecipitation to attain the purity.
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Thus, it poses the question of getting the salts out as solids and simply containing in a
secure landfill. This challenge does not find proven answers from the advanced countries
because these countries almost as a rule outsource such industrial processes as a whole to
the developing third world countries and procure the final products only with of course
support to the extent possible in the local RO reject practices.
Perhaps the notable contribution in this direction has been the demonstration R&D on
leather tannery soak liquor disposal in the tanneries at Ambur, India by the United
Nations Industrial Development Organization (UNIDO) and the wood stock wind
assisted evaporator for textile dyeing effluents at Tiruppur India by GTZ, the German
Agency for Technical Co-operation. But then, these have been site specific.
Although the various desalination techniques and their practical applications have been
discussed in-depth in the previous chapter R & D carried out by various researchers are
presented in brief in this chapter.
Applications that have been reported for RO processes include the treatment of organic
containing wastewater, wastewater from electroplating and metal finishing, pulp and
paper, mining and petrochemical, textile, and food processing industries, radioactive
wastewater, municipal wastewater, and contaminated groundwater (Slater et al., 1983a;
Cartwright, 1985; Ghabris et al, 1989; Williams et al., 1992). A review of RO wastewater
treatment follows; a thorough discussion of the application of RO membranes to
seawater, brackish water and industrial waste water
2.54 RO FOR SEPARATION OF ORGANIC POLLUTANTS
Sourirajan (1970) and Sourirajan and Matsuura (1985) compiled separation and flux data
of cellulose acetate membranes for a large number of organic compounds, including
many organic pollutants. They found that organic separation can vary widely (from <0%
to 100%) depending on the characteristics of the organic (polarity, size, charge, etc.) and
operating conditions (such as feed pH, operating pressure, etc.).
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In an early study, Anderson et al., (1972) reported some of the factors influencing
separation of several different organics (including acetone, urea, phenol, 2,4-
dichlorophenol, nitrobenzene) by cellulose acetate membranes. Rejections varied
considerably for the different solutes, and rejections of ionizable organics were greatly
dependent on degree of dissociation; nonionized and hydrophobic solutes were found to
be strongly sorbed by the membranes and exhibited poor rejection.
Edwards and Schubert (1974) reviewed some of the early separation results of herbicides
and pesticides with RO membranes. They also conducted studies with the herbicide 2,4-D
and found separations were <51%. It was noted that solute adsorption could occur.
Duvel and Helfgott (1975) also found organic separations varied with molecular size and
branching; they postulated organic separation was also a function of the solute's potential
to form hydrogen bonds with the membrane.
Chian et al. (1975) reported high rejections (>99%) for several pesticides with cellulose
acetate and a composite membrane and significant adsorption was noted.
Fang and Chian (1976) conducted studies on the separation of several polar organic
compounds with various functional groups using cellulose acetate and several other types
of membranes. This study found that the organic rejection varied considerably not only
with solute but also with membrane type.
Shuckrow et al. (1981) also listed cellulose acetate rejections of several different
organics; rejections were poor to moderate (such as only 10% for methylene chloride, up
to 73% for acenapthene). Several studies have compared organic rejections of cellulose
acetate with other membranes, and these have indicated aromatic polyamide and
composite membranes with organic rejections greater than those of cellulose acetate.
Kurihara et al. (1981) listed several organic rejections of the Toray composite membrane
PEC-1000 (polyfuran); as high, including 97% for acetone and 99% for phenol.
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Koyama et al. (1982) and Koyama et al. (1984) reported separation results for several
polar organic solutes (alcohols, phenols, carboxylic acids, amines, and ketones) and
various phenolic derivatives for a composite membrane. They found that the main factors
affecting rejection included molecular weight, molecular branching, polarity, and degree
of dissociation for ionizable compounds.
Lynch et al. (1984) compared cellulose acetate and thin-film, composite membrane
(Filmtec FT30, a cross linked aromatic polyamide) separations with a wide variety of
organic pollutants. The composite membrane rejections (greater than 90% for most of the
organics studied) and water fluxes were substantially better than the cellulose acetate
membrane; however, adsorption of some of the organics on the membranes was noted.
Rickabaugh et al. (1986) also indicated polyamide membrane rejections of chlorinated
hydrocarbons (>95%) were much greater than those of cellulose acetate membranes.
Bhattacharyya et al. (1987) and Bhattacharyya and Madadi (1988) investigated rejection
and flux characteristics of FT30 membranes for separating various pollutants (PAHs,
chlorophenols, nitrophenols) and found membrane rejections were high (>98%) for the
organics under ionized conditions. They also found substantial water flux decline
occurred even for dilute (< 50 mg/L) solutions of nonionized organics and observed
significant organic adsorption on the membrane in some cases.
Pusch et al. (1989) reported separation results for several membranes (four composite and
two asymmetric) for a variety of single and multicomponent organic solutions, including
many organic pollutants. Rejections varied from only 25% up to >99% depending on the
solute, but generally the composite membrane rejections were higher.
Williams et al., (1990) and Bhattacharyya and Williams (1992a) investigated
FT30membranes with ozonation as a feed pretreatment to remove chlorophenols and
chloroethanes and reduce declines in water flux caused by the organics.
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Feed TOC rejections of ozonation intermediates were 80% to 96%, and overall removals
of >99.8% were found for the model pollutant compound 2,4,6-trichlorophenol. Batch
adsorption experiments and material balances indicated that nonionizedchloro- and
nitrophenols could strongly adsorb on the membrane.
Rautenbach and Gröschl (1990a) also discussed that while high separations of organics
could be achieved by RO membranes, significant decreases in water flux could occur
even when only traces of organics were present. They indicated these flux declines could
be caused by organic sorption on the membranes.
Saavedra et al., (1991) considered the use of polyamide membranes for the treatment of a
phenol production waste stream; the stream contained organic acid salts and organic
peroxides. While the organic salts were highly removed (>94%), the peroxides were
poorly rejected. Studies with the peroxides indicated that some of these could cause
significant water flux drop.
Cheng et al., (1991) reported the effects of dilute solutions of the halocarbons CHCl3,
CHBr3, and CCl4 on the performance of DuPont cellulose acetate, polyamide, and thin-
film composite membranes. The halocarbons were mostly poorly rejected (5% to 83%)
by the three membranes; however, these caused water flux drops of up to 31%. The
results indicated that water flux drop was caused by halocarbon adsorption.
2.55 RO TREATMENT OF INDUSTRIAL WASTEWATER
2.55.1 Electroplating and Metal-Finishing Process Wastewaters
In most cases, process wastewaters from the electroplating and metal-finishing industries
must be treated to remove heavy metals before being discharged. Reverse osmosis is
ideal for this wastewater treatment for many of these operations since it allows both
recovery of the heavy metals and reuse of the product water in the process. The RO
process has been used in the treatment and recovery of wastewater containing nickel, acid
copper, zinc, copper cyanide, chromium, aluminum, and gold (Schrantz, 1975; Sato et al.,
1977; Kamizawa et al., 1978; Cartwright, 1985).
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McNulty et al. (1977) reported high rejections of nickel and total solids from
electroplating bath rinse water. Spatz (1979) discussed the use of RO in the nickel plating
industry to recover nickel from nickel plating bath rinse water. In this process the
permeate was recycled as rinse water, and the concentrate was recycled back to the
plating bath. This allowed 97% recovery of rinse with economy in nickel consumption.
Robison (1983) also discussed the use of a RO process to recover nickel from plating
rinse water; recycle of permeate and nickel concentrate resulted in substantial savings.
Imasu (1985) reported on the use of cellulose acetate and polyamide (FT30) membranes
at three Japanese plating shops with nickel, chromium, and gold plating lines. Up to 80%
water recoveries with high metal and TDS (>95%) rejections were possible, and the
product water was recycled. The RO processes were found to be cost-effective in treating
the wastewaters, and the compact nature of the RO system made it highly desirable to the
customers because of space limitations.
Thorsen (1985) discussed the RO treatment of effluent from an electrolytic polishing
process for aluminum products. The streams contained phosphoric acid and aluminum
from rinse water. DDS HR-98 membranes allowed 96% to 98% acid recovery (up to an
acid concentration of 20%) and produced permeate water suitable for reuse. The
membranes are stable even at the low pH values (0.9 to 1.0) found at high recoveries.
Davis et al., (1987) discussed two case histories of heavy metal wastewater treatment
using RO membranes. In the first case, spiral-wound polyamide membranes allowed 75%
water recovery with TDS rejections of >99% for a heavy metal-containing wastewater.
Scaling and fouling were reduced by pretreatment and periodic cleaning.
In the second case, rinse water effluents from a metal forming facility were treated.
Polyamide membranes gave rejections over 99% for calcium, cadmium, chromium,
copper, iron, magnesium, manganese, molybdenum, nickel, and tungsten and up to 90%
recovery of the effluent as purified water for reuse in the plant was found to be possible.
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It was noted subsequent treatment to recover molybdenum for reuse in the facility was
also possible. The RO system was cost-effective alternative to evaporation.
Slater et al., (1983a) reported on the use of RO membranes to remove cadmium from
metal processing wastewaters. The FT30 membranes used had cadmium rejections of
>99.5% in most cases and produced a high quality product water suitable for reuse.
Rejections of other metals (zinc, silver, copper, nickel, and tin) and overall conductivity
were >97% even at water recoveries up to 75%, and water fluxes remained at reasonably
high levels. It was concluded that the RO could be an efficient and cost-effective process.
2.56 PULP AND PAPER PROCESSING WASTEWATERS
The use of RO membranes in combination with other processes to treat wastewaters in
the pulp and paper industry has also been investigated. Morris et al., (1972) and Wiley et
al., (1978) conducted early studies with pulp and paper wastewaters. Glimenius (1980)
and Olsen (1980) outlined the use of RO to concentrate spent sulphite liquor (SLL, which
consists of lignosulfates and other organics as well as various inorganics) containing
wastewater before it was sent to an evaporator, resulting in lower energy costs for the
evaporator. Paulson also detailed the use of RO and ultrafiltration/RO processes to
concentrate SLL wastes before further treatment by evaporation. In the process RO
membranes concentrated solids from less than 2% to10%; it was noted that this
preconcentration would greatly reduce evaporator costs because of reduced volume to be
treated. High rejections of solids (>95%), BOD (88%), and COD (>96%) were reported
for short-term tests. Ultrafiltration treatment prior to a high pressure RO membrane was
reported to allow even further preconcentration prior to evaporation. It was pointed out
that RO processes would also produce water for reuse in pulping. Jönsson and
Wimmerstedt (1985) discussed the use of RO concentration prior to SLL evaporation,
concentration of weak black liquor by RO and the use of RO to treat bleach effluent;
rejections of both organics and inorganics in these effluents were >90%. They also
reported the use of tubular membranes to treat waste paper white water at reductions of
TDS at 99.4% and COD at 99.8% at recoveries of 95%).
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Hart and Squires (1985) indicated ZF99 membranes gave high rejections of lignin, TOC,
sugars, and color in wash waters, making the permeate suitable for reuse; however,
periodic membrane cleanings were required to restore water flux of the membranes.
Simpson and Groves (1983) and Ekengren et al., (1991) have reported some success in
the use of membranes to treat bleach plant effluent. The ultrafiltration and RO processes
used gave high removals of inorganics, COD, and chloroorganic compounds.
Dorica et al., (1986) also studied the use of ultrafiltration and RO processes to minimize
discharges of chlorinated organics and other pollutants in bleach plant effluents. Reverse
osmosis membranes completely removed color and 95% to 99.8% of organics, chloride,
and organic chlorine for water recoveries of 75% to 85%; feeds consisted of
ultrafiltration filtrate of caustic extraction effluent and effluent from a chlorination stage.
2.57 FOOD PROCESSING WASTEWATERS
Reverse osmosis also has been used to treat food processing wastewaters so that these
could be discharged or recycled; in many cases it was indicated a concentrate stream rich
in nutrients was produced. Hart and Squires (1985) discussed the use of ZF99 tubular
membranes to concentrate slaughter house effluent rich in COD, and Gekas et al., (1985)
also reported on the use of a RO system to treat meat processing wastewaters. Canepa et
al., (1988) studied treatment of olive mills wastewater containing high total solids and
COD with a combination ultrafiltration/RO process.
For the RO membranes rejections of TDS were >99% and COD were 93% for water
recoveries of 70%. The permeate was suitable for recycle. The use of an
ultrafiltration/RO process to reduce effluents from olive canning operations and allow
recycling of processing water has also been reported (Anonymous, 1988a).
Mohr et al., (1989) discussed several uses of RO in wastewater treatment in the food
industry, including for concentration of whey, fruit processing waters, and stillage waters.
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2.58 RADIOACTIVE PROCESSING WASTEWATERS
Because of high rejection of inorganic compounds, RO membranes have been studied for
treatment of radioactive effluents. Ebra et al., (1987) described a treatment facility that
included RO processes to remove low levels of radionuclides and hazardous chemicals
prior to discharge. Hsiue et al., (1989) reported on the use of RO membranes to treat
uranium conversion process effluent containing toxic, corrosive, and radioactive
compounds. The FT30 membranes studied had rejections of uranium ≥99.5% for water
recoveries up to 70%, and the results indicated that the treated effluent would meet
regulatory discharge standards. Chu et al., (1990) used a three stage process consisting of
nanofiltration, reverse osmosis, and precipitation to treat uranium effluents. The process
removed both soluble and suspended uranium species; it was found that 95% uranium
recovery was possible, and the treated effluent met environmental standards. The RO
membranes (FT30) gave uranium rejections of >99%. Prabhakar et al., (1992) indicated
cellulose acetate membranes could effectively remove 99% of uranium from effluents
containing uranium nitrate when the uranium was complexed with EDTA. Garrett (1990)
also studied removal of uranium and other radioactive elements by RO membranes.
2.59 RO TREATMENT OF OTHER WASTEWATERS
Reverse osmosis has also been applied to a variety of other wastewaters. Terril and
Neufeld (1983) used RO membranes to remove contaminants (calcium, magnesium, zinc,
sulfate, chloride, ammonia and others) in blast-furnace scrubber water, allowing recycle
of the product water. Hart and Squires (1985) discussed the use of RO to treat coal mine
drainage (containing mostly sodium salts); TDS removals from the permeate were high.
Sinisgalli and McNutt (1986) described a process in which RO was integrated with other
treatment systems to remove contaminants from a complex industrial wastewater; this
wastewater contained contaminants from semiconductor manufacturing lines and plating
baths as well as cooling tower blowdown and other facility wastewaters. The treatment
process allowed recycle of the product water, reduced operating costs, and compliance
with environmental regulations. Bhattacharyya et al., (1984) used FT30 and DuPont B9
(polyamide) membranes to remove contaminants from biotreated coal-liquefaction
wastewater with rejections of TDS at >77%, organics of 94% to 98% and colour at 100%.
79
Siler and Bhattacharyya (1985) reported on the use of RO membranes to treat oil shale
retorting wastewaters containing organics (aliphatic acids and phenolics), inorganics
(NH3, S2-, Cl-, alkalinity), color, odor, oils, and suspended solids. Rejections with and
without various pretreatment by activated carbon, filtration, etc. (which greatly affected
flux) ranged from 60% to 94% for conductivity and 75% to 88% for TOC. McCray and
Ray (1987) used a RO system to treat process condensate wastewater from a synfuel
process which contained high concentrations of organics (phenols, oils and greases,
carboxylic acids, cyclic hydrocarbons, etc.) and inorganics such as ammonia, sulfides,
carbonates, cyanides, and heavy metals. Studies at high pH indicated contaminants were
rejected >95% and fluxes could be maintained at acceptable levels even for water
recoveries up to 80%. Krug and Attard (1990) conducted studies using ultrafiltration
followed by RO for the treatment of oily wastewater; oil removals greater than 96% .
2.60 RO TREATMENT OF CONTAMINATED WATERS
2.60.1 Leachates
Several studies have been conducted on the treatment of landfill leachates with RO
processes. Chian and De Walle (1977) found RO membranes could be used to remove
>91% ofTOC from sanitary landfill leachate. Slater et al. (1983b) discussed the use of
tubular cellulose acetate membranes to treat industrial landfill leachates and found TDS
removals of 98% and COD removals of 68%. Water recoveries of up to 75% were
possible without significant fouling.
McArdle et al., (1987) indicated that RO membranes could be used as a treatment
technology for leachate from hazardous waste land disposal facilities. Kinman and Nutini
(1990) also described RO treatment of landfill leachate; removals of 94.5% alkalinity,
97% COD, 97% total solids, 92.1% volatile solids, and 96.6% ammonia. Stürken et al.,
(1991) and Peters (1991) also indicated RO membranes could remove 98% of COD,
TOC, and ammonium ions, 96% of nitrate, and heavy metals. Bhattacharyya and Kothari
(1991) used FT30 membranes to treat soil wash leachates so that the treated water could
be recycled back to the soil-washing step.
80
The leachate contained heavy metals and organic contaminants. TOC rejections as high
as 80-85% and heavy metal (Pb, Zn, Ni, Cu) rejections of 94% to 98% were found.
However, water flux decreases of up to 33% were noted. The effects of addition of
EDTA or surfactant and feed preozonation were also investigated; feed preozonation
substantially improved membrane water flux. Specific organic rejections included >98%
for pentachlorophenol and 2,4-dinitrophenol, >97% for ethylbenzene, >81% for xylene,
and >90% for chloroaniline. Lepore and Ahlert (1991) reported the treatment of landfill
leachates containing organic acids; they found good separations of volatile fatty acids,
and TDS was removed sufficiently to allow discharge of the product water.
2.60.2 Contaminated Drinking Water
The ability of RO membranes to remove both inorganic and organic compounds have
made these attractive for the treatment of contaminated drinking water supplies (AWWA,
1992). Reverse osmosis processes can simultaneously remove hardness, color, many
kinds of bacteria and viruses, and organic contaminants such as agricultural chemicals
and trihalomethane precursors. Eisenberg and Middlebrooks (1986) reviewed RO
treatment of drinking water sources, and they indicated RO could successfully remove a
wide variety of contaminants. Chian et al., (1975) and Johnston and Lim (1978) studied
several agricultural chemicals which can contaminate water supplies and found removals
were good; however, these adsorbed on the membranes were studied. Regunathan et al.,
(1983) reported significant removals of the pesticides endrin and methoxychlor as well as
Trihalomethanes (THMs) with an RO-adsorption system.
Nusbaum and Riedinger (1980), Odegaard and Koottatep (1982), and Bhattacharyya and
Williams (1992a) reported that humic and fulvic materials, which are THM precursors,
were highly removed by RO membranes. Clair et al., (1991) also found excellent
removals (>95%) of dissolved organic carbon from natural waters using FT30
membranes. Sorg et al. (1980) showed that a RO system could effectively remove radium
from contaminated water. Sorg and Love (1984) conducted studies with actual
groundwater in which only a few of the pollutants being studied were spiked. Several
different commercial membranes were studied.
81
It is found that most inorganics were highly (>90%) rejected while organic rejection
dependent upon the organic and membrane studied. Baier et al., (1987) studied removal
of several agricultural chemicals from groundwater using different membranes.
Rejections ranged from 0% to >94% for the different compounds and membranes
studied. Pilot plant experiments indicated that water fluxes could be maintained over long
terms with periodic cleaning. Fronk (1987) investigated RO removal of over twenty
VOCs and pesticides using several different RO membranes. Average organic removals
were 80%. The study indicated that RO could be used to effectively remove both
inorganics and organics from drinking water supplies. Taylor et al., (1987) found that RO
membranes could be used to remove 96% of DOC, 97% of color, 97% of
Trihalomethanes formation potential (THMFP), and 96% of total hardness. Tan and
Sudak (1992) examined several RO membranes and found all were capable of acceptably
removing color from groundwater over long operating periods.
2.60.3 Municipal Wastewater
Early studies (Cruver, 1976; Fang and Chian, 1976; Lim and Johnston, 1976) showed that
high removals of TDS and moderate removals of organics could be achieved. Tsuge and
Mori (1977) showed that tubular membranes (with a substantial pretreatment system)
could remove both inorganics and organics from municipal secondary effluent and
produce water meeting drinking water standards. Stenstrom et al., (1982) studied
municipal wastewater treatment over a 3 year period using tubular cellulose acetate
membranes. TDS rejections were 81%, and TOC rejections were >94%, making the
permeate suitable for reuse. However, feed pretreatment was necessary to maintain high
water flux levels. Richardson and Argo (1977), Allen and Elser (1979), Argo and Montes
(1979), Nusbaum and Argo (1984), and Reinhard et al., (1986) have discussed municipal
wastewater treatment at a large scale plant (Water Factory 21, Orange County,
California). The feed to the plant consisted of secondary effluent, and the process was
composed of a variety of treatment system including RO membranes (several different
types) with a 5 MGD capacity. The process reduced TDS and organics to levels that
allowed the effluent to be injected into groundwater aquifers used for water supplies.
82
Suzuki and Minami (1991) reported the studies on use of several RO membranes to treat
secondary effluent containing various salts and dissolved organic materials. TDS
rejections of up to 99% and TOC rejections as high as 90% were found possible, and
fecal coliform group rejections were >99.9%. Losses in water flux were noted but could
be partially restored by periodic cleaning.
2.61 UNCONVENTIONAL RECENT EFFORTS
There have recently been some unconventional technologies focusing essentially on
locally contrivable facilities and avoiding sophisticated equipments and vendor
dependencies. These are reviewed herein.
2.61.1 Net Evaporator for Textile Spent Dye bath
This system in Fig. 2.32 is inspired by the WAIV of Israel and is for spent dye bath.
The spent dye bath is received in a sump and pumped onto 6 m broad; 3 m depth deep
nylon net fabrics suspended as parallel drapes at 10 cm spacing. The distribution is by the
grid of piping supported atop the nettings and 3 mm holes in the pipeline at about 30 cm
centers. The liquid is recirculated continuously. Organized evaluation is not yet reported.
2.61.2 Net Evaporator for ROR from a Textile CETP in ZLD Mode
This is a system again inspired by the WAIV. The location is a textile CETP with ZLD
and the ROR is put through this ad hoc system as in Fig. 2.33.
Fig. 2.32 The netting drapes and distribution pipings at the textile net evaporator
83
Though the system has been in use for over two years, the continual refinements are still
going on and an organized evaluation hass not been reported.
2.62 CASE STUDY OF THERMAL EVAPORATORS FOR ROR
In general, industries are reluctant (understandably) to report on realities of thermal
evaporators in regard to the stoichometry, the operating problems, material corrosion etc.
These are mainly in tannery and textile sector ROR matters. The reports available are
centered more on the day to day issues of operational costs and replacements reinforcing
the non-applicability of these for small scale installations. Some of the pictures thereof
are reproduced from the reports as in Fig. 2.34 and Fig.2-35.
The cost figures of the operation and maintenance aspects are more critical and are
reproduced in Tables 2.8, 2.9 and 2.10.
Fig.2.33. Bird’s eye view of the CETP and the WAIV inspired system for ROR
Fig. 2.34 Mechanical vapour
Recompressor installation
Fig. 2.35 Falling film and forced circulation
evaporator installation
84
Table 2.8
Electrical Power Consumption in ZLD Encompassing the Thermal Evaporator
Sl
No Component of ZLD
kWhr / cum
of feed
% of
effluent
Equivalent
of raw
1 Primary Treatment like equalization,
chrome precipitation, neutralization etc 0.9 100 0.9
2 Biological Treatment in aeration 1.5 100 1.5
3 Cross Flow membrane filtration 3.2 100 3.2
4 R O desalting membrane filtration 2.4 100 2.4
5 Thermal evaporation 6.0 15 0.9
Total / cum of raw effluent 8.9
Table 2.9
Operation and Maintenance (O&M) Cost in INR / cum of Feed
Sl
N
o
Segments
of ZLD
Mechanical Vapour
Recompression and Multiple
Effect Evaporation
Multiple Effect Evaporation only
(A) (B) ( C ) Total (A) (B) ( C ) Total
1 Primary 6.00 9.00 0.00 15.00 6.00 9.00 0.00 15.00
2 Biological 0.50 15.00 0.00 15.50 0.50 15.00 0.00 15.50
Sub-total 31.00 Sub-total 31.00
3 U F 0.50 32.00 0.00 32.50 0.50 32.00 0.00 32.50
4 RO 3.25 24.00 0.00 27.25 3.25 24.00 0.00 27.25
Sub--total 59.75 Sub-total 59.75
5 Evaporator 36.00 45.00 22.50 103.5 36.00 60.00 87.00 183.00
Totals 46.25 125.00 22.50 193.7 46.25 140.00 87.00 273.25
(A)-Chemicals; (B)-Power; ( C ) Steam
85
Table 2.10
Split up of Costs per Kl for Each Section
MVR+MEE MEE only
Primary 15.00 15.00
Biological 15.50 15.50
UF + RO membrane 59.75 59.75
Evaporator 193.75 273.25
The effluent going into evaporator as derived from R O reject is about 15 %. Thus, the
equivalent cost for evaporator for raw effluent is 15 % of the true evaporator O&M cost
Evaporator O&M 29.00 41.00
The total O&M cost 120.00 132.00
Source of above tables-Implementation of ZLD, N Abdur Rahman, LERIG-CLRI-2014
When the CETPs were set up initially for merely adding Lime and Ferrous Sulphate and
discharging the treated effluent without removing the TDS, the O&M cost for the
industry was only INR 15 per Kl of raw effluent. When suddenly the ZLD was slapped
this shot to 120 / 132 at an 850 % jump. Clearly, the blame for not achieving the true
ZLD will apportion to the PCB as well because it has not brought out a sustainable
technology and became like the (in) famous Shylock of Shakespeare drama.
2.63 OBSERVATIONS FROM LITERATURE REVIEW
The literature review highlights the utilization of industrial and municipal wastewater to
treat using RO plants which produce RO rejects as part of the Zero Liquid Discharge
(ZLD) practices mandated by the pollution control authorities. While the issues relating
to ocean discharge of SWRO plants are already engaging the attention of WHO, the
disposal / utilization issues of the other two namely inland BWRO as also industrial
wastewater ZLD caused ROR brings out a complex picture with inadequate clarity and
each scenario seems to be drifting in its own complexity and inherent sub issues.
86
The disposal of ROR into Surface Water Discharge, Sewer Discharge, Deep Well
Injection, Evaporation Ponds, Spray systems and Land application are to be effectively
treated as the bygones of yesteryears as the consequent environmental damages have by
now been well documented and their irreversible nature have also been recognized.
The later set of technologies like Two-Phase RO with Chemical Precipitation, Two-Phase
R O with Biological Reduction, RO with Softening and High pH Operation, Two-Pass
Nano filtration, Seeded Slurry Precipitation & Recycle, Membrane distillation,
Capacitive deionization, Dewvaporation, Forward osmosis and RO separation of organic
pollutants as reviewed and discussed herein are all inherently complicated enough and
need adequate human resource and financial outlay besides repairs and renewals. All
these can be justified only when there is a value recovery and value addition. But then, in
the case of ROR, the only such value can be the recovered water and the salts that too not
in their entire purity. This being so, it is impossible to expect industry to invest on these
more so as the volume per se will be at best 15 % of the effluent volumes.
The thermal evaporators are perhaps the non-starters even at the capital costs leave alone
the disproportionate O&M cost as illustrated in Table 2-10 which shows the O&M cost in
INR / Kl of ROR as 31.00 for primary, 59.75 for membrane and a very high cost of 103
for MVR + MEE and 183 for MEE only. Thus by investing INR 59.75 at least 85 %
water becomes available for general uses but spending additional INR 103 or 183
practically only 10 % of the water can be recovered. This 10 % is again in the 15 %
volume as ROR and effectively this means it is only 1.5 % of equivalent wastewater
volume. The scale of operations also influences the choice of technology. Most of the
inland industries deal with water volumes of 300 to 500 kilo liters daily (kLd) and the
ROR is about 100 to 200 kLd. Clearly mechanized units are neither easily available nor
affordable. Besides, the TDS of ROR varies from 1500 to 900 mg/L and in some cases
40,000 mg/L thus the need is to address the mainly lower ranges. Thus quite clearly,
getting into ROR implies the need for a technology where it can be safely disposed off as
water vapour into the atmosphere and the salts contained as slurry for concentration and
containment in secure landfills to be reclaimed as useable land in years to come.
The Figs 2.36 and 2.37 bring out the TDS issues more clearly.
87
Fig. 2.36 Range of TDS in identified industrial wastewater segment
Fig. 2.37 Range of TDS in identified domestic and public water segment
88
The literature review of nearly 140 scrutinized articles in the past 41 years throws up an
array related to issues linked to 59 high TDS wastewaters, 24 seawaters, 2 saline brackish
waters, 50 industrial wastewaters and only 5 on ROR. Recognizing that the objectives of
this thesis were enshrined upon at the outset as (1) to identify a prospective candidate
technology for easier replication locally, (2) to study the performance within the known
boundary conditions and (3) to bring out a design algorithm with variables, the only
technology that can be addressing all these appears to reside in the wing aided nature
induced net evaporator systems in so far as India is concerned with its bulk of land mass
land locked inland and land availability not a great concern. The only two ventures in this
direction are the net evaporator for textile spent dye bath and for ROR of textile CETP as
identified herein. Thus it stands to reason to evaluate the performances of these two units
to bring out their thermal dynamics, validate the observation for a fitment into a three
phase mass transfer and thereafter set up an experimental facility to verify and bring out a
possible design basis for such systems within the boundary conditions studied and more
specifically permitting cannibalization.
89
CHAPTER 3
EXPERIMENTAL SET UP AND METHODOLOGY
3.1 THE MAGNITUDE OF THE ROR PROBLEM
A screening of the TDS in the ROR in a variety of industrial, IT Parks, Hotels and
Apartments is compiled in Table 3.1 and brings out the position of ROR being about
1000 mg/L minimum value to as high as 50,000 mg/L as highest value. The continued
discharge of these into environment will only hasten the irreversible damage to raw water
resources and eventually a situation where two stages RO will become a compulsion with
much higher TDS in ROR and the vicious cycle will strangulate the society. This can be
halted only by such locally sustainable technologies as net evaporators and secure
landfills. Conceding this position, the need of the hour is to study the performance of the
two installations reported in India within the known boundary conditions and to bring out
a design algorithm validated in an experimental unit within the known variables.
Accordingly, the same is presented.
3.2 STUDIES ON NET EVAPORATOR FOR TEXTILE DYE BATH
This facility is at a textile fabric dyeing industry on the outskirts of Chennai and is for
evaporating the textile spent dye bath which has Sodium Chloride with TDS in the range
of 45,000 to 65,000 mg/L, temperature 45 to 55 deg C and volume of up to 40 cubic
meters / day. The net evaporator Installation with Hanging Drapes of Greenhouse
Nettings Suspended into a Sump containing the Spent Dye Bath and being recirculated
over the drapes by continuous pumping to bring about maximizing evaporative area as
compared to the structural foot print area. The photoes are in Fig 3.1.
Fig. 3.1 The author amidst the textile net evaporator and in the laboratory.
90
Table 3.1
TDS in Feed, R O Permeate and R O Rejects in Selected User Categories
User Agency Surveyed Use in TDS in TDS in TDS in rejects
utility Feed Permeate Industry IT Park Hotels Apartments
1. Dairy (Puducherry) WTP 1500 < 100 3200
2. Extrawave (Coir inductries ) WTP 1500 < 100 3500
3. Industrial (Chryso) WTP 1600 100 4000
4. Industrial( TVS Motor) ETP 20000 500 37500
5. Industrial(Sundaram Fastners ) ETP 6000 250 25000
6. Industrial( Titan Industries ) ETP 1600 200 2500
7. Industrial( Catterpiller) STP 1500 100 3000
8. Industrial( Power plant) WTP 3500 100 7000
9. Industrial( Balakrishna Tyres) WTP 1400 50 2800
10. Industrial( Kosei minda) ETP 5000 200 12000
11. Industrial( minda) WTP 1100 75 3500
12. Industrial (Mahindra & Mahindra) WTP 2100 100 7500
13. Industrial (NDDP - Kalpakkam) WTP 800 30 2000
14. Industrial (Volvo) WTP 2300 250 6500
15. IT Park Kolkata WTP 1200 100
3200
16. IT Park Siruseri Chennai STP 2500 150
10000
17. Hospital Puducherry WTP 500 100 1000
18. GRT Institute of Management WTP 1200 500
2500
91
TDS in Feed, R O Permeate and R O Rejects in Selected User Categories
User Agency Surveyed Use in TDS in TDS in TDS in rejects
utility Feed Permeate Industry IT Park Hotels Apartments
19. GRT Institute WTP 1500 150
3750
20. GRT Hotels and Resorts WTP 1500 150
3750
21. Hotel Radisson Blue STP 700 100
1600
22. Hotel Radisson Blue STP 1500 75
3750
23. Hotel Aitkin Spence WTP 2000 100
4500
24. Rail Station WTP 2370 100
5825
25. Residential Appasamy Real Estate WTP 2000 100
4000
26. Residential Real Value Promoters WTP 20000 500
40000
27. Residential Real Value Promoters WTP 25000 500
40000
28. Residential Real Value Promoters WTP 25000 500
50000
29. Residential Navy WTP 25000 500
50000
30. Residential Lancor WTP 2000 100
4000
31. Residential Parsan WTP 2000 100
4500
32. Municipality Kancheepuram WTP 2500 600
5000
33. Average
4952
34. Lowest TDS in RO reject
500
1000 3200 1600 4000
35. Highest TDS in RO reject
25000
37500 10000 5825 50000
36. Numbers in each category
14 2 7 8
92
The schematic of the operational pattern is shown in Fig. 3.2.
The setup has compartmentalizable segments in the bottom sump and one of them is
always taken out of service to look into scrapping out the concentrated slurry for being
taken to landfill and also looking into repairs and renewals of the drapes / nettings.
The spent dye bath is received in a sump and pumped onto 22 nylon net fabrics of 6m
breadth, by 3m height at 10 cm centers suspended into the 11.5 m * 8.45 m foot print
sump. . Distribution of pumped volume onto the nettings is by the grid of piping atop the
nettings and 3 mm holes at 30 cm centers. The recirculation pump duty was 15 Cubic
meter per hour. The spent dye bath temperature was 45 to 55 Degree Centigrade( Deg C),
Humidity 75 %, Rainfall-nil, temperature of ambient air 33 to 36 Deg C. dry bulb 35.8 to
36.4, wet bulb 24.6, wind speed-15 to 17 km / hr and cloudiness nil. TDS in bottom sump
gets concentrated and the sump is solar dried to scrap out the salty sludge. Samples of the
liquid in the sump at three fixed surface locations were tested for EC as a measure of the
TDS. The spent dye bath is added to the sump during operating hours.
3.2.1 The Method of Testing
The testing was carried out during the operating hours of 9 AM to 7 PM. The industry
remains shut during the hours outside this time and no activity is permitted. The ambient
and dye bath temperatures as also the EC were measured as they occurred. The humidity,
wind force, dry bulb and wet bulb temperatures were taken out of meteorological records.
The liquid depth in the sump was measured by a calibrated staff. The testing was carried
out continuously for one working week.
Receiving Sump with
bottom flow maker
for forward mixing Net Evaporator as wind aided falling
film evaporation and bottom slurry
solar-dried in summer as in-situ
(In standby for preventive
maintenance)
Pumped Recirculation
Net Evaporator as wind aided falling
film evaporation and bottom slurry
solar-dried in summer as in-situ
(In active operation)
in operation
Pumped Recirculation
Secu
re La
ndfil
l
Fig. 3 Schematic of the Demonstrated Alternative System for High TDS Wastewaters
Fig. 3.2 Schematic of the net evaporation system operating sequence
93
3.2.2 Results of Testing of the Evaporator
The summary results thereof are given in Table 3.2.
Table 3.2
Observations on the net evaporator system for six consecutive days
Physical Dimensions
Height of each net, x width of each net, m 6m x 3m
Number of nets 22
Total wetted area of nets, sqm 792
Plan length of sump x width of sump, m 11.5 x 8.45 m
Plan area of sump, sqm 97
Ratio of Net wetted area to area of sump 8.15
Enhancement of Pan Evaporation Rate
Initial volume in cum 61.22
Added Volume in cum 97.05
Total volume subjected to evaporation in cum 158.27
Total volume remaining after test in cum 131.19
Volume evaporated in cum 27.08
Hours operated per day 10
Number of days operated 6
Total hours operated 60
Evaporation in cum/Hr 0.45
Evaporation per 24 hours by extrapolation in cum 10.83
Evaporation per day from water surface in sump as mm 111.49
Normal pan evaporation at the site per day in mm 5.00
Increase in evaporation rate 22.30
Mass Balance
Mass at beginning in sump as Tonne times EC (Tonne of wastewater * EC) 17717
Mass at end of study as Tonne times EC (Tonne of wastewater * EC) 18279
Mass variation as % of initial ( this is statistically within agreeable limits) 3.17
The enhancement of evaporation is 22 times compared to the pan evaporation rate
reported for the location by the meteorological office for tap water. This is significant as
the TDS of dye bath was about 60,000 mg/L as compared to that of fresh tap water which
is just about 500 mg/L. In addition, the presence of dye colours and trhe viscous nature
arising from the high TDS are to be admitted as deterrents for evaporation and have to be
conceded as a favourable parameter in this experiment. More detailed results of the
studies are compiled in Table 3.3 and inferred out in Table 3.4.
94
Table 3.3
Inference from the results of net evaporator for textile spent dye bath
Sump-11.5m * 8.45 m; Area-97.2 sqm; Nettings 22 * 6m * 3m; Area=792 sqm
Packing Density (PD) = 792 / 97.2 = 8.15,
Circulation of dye bath at 15 cum / hr, Flux = 15,000 /60/792 = 0.32 lpm/ sqm
Day-1 Spent dye bath added lit / day 15650 Dye bath EC, ave. 62500
Site 9:00
AM
11:00
AM
1:00
PM
3:00
PM
5:00
PM
7:00
PM Average
1 132000 132500 133800 140100 141000 142500 136983
2 131000 131800 134100 140200 139100 141700 136317
3 132400 133100 136800 141900 143000 143050 138375
Average EC in evaporation tank 137225
liquid depth in cm at stated location loss in cm
2 63 60 56 52 47 41 22
Volume of dye bath moisture evaporated in the tank in liters 21379
Evaporation in liters per hr per sqm of netting 2.70
Day-2 Spent dye bath added lit / day 13750 Dye bath EC, ave. 62500
1 106000 107500 111400 108200 106800 100100 106667
2 111800 108900 108700 107700 106000 102000 107517
3 111000 107300 108700 107700 106600 102900 107367
Average EC in evaporation tank 107183
liquid depth in cm at stated location loss in cm
2 50 43 39 36 33 25 25
Volume of dye bath moisture evaporated in the tank in liters 24294
Evaporation in liters per hr per sqm of netting 3.07
95
Table 3.3 (Continued)
Inference from the results of net evaporator for textile spent dye bath
Sump-11.5m * 8.45 m; Area-97.2 sqm; Nettings 22 * 6m * 3m; Area=792 sqm
Packing Density (PD) = 792 / 97.2 = 8.15,
Circulation of dye bath at 15 cum / hr, Flux = 15,000 /60/792 = 0.32 lpm/ sqm
Day-3 Spent dye bath added lit / day 17500 Dye bath EC, ave. 62500
1 102000 100700 103300 103000 104800 103800 102933
2 101700 100600 102900 104700 104900 103900 103117
3 102200 100700 102400 104700 104800 103900 103117
Average EC in evaporation tank 103056
liquid depth in cm at stated location loss in cm
2 53 48 41 36 31 25 28
Volume of dye bath moisture evaporated in the tank in liters 27209
Evaporation in liters per hr per sqm of netting 3.44
Day-4 Spent dye bath added lit / day 16600 Dye bath EC, ave 62500
1 104800 104700 106800 107700 109200 107000 106700
2 104500 104500 106500 107500 109200 107500 106617
3 105000 104800 106900 107900 109200 107700 106917
Average EC in evaporation tank 106744
liquid depth in cm at stated location loss in cm
2 53 47 41 54 29 26 27
Volume of dye bath moisture evaporated in the tank in liters 26237
Evaporation in liters per hr per sqm of netting 3.31
96
Table 3.3 (Continued)
Inference from the results of net evaporator for textile spent dye bath
Sump-11.5m * 8.45 m; Area-97.2 sqm; Nettings 22 * 6m * 3m; Area=792 sqm
Packing Density (PD) = 792 / 97.2 = 8.15,
Circulation of dye bath at 15 cum / hr, Flux = 15,000 /60/792 = 0.32 lpm/ sqm
Day-5 Spent dye bath added lit / day 17100 Dye bath EC, ave 62500
1 107000 107700 110000 112100 109000 107900 108950
2 107700 107800 110500 112200 109700 108300 109367
3 107800 108100 111100 112000 109700 108700 109567
Average EC in evaporation tank 109294
liquid depth in cm at stated location loss in cm
2 58 43 38 33 30 27 31
Volume of dye bath moisture evaporated in the tank in liters 30124
Evaporation in liters per hr per sqm of netting 3.80
Day-6 Spent dye bath added lit / day 16450 Dye bath EC, ave 62500
1 114700 114200 115700 118200 119200 118500 116750
2 116230 116320 116830 118230 118690 118200 117417
3 118200 118450 119420 119650 120370 119890 119330
Average EC in evaporation tank 117832
liquid depth in cm at stated location loss in cm
2 43 38 31 24 19 15 28
Volume of dye bath moisture evaporated in the tank in liters 27209
Evaporation in liters per hr per sqm of netting 3.44
97
Table 3.4
Inferred findings from the results of net evaporator for textile spent dye bath
Sl No. Parameters of Performance Values
1 Initial volume in cum 61.22
2 Added Volume in cum 97.05
3 Total volume subjected to evaporation in cum 158.27
4 Total volume remaining after test in cum 14.58
5 Volume evaporated in cum 143.69
6 Hours operated per day 10
7 Number of days operated 6
8 Total hours operated 60
9 Evaporation in cum/hr 2.39
10 Evaporation per 24 hours by interpolation in cum 57.48
11 Evaporation area in netting, sqm 792
12 Evaporation area in pan, sqm 97.18
13 Total evaporation surface, sqm 889.18
14 Evaporation per day from total evaporating surface as mm 64.64
15 Normal pan evaporation at the site per day in mm 5.00
16 Evaporation Index row 14 / row 13 is 64.64 / 5.00 12.93
17 Packing Density of nettings (from Table 3.3) 8.15
98
3.2.3 Observations
3.2.3.1 Dye Bath Evaporated in Excess of Daily Added Volume
The volume of spent dye bath evaporated exceeds as for example in day 1 as 21.38 cum
whereas the volume of spent dye bath added is only 15.75 cum. This excess evaporated
volume has to come from the volume present in the sump itself. As otherwise there is no
other liquid to come into play. This facilitates progressively higher EC concentrations in
the sump and which facilitates enhanced evaporation rates.
3.2.3.2 Dual Use Potential for both Chlorides and Sulphates
The facility can also serve for both chloride laden or sulphate laden waters with the
provision to compartmentalize in the case of chlorides to switch over to solar evaporation
mode by pushing aside the drapes once the liquid becomes a slurry of chlorides.
3.2.3.3 Evaporation Index (EI)
The EI calculated as equivalent of pan evaporation rate establishes the efficiency of this
system at 12.93 times higher than the simple pan evaporation.
3.2.3.4 Packing Density
This is calculated as ratio of area of drapes to plan area of evaporation sump and is
looked upon as a parameter to establish the packing density of the drapes as a design
parameter for replication of the results or to build a model for future design. .
3.2.3.5 Cost Considerations in O&M
The system involves only a non-clog circulation pump operating at INR 1 per cum as
compared to Rs. 120 to 150 per cum for thermal evaporator system.
3.2.3.6 Pointer
An EI of 12.93 is achievable at a packing density of ratio of 8.15 within the boundary
conditions of TDS, viscosity, dry bulb cum wet bulb temperatures and wind velocity
besides the nil rainfall and nil cloudiness typical of inland arid settings.
99
3.3 STUDIES ON NET EVAPORATOR FOR ROR OF TEXTILE CETP
This CETP is located in the desert location of Jaipur in northwest of India for a group of
textile dyeing and processing industries. It has an equalization tank, biological aeration,
fine filtration, oxidation-reduction, ultra filtration membrane (UF) and RO. The ROR is
put through an ad-hoc net evaporator system of drapes as shown in Fig. 3.3
The RO reject is received in 11.6 m * 5.85 m * 0.8 m water depth sump and sprayed on
21 * 6m * 6m greenhouse nettings and contained by kerbs. The spray is by a pipe grid
with 3 mm holes at 30 cm centre to centre on both faces. The temperatures were (Deg C)
ambient of 33-36 in day, 26-28 in night and R O reject 29-32. The humidity was a 45 to
51 % low to 85-89 % high. The wind speed was 3 m/s mean to 6 m/s maximum. The dew
point in Deg C was 20-22 low to 25 high. The packing density is 12.64.
3.3.1 The Method of Testing
The upstream biological treatment is sustained in non functioning days of industries by
supplementing the wastewater and nutrients from elsewhere as slug additions. Thus, the
typical need is to store the wastewaters and bring up the RO as and when needed by
filling up with the ROR and continuing the evaporation for a week. The temperature of
ambient & ROR were measured as they occurred. The TDS was tested in laboratory and
humidity, temperatures, rainfall and wind force were from meteorological records and the
liquid depth in sump was measured by a calibrated staff. The evaporator worked
continuously as batch mode from 3 pm to 6 pm on 5th day.
Fig.3.3 View of the net evaporator at textile ZLD CETP at Jaipur India
100
3.3.2 The Results
The results are in Table 3.5 and a relationship is drawn as in Fig. 3.4.
Table 3.5
Results observed during the on-field study on batch operation
No. Days Time, Operating
interval/day
Total
Interval,
Sump fluid depths, cm TDS in
sump
fluid At start Loss
hrs hrs hrs cm Cm mg/L
1
1
3.00pm
50 11500
2 4.30 pm 1.5 1.5 49.6 0.4 12005
3 6.00 pm 3.0 3.0 49.3 0.3 12258
4 7.30 pm 4.5 4.5 49 0.3 14446
5
2
8.30 am
17.5 45.5 3.5 14952
6 11.30 am 3.0 20.5 44 1.5 15709
7 4.00 pm 7.5 25.0 41.5 2.5 18656
8
3
9.30 am
42.5 36.8 4.7 19834
9 1.00 pm 3.5 46.0 35.2 1.6 19834
10 4.30 pm 7.0 49.5 33.4 1.8 20171
11 6.30 pm 9.0 51.5 33 0.4 22781
12
4
10.00 am
67.0 28.7 4.3 23286
13 2.00 pm 4.0 71.5 27.1 0.6 24128
14 7.00 pm 9.0 76.5 24.8 2.3 26821
15 5 11.00 am
92.5 20.7 4.1 27411
X-axis, TDS in mg/L at Initiation of the Time Interval
Y-axis, Evaporation Index as multiple of Observed to Pan Evaporation rate.
Fig. 3.4. Variation of evaporation index with arising TDS in the net evaporator
X-axis, TDS in mg/L at Initiation of the Arising Time Interval
Y-axis, Evaporation Index as multiple of Observed to Pan Evaporation rate.
101
3.3.3 Observations
The evaporation occurs more in the netting as the area of evaporative surface in the
netting is 1512 sqm as compared to only 67.86 sqm in the sump. As such it is necessary
to consider the total evaporation brought about by the system and express it as a function
of the plan area of the sump, with the area of nettings to area of the sump as a minimum
“packing density”. Thus as long as the packing density is not less than in the evaluated
system, the relationship of EI and TDS can be used as a design basis. The results as in
Fig. 3-4 follows a sinusoidal relationship and reinforces the concept brought in by Dalton
who cited the solar radiation in daytime and the less intensity sky radiation in the night.
3.4 COMPARISON OF ATTRIBUTES OF THE TWO SYSTEMS
Given the objective of this thesis being to bring out a design algorithm, it is necessary to
first study the relative functional attributes of the two systems as correlated to the TDS
and the resulting EI. This is shown in Table 3-6.
Table 3.6 Attributes and performances of the two net evaporator systems
Sl
No. Attributes and Performances
Net Evaporator Systems for
Spent Dye Textile ROR
1 Packing density, sqm of nettings / sqm of sump 8.16 12.64
2 Application flux on nettings, lpm / sqm 0.31 0.12
3 Evaporation Index 12.93 11.60
4 Mass variation as % of initial (EC times volume) 3.17 4.09
5 Lower TDS during the experiment, mg/L 40,000 6500
6 Higher TDS during the experiment, mg/L 51,000 12,000
Of course, there are variables as temperature of the liquid and ambient, solar radiation,
sky radiation and wind speed besides rainfall and its resulting humidity. But then, these
are factors which are external to the system attributes and which cannot be shaped by the
designer and instead have to be duly accounted for in the algorithm. The rainfall
however, is best relegated as its frequency and intensity are of extreme unpredictable
occurrences and the effect can even otherwise be easily offset by inserting a makeshift
cover in such times and drains away the precipitation to harvesting structures and this
will also avoid polluting the precious rain water and instead its roof top collection.
102
3.5 VARIABLES TO BE EVALUATED IN THE SYSTEM
Given the precincts of the foregoing paragraph, the variables that need to be duly
considered in the development of algorithm by the experimentation of the pilot system
can be identified as functional variables and incidental variables. In order to do so, we
need to refrain from embarking on sophisticated mathematical equations which bring in
variables beyond the boundary conditions chosen and instead persist and pursue with a
simpler and straightforward schematic of first principles as in Fig.3.5.
Fig. 3.5 Simplified schematic of evaporation from water bodies
The mathematical equation that is proposed is the time-honoured empirical one adapted
from (http://www.engineeringtoolbox.com/evaporation-water-surface-d_690.html) and is
E = (25 + 19V)*A*(Xs-X)
Where
E = Water evaporated in kg / hr.
V = Wind velocity skidding the water surface in m/s
A = water surface area in sqm
Xs = Humidity ratio in saturated air at water temperature in kg H2O in kg dry air
X = Humidity ratio in air as kg H2O in kg dry air
The functional variables are V, Xs, X for fixed variables of A and given instantaneous
ambient temperature vis a vis that of applied water. Besides, the TDS concentration also
plays its part as the rate of vaporization is proportioned to it. All of these would render
the theorization as an endless pursuit. Moreover, any attempt to bring out a design basis
must also relate to postulates of phase and mass transfer in literature.
The Water Body
Heat from Solar / Sky Evaporation Wind
103
The simplistic understanding of evaporation is that the rate of evaporation of water from
any surface is directly proportional to the specific humidity difference between the
surface and the adjoining air. But then, as pointed out by Dalton (1802) it is also related
to wind pressure, solar radiation and sky radiation. He stressed that the wind speed affects
this proportionality. Vuglinsky.V.S. postulated that the evaporation rate of salty water is
lesser than fresh water and is explained by the fact that when water is evaporating, the
vapour springing out of the salty water has to get over not only the gravitation forces of
water molecules but also the gravity of the matter dissolved in water. If we apply these
philosophies onto the evaporation mechanism as occurring in the study installation, the
solar & sky radiation as also initial TDS is also to be duly recognized. The Vuglinsky
postulation officialized the often quoted theory of rate of evaporation being inversely
proportional to the concentration of solute in the solvent being evaporated. The position
taken by Vuglinsky about the vapour springing out of the salty water to get over not only
the gravitation forces of water molecules but also the gravity of the matter dissolved in
water is also not applicable in the study case because the evaporation is taking place in
the falling film gravitating over the drapes.
Furthermore, the cited variables relate to the ambient and wastewater temperature which
in their own way control the other variables.
The geographical elevation of the event has no direct relationship and it is the relative
humidity that matters and defined as the ratio of how much water vapor is present to the
maximum that can be present. For example, if we consider a temperature of 59 deg F the
maximum will be 17 millibar and if there is only 8.5 millibar of water vapor, the relative
humidity becomes 50%. If we consider a situation at sea level with a pressure of
1013 millibar and the air temp is 59 deg F and the 8.5 millibar water vapor content, this
means the relative humidity is still 50%. If it is a hillock and the pressure is 942 millibar
with 8.5 millibar water vapor and temp 59 deg F, the relative humidity is still 50 %.
Thus the relative humidity depends only on the temperature and actual water vapor
present and has nothing to do with the air pressure or the geographical elevation itself.
104
Thus, the objective of the present study of evolving a design algorithm has to be pursued
from deductive logic borne out of experimentally tested and validated systems under a
chosen set of variables instead of theoretically assembled procedures. It thus looks
inescapable to concede that though this technology of net evaporator has its phenomenal
application in becoming a panacea for the ROR challenges in ZLD projects, still the
current knowledge is only in ad hoc bits and pieces and an experimental study is needed.
A design algorithm evolved on these lines from a pilot plant would still need a “baby
evaporator” alongside to continually evolve refinements to the algorithm as and when
production processes change in the industry and consequently the ROR characteristics
will also keep changing. After all the art and science of fluid and thermo dynamics is as
fluid as the wastewater itself.
3.6 APPROACH FOR TESTING AND INTERPRETATION OF RESULTS
Considering the foregoing reasoning, the area of the water surface undergoing
evaporation becomes one of dimensionally the same at all times being the total area of
the nettings and neglecting the area of the sump below as a minor fraction thereof and to
be treated as a built in safety in design. It is easier to incorporate the multiple of the sump
area and packing density instead of dealing with the absolute value of the area of the
sump or that of nettings because the flexibility of using the required packing density
alone during times of low flows is enabled in actual operation. The issue of TDS however
does not seem inbuilt in the process of equation befitting. But then, as said in the outset,
we are trying to work within a set of boundary conditions and not to evolve a universal
design statement. So much so, within the TDS range of an experiment, the fitment into
the above said equation has to be taken as applicable for replication elsewhere. This is
bare fact as the thesis is not on fundamentals of kinetics of evaporation of the ROR or
high TDS waters and instead the objective is to identify the configurations best suited for
a given set of boundary conditions typical of the inland situation of ROR and high TDS
waters as addressed in Chapters 1 and 2 earlier. Thus the approach will be to carry out
experiments on various TDS contents as in ROR samples or high TDS wastewaters under
variable packing densities and flux over the nettings. The pilot testing will record the
TDS, temperatures of air vis a vis fluid and fluid depth in the sump.
105
The computed parameters will be the area of evaporation as area of sump multiplied by
packing density and the flux as application rate in lpm from circulation divided by the
area of evaporation. These two parameters will be correlated within a band of observed
temperatures and evaluated for the evaporation and depending on the degree of fit, a
design algorithm will be postulated within the chosen boundary conditions. This will be
straightforward approach than trying to universalize the algorithm for a wide range of
conditions and getting mired into intra-inconsistencies. The objective of the thesis is to
find an answer to the ROR and high TDS wastewater issues in a ZLD concept and not to
develop a universal model. To this end, the piloting proceeds as under. .
3.7 THE EXPERIMENTAL PILOT PLANT
The pilot plant is a mimic of the two net evaporator systems in a manageable dimension.
Thus, the unit was chosen as the compartmented acrylic material transparent sump, the
recirculation pump, the distribution pipe grid and the drapes anchored in place by guide
tubes at top and bottom. The classical flexibility is maintained by permitting the sump to
be used in two hydraulically independent compartments or a single hydraulically
connected compartment. Even within this the number of nettings used can be adjusted by
moving the mounting pipe skids at will. The suction of the circulation pump can be taken
out from either of the compartments to permit the other to be set at rest when not needed.
The delivery piping of the pump has a branch piping and valve to suck and clear the
contents fully in between the testing regimes for various TDS content ROR samples and
high TDS wastewaters. The delivery pipe to the top grid was also provided with an air
release valve to avoid potential air locks. All materials in contact with the aqueous
medium were made of synthetic material to take of potential corrosion. The nozzles
impinging the fluid onto nettings had a downward cap to flush out any accumulations of
suspensions in due course. The unit has a 134 cm * 90 cm * 25 cm deep sump and
7 nettings of each 70 cm * 90 cm deep with a pump set of 1000 liters per hr duty. The
entire unit can be dismantled and assembled easily for any on the spot pilot testing at any
industry. The unit permits a temporary tarpaulin drape enveloping it for the top and sides
to a depth of about 30 cm to prevent rainfall when it occurs. As otherwise, it is a roof top
assembly with open to sky at all times. The unit is shown in Fig. 3.6.
106
Fig. 3.6 The experimental pilot plant for testing under various ranges of RORs.
107
Top Left-Individual Netting hung securely and permitting cross wind; Top Right-
The fluid application grid and the support pipings. Middle -The nozzles spraying
onto nettings; Bottom- Bottom-Research Guide with Industrial consultant experts
shaping the model.
Fig. 3.7 The drape nettings and distributor grid of the experimental pilot plant
108
Fig. 3.8 The testing protocols with coloured spent dye baths and high TDS ROR
109
3.8 THE TESTING PROTOCOL
This was for the following wastewater / ROR to match with the characteristics of the
studies already carried out. The samples of spent dye bath were transported to the site of
roof top testing and each run was for a continuous period of six days to be co-terminus
with industrial working days in the region. Similar was the case with freshwater ROR
samples. Five wastewater ROR samples and three freshwater ROR samples were studied.
3.9 THE METHODOLOGY
Only one compartment was used throughout the studies. The other compartment was held
in reserve. Each of the samples was put through a day run. The unit drapes were taken
out, hosed and re-erected in between each experiment. The readings were taken daily at
the same time for pH, ambient temperature, ROR temperature, depth of liquid in the
compartments and EC as indicator of TDS. Spent dye bath samples were transported by
HDPE containers from nearby industries as also ROR for high TDS waters.
110
CHAPTER 4
RESULTS AND DISCUSSIONS
4.1 THE APPROACH
As reasoned out in chapter 3, the prima facie results of the two tests done on the net
evaporators at Chennai for the spent dye bath and that at Jaipur for the textile CETP-ZLD
plant ROR component are to be assessed to establish the extent to which the variables
can be impacting a design algorithm. Thereafter, the results of the experimental pilot
plant would be deciphered to pursue the possibility of developing an algorithm.
4.2 THE RESULTS OF THE TEXTILE CETP ROR NET EVAPORATOR
The table 3.5 is referenced back here and is extracted as the relationship between the time
in hours and the TDS in the sump as in Table 4.1
Table 4.1 Continuous hours of run and TDS in the circulation sump for dye bath
Time in
24 hr mode 18 19.5 32.5 35.5 40 57.5
TDS in mg/L 12258 14446 14952 15709 18656 19834
Time in
24 hr mode 61 64.5 66.5 82 86.5 91.5
TDS in mg/L 19834 20171 22781 23286 24128 26821
To start with, it is necessary to look into the extent by which the TDS increases in the
circulation sump and verify the postulation of evaporation prima facie occurring and if so
the rate with respect to the time of occurrence. Thereafter, considering the Dalton
postulation, the acceleration and retardation of the evaporation and hence the buildup of
TDS needs to be addressed. This is considered necessary to decipher the pilot plant
results and approach its interpretation towards deducing a design algorithm if it does
become feasible without getting sucked into the whirlpool of atmospheric percepts of
humidity, saturation humidity, wet bulb-dry bulb temperatures etc which are not merely
variables even on successive days but also in a way vagaries of the climate and thus
forestall the vitiation of the objective which is not towards fundamental research.
111
4.2.1 Time of Occurrence and the Resulting TDS
This is computed as the respective time zones of steeper buildup of TDS in the total
duration of this study and is presented in Fig 4.1. It is seen that steeper gradients of TDS
buildup Vs time interval occurs at 6 to 7-30 pm, 11 am and 4 pm, 4-30 pm and 6-30 pm
and 2-30 pm and 7 pm on the successive days. Prima facie there does not seem to be a
pattern in this, but then, a closer insight reveals the following. The exercise has
commenced in the evening of day 1 at about 3 pm and soon thereafter clearly the solar
radiation would have tapered off, but the system has been in operation anyway. On the
second day, the chillness effect of the night would have reduced the temperature of the
circulating water and this takes time to drive off the dissolved gases which ingress at
colder temperatures. This phenomenon will need exposure of the circulated water to the
solar radiation and to drive off the same as a two phase mass transfer from the fluid in
circulation. This would have become able to receive and hold the latent heat after quite a
few hours of daylight. Hence, this explains the buildup gradient on the succeeding day
picking up at 11am. The mean sunshine hours at Jaipur at the study time is shown in
Table 4.2 to back up this statement.
Table 4.2
Typical mean sunshine hours at Jaipur for the study month
The peak sunshine hours are 11 am to 5 pm with the latent heat persisting thereafter.
These are plotted with the time and arising TDS for each gradient in Fig. 4.2.
12258 to 14446 between 6 and 7-30 pm in 90 minutes or 24.3 per minute
15709 to 18656 between 11 am and 4 pm in 300 minutes or 9.8 per minute
20171 to 22781 between 4-30 pm and 6-30 pm in 120 minutes or 21.8 per minute
24128 to 26821 between 2-30 pm and 7-30 pm in 300 minutes or 9.0 per minute
112
Fig. 4.1 Buildup of TDS in circulation sump in the 24 hr mode
113
It may be seen that the gradient steps up at about the same 11 am, but tapers off even by
4-30 pm though the sunshine is available up to 5 pm. As already reasoned out,
application of fundamentals beyond a level of interpretation may not pave the way for a
clarity towards the reaching of an explanation suffice to say that parameters which are
incidental to the system needs to be accommodated and these variables taken as system
incidentals. A further observation as in Fig. 4.3 shows the solar radiation in the site peaks
only in between March and June and thereafter briefly in September.
Fig. 4.3 Variation of monthly average solar radiation in kwhr/sqm/day at Jaipur
Source-http://www.synergyenviron.com/tools/solar_insolation.asp?loc=Jaipur%2CRajasthan%2CIndia
Fig. 4.2 TDS buildup gradient with time of occurrence and arising TDS
114
In fact it tapers off on both sides of these months. It is also a compounding factor that
another crucial variable is the wind speed which also varies widely as in Fig. 4.4.
Fig. 4.4 Variation of wind speed in m / sec at Jaipur
Source-http://www.synergyenviron.com/tools/wind_data.asp?loc=Jaipur%2C+Rajasthan%2C+India
These are the reasons to desist from attempting uncontrollable day to day variables and
first principles model. Instead it will be a deductive logic from observed data within the
boundary conditions of RRR of inland industries and high strength TDS wastewaters.
4.3 THE RESULTS OF THE SPENT DYE BATH NET EVAPORATOR
The table 3-3 is referenced back here. In this case, all the results relate to a fixed time
interval of 9 am to 7 pm and the relative occurrences are not related to the time slots.
Thus, it is considered adequate to verify the TDS buildup gradient as related to the arising
TDS in each case. This is extracted in Table 4.3
Table 4.3
Continuous hours of run and EC in the circulation sump for ROS
Day 1 2 3 4 5 6
Arising TDS 132000 106000 102000 104800 107000 114700
Gradient of
TDS Buildup 0.048 0.013 0.011 0.020 0.024 0.040
It may be seen that whereas there is an ascending gradient of EC buildup in general and
which may satisfy the purists, still we need to recognize that the gradient dips when the
EC is 106000 whereas it ascends at 104800 and 107000. The tendency will be to set aside
this lone occurrence and precede with the rest of the data series.
115
However, this will be a fallacy in this case and in general dealing with industrial
wastewaters of especially textile and similar tannery spent dye baths, there are exotic
ingredients that go into the dye imparting stages with such chemicals as mineral oils
being added at times depending on the desired end products. For example, when
polyester yarn is brought in for a brief spell of dye imparting, the use of kerosene oil is a
closely guarded industry secret and outsiders or for that matter, even the insiders other
than the person known as the “dye master” may never know about this dosage or
sequence of addition etc. In respect of tanneries, the matters are much more complex
about the dyes and additives which are the closest secrets of any tannery-understandably.
Thus, when it comes to industrial high TDS wastewaters, it is not a simple kinetics of
phase and mass transfer unlike the drugs manufacturing sector where the reactions like
the Fidel-Crofts are a standard content. Thus it is prudent to take the readings in the
present case as they are and this is shown in Fig. 4.5.
Fig. 4.5 Buildup of EC with rising EC for the textile spent dye bath net evaporator
116
Conceding that the R square value of correlation at 0.937 has to be taken as perhaps the
closest to the ideal unity value in industrial high TDS wastewaters, the above relationship
has to be considered as a possible relationship within the tested boundary conditions in
the present study. The solar incidence and wind velocity pattern for Chennai are shown in
Fig. 4.6 and these also exhibit alternating peaks at different months.
The testing protocol was in the month of May when there was no rainfall. Other
environmental conditions are given in Table 3.3 earlier. The fact that all tests were
conducted on successive days, they were under the same environmental variables. Thus it
is possible to infer that the TDS / EC buildup is proportional to the arising TDS / EC and
this can be attempted to be used for development of an algorithm.
4.4 THE CHOICE OF SAMPLES FOR TESTING
Actual wastewater and ROR samples were collected from a range of identified industries
in the region and transported to the pilot plant site near Chennai. Spent textile dye bath
samples were taken in respect of both the hard dark coloured dye baths as also the light
coloured dye baths. These have a good shelf life and do not undergo degradation. Thus it
was possible to source these as and when the various colours were used in the industries.
Moreover, the pilot testing was carried out for a full 24 hour cycle to include the effects
of day and night times as also solar and sky radiations. In actual practice, the ROR and
high TDS wastewaters are stored till a reasonable continuous run of thermal evaporators
is possible as otherwise there is no operational economy by frequent switch on and
switch off practices in these thermal evaporators.
Fig. 4.6 Typical Chennai Solar insolation in kwhr/sqm day and Wind Speed in m/s. http://www.synergyenviron.com/tools/solar_insolation.asp?loc=Chennai%2C+Tamil+Nadu%2C+India
http://www.synergyenviron.com/tools/wind_data.asp?loc=Chennai%2C+Tamil+Nadu%2C+India
117
Moreover, the net evaporator can be left to operate by itself even in the nights because it
is merely a circulation of the ROR or high TDS wastewaters.
4.5 THE EXPERIMENTAL PILOT TEST RESULTS
One of the test results carried out on black spent dye bath is presented in Table 4.4
The testing protocol was varied with 3, 5 and 7 nettings in the compartment to modulate
flux variations of 0.19, 0.26 and 0.44 lpm of applied fluid over unit square meter of the
nettings per minute. The values in the two net evaporators studied earlier for spent dye
bath and ROR were 0.31 and 0.12 respectively. The range now chosen permits a lesser
flux as also a higher flux to be evaluated. In actual practice in all such fluid flows over
nettings there is an optimum over the net flow such that a minimum velocity is ensured to
scrub deposits of salt micro deposits and keep them sloughed off. At the same time, a
higher velocity from the flux may not yield the residence time for enabling the mass
transfer and bring out evaporation.
118
Table 4.4
Results of tests on textile black spent dye bath on pilot net evaporator
Nettings used 7 Nettings used 5 Nettings used 3
Packing density 14 Packing density 10 Packing density 6
Sump fluid temp 35 / 38 OC Sump fluid temp 35 / 38 OC Sump fluid temp 35 / 38 OC
Ambient temperature 38.3 to 40.8 deg C
Flux
lpm/sqm/m
Fluid
Depth Cm
EC of fluid
in sump
Flux
lpm/sqm/m
Fluid
Depth Cm
EC of fluid
in sump
Flux
lpm/sqm/m
Fluid
Depth Cm
EC of fluid
in sump
3 0.19 25.0 67500 0.26 25.0 66740 0.44 25.0 68500
6 0.19 23.7 71200 0.26 23.5 74260 0.44 23.5 73000
9 0.19 22.1 75000 0.26 21.5 80652 0.44 22.0 79810
12 0.19 21.0 79200 0.26 19.0 88971 0.44 20.9 84230
15 0.19 19.7 83200 0.26 17.0 95598 0.44 19.8 90630
18 0.19 18.1 86500 0.26 15.0 102930 0.44 18.6 95500
21 0.19 17.9 89900 0.26 13.2 110356 0.44 17.2 101080
24 0.19 17.0 94500 0.26 12.0 117030 0.44 16.0 107000
% fluid evaporated 32.0
52.0
36.0
% EC in fluid gained
40.0
75.4
56.2
Depth evaporated, cm 80
130
90
Duration of evaporation 21 hours for all tests
Pan evaporation, mm 5 mm per day from local meteorological data
Evaporation Index 18.2
29.7
20.6
Tim
e in
terv
al o
f te
sts
in e
xper
imen
t, H
rs
119
The results in Table 4.4 are discussed hereunder.
4.5.1. The black reactive dye was chosen at the outset for this initial testing due to it
perhaps being the strongest in adhering to fabrics. At the same time, this renders the
evaporation of its dissolved dye bath as equally challenging. The dye itself belongs
to the class of reactive dyes which are however inorganic synthetic dyes and to that
extent is devoid of retardants in evaporation like the organics, colloids etc. The
bond between the chemical molecules in these class of dyes like black, red, blue,
black etc or combinations thereof are typical N=N bond as in Fig. 4.7.
Fig. 4.7 Typical structure of the reactive group of modern dyes
4.5.2. The N=N bond is a relatively strong bond and does not permit the easy phase
separation by heat energy in evaporation and the colour gets all concentrated and
forms a coating over the heat exchanger surfaces and also its chemical oxygen
demand makes the RO process as hindered. As a result, the only proven
technology for resource recovery as reusable water is the wet oxidation whereby
freshly formed Ocl ions are brought into play to break the N+N bond. That
technology in turn involves the use of chlorine gas released through ejectors but
then the chlorine usage has its own challenges of a hazardous chemical. On top of
all this, even when the water is recovered by membranes or evaporators, the
purity of the same for commercially crucial apparel manufacturing is sluggish and
these are the reasons for reposing faith and confidence in the net evaporator
technology to bring about the maximum water evaporation and then the solid
residue taken to secure landfills. The sloughing velocity if adequately maintained
will ensure the net evaporator as a rather trouble free technology option and
within the ambit of local assembly and later on cannibalization.
120
4.5.3. Given this importance, it is worth going into the results in more critical acclaim.
The prototype installation at Chennai as cited in Table 3.4 operated at a flux of
0.31 as compared to the pilot plant which was operated at three flux values of
0.19, 0.26 sand 0.44. The lesser flux implies reduced sloughing over the nets and
a longer contact time for mass transfer but it can precipitate the salts slowly but
steadily on the interstices of the netting and render it as redundant. However, the
use of higher flux values will result in progressively increasing downward drag of
the applied liquid on to the netting drapes and also reduce the phase transfer
between the solid and liquid phases due to increasing mass per unit of depth.
4.5.4. A point of interest is the real numerical value of the flux applied on to the vertical
faces of the nettings. The flux is a term commonly used in engineering hydraulics
and fluid dynamics to define the quantum of liquid coupled mass inherent in it.
For example, when the applied salt water onto a desalination membrane is
referred to the same term flux is used wherein it signifies the applied liquid
volume per unit area of the membrane per unit time. The rather moot issue is the
area refers to the total surface area of the membrane contained in one membrane
element housing and the volume referred to be what is applied onto the membrane
housing. In actual practice, the volume applied to the membrane at the start end
gets filtered as permeate and reject streams and the permeate stream passes in
between the membranes to the tail end module housing whereas the reject stream
keeps going through the membrane spiral and splitting into the two streams as
above. Thus literally speaking the flux is something which keeps dynamically
changing across the length of the membrane housing and that too depending upon
the ionic balance and TDS mass, the split between the permeate and reject keeps
changing along the length of passage through the membrane housing. But then,
universally the initial applied flow rate and the total area of membrane element in
housing alone is considered purely as an empirical basis for the design. It needs to
be recognized there is no such thing as design of RO membranes from first
principles based on a stoichometry principle anywhere in the world. In fact it is
always the empirical relationship developed by the membrane manufacturer.
121
4.5.5. Similar is the present case in the usage of the term referred to as flux. The volume
of liquid applied at the top end through the distribution grid over the nettings as a
whole or rather the circulation pump duty is taken and the total area of all the
nettings is taken to develop this parameter as liters per minute per sqm. There has
to be a beginning somewhere instead of perpetually attempting and searching for
intangibles in a fluid that is in constant dynamic motion with split into two fluids
with vastly different densities as permeate and reject.
4.5.6. This being the case, in so far as the netting behaviour is concerned, the crucial
difference between the RO membrane practice and the net evaporator is that
while the total fluid flow as also the total mass remains the same until the applied
fluid exits the membrane, it is not so in the case of nettings. The applied liquid
gets progressively evaporated along the depth of the nettings.
4.5.7. Given that the higher the flux for a given netting bank, it means a higher
downward velocity along the depth of the nettings and hence, the lesser overall
contact time intervals between entry in to netting bank and exit from thereof.
Conversely the lesser the flux, it is higher contact time intervals.
4.5.8. Thus there arises two engineering dynamic factors namely, the contact time
intervals and the downward drag force. Though, there is also a third parameter
which is the salt impregnation into the netting material texture which may cause a
resistance to the uniform downward sink of the flux rate, this however, is not
significant in the present exercise as the netting chosen has not exhibited this. .
4.5.9. The downward drag force is actually a function of the flux and the EC as indicator
of TDS as the gravitated fluidized mass. Thus a parameter can be ascertained as
flux times TDS as an indicator of the causative variable in this experiment and the
EI (evaporative index) as the resultant variable given the boundary conditions.
122
4.5.10. Set in this reasoning and hypothesis, the test results in Table 4.4 would transform
into a cause-effect relationship as in Tables 4.5 to 4.7 and Fig. 4.8 to 4.10.
Table 4.5
The cause-effect relationship of the pilot test results for flux of 0.19
Flux*EC/1000,
EC times lpm/min/sqm 12.8 13.5 14.3 15.0 15.8 16.4 17.1 18.0
Fluid Depth in Sump,
cm 25.0 23.7 22.1 21.0 19.7 18.1 17.9 17.0
Fig. 4.8. Fluxmass Vs fluid depth in sump for a flux of 0.19 lpm/min/sqm
The relationship results in an equation as
y = -0.01x5 + 0.778x4 - 24.11x3 + 371.8x2 - 2856.x + 8774,
where
y is the depth of fluid in the circulation sump in cm
x is the corresponding mass applied per minute per sqm on the nettings
and the R² correlation is almost unity at 0.994
123
Table 4.6
The cause-effect relationship of the pilot test results for flux of 0.26
Flux*EC/1000,
EC times lpm/min/sqm 17.4 19.3 21.0 23.1 24.9 26.8 28.7 30.4
Fluid Depth in Sump,
cm 25.0 23.5 21.5 19.0 17.0 15.0 13.2 12.0
Fig. 4.9. Fluxmass Vs fluid depth in sump for a flux of 0.26 lpm/min/sqm
The relationship results in an equation as
y = 0.004x3 - 0.298x2 + 5.722x - 6.896,
where
y is the depth of fluid in the circulation sump in cm
x is the corresponding mass applied per minute per sqm on the nettings
and the R² correlation is almost unity at 0.999
124
Table 4.7
The cause-effect relationship of the pilot test results for flux of 0.44
Flux*EC/1000,
EC times lpm/min/sqm 30.1 32.1 35.1 37.1 39.9 42.0 44.5 47.1
Fluid Depth in Sump,
cm 25.0 23.5 22.0 20.9 19.8 18.6 17.2 16.0
Fig. 4.10 Fluxmass Vs Fluid Depth in Circulation Sump for a Flux of 0.44 lpm/min/sqm
The relationship results in an equation as
y = y = 0.000x4 - 0.028x3 + 1.685x2 - 44.55x + 468.0
where
y is the depth of fluid in the circulation sump in cm
x is the corresponding mass applied per minute per sqm on the nettings
and the R² correlation is almost unity at 0.999
125
4.5.11. The parameter of Fluxmass is a multiplication result of the applied flux as lpm per
sqm per minute and the EC present in the circulation sump at the instant time. The
EC is a function of the TDS. Thus, the parameter of lpm multiplied by EC as a
function of the TDS in mg/l becomes an indicator of mass per minute applied on
the nettings and the factor used here as the mass on nettings per sqm per minute at
the time of the EC used in the calculation.
4.5.12. The degree of fit at almost closest to unity at 0.994 indicates the reliability of
using this approach to develop an algorithm to depict the performance of the net
evaporator pilot plant tested and reported as in Table 4.4. Thus, it may be seen
that the applied mass at the top end of the netting can be used as a practicable
indicator. Even otherwise, the mass applied decides how much evaporation can be
brought about and hence, the drop in fluid level at the circulation sump.
4.5.13. The effect of flux on the evaporation is also of importance. It stands to reason that
as flux increases, the velocity of downward glide of the fluid would increase
almost in proportion. But then, the converse may not always be true because of
very low flux values, the glide may be getting held up at the meshing in the net
and also because of the possible salt crystals depositing out, the fluid may get
retention and flush out in cycles. Thus, the relationship in Fig. 4-11 is important.
Fig 4.11 Variation of applied flux and resulting percent evaporation.
It is seen that within the range of flux studies the mid value of 0.26 appears optimum.
126
4.5.14. The influence of flux on evaporation index is shown in Table 4.8.
Table 4.8
Effect of flux on evaporation index in the pilot testing
Flux in lpm / minute / sqm 0.19 0.26 0.44
Evaporation Index (EI) 18.2 29.7 20.6
For near about the same flux of 0.31, the EI was only 12.93 in the prototype spent dye
bath net evaporator and for a flux of 0.12 the EI was only 11.6 for the ROR unit and this
is because, unlike the pilot unit, the uniform application of the fluid over the full top area
of the nettings bank is not an easy installation as can be seen in comparison in Fig. 4.12.
Fig. 4.12. The perfect distribution in the pilot plant and inadequacies in prototypes
In fact, this structural aspect of anchoring and more so maintenance access to the
distribution grid atop the nettings is a major challenge in respect of large installations.
127
This is a classical case of not only the technology but also the engineering that needs to
combine and merge to realize the intended true extent of the results in actual practice,
suffice to say this aspect is however beyond the committed purview of this thesis.
4.6 PILOT TESTING RESULTS FOR OTHER DYE BATHS AND RORs
Having narrowed down to the flux of 0.26, the other experiments were carried out on this
setting and for three samples of other spent dye baths from textiles and three samples of
ROR from fresh brackish water desalination installations. The elaborate tabulations are
avoided and the gist is condensed in Table 4.9.
Table 4.9
Gist of results of other samples put through pilot experiments
Sl
No. Fluid Tested
Depth of liquid in sump EC of liquid in sump
Start end lost % start end buildup %
1 Blue-black
dye bath 20 10.5 9.5 47.5 45000 79000 34000 75.5
2 Yellow
dye bath 20 9.5 10.5 52.5 36000 56000 20000 55.5
3 Indigo
dye bath 20 11.5 8.5 42.5 52500 86500 34000 64.8
4 Saline water
ROR 20 8.0 12.0 60.0 9500 17500 8000 84.2
5 Saline water
ROR 20 11.0 9.0 45.0 14500 19500 5000 34.4
6 Pharma ETP
ROR 20 11.5 8.5 42.5 15000 24500 9500 63.3
Test conditions were maintained as the same reported in Table 4-3 for the flux rating of
0.26. Rainfall was nil. Temperatures of fluids were in the range of 34 to 38 Deg C.
Humidity was in the range of 75 to 80 %, Wind Speed was in the range of 5 to 5.5 m/s.
4.6.1. The percent of fluid depth evaporation does not have a pro-rata relationship with
the percent of buildup of EC. This was similar in the earlier tests also. In regard to
the textile spent dye bath samples, the intra-relationship between these two is
again not pro-rated to the arising EC of the fluid at the start. This may be due to
retardation effects of the types of dyes and their chemical compositions. This lays
stress on the need to place reliance more on the depth of fluid evaporated.
128
4.6.2. The reliance on increase in EC is actually insignificant in so far as the field
installations are concerned because once the fluid consistency reaches a
concentration where it cannot be put through the net evaporator system, the
nettings are taken out and the contents are solar dried and the salty paste is
eventually transported to secure landfill and thus there is no value byproduct.
4.6.3. The inland installations practicing ZLD are mostly industries with compulsion to
go in for evaporation whereas the drinking water RO plants are in general
permitted to put the ROR into nearby drains. Thus, the net evaporator installation
in industry is more concerned only with getting rid of the water in the ROR.
4.6.4. It brings forth the postulation that the experimental conditions as in Table 4.8
above can be adopted for the day to day adoption in the said installations as an
economical, locally sustainable and permitting cannibalization and thus opening
out a vista of ROR and high TDS wastewater disposal for ZLD compliance.
4.6.5. The equation presented in Fig. 4.9 can be used as a design algorithm for sizing the
net evaporator within similar boundary conditions. Taking the cue as 25 cm initial
depth and calculating how much depth of fluid has to be evaporated to meet ZLD
in ROR, the equation will give the Fluxmass in terms of EC times flux in lpm per
minute per sqm and using the packing density as in Table 4.3 for this flux, the
area of nettings can be calculated. Once this is done, the height of the netting can
be advantageously kept at about 5 m to safeguard undue wind oscillations and the
total width becomes available. Depending on the width of the sump minus the
kerbing clearances, the number of nettings can be arrived at.
129
CHAPTER 5
SUMMARY AND CONCLUSIONS
5.1 GENESIS
Readily potable water sources are fast shrinking in the Asia-Pacific, Latin American.
Middle East and coastal settings of European Union denting 2.3 billion people.
Exploitation of ground and seawaters with Reverse Osmosis (RO) has become the
practice but with challenges of high power needs and safe disposal of high salt RO rejects
(ROR). While the power needs are addressed by Government policies, the issues of ROR
are addressed only in public water supply seawater RO plants by putting it back far far
away into the sea, but then for how long is a disturbing question. Similar is the story for
industrial wastewaters which are all of late required to practice Zero Liquid Discharge
(ZLD) by way of recovery and reuse of the water in ROR and containment of salt in
secure landfills. Clearly, large industries like petrochemicals possess the required finance
and wherewithal to follow this at a staggering cost of close to Indian National Rupee
(INR) 250 per thousand liters as compared to the cost of only INR 50 for even SWRO
itself. Pharmaceuticals, insecticide and pesticides etc somehow manage this by increasing
the sale price of the products. This however is not the case of textiles and tanneries which
are more of daily needs of mankind and already the installed production capacity in India
is curtailed to just about 30 % with stagnation of infrastructure, human resources etc
besides migration of the industry itself to nearby regions with abundant perennial water
bodies for disposal after treatment for all parameters except the salt content. The inland
small and medium industries however facing the brunt and are observing the ZLD more
by surreptitious discharges than compliance. The situation points to the need for ROR
technologies that are locally sustainable with cannibalization of repairs and renewals and
a cost factor that is reasonable commercially.
5.2 THE STUDY
Alternative systems like the ad hoc solar ponds and spray ponds have been used but the
environmental windages have steadily lead to the decline of these in public acceptance
and right now there are no alternative validated technologies for these.
130
The Objective of the study were (1) to identify a prospective candidate technology for
easier replication locally, (2) to pilot and validate it within the known boundary
conditions of inland small and medium scale industries in the region and (3) to evolve a
design permitting continual localized Research and development.
5.3 FINDINGS OF THE STUDY
The study has demonstrated and validated a system of nature based evaporator facility
whereby a series of parallel drapes of greenhouse netting fabrics of 6m height are hung
from a grid atop and the ROR is sprayed on top to induce phase transfer between the
liquid, the salt and the vaporization in batch mode. The test liquids studied were ROR
from a textile effluent ZLD facility and spent dye bath of a textile fabric dyeing industry.
The TDS of applied liquid was about 45,000 to 50,000 mg/L and the evaporated liquid is
recirculated again in a dynamically changing equilibrium till its saturation to about
3 times. Computing an evaporation index (EI) defined as the achieved evaporation in the
facility to that of simple pan evaporation for the identical plan area, the EI is achieved at
7 to 21 in cool night hours and peak heat day time. This reinforces the concept of Dalton
who cited the solar radiation and sky radiation as influencing factors with the solar
radiation in day time and the sky radiation in night hours. A design basis for boundary
conditions similar to those tested has been postulated.
5.4 SIGNIFICANCE OF THE FINDINGS
The textile and tannery sector as well as inland water based industries in India are facing
a survival crunch on the ZLD front due to the insistence of thermal evaporators by the
pollution control authorities and as a result migration of industries to neighboring
countries where TDS is not a criterion in discharge continues which is not the way for the
futuristic growth of the country. The system now demonstrated and validated can help
reverse this trend by virtue of local fabrication and repairs if any besides the O&M cost is
hardly Indian National Rupee (INR) 10 per thousand liters of feed as compared to INR
250 for the thermal evaporator system. The validation is theoretically sound and is
potentially a panacea for the industries now being confronted on the ROR front in ZLD
131
5.5 SPECIFIC ADVANTAGES OF THE FINDINGS
(a) The system is not covered by any patent
(b) Eliminates steam generators and induced thermal evaporative operation
(c) Eliminates dependence on specialist trained high-skill operators
(d) Eliminates dependence of vendors for equipment repairs and renewals
(e) Eliminates back up high energy diesel generator sets
(f) Eliminates need to keep “warm” even during “no-ROR” periods
(g) O&M costs are only 5 % of that for thermal evaporators
(h) Completely nature based system with phase transfer
(i) Permits switch-on and switch-off as and when needed
(j) The nettings are readily available off the shelf green-house nettings
(k) Efficiency can be maximized using spray nozzles on nettings
(l) Temporary roofing using tarpaulins can help functioning even in rains.
(m) Permits removing and re-erecting the nettings easily
(n) Locally designed, built and operated even in remote locations
(o) The schematic is simple in concept and practice as under
(p) The system is now proven in a coastal setting and another in a desert setting
(q) These two are in use for over two years but on an ad hoc basis
(r) The study has founded them on phase separation kinetics and inherent factors
(s) It is possible to design future systems precisely instead of the above ad-hocs
(t) Above all, it can reverse the small industry exodus from this country.
Receiving Sump
with bottom flow
maker for forward
mixing
Net Evaporator as wind aided falling
film evaporation and bottom slurry
solar-dried in summer as in-situ
(In standby for preventive work)
Pumped Recirculation
Net Evaporator as wind aided falling
film evaporation and bottom slurry
solar-dried in summer as in-situ
(In active operation)
in operation
Pumped Recirculation
Sec
ure
Lan
dfi
ll
132
5.6 SALIENT CONCLUSIONS
1 The net evaporator system needs only a circulation pump and nettings and can be
fabricated by native semi-skilled talent and repaired if at all any repair arises
2 The O&M cost is only a maximum of Rs 7 to 10/cum of RO rejects / high TDS
wastewaters as against Rs. 150 to 200 / cum for thermal evaporator.
3 The net evaporator is apt for ZLD with bare electrical energy.
4 The study has significance to reality in ZLD based treatment plants with high
TDS wastewaters / RO rejects which may not be arising all the time and the
evaporator can be operated co-terminus with the operation of such plants.
5 The theoretical explanations of evaporation and salt segregation in these net
evaporators are encompassing not just the fundamentals of mass transfer between
phases but also involves such complexities as such factors as continuous shear of
the liquid over a friction surface of pre-adhered salts on the netting and possible
crystallization etc and needs piloting to evolve the system configuration but then,
even for thermal evaporators, it is the same situation.
6 The air-drying and containment of the resulting salts in secure landfill is a
common denominator for any type of evaporator and does not impact the
evaporator per se.
7 A one year compilation of the operating evaporation data for the Chennai study is
presented in Figs 4.8 to 4.10 and can be used for planning pilot installations
133
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APPENDIX – A
CLIMATIC CONDITIONS OF CHENNAI
149
Table A2 Variation of Typical Variation of
Dry Bulb (DB) and Mean Coincident Wet Bulb (MCWB) Temperatures at Stated %
0.40% 1% 2%
Month DB MCWB DB MCWB DB MCWB
Jan 31.2 22.8 30.6 22.8 29.9 22.7
Feb 33.6 24.4 32.8 24.3 32 23.9
Mar 35.6 24.7 35 24.8 34.4 24.9
Apr 38.2 26.3 37.2 26.6 36.2 26.7
May 41.1 25.5 40.1 25.2 39.2 25.6
June 39.2 25.2 38.5 25 37.9 24.9
July 37.3 24.8 36.8 24.8 36.1 24.8
August 36.4 24.7 35.8 24.6 35.2 24.6
September 35.9 25 35.2 25 34.8 25
October 34.1 25.3 33.5 25.3 33 25.3
November 32.2 24.4 31.5 24.4 30.9 24.4
December 30 23.8 29.6 23.3 29.1 22.8
Average 35.40 24.74 34.72 24.68 34.06 24.63
Highest 41.1 26.3 40.1 26.6 39.2 26.7
Lowest 31.2 22.8 30.6 22.8 29.9 22.7
Monthly
Difference 9.9 3.5 9.5 3.8 9.3 4
Average
Highest 33.33
Average
Lowest 26.67
Yearly
Difference 6.67
150
DEW_POINT_TEMPERATURE_C
151
APPENDIX – B
CLIMATIC CONDITIONS OF JAIPUR
Jaipur-Dew Point-July-2015
Jaipur-Humidity-July-2015
152
Jaipur-Rainfall-July-2015
Jaipur-Temparature-July-2015
153
Jaipur-Wind Speed-July-2015
154
LIST OF PUBLICATIONS
International Journals
1. S. Virapan, R. Saravanane and T. Sundararajan, “Recovery & Reuse of RO reject
water: A State-of-the Art Review,” International Journal of Civil and
Environmental Engineering, ISSN:1701-8285, Vol. 36, Issue.2,(2014),
pp.1321-1338
2. S. Virapan, R. Saravanane and T. Sundararajan, “Performance Evaluation of
Automobile Industry Effluent Treatment Plant to Achieve Zero Discharge,”
International Journal of Applied Engineering Research, ISSN 0973-4562, Vol. 10,
no. 9(2015), pp. 21971-21982.
3. S.Virapan, R.Saravanane and V.Murugaiyan, “Reverse Osmosis Desalination
Performance using Artificial Neural Network approach with optimization”. Asian
Journal of Water, Environment and Pollution, ISSN 0972-9860, Vol.13, No.3
(2016), pp.95-102.
4. S Virapan, R Saravanane and V. Murugaiyan, “ Study on Reverse Osmosis Reject
handling of Food industry Waste water” Pollution Research, ISSN 0257-8050
Vol. 35, Issue 3, 2016, pp. 511-514.
5. S Virapan, R Saravanane and V. Murugaiyan, “ Zero Liquid Discharge (ZLD) in
Industrial Waste waters in India – Need for Sustainable Technologies and a validated
case study”- International Journal of Environmental Engineering and
Management, ISSN 2231-1319 Vol.7,no.1,pp.25-33.
6. S Virapan, R Saravanane and V. Murugaiyan, “ Treatment of Reverse Osmosis
Reject water from Industries”- International Journal of Environmental Sciences
(Accepted for Publication)
National Journals
7. S Virapan, R Saravanane and V. Murugaiyan, “Evaporation rate and volume
estimation by non thermal evaporation method”, International Journal of Pharmacy
and Technology. (Accepted for Publication)
8. S Virapan, R. Saravanane, V Murugaiyan, “Treatment of Industrial Waste by non-
thermal techniques – A case study”, International Journal of Chemical and
Pharmaceutical Research. (Accepted for Publilcation).
155
National Conference 1. S. Virapan, R. Saravanane and T. Sundararajan, “Study on Recovery and Reuse of
RO Reject water”, in National Conference on Challenges of Water Resources and
Environmental Management – NCCWE 2014, January 2014
International Conferences 2. S. Virapan, R. Saravanane and T. Sundararajan,“Impact and Management of RO
reject disposal”, in VIII WAC 2014 International conference on Balancing
Development and Environment, New Delhi - November 2014.
3. S. Virapan, R. Saravanane and T. Sundararajan , “Disposal of High Dissolved Solids
Wastewaters at Inland locations – Pointers for India”, in 9th WATMAN
International Conference and workshop, Chennai–February 2015.
4. S. Virapan, R. Saravanane and T. Sundararajan , “Sustainable Environment in Zero
Liquid Discharge of Industrial Effluents”, in International Conference on
Sustainable Energy and Built Environment in association with ASCE Indian
section, Vellore, March 2015.
156
VITAE
VIRAPAN. S, the author holds the position of Joint General Manager in the Indian
International premier engineering firm of M/S Larsen & Toubro Constructions and is
presently the Research Scholar in the Department of Civil Engineering at the Pondicherry
Engineering College of the state of Puducherry in India. He holds a B. Tech (Civil Engg)
from this college in 1991 and later M. Tech (Environmental Engg.) from the Annamalai
University in 1994.
His professional experience since 1994 is in the field of construction engineering which
encompasses vast exposure in the design of Public Health Engineering / Fire protection
systems for residential and commercial buildings, mentoring turnkey contracts involving
high end finishes and sophisticated Mechanical & Electrical Plumbing services and
project management of mega projects in lead roles in prestigious projects like the
Mumbai National and International airports.
He is an active member in disseminating knowledge through professional institutions like
IPA (Indian Plumbing Association), IWWA (Indian Water Works Association), IPHE
(Institution of Public Health Engineers), and WEF (Water Environment Federation) and
IEI (Institution of Engineers, India). He has ardently participated in various international
conferences by presenting several papers and moderating discussions.
His primary area of interest pertains to waste water management, RO processing and
recycling process. Besides these, as a part of Corporate Social Responsibility initiative,
he has been instrumental in establishing training schools for PHE trade to provide
training to rural youth in plumbing trade so as to develop their basic skills to take up local
employment opportunities and serve the local habitation as also sustain themselves.
