Journal of Scientific & Industrial Research

Vol. 61, January 2002, pp 53-60

Chemical Industry Wastewater Treatment Using Adsorption A K A Rathi*

Technica l Adviser (Chemica l), Government of Gujarat, Industries Commissionerate, Udyog Bhavan, Gandhinagar 382017

and

SA Puranik VVP Engineering College, Rajkot 360 005

Received: 3 1 July 200 I; accepted: 02 November 200 I

In a typical wastewater treatment fl ow sheet used by several industrial units in Indi a. various stages of treatment include primary treatment. foll owed by secondary treatment . and tertiary treatment. The concentration of total dissolved solids increases during neutrali zation of the wastewater with acid/ alkali during primary treatment. which adversely affects the activity of microorgani sms during biological treatment. The present study aims at demonstrating that adsorption as the Iirst stage of treatment shall increase efficiency of the subsequent biological treatment. Experiments were carried out on different wastewater sampl es from chemical pl ants on adsorbents viz. acti vated carbon. bentonite. and lignite. The effecti veness of adsorbents in the removal of refractory organics by way of reducing chemical oxygen demand and colour is evaluated. The results of COD reduction are fitted into diffe rent models ava ilable in literature including the new model Rat"i Puranik equation . which requires least experimentati on for predicting COD values.

Introduction

A wide range of adsorbents (granulated as we ll as finely powdered) including activated carbon , clays, bentonite, tly ash, alumina, magnes ium ox ide, ferric oxide, silica, saw dust, zeo li tes , and activated anthrac ite volcanic ash soil s are used in wastewater treatment for the removal of heavy metals, and dissolved organic compounds which result in the reducti on of COD, BOD, and colour. For treatin g wastewater from multiproduct chem ical plants containing organic chemical substances in varying compositi on and concentration, which are difficult to degrade biologicall y, adsorption process I in combinati on with other processes is cons idered very effective in reducing COD and colour.

Adsorbents in industrial wastewater treatment with adsorptive properties of adsorbents , ac ti vated carbon, inorganic adsorbents and effici ent app licati ons of activated carbon adsorpt ion processes

* Author for correspondence Tcl: 079 3225837. Fax : 079 3225S2S. c-mail: env @ic.guj .nic.in

were reviewed2. The use of activated carbon in water

and wastewater treatment, including the increasin gly important role of adsorption" for removal of specific target compounds or classes of compounds from

. water and wastewater containing complex organic substance mi xtures has also been reviewed. The wastewater was biologically treated , and the residual BOD and COD were removed further with activated carbon~ . Powdered acti vated carbon and granular acti vated carbon) were used for the terti ary treatment of wastewater from a petrochemical plant. It was inferred that low COD and colour removal effici encies were due to the presence of organic co ll oids. whi ch were not adsorbed by the carbon. Granu lated carbons prod uced colourless efflu ent from the amber-coloured intluent. The results of removal of phenols and cyanides6 by adsorption by acti vated carbon in a pilot-plant were presented. Some industrial act ive carbons were used as adsorben ts in phenol and pyridine? removal processes and in adsorption of resins and oi ls from coki ng plant wastewater. It was observed that phenols were more easil y adsorbed than pyridines. It is reported that

54 J SCIIND RES VOL 61 JANUARY 2002

anionic, cationic, or nonionic polyelectrolytes or clay minerals8 did not inhibit adsorption of phenol on activated carbon. The phenol concentration In wastewater9 was reduced to less than 0 .5 mg/L by pass ing the wastewater through a three-s tage­adsorbing tank , each stage packed with activated carbon.

More than 80 per cent COD removal was obtained from wastewater containing be nzene derivatives. carboxylic acids, pesticides. and phenols by sequential adsorption on sorbents combination of activated anthracite PorolasT ion exchange resin activated anthracite 10. Magnesium oxide con tai ning adsorbents ll are reported to have been used for the treatment of wastewater from pulp manufac turing plants.

Waste Physico-

Water pH Chemical!

Adjustment .. Biological

~ Treatment

to be 90 per cent. The remaining sodium c hloride and sodium carbonate were recovered and reused in soda manufacture .

Methodology

The conventional flow sheet of wastewater treatment used by most of the nndu "trial unit s, inc ludes primary treatme nt , followed by secondary and tertiary treatments.

During primary treatment , neutralizati on of the wastewater results into increase of salts (total di ssolved sa lts). Salts in hi gh concentration inhibi t biological act ivi ty ' 6, and may cause an increase in nonsettleable suspended solids in the treated wastewater I? The tlow sheet g iven sub equentl y is, the refore,proposed, wherein adsorpti on with

.. Adsorption

Treatecl wdSte Wolter

Conventional flowsheet

Wastewater contain ing heavy metal s was treated with fly as h ' 2 from coal combust ion. resu lting in an increase in pH to more than 8, a decrease in COD. and removal of the meta ls . Methods for reducing concentrat ion of surface-active agents in industri al wastewater 13 were examined and it was observed that adsorption on coal guaranteed a satis fac tory concentration reduction for the ca rboxyli c and alkylsulphate surfactants but not the ami ne. which was best removed by adsorpti on on benton ite. The performance of wood charcoa l' ~ for the re mova l or DDT from the aqueous phase was in vest igated. The influence of parti c le s ize, pH , and the time of contact. which affect the sorption process, was studi ed in batch experiments.

Adsorption 15 was e mpl oyed to re move organic impuntles from wastewater con tallllllt! sodium ch loride 5-15, sodium carbonate 1.5. and sodium nitrate O. I per cent and monochlorobenzene 0 .3. polyamines 0.3 , 4,4' diaminodiphenylmethane 0. 3. and toluenediamine 2 mg/L for subsequent salt recovery. The efficiency of the organic impurity removal from isocyanate manu fac ture was obse rved

inexpensive adsorbents could be employed, pr ior to the conve nti ona l primary treatment for increas in g effic iency of the biologica l treatment.

This is expected to reduce refractory organi cs (COD) as well as BOD of the wastewater substantially a t the first stage of waste wate r treatment itself, facil itating further treatme nt. From multi -stage production processes used in the producti on of organic c hemica ls, wastewater stream is li ke ly to

contain several organic as we ll as Inorganic substances including products . inte rmed iates. side prod ucts , byprod ucts and unreacted raw materia ls. The industria l wastewaters being hi ghl y complex and vary ing widely in the adsorbability o f the compounds present l ?, the detailed analys is of such wastewater streams and study of their adsorpt ion on d i fferent adsorbenrs was very compl ex . It was, therefore. decided to consider COD as the measure of organi c so lutes. The colour of the wastewater was a lso measured . These parameters (COD and colou r) reflect the practical aspects of wastewater treatment on the industrial scale. T hus. such a stud y should be of much relevance to the industry in selecting cost-

.J

RATHI & PURANIK : CHEM ICAL INDUSTRY WASTEWATER TREATMENT 55

Physico-pH Chemical! Waste

Water Adsorption

.. Adjustment ~ Biological ~

Treated waste water .. Treatment ..

Proposed flowsheet

effective wastewater treatment technique for complying with the statutory regulation s. The approach fo ll owed in the evaluation of adsorption performance of different adsorbents viz. acti va ted carbon, bentonite, and lignite in the treatment of wastewater is thus based on detection of COD and colour (optical density) in the wastewater with varying degree of treatment. Thi s approach is entirely different from that followed by many of the researchers who prepare wastewater samples from known solutes in the laboratory and carry out chemical analysis of the treated sample.

The COD determination IX is a measure of the oxygen equivalent of that portion of the organic matter in a sample that is susceptible to oxidation by a strong chemical oxidant. It is an important, rap idl y measured parameter for industrial wastewater studies and for control of wastewater treatment processes . The dichromate reflux method was used for the COD determination because it has advantages over other oxidants in oxidizabi lity, applicabi lity to a wide variety of samples and ease of manipulation . The colour absorbance was measured as optical den sity in the UV visible range, with the help of spectrophotometer at the wavelength of maximum absorbance. The measurements were done on neat undiluted wastewater samples. In the cases, where the absorbance readings went beyond the scale the samples were diluted and the same dilution factor was app lied to treated samples also.

Experimental Procedure

For the contact time experiments, eleven wastewater samples from different production plants were collected in labeled carboys and the carboys were then sealed. These plants included dye intermediates (H-acid , dihydroxydibenzanthrone. dibenzyl oxybezaldehyde, dibenzanthronyl, and benzanthrone crude; sample nos. I to 5. respectively) ,

two from ethanol (before and after biogas generation ; sample no. 6 and 7), one from drug intermed iate (diethyl malonate; sample no. 8), two from a complex manufacturing vat dyes and intermediates (before and after neutrali zation ; sample no. 9 and 10). and one from a complex manufacturing various dyes and intermediates; sample no. 11 ). These samples were taken directly from the process plant streams, before these had any chance of getting mixed with any other streams. In most of the cases these were concentrated streams, often referred as mother liquor. While carrying out experimental stud ies on the wastewater from each carboy the sample was analyzed for pH . colour and COD. Then 500 mL of sample was taken from the respective carboy in a cylindrical tlask. 2.5 g activated carbon (AC) was added into the flask and magnetic stirrer was started. 5-10 mL sample was drawn every 15 min from this mass, filtered on filter paper and the fi ltrate analyzed for pH, colour and COD. At the end of 2 h, the stirring was stopped and the experiment was terminated. The experiments were repeated with 5 g bentonite (WP) as well as 5 g li gnite (BP). All the experiments were carried out at

room temperature of around 320 C. The properties of adsorbents used are given in Table I .

Results and Discussions

Performance ofAdsorbents

The performance of different adsorbents used in wastewater treatment with respect to COOl colour reduction has been analyzed by considering the fo llowing graded scale:

Performance

Effective

Moderately effective

Not effect ive

Per cent reduction in

COOl colour

>40

20- 40

< 20

56 J SCIINO RES VOL 61 JAN UA RY 2002

Table 1- Properties of adsorbents

Activated carbon Bentonite Lignite

Appearance Fine hlack powder. free from gritty matter

Fine white powder. free from gritty matter

Fine black powder. free from gritty ma tter

Acidity! alkalinity 3g boiled in 60 mL water should pH : 8.76 give a neutral and colourless

Moisture. per cent by oven at 100" C

Volatile matter. per cent

Fixed carbon. per cent

Adsorption on kerosene, mLiI 00 g

Porosity, per cent

Melting point, "c Specil1c surface. sq m! g

Refracti ve index

Ash content , per cent.

Oecolourization capac ity. per cent

Particle size. micron

Mesh size. per cent

-BS 72:

-BS 100

+BS 100

-BS 100 + BS 200

-8S 200 + BS 300

-8S 300

COD Reduction

tiltrate

5

2 - 3

40

10 - 100

90

The COD reduction by the three adsorbe nts over time for sample nos. I to 5 and 6 to II is plotted in Figure I and 2, respecti ve ly. It can be observed that for COD reduction , AC is effecti ve for wastewate r from H-acid , dihydroxydibenzanthrone, e thano l (before biogas recovery) and diethyl malonate, and moderate ly effecti ve for wastewater from the plants manufacturing dibenzanthronyl , benzanthrone crude and e thanol (after biogas recovery), and the complex manufacturing vat dyes and the ir intermediates. AC is not effective for wastewate r from dibenzy l oxybenzaldehyde. WP is effecti ve for was tewate r d ihydroxydi benzanthrone, e thanol (bot h before and after biogas generati on) and from diethyl ma lonate. and the complex manufacturing different dyes (other than vat) and intermediates, and moderately effective for dibenzyl oxybezaldehyde, dibenzanthronyl and benzanth rone crude, and the complex manufacturing vat dyes and the ir intermediates. WP is not effective

10.2 10 - 20

30 - 35

20 - 22

28

19.5

1550

220

1.502

12 - 20

10 - 100 10 - 100

100

0.45

27 .22

11 .77

60.56

for wastewater from H-acid. BP is e ffective for wastewate r from dihydroxydibenzanthrone and e thanol (both before and after bi ogas gene.rat iun). and the complex manufacturing diffe rent dyes (othe r than vat) and inte rmedi ates, and moderately effecti ve for dibenzanthronyl, benzanthrone crude and di ethyl malonate, and the complex manufacturi :lg vat dyes and their intermed iates. BP is not effect iv" for H-acid and dibenzyl oxybenza lde hyde.

Thu s the performance of a ll the three adsorbents is comparab le for reducing COD of the was tewater from the plants manufacturing dih ydroxy­dibenzanthrone, dibenzyl oxybenzaldehyde, diben­zanthronyl. benzanthrone crude and e thanol (both before and after biogas recovery ). AC is obse rved to perform better than both WP and BP for wastewater from H-acid . In the case of wastewater from diethyl malonate p lant , the performance of AC and WP is comparable. and better than BP. The performance of WP and BP is comparable for mi xed wastewater from

..

\

RATHI & PURANIK: CHEMICAL INDUSTRY WASTEWATER TREATMENT 57

----_._----- _ ._-- -- --- ---- - 1 --+--lAC ...-lWP -.-1I1P -M-2AC _+_2WP __ 2SP -+-3AC -2WP -3BP - ·:·-~c ':.j-. 4WP -'\- 48P -+t-- SAC - lII- &WI' ___ _

0.8

0.5

~ " 1 8 0.3 U

0.2 .r_ ;'j ' -

0.1

Figure I - COD red uction over time

--+--SAC _+_SWP -'-6BP ~7AC -+-7WP --+--7BP -+-SAC -8WP -SBP ... , - SAC

0.6 -Jc"' gWp -'-A- IIBP -H'- 10AC ""·:r. .. 1OWP -·",- ·1011P -- -i - llAC -llWP -11BP

0.5

I 0.4

" I § 0.3

0.2

0.1

0.25 0.50 0.75 1.00 t,h

1.25 1.50 1.75 2.00

Figure 2 - COD reduction over time

the compl exes manufac turing di fferent dyes and the ir intermediates and it is better than AC for wastewater from the complex manufac turing d ifferent dyes (other than vat) and intermediates.

CoLour Reduction

For colour reduction, AC is found to be effecti ve fo r wastewater of dihydroxydibenzanth rone. d ibenzyl oxybezaldehyde. di benzanthronyl and

benzanthrone crude, and the complex manu fac tu ring vat dyes and the ir intermediates, and it is moderately effecti ve for ethanol (both before and after biogas recovery. W P is effecti ve for wastewater of dibenlyl oxybezaldehyde and moderate ly effect ive for dihydroxydibenzanthrone, benzanthrone crude and ethanol (both before and after biogas recovery ). and the complex manufac turing different dyes (other than vat) and intermediates. WP is not effective fo r

58 J SCIIND RES VOL 61 JANUARY 2002

wastewater from dibenzanthronyl, and the complex manufacturing vat dyes and their intermediates. BP is effective for wastewater from dihydroxy­dibenzanthrone and benzanthrone crude dibenzyl oxybezaldehyde, and the complex manufacturing vat dyes and their intermediates, and is moderately effective for and ethanol (both before and after biogas recovery), and the complex manufacturing different dyes (other than vat) and intermediates.

It may thus be observed that the performance of all the three adsorbents is comparable in reducing colour from the plants manufacturing ethanol. AC is better than WP and BP, and BP is better than WP in the case of wastewater from the other plants . Comparing the cost of adsorbents used in the experiments, it is found that activated carbon is about ten-times expensive than either bentonite or lignite . The spent activated carbon or lignite, considering their calorific value, could be disposed easily and gainfully along with coal in boilers. The adsorbate organic matter from wastewater would also contribute to calorific value to some extent. At high temperatures in the boilers, large molecules of organic adsorbate would get disintegrated into harmless non-toxic small molecules like carbon dioxide and water, and the statutory authoriti es may permit this. Thus, spent activated carbon and lignite have the advantage of easy and safe disposal; and lignite has the cost advantage over activated carbon.

Comparison of Models

The COD values at differen t durations were predicted, using the following mode ls available In

literature:

Weber and Morri ' s equation (Eq. I)

(C;-C)/ Ci = m I to.5 + c I'

Lagergren equation (Eq. 2)

log (C - Ceq) = m2 t + c2 .

Rathi Puranik equation 19 (Eq. 3)

log (CODRT) = m t + c.

.. . ( I )

. . . (2)

... (3)

The values of COD predicted from these three models at differen t durations are compared with the experimental COD values in Figures 3 to 5, for three adsorbents . It may be observed that Eq. 3 predicts the COD with least errors as compared to the other two

models.

"""'"

• • ....", ul4RP

100000 ...... 300000 _

Exper1_1 coo, mill L

Figure 3 - Experimental and estimated COD-AC

/

"WM Pl4RP

tOOOOO 200000 300000 400000 5(0000 iOOOOO

Experimental COO, mgI L

Figure 4 - Experimental and estimated COD-WP

COD Equilihrium Prediction

It may be seen that Eq.(2) requires data on the equilibrium value of the COD for the prediction of COD at a given time. necessitating expe riments for each system. Eq.(3) does not require equ ilibri ull1 value of COD for predicting COD of a given system at any time. In fact, Eq.(3) can predict equ ilibriull1 value of COD. COD equilibrium va lues so predicted are compared with the experimenta l values in Figure 6. It may be observed that the predicted values are in agreement with the expe rimental va lues

RATHI & PURANIK: CHEMICAL INDUSTRY WASTEWATER TREATMENT Sl)

"""" ]

~ , ) 1

- j , I

Q I o 0--.0 .

I I

Ex~ coo, mgI L

Figure 5 - Experimental and estimated COD-BP

obtained at the end of 2 h of each experiment, in most of the cases, which are considered to be equilibrium values.

Conclusion

Rathi Puranik model, represented by Eq.(3) , can be used to predict COD at any time in a given system, using adsorption for wastewater treatment. This model requires two data points, whereas other models available in literature require detailed experi­mentation on a given system. Thus, Eq.(3) can be used to predict COD values of a sample in a given system at any time with least experimentation. This model can also predict equilibrium values of COD. The prediction of COD and COD equilibrium values will be useful in the design of adsorption systems.

Considering the rate of reduction of COD obtained for different adsorbents, effecti veness and cost of the adsorbents , and ease of disposal of spent adsorbents, suitable adsorbent or a combination of adsorbents could be se lected for optimizing the cost of wastewater treatment. The performance of lignite is observed to be comparable with that of activated carbon. Lignite is, therefore, considered to be cost­effective adsorbent in reducing COD as well as colour from wastewater. This study will be useful to

chemical manufacturers, especially the small and medium enterprises in the developing countries. having limited resources20 in resolving water pollution problems economically.

1I0000 1

150000 1 ...l I t,_ 1 ; . 'C 1

1I0000 j Q o o

i-I - 1

I

References

e AC .WP .l BP

30000 60000 90000 120000 150000 1I0000

ExperimenbolCODequllibrium. mgl L

Figure 6 - COD equilibrium valucs

Ullmann '.r encyclopaedia of indLlstrial chemistr\'. edited hy Wolfgang Gerhartz. Barbara Elvers. Michael Ravcnscroft. James F Rounsavilla and Gail Schulz. (VCH Vcrlag. Bascl. Switzerland) 1988 . 83. 9.49.

2 Saito Toshihide & Hagiwara Kazuyoshi. Research survey on adsorbents in wastewater treatment. Osaka KoSY" Gijlll .m Shiken.lho Kiho. 36(4) (1985) 237-45.

3 Weber WJ (Jr) & Smith EH . Activated cmbon adsorpt ion: the state-of- the-art. SILld Environ Sci. 29 ( 1986) 455 -9 2.

4 Derika Engineering. COD removal hy adsorption . .I1J/1 Kokai Tokkyo Kollo . .IP 5912.792 ( 1984) 3pp.

5 Guarino C F. Da-Rin B P. Gazen A & Gocllcms E P. Activated carbon as an advanced treatmelll for petrochemicals wastewaters. Water Scii Techllol. 2U( 10) ( 1988) I 15-30.

6 DiStefano Vettorio. Colaiacovo F. Colletta A & Dcrch i D. Elimination of phenols and cyanides from cokin g pl ant wastewater using activatcd charcoal at pilot scalc. CO IIIIII Eur CommLlnities, EUR. 7197 (198 1) 159- 74 .

7 Kel' tsev A V. Vorobleva T I. Korolev Yu G & Sysko" K I. Characteristics of some act ive carbons as reagcnt~ for the purification of wastewaters. Koks Khim . 8 ( 1976 ) 29 -J ~ .

R Huang Ju-Chang & Garett Jack T. Effec ts of pol yc lcc tro lytcs and clay colloids on carbon adsorpti on. Water Sf' lI 'age

Works . 124(3)(1977)64-67, 9 Xi Yong. Process for treating industrial wastcwater

containing phenol. Fallling Zhuall ii Sh enqillg GOlIgkai ShllolllingsllLl. CN 85 . 108.327 ( 1986) 6pp.

10 Podlesnyuk V V. Fridman L E. Mitchenko T E. Savchllla L A & Postolov L E. Adsorption treatment of wastewatcr from a chemical plant us ing a combi nation of differcilt typcs Ill' adsorbents. Khilll Teklmol Vodv. 13(6) ( 199 1) 503 -6 .

I I Ikari Yoshlmasa. ZosLli GijutslI. 11(4) ( 1985) 14-23. 12 Hoclter Heinz, Method for removal of heavy mctal s from

wastewater. Gel' Offen DE 3.732. 329 ( 1989) 2pp.

60 J SCIIND RES VOL 6 1 JANUARY 2002

13 Alfano G. Carta M. Del Fa C & Ghiani M. Some means of fi ghting pollu tion caused by surface-ac ti ve agent s in industrial wastewaters . .I Etud PO/lltl Mar Mediter. 6 ( 1983) 525 - 8.

14 Keerthinarayana S. Vijayshankar Y N. Shivalingaiah B & Visweswariah K. Sorption mechani sm of DDT from aqueous phase, J Environ Sci Health Part B. 25(4) ( 1990) 493 - 509 .

15 Meghea Aurelia. Draganoi u Mihaela. Nicolau Margareta & Liebman Agneta. Removal of organic impurities from sa line was tewater by adsorption. Rev Cltilll , 40(5 ) ( 1989) 44 1 - 5.

16 Principles of water quality lIIanagelllent, by W Wes ley Eckenfelder (Jr) (CBI Publi shing Company. Inc .. Boston. US A) 1980.315

17 Industria l H'C/ ter pollution control, by W Wesley Eckenfelder(Jr) (McG raw- Hill Book Company. Singapore) 1989.229.165

18 Standard lII ethods for tlt e exolllill a tio /l of Ivater and wastewater by Franson Mary Ann H. (A merican Puhlic Health Association) 1995.5. 12-5 . 15.

19 Rathi A K A & Puranik S A. Treatment of was tewater pollutants from direct dyes. Alii Dvesl!iff Rei' , 88(7) ( 1999) 42-50.

20 Rathi A K A, & Puranik S A. Small -scale chemical industry in Gujarat- some attributes. Indian Clt elll Eng, 40 (2) ( 1998 ) 178 - 86

Abbreviations and notations AC BOD BP

- Activated carbon - Biological Oxygen Demand - Lignit e

c, c l '

C

c2 _ Constant

Ci

Ceq COD CODRT

m

t WP

- COD at time t - COD initial

- COD at equilibrium

- Chemical Oxygen Demand , mg/L - (C i - C)/ t

- Slope of the strai ght line log CODRT vs time for a given adsorbent and a given sample

- Slope of the s traight line (Cj-C)/ C i vs

square root of time for a g iven adsorhent and a given sampl e

- Slope of the straight line log(C-Ceq ) vs

time for a given adsorbent and a g iven sample

- Time, h - Bentonite