Hosur WTP Rehabilitation NEERI Feb 2011
Transcript of Hosur WTP Rehabilitation NEERI Feb 2011
Resurrection of an abandoned 23 MLD Sewage Infested Surface Water Treatment
Plant (WTP) by Disinfection at High Lime and Neutralization by CO2 at Hosur, India
Er. Dr. S. Saktheeswaran, (Ph. D, UK), MRSPH (London)[email protected]
NEERI-Nagpur-India-February-9-2011
The Bangalore Metropolis, India
The Pennaiar River for surplus sewage of Bangalore Water and the Dam
The Pennaiar River for surplus sewage of Bangalore Water and the Dam
Statement of The Problem
• Water source to the WTP is a river water impoundment• The river water has flows only in July-September • Upstream population discharges non point untreated sewage• The benthos of impoundment bears the brunt of this pollution• In summer months of March-June, the pollution is heightenedand exceeds the self purification limit
• The result is aquatic organisms became devoid of aerobic state in the upper layers and algae started decaying and water stinking.
• The 23.5 MLD capacity WTP was not designed to handle this
• To add to the woes, the ground water availability at the site was at nearly 200 m depth and the public could not afford drawing it be deep wells on a domestic scale. It resulted in exodus.
Appearance Greenish Sodium as ‘Na’ 85 to 95
Appearance after 24 hours
Greenish Potassium as ‘K’ 7 to 10
Odour Algal Total Dissolved Solids 630 to 670
Odour after 24 hours Foul stench Iron total as ‘Fe’ 0.24 to 0.52
Turbidity, NTU 13 to 20 Manganese as ‘Mn’ Nil to trace
Total hardness as ‘CaCO3’
320 to 350Oxygen absorbed, 4 Hours
5.6 to 6.8
Calcium as ‘CaCO3’ 180 to 210 BOD 14 to 18
Magnesium as “CaCO3’ 81 to 85 COD 48 to 65
Iron total as ‘Fe’ 0.24 to 0.50 Chloride as Cl 150 to 170
Manganese as ‘Mn’ Nil to trace Sulphate as SO4 40 to 52
Alkalinity Phe / total CaCo3
0 / 380 - 450 Fecal coliform / 100 ml40000 to
80000
The Raw Water Quality in the Dam in High Summer Times
Treatment Options – Chosen Option
The options considered were
1 Heavy pre-chlorination, SMBS, lime clariflocculation-rapid sand filtration, post chlorination,
2 Copper sulphate use in the impoundment,
3 Micro strainers for algae filtration and existing treatment,
4 DAF followed by existing treatment,
5 Upstream spin klin disc filters & UF membranes,
6 High Lime followed by ammonia stripping and carbonation.
No. Technology Advantages Disadvantages Choice
1
Heavy prechlorintion, SMBS, lime clariflocculation-rapid sand filtration, post chlorination
1.Prechlorintion combined with ammonia can result in chloramines 2.Chloramines result in lower concentrations of disinfection byproducts3.Chloramines do not tend to react with organic compounds and less of taste and odor complaints
1. Chlorination of decaying organisms implies potential THM formations and carcinogens.
2. Precise control of chlorine dosages is negated in this outskirts of the city
3. Leaks of chlorine gas may affect the effort by public who are already upset
No
2
Copper sulphate use in the impoundment
1.Elimination of fresh growth of algae2.Ease of application by dosing from a boat 3.Saving at least the future impoundment
1. If Cu concentrations appear in raw water, there is no way of removal in the WTP
2. The dosing will not be precise & exceed
No.
No. Technology Advantages Disadvantages Choice
3
Micro strainers for algae filtration and existing treatment
1.Micro strainers can eliminate algae2.The downstream treatment can be easier3.Toxicity from chemical dosages is avoided
1. Micro strainers may not deal with algal lysis
2. Decaying algal stench cannot be removed
3. Basic problem of foul odour remains
No
No. Technology Advantages Disadvantages Choice
4
DAF followed by existing treatment
1.DAF can be effective in floating out algae2.Algal scum can be put through filter press3.Resulting cake can be composted
1. Decaying algal stench cannot be removed
2. No guarantee of complete algal removal
3. Dependence on prechlorintion continues
No
No. Technology Advantages Disadvantages Choice
5
High lime, CO2, and rapid sand filter and post chlorination
1. High ph disinfects microbes & microbes
2. It removes colour, stench, NH4 and PO4
3. No danger of THMs due to prechlorintion
1. Sludge from high lime has to be addressed
2. Need to store and use CO2 in containers
3. Ambient levels of ammonia to be monitored
Yes
No. Technology Advantages Disadvantages Choice
6
Spin klin filters, UF membranes, existing treatment
1.Spin klin filters & UF can eliminate algae2.Avoiding dosing of chemicals
1.Dependence on the single vendor for ever2.Basic problem of foul odour remains
Next best.
No. Technology Advantages Disadvantages Choice
Cascade and Prechlorintion
Lime Polyelectrolyte
Clariflocculation, rapid sand filter & chlorination
Cascade – No prechlorintion
High Lime pH 11 Polyelectrolyte Clariflocculation,
NH3 air stripping
Carbonation Rapid sand filter & chlorination
Existing Treatment Process / Facility
Retrofitted Treatment Process / Facility
The water that was delivered from the WTP - foul odourous & coloured
Rejected by public
Put up with by industry
Silent testimony by nearby Banyon
The Supplied Vs the Desirable The Supplied Vs the Desirable
What was Really Needed
•Learn from USA and Namibia and Singapore •Excess Lime and recarbonation•A pity this was not used for 2 years
Reasons for Abandoning Public Water Supply for 2 years
•Algal stench in treated water•Foul odour upon storage•Knowledge of sewage pollution•The tolerance - basic strength of India
The unused Gantry
Proposed to installa slotted SS tray deck over the tank sidewalls for direct placement of Lime bags
Inlet water line will be elevated to rain the water on pierced Lime bags to drain Lime solution into tanks below
Old agony and present ecstasy
Absence of algal stenchPresence of fresh odourAbsence of algal colourPresence of clarityAbsence of foulness on storageAbsence of colour in boiled riceAbsence of itching on bathingLathering on cloth washing is enhancedAesthetic willingness to drink Silent testimony by nearby Banyon
Parameters
Test Results for sample codes as underDrinking Water Standards of .Raw water
After high lime, NH3 stripping & carbonation
After rapid sand filtration & chlorination
Appearance Greenish Clear and colourless unobjectionable
Odour Algal Pleasant unobjectionable
Turbidity, NTU 13 2 1 1 - 10
Total Dissolved Solids 730 920 950 500 - 2000
pH 7.30 7.31 7.23 6.5 to 9.2
Alkalinity phe. as ‘CaCO3’ 0 0 0 No mention
Alkalinity total as ‘CaCO3’ 400 680 630 200 - 600
Total hardness as ‘CaCO3’ 290 540 515 200 – 600
Calcium as ‘Ca’ 80 210 200 75 - 200
Magnesium as ‘Mg’ 20 4 3 30 - 150
Ammonia as ‘NH3’ 14.96 4.5 nil No mention
Phosphate as ‘PO4’ 5.2 0.07 nil No mention
Oxygen absorbed, 4 Hours 5.6 0.6 0.2 No mention
BOD 7 nil nil No mention
TOC 50.99 14.50 1.50 No mention
Fecal coliform / 100 ml 50,000 2,000 Nil Nil
Sequential Water Quality During Treatment
No Parameters Prechlorintion High Lime - Carbonation
1 Colour Reverses on storage beyond 6 hours Does not reverse even after a week
2 Odour Repulsive decaying odour persists Decaying odour is completely gone
3 Keeping quality Worsens on storage of even a day No deterioration even after a week
4 Fecal coliform 50 mg/l as Cl for elimination 200 mg/l as CaO for elimination
5 TDS No appreciable increase Increases by about 200 mg/l
6 Phosphate No change Is eliminated
7 Magnesium No change Is almost eliminated
8 Calcium No change Increase by about 130 mg/l
9 Handling Hazardous Relatively safer
10 Rejects No solid wastes Sludge with high pH
11 Ambience Disturbing due to chlorine escapes Pleasant and fresh
12 Byproducts Possibility of THM and carcinogens No risk of THM and carcinogen
13 Heavy metals Cannot be removed Can be precipitates as their oxides
Relative Merits / Demerits of Chlorination Vs High Lime Neutralization
Applicability to the Disinfection Aspect of Raw Waters
The fact that raw surface waters are increasingly getting polluted by non point faecal sources as raw sewage, open defecation and disposal of rotting vegetables etc into river courses cannot be denied. It is necessary to refer to the status of pathogens in some major river waters in India
Introspection
Whereas we all accept that raw water sources should be first disinfected to become free of pathogenic coli forms, is it going to be all right to dump chlorine gas at high concentrations as 50 to 100 mg/l in raw waters and compound the issues of chlorine-decaying organics interactions with potentials of formation of THMs and carcinogens ? There is so much being written and debated on disinfection by products especially on chlorination and do we add over 50 mg/l of chlorine gas without ant concerns? Whereas we all agree that sanitation systems need to be enhanced to prevent the ingress of pathogenic & faecal organisms, is it easy to achieve it in such a vast country as India? What are we going to do by continuing to build conventional WTPs of mere prechlorintion, lime clarification, rapid sand filters and post chlorination?
Conclusion
It is high time to recognize that technologies like the high Lime-
carbonation have a significant role to play in our national
programme particularly in surface water sourced WTPs and it is
high time these are standardized by institutions as NEERI and
pollution control Boards under a central grant funding from the
GOI. It is already late considering that tenders for Agra city
WTP was invited with river Yamuna as source with lot of
fanfare but has been quietly hibernating for long.