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Introduction

Powai Lake under National Lake Conservation Plan.. In the Year 1995 under National Lake Conservation Plan of MOEF of Govt. of India, Powai Lake of MCBM was reviewed and identified as one of the Ten major lakes in the country for revival and improvements.A high level committee was therefore formed to check the pollution levels of the lake and to take steps to create public awareness to save the lake.Detailed Feasibility Report (DPR) prepared by consultant M/s. Wockhardt Ltd. was approved by32087

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Introduction

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    1. Introduction Salient Features of Powai Lake Location : Powai Lake is located about 27 Km away in the North - East of Mumbai City Year of construction : 1891 Catchment Area : 6.61 sq. km. and Water spread when lake is full ---2.10 sq.km. Length of Dam : 110 Mts. (stone masonry construction) Height of Dam : Varying from 3 Mts to 6 Mts, with top of dam is 58.5Mt.THD (Town hall Datum) Water quality : Non potable. Used for recreation, gardening, cattle washing and fishing . The only tourist attraction in the Heart of the city of Mumbai. Lake water got highly polluted due to untreated disposal of sewage and garbage from nearby residential and slum colonies. So as to save the lake it was necessary to revive and rehabilitate it urgently.

    2. Powai Lake under National Lake Conservation Plan. In the Year 1995 under National Lake Conservation Plan of MOEF of Govt. of India, Powai Lake of MCBM was reviewed and identified as one of the Ten major lakes in the country for revival and improvements. A high level committee was therefore formed to check the pollution levels of the lake and to take steps to create public awareness to save the lake. Detailed Feasibility Report (DPR) prepared by consultant M/s. Wockhardt Ltd. was approved by MOEF GOI and sanctioned Rs.6.62 Crore as grant to MCBM for implementation of the scheme on priority.

    3. Importance and Status of Powai Lake Powai Lake which is located in the heart of suburban of Mumbai is surrounded by NITIE , IIT, large housing complexes and unauthorized Hutment colonies. The water of the lake is supplied to M/s L&T company and Aarey colony for non domestic uses. During last few decades, Population surrounding the lake has increased substantially. Heavy siltation occurred which has an estimated quantity of 4.5 lakh Cu.M. approx. Eutrophication of lake was observed with abundance of hyacinth & floating weeds on the surface of lake. Dissolved Oxygen level at the bottom of lake has gone low as 0.71 mg/ltr.

    4. MAJOR CAUSES OF DETERIORATION OF LAKE Uncontrolled development and unauthorized quarrying activities in the catchments area. Ingress of untreated sewage from the residential areas. Dumping of garbage and other waste materials in the lake. Washing of clothes, vehicles, open defecation etc. On the lakeshore.

    5. Pollution Levels of the Lake A physical and analytical survey was carried out to ascertain the pollution levels and Eutrophycation condition in the lake Water Analysis Parameter Average Values 1) pH 7.2 2) Total suspended solid 43.00 mg/Ltr. 3) Nitrate Nitrogen 0.23 mg/Ltr. 4) Total phosphorus, 0.25 mg/Ltr. 5a)D.O. (Top) 4.11 mg/Ltr. 5b)D.O. (Bottom) 0.71 mg/Ltr. 6a)C.O.D. (Top) 42.70 mg/Ltr. 6b)C.O.D. (Bottom) 119. 00 mg/Ltr.

    6. Sludge Analysis verage valuesverage values

    7. Chlorophyll A Contents in Lake Water Sr. Sampling Site Chlorophyll A (mg/ m3) No (Average of Three Sample analyzed) 1 Boat Club 14.68 to 18.34 2 Powai Garden (Hill Side) 38.66 to 55.12 3 Near Sonar Baug Bay 86.04 to 104.44 4 Kol Dongri Side 44.24 to 86.44 5 Road Side Near Ghat 24.22 to 42.88 6 Near Centre of the Lake 138.48 to 166.22 7 In the Lake Centre 66.88 to 84.14 8 IIT Side (Near Temple) 28.86 to 64.66

    8. Scientific parameters to Establish Eutrophication Condition of the Lake Water Tropic state Phosphorus Chlorophyll A (mg/m3) Average Maximum Oligotrophic 4 - 10 1 - 2.5 2.5 - 8.0 Mesotrophic 10 - 35 2.5 - 8.0 8.0 - 25.0 Eutrophic 35 - 100 8.0 - 25.0 28.0 - 75.0 Hypertrophic 100 25 75 Phosphorus & Chlorophyll A levels observed in the water analysis showed that the lake was under the Hypertrophic condition. Scientific parameters to Establish Eutrophic Condition of the Lake Water Tropic state Phosphorus Chlorophyll A (mg/m3) Average Maximum Oligotrophic 4 - 10 1 - 2.5 2.5 - 8.0 Mesotrophic 10 - 35 2.5 - 8.0 8.0 - 25.0 Eutrophic 35 - 100 8.0 - 25.0 28.0 - 75.0 Hypertrophic 100 25 75 Phosphorus & Chlorophyll A levels observed in the water analysis showed that the lake was under the Hypertrophic condition.

    10. Lake Revival Project Implementation Strategy The work was divided in two parts. Part I :- Pretreatment activities. Part II :- Contract for revival using aeration and bio- remediation technique. Contd

    11. Pretreatment activities consists of:- a) Stop entries of all untreated sewage into the lake by providing treatment facility or connect it to main sewerage system. b) Installation of penstock gates on four major nallahs along Adi Shankaracharya Marg to prevent entry of silt and sullage water into the lake. c) Preventing the activities like open deification, throwing of garbage, washing of cars and clothes on the bank of the lake. Contd Lake Revival Project Implementation Strategy

    12. Contract work consists of :-- a)Collection of baseline data. b)Removal of floating and unrooted weeds. c)Providing aeration system. d)Application of speciality Bio-products for biodegradation of sludge. The project work of revival and treatment was proposed to be executed on turnkey basis. The work was awarded to M/s. Ace Housing & Construction Pvt. Ltd. in association with M/s. Clean-flow International USA at the total cost of Rs.4.69 crore (including execution, maintenance and monitoring), who claimed to have international experience in treatment and restoration of large water bodies. Contd Lake Revival Project Implementation Strategy

    13. The contract period for the project was 12 months for execution and 36 months for maintenance and monitoring. The work commenced on 20-4-2002 and completed within the stipulated period of contract i.e. on 19-4-2003. Further the maintenance period was started from 20-4-2003 and will get over on 19-4-2006. Aeration System:- Consisting of 6 nos of air compressors (5 HP to 40 HP capacity) installed on floating jetties & on the bank of the lake & 195 Nos of Air diffusers. The Aeration System was operated initially for a period of 18 to 20 Hours per day & further it was reduced to 8 to 12 Hours during night time. Contd

    15. First dose in liquid form was spread on 18th July 2002 all over the lake @ 1.5 liters / hector.( Total quantity=300 ltr.) Second dose was spread on 12 th Feb 2003 @ 3.33 liter / hector . ( Total quantity=700 ltr.) On 12 th April dose of Enzyme was added to activate the bio-degradation process.Quantity-2000 Ltr. The improvement in various parameters monitored is shown in the following table.

    16. Water sampling points for monitoring quality

    17. Values of various parameters before the start of work and after completion of work. Sr Parameter Units Value for No Eco-balance Value (initial) Value (final) D.O./ top mg/l 5 2.87 6.85 2 D.O./ bottom mg/l 2 1.30 5.45 C.O.D/ top mg/l 10 to 30 57.50 20.70 4 C.O.D./ bottom mg/l 10 to 30 103.90 28.90 5 Phosphate / top mg/l 0.01 to 0.035 3.971 0.0188 6 Phosphate / bottom mg/l 0.01 to 0.035 5.618 0.0178

    18. Sr Parameter Units Value for No Eco-balance Value (initial) Value (final) 07 Nitrate / top mg/l < 0.1 2.063 0.727 08 Nitrate /bottom mg/l < 0.1 3.100 0.0692 09 pH / top No 7 to -8.5 7.730 7.60 10 pH / bottom No 7 to -8.5 6.980 7.88 11 S. Solids / top mg/l < 10 65.00 8.30 12 S. Solids / bottom mg/l < 10 131.500 8.20 13 Chlorophyll A/ top mg/cu.m. 8 tp 25 60.00 23.90 13.a. Chlorophyll A/Bottom mg/cu.m. 8 tp 25 20.720 10.00 Values of various parameters before the start of work and after completion of work (contd)

    19. Dissolved Oxygen at Bottom.

    20. Dissolved Oxygen at Top

    21. Phosphates at Top and Bottom

    22. Chlorophyll-A at Top & Bottom

    23. FINANCIAL STATUS OF THE PROJECT Total Cost of the Project : Rs.4,69,82,000.00 Amount Received from MOEF : Rs.4,69,82,000.00 of Govt. of India 3) Total Expenditure Incurred : Rs.4,32,00,000.00

    24. CONCLUSION Powai lake having catchment area of 6.61 Sq. Kms & lake surface area of 2.10 Sq. Kms is improved within a period of 12 months. This is the 1st successful project executed in India using Aeration and Bio-remediation Technique. The status of lake was transformed from Hypertrophic condition to Mesotrophic condition. Use of the aeration and bioremediation technique was effective for improving the quality of lake water to the accepted standard for water bodies being used for fishing and recreational purposes. Though the installation cost of equipment, power and monitoring the water quality is high, the cost of maintenance is relatively low.

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