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Municipal Sewage Treatment, Reuse, Recycle

Municipal Sewage Treatment, Reuse, Recycle. Waste Technology India Expo Mumbai January 18-19-20, 2017 Yogen Parikh Consulting Engineer. WHAT IS SEWAGE. World Bank Economist Drinking water polluted by human excreta? Liquid responsible for polluting our water-bodies? Resource?. QUANTITY.

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Municipal Sewage Treatment, Reuse, Recycle

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  1. Municipal Sewage Treatment, Reuse, Recycle Waste Technology India Expo Mumbai January 18-19-20, 2017 Yogen Parikh Consulting Engineer

  2. WHAT IS SEWAGE World Bank Economist • Drinking water polluted by human excreta? • Liquid responsible for polluting our water-bodies? • Resource?

  3. QUANTITY Out of 150 liters of drinking quality water supplied per capita per day approximately • Up to 40 % (60 L/capita/day) is used for toilet flushing • The remainder is kitchen, bathroom etc waste called grey water • 80% (120/L/capita/day) ends up as sewage So 150 L/capita/day of drinking water becomes 120L/capita /day of sewage or polluted water

  4. SEWAGE MANAGEMENT The handling of this sewage – sewage management - has three components • Collection & Conveyance • Treatment • Disposal

  5. COLLECTION & CONVEYANCE • The most expensive component of all – almost 70% of the total cost • Not a difficult engineering feat but implementation has problems • Most of the cities and towns have very old systems which serve only a part of the population

  6. NALLAS AND CANALS Almost all megacities and towns in India have manmade open storm drains and natural open drains (nallas) that carry the storm water during monsoon to the receiving water bodies. Unfortunately inadequate sewerage results in significant amount of sewage finding its way into nallas and canals and almost all of these drains have become open sewers carrying domestic and industrial wastewaters. These drains ultimately discharge untreated sewage into receiving body – Ponds, Lakes, Rivers, Sea.

  7. Typical Characteristics of Raw Sewage

  8. Raw Sewage Treatment Plant Treated Sewage BOD COD Suspended Solids Nitrogen Phosphorus TDS Oil & Grease pH Trace Elements Toxic Materials Adequately – sized Well Operated Well Maintained Functional Not overloaded Nutrient Balance Temperate conditions Corrosion Structural Stability Hydraulic Design Environmental Impact BOD COD Suspended Solids pH Total Nitrogen Total Phosphorus TDS/Conductivity Oil & Grease SEWAGE TREATMENT PLANT +

  9. TREATMENT Basically four steps • Preliminary – Screening, Grit removal • Primary – Clarification (with or without chemicals) • Biological – Aerobic, Anaerobic • Tertiary – Coagulation, Filtration, Activated Carbon, Membrane etc.

  10. Preliminary Influent Primary Nutrient Sludge Secondary Tertiary Treated Sewage Typical Treatment Schematic

  11. TREATMENT PROCESSES LARGE PLANTS SMALL PLANTS • Screening 1. Screening • Grit Removal 2. Biological Treatment • Coagulation 3. Tertiary Treatment • Sedimentation 4. Sludge Handling 7. Biological Treatment • Tertiary Treatment • Sludge Handling

  12. BIOLOGICAL TREATMENT The aerobic biological treatments range from simple natural processes requiring large land areas with little on no power and relatively lower performance level (Oxidation ponds, wetlands etc.) to highly complex systems like Membrane Bio-reactor (MBR) and Moving Bed Bio Reactor (MBBR) which have a very low foot print and high performance level.

  13. SLUDGE HANDLING Sewage treatment will generate solids depending upon the processes used. Biological sludges may have to be treated for stabilization. The sludges have to be dried/dewatered to reduce their volume before ultimate disposal. Sludge Thickener and mechanical dewatering devices like Centrifuge, Filter Press, Belt Press Filter are commonly used. Ultimate disposal will depend on the nature of the sludge – hazardous or non-hazardous.

  14. TREATMENT & SLUDGE HANDLING The choice of technology/process will depend on many factors such as • Availability of land • Mode of disposal • Capital & operating costs • Skill of operator Indian experience with sewage treatment has been, unfortunately, rather dismal.

  15. WAY AHEAD Ideally, to protect the quality of our water- bodies, not only all sewage must be collected and treated to comply with the prescribed standards, all discharges of sewage into the water-bodies even after treatment should be stopped. Realisticallythe aim should be to maximize reuse/recycle and minimize disposal into water- bodies.

  16. WAY AHEAD Some reuse/recycle options Local (decentralized) • Residential complexes a) Separation of grey and toilet water Grey to gardens Toilet after treatment to recycle for flushing b) Treatment of sewage (grey + toilet) Recycle after treatment for gardens, car wash, flushing

  17. CASE-STUDY OF HOUSING COMPLEX IN MUMBAI Housing complex has 17 towers, 73 flats/tower and 5 persons/flatTotal number of residents = 17*73*5 = 6205Water supply : 140 lpcd, Total water supply : 870 m3/dayWastewater / Sewage Generation : 750-800 m3/dayRaw Sewage Characteristics:

  18. CASE-STUDY OF HOUSING COMPLEX IN MUMBAI • Treated Sewage Characteristics :

  19. TREATMENT SCHEME ScreeningDegrittingAnoxic Tank Aerobic Biological Treatment - MBRDisinfectionSludge Handling - Filter Press

  20. COST BENEFITS Year of Installation : 2010 Capital Investment : Rs. 2 CroreQuantity of Recovered Water : 750-800 m3/dayAnnual Savings on Water Charges : 1.1 Crore / annum @ Rs. 40 / m3 water (Tanker water rates in Mumbai – Corporation provides only drinking water)Annual Savings on Sewerage Charges: 7.2 lakhs / annumPlant Annual O&M Cost including Power : 32 lakhs / annum

  21. WAY AHEAD Some reuse/recycle options Local (decentralized) Commercial Treatment and recycle for (as an example) air-conditioning make up water Many High Rises in Mumbai have been using treated sewage as make up water for air conditioning for more than 20 years. e.g. Air India, SBI, Express Tower, Oberoi, Free Press, Metro theatre, etc. Many commercial establishments like malls, theatres, amusement parks etc. also use treated sewage for various non potable applications.

  22. WAY AHEAD Local • Industrial Many industries are using sewage generated within the industry and/or their adjacent housing colony after treatment for gardening and some low end applications e.g. Floor washing Toilet flushing

  23. WAY AHEAD Local • Industrial Many industries are using treated municipal sewage for various industrial applications e.g. Union Carbide Madras Refinery Madras Fertilizers Rashtriya Chemicals and Fertilizers

  24. WAY AHEAD Centralized • Industrial Reuse of sewage for industrial purposes is a “win - win” situation with the municipal corporation earning revenue, industries saving money and having the added advantage of releasing fresh water presently being used by industry for domestic/irrigation purposes. Especially where city/industry “coupling” is possible Thane Municipal Corporation and Thane Belapur Industrial area Vapi & Vapi GIDC, Ankleshwar & Ankleshwar GIDC etc. The water used by industrial estates could then be released for domestic use of the cities.

  25. WAY AHEAD Centralized • Industrial The most recent example is a Tertiary Treatment Plant (TTP) built by the Surat Municipal Corporation (SMC) to treat about 60 mld sewage to produce 40 mld of sewage treated to industrial grade water  This water (tertiary treated sewage) is then supplied to a nearby industrial estate (Pandesara) for about Rs.18/m3 (18.20/m3) while earlier the fresh municipal water was supplied at Rs. 22/m3. Industries are thus getting water at a discount of about Rs. 4/m3 (3.80/m3).

  26. WAY AHEAD Centralized • Irrigation Treated sewage can be used for irrigation after meeting the required standards for unrestricted/restricted use and for appropriate crops Bombay Municipal Corporation Master Plan 1979 considered use of Mumbai city sewage after treatment for irrigation in nearby Thane, Wada areas and found it economically viable.

  27. WAY AHEAD It is necessary to recognize the following facts • Treatment of sewage for reuse/recycle is much simpler than that for industrial wastes • The sewage needs to be treated only to the level of municipal water quality and this is achieved by adding simple water treatment unit processes to the sewage treatment plant • Privatization of centralized STPs supplying water to industries at a reasonable profit would open up a new market

  28. WAY AHEAD • Formulating Environmentally Sound Policies – Leading to sustainable water management • Peoples thinking, attitude and approach • Subsidising / reducing tax burden for cost effective solutions (Recycling should not cost more than fresh water) • Benefits/recognition for practitioners

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