1. Municipal Sewage Treatment, Reuse, Recycle
Waste Technology India Expo
Mumbai
January , 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
Parameter
Concentration mg/l
BOD
COD
Suspended solids
Total nitrogen (as N)
20 – 85
Ammonia (NH3 as N)
10 – 30
Organic phosphorus (as P)
1 – 2
Inorganic phosphorus (as P)
3 – 10
Oils, fats and grease
Total inorganic constituents (Na, Cl, Mg, S, Ca, K, Si, Fe)
100
Heavy metals (Cd, Cr, Cu, Pb, Hg, Ni, Ag, Zn)
< 1mg/l each

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

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

11. TREATMENT PROCESSES LARGE PLANTS SMALL PLANTS Screening 1. Screening
Grit Removal Biological Treatment
Coagulation Tertiary Treatment
Sedimentation 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. Realistically the 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/flat Total number of residents = 17*73*5 = Water supply : 140 lpcd, Total water supply : 870 m3/day Wastewater / Sewage Generation : m3/day Raw Sewage Characteristics:
Sr. No.
Parameter
Units
Value 1
Flow
M3/day
850 2 pH
6.5 – 8.0 3
Biochemical Oxygen Demand, C
Mg/l
300 4
Chemical Oxygen Demand
500 5
Total Suspended Solids

18. CASE-STUDY OF HOUSING COMPLEX IN MUMBAI
Treated Sewage Characteristics :
Sr. No.
Parameter
Units
Value 1
Flow
M3/day
850 2 pH
7.0 – 8.5 3
Biochemical Oxygen Demand, C
Mg/l
< 5 4
Chemical Oxygen Demand
< 20 5
Total Suspended Solids

19. TREATMENT SCHEME Screening Degritting Anoxic Tank
Aerobic Biological Treatment - MBR Disinfection Sludge Handling - Filter Press

20. COST BENEFITS Year of Installation : 2010
Capital Investment : Rs. 2 Crore Quantity of Recovered Water : m3/day Annual Savings on Water Charges : 1.1 Crore / Rs. 40 / m3 water (Tanker water rates in Mumbai – Corporation provides only drinking water) Annual Savings on Sewerage Charges: 7.2 lakhs / annum Plant 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 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