Sewage is the untreated municipal liquid waste requiring treatment in a sewage treatment plant. Sewage contains about 99.9% of water, while the remaining content may be organic or inorganic. Sewage denotes both black water and grey water at the household level, where black water refers to waste water generated in toilets and grey water to the waste water generated in kitchen, bathroom and laundry.
Sewage sludge is the semi-solid precipitate produced in wastewater treatment plants. Such sludge can also occur in untreated sewage disposed off into lakes and other water bodies.
Sewage Generation and Management in India
Total sewage generation from urban centers in India is around 38 billion liters a day while the total sewage treatment capacity at present is estimated to be around 12 billion liters a day.
Sewage sludge generation in India is increasing at a faster rate as more and more sewage treatment plants (STP) are being developed. At the present moment, sewage sludge and effluents from these STPs are frequently disposed off on agricultural lands for irrigation/manure purposes.
In India, wastewater disposal systems are usually managed by local bodies. In a few specific cases, these are managed by State Government Departments/Statutory Boards set up by State Governments. This service facility falls under the water supply and sanitation sector.
Municipal Sewage Treatment Value Chain
Sewage treatment is the process that removes the majority of the contaminants from waste-water or sewage and produces both a liquid effluent suitable for disposal to the natural environment and sludge. The flow scheme of an ideal sewage treatment plant in India is illustrated below:
Potential of Energy from Sewage
Estimates from MNRE suggest that there is a potential of about 226 MW from sewage sludge - from treated and untreated sewage together.
To know about the primary technological options available for generating energy from sewage, Click Here