The Chennai Metropolitan Water Supply and Sewerage Board commissioned the construction of Sewage Treatment Plants which generate biogas and power from waste-water. This resulted in energy savings, earning of carbon credits, and the use of recycled water by the industry. This was achieved through providing contract-related conditions, which encouraged the optimal use of land and of methane-based power.
Chennai is the capital of Tamil Nadu, and is located on the Coromandel Coast of the Bay of Bengal. It has an estimated population of 7.5 million (2007) and an area of around 181 sq. km. The Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB) was constituted under the Chennai Metropolitan Water Supply and Sewerage Act in 1978, to provide water supply and sewerage services in the city.
The CMWSSB used secondary, treated effluent from sewage treatment plants (STPs) for the cultivation of Para grass, which would then be auctioned. The treated sewage was discharged into the nearby watercourses. In order to prevent untreated sewage flow reaching waterways, CMWSSB undertook the construction of additional sewage treatment plants with a capacity of 264 MLD at four locations, and outsourced the activity to a contractor.
Tenders were called for the design, construction, and 10-year operation and maintenance of STPs. It was decided to load 5% of guideline value of the land cost in the total tender cost in order to ensure that bidders would propose minimum land for the STP construction. Bonus and penal clauses on the consumption of power from the grid were also included in the bid document to promote the reduction of power consumption. The contractor constructed STPs that operate under an activated sludge process with sludge digesters from which biogas is generated. This biogas has methane content of 60% to 70%, and is used as fuel for running a gas engine after the removal of moisture and hydrogen sulphide in a scrubber. The production of electricity is based on the methane content of the biogas.
Four sewage treatment plants were constructed, which generated biogas and power from wastewater. The power generated is sufficient to cover the power requirements of the STPs. The use of recycled water by industry has reduced the demand for potable water, thereby reducing the cost of supplying water.

Minimal land was used for construction of STPs, since priority was given in the tendering process to bids that would use less land. Due to penalty and bonus clauses for power consumption from the grid, the use of biogas power was maximised, and the use of grid power minimised. Methane-produced power has reduced power bills. Four STPs saw energy savings of Rs. 387.45 lakh per year. Capturing of harmful methane gas (21 times the global-warming potential of CO2) contributed to the reduction of global warming, and its use as a fuel helped in the conservation of natural gas. This has enabled CMWSSB to earn additional revenue through the sale of carbon credits under the clean development mechanism (CMD).

The water treated by the STPs was recycled and used by industry, which in turn reduced demand for potable water, and also reduced the cost of water supply. With untreated sewerage no longer being discharged into streams, the quality of the environment improved considerably. This also meant improved living conditions for those living in areas surrounding the STPs.

After the implementation of the initiative, the board is earning revenues of approximately Rs. 10 crore annually through the sale of treated sewage to the industry. An additional benefit of Rs. 43 lakh per month accrues to it through power generation.

Savings in Electricity Consumptions (Rs. in lakh)

#	Location of STP	Plant Capacity (mld)	Average power production through gas engine per month (KWH)	Equivalent of Tamil Nadu Electricity Board @ Rs. 3.50 / KWH (unit) per month
1.	Kodungaiyer (Zone I & II)	110	450,000	15.75
2.	Koyambedu (Zone III)	60	210,000	7.35
3.	Nesapakkam (Zone IV)	40	120,000	4.20
4.	Perungudi (Zone V)	54	450,000	15.75
	Total	264	12,30,000	43.05
	TN Electricity Board (TNEB) Power Saving per month			43.05
	TNEB power saving per Year* (9 months)			387.45

* = An allowance of 3 months has been given for less gas production during winter season, also taking into account for repairs and maintenance work.
Optimal land use, energy savings through the production of biogas, and earning of carbon credits, was stimulated through building in appropriate contract conditions and technical specifications. As most parts of India have a tropical climate, the production of biogas is a viable proposition.

For further details, contact:

Mr. Shiv Das Meena, IAS
Managing Director
Chennai Metropolitan Water Supply & Sewerage Board (CMWSSB)
No. 1, Pumping Station Road
Chintadripet, Chennai – 600 002