Chennai: Chennai’s sewage treatment plants could soon become a source of compressed biogas (CBG), with Metrowater planning to appoint a consultant to examine the feasibility of purifying and compressing biogas produced from sewage sludge for sale as a fuel, The Times of India reported.
The Chennai Metropolitan Water Supply and Sewerage Board (Metrowater) is considering developing the project through a public-private partnership (PPP) model. The proposal covers 11 sewage treatment plants (STPs) with a combined capacity of 844 million litres per day (mld).
Metrowater operates 20 STPs with a total treatment capacity of 957.8 mld and currently treats around 650 mld of sewage. The treatment process generates large quantities of sludge, which produces biogas through anaerobic digestion. At present, much of this biogas is either flared or used to generate electricity for the treatment plants.
According to Metrowater officials, around 50 kg of biogas is generated for every 1 mld of STP capacity. The gas could instead be captured, purified, compressed and sold as CBG. An official said the existing system of using biogas for power generation captures around 65% of the methane in the generated gas.
The proposed feasibility study will cover 11 STPs where facilities for generating biogas are already available. These include the plants at Kodungaiyur, Koyambedu, Nesapakkam and Perungudi.
The consultant will collect wastewater and sludge samples from all 11 plants and examine wastewater quality, the quantity and quality of sludge generated and the potential for increasing biogas production. The study will also compare the theoretical quantity of biogas that could be produced with the actual generation at the plants.
A key part of the study will be to compare the existing use of biogas for electricity generation with the possibility of supplying the gas through a pipeline for sale. The consultant will assess the infrastructure required for sludge thickening, anaerobic digestion, biogas purification, gas storage, flaring and bottling.
The study will also examine whether the carbon dioxide separated during biogas purification can be further purified and sold if the option is financially viable. Potential revenue from the digested sludge will also be assessed, including its possible use for composting.
The consultant will identify potential buyers for the CBG, including oil marketing companies, city gas distribution companies, CNG retail outlets, public and municipal transport fleets, commercial establishments and industrial users.
The study will assess market demand, transportation and other logistical requirements, infrastructure needs and the applicable regulatory framework. It will also recommend the most suitable PPP structure, revenue-sharing or concession arrangement and implementation strategy based on the project’s technical and financial feasibility.
