Chennai Metropolitan Water Supply and Sewerage Board (Metrowater) has planned to appoint a consultant to assess the feasibility of monetising biogas generated from 11 sewage treatment plants (STPs) in Chennai, Tamil Nadu, by converting it into compressed biogas (CBG).

Metrowater plans to appoint a consultant to assess the feasibility of purifying, compressing and commercially selling biogas produced from sewage sludge. The utility intends to develop the project under a PPP model, covering 11 STPs with a combined capacity of 844 million litres per day (MLD). Metrowater currently operates 20 STPs with an aggregate treatment capacity of 957.8 MLD and processes around 650 MLD of sewage. These facilities generate substantial quantities of sludge, which is anaerobically digested to produce biogas. At present, a significant portion of the biogas is either flared or used to generate electricity for the treatment plants.

Metrowater estimates that around 50 kg of biogas is generated for every 1 MLD of sewage treatment capacity. The utility plans to capture, purify and compress this gas for sale as CBG. Currently, the biogas is primarily used for power generation, which recovers around 65% of the methane contained in the gas. The proposed feasibility study will cover 11 STPs equipped with biogas generation facilities, including those at Kodungaiyur, Koyambedu, Nesapakkam and Perungudi. The study will include wastewater and sludge sampling at all 11 STPs, along with assessments of wastewater characteristics, sludge generation and sludge quality. It will compare theoretical biogas production potential with actual generation levels and conduct treatability studies to identify opportunities to increase biogas output.

The consultant will also identify potential CBG off-takers, including oil marketing companies, city gas distribution companies, CNG retail outlets, public and municipal transport operators, commercial establishments and industrial users. The assessment will cover market demand, offtake mechanisms, logistics, infrastructure requirements and the applicable regulatory framework. Based on the techno-economic assessment, the study will recommend an appropriate PPP structure, revenue-sharing or concession model and implementation strategy.