Chennai’s sewage sludge can boost biogas by 28% with advanced treatment, says study
A recent study by Anna University has revealed that adopting advanced treatment technology in Chennai’s sewage treatment plants (STPs) could increase biogas production by nearly 28% and enable safe reuse of treated sludge. The research, funded by the Central Public Health and Environmental Engineering Organisation under the Union Ministry of Housing and Urban Affairs, analysed sludge samples from 12 of Chennai Metrowater’s STPs over 18 months.
The study found that sewage sludge generated in Chennai contains low concentrations of heavy metals, within international standards, making it viable for reuse after proper treatment. However, raw sludge samples showed significant microbial contamination, including salmonella and faecal coliform, exceeding prescribed standards. This pathogen risk is a major barrier to sludge reuse and necessitates additional treatment.
Chennai currently treats 650 million litres of sewage per day through 20 STPs, generating nearly 94 tonnes of dry sludge daily. Of these, 11 STPs produce about 24,500 cubic metres of biogas. The study demonstrated that with sustainable thermal-based sludge stabilisation and resource recovery technology, an STP could yield up to 31,365 cubic metres of biogas — a 28% increase over current generation.
The treatment process also effectively removes faecal coliform and significantly reduces salmonella, enabling treated biosolids for safer reuse. Researchers noted that the cost-effective technology reduces sludge volume requiring disposal by about 60%. Treated biosolids can be used for land restoration, urban forestry, soil rehabilitation, and co-composted with green waste to improve soil fertility.
S. Kanmani, principal investigator and head of the Department of Civil Engineering at Anna University, emphasised the need for STPs to evolve beyond pollution control and prioritise reuse. The study's co-principal investigator, Saranya Kuppusamy, highlighted that the technology improves renewable energy recovery and supports land reclamation. Anna University is exploring pilot projects with industry partner Larsen and Toubro to scale up implementation across Tamil Nadu.
