In two years, Chennai will have a more efficient system of sewage treatment and thus mitigate the problem of pollution of its rivers and canals.
Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB) is setting up sewage treatment plants (STPs) across the city. Equipped with the latest treatment technology, the new plants are expected to ensure better quality of treated sewage flowing into the waterbodies.
At present, the city generates about 581 million litres of sewage daily which is treated at STPs in four locations.
The water board is setting up STPs at Kodungaiyur, Sholinganallur, Perungudi and Nesapakkam.
Officials said the pace of work had slowed down because of the pandemic. About 25% of the work on new plants had been completed.
The projects, with an outlay of ₹636 crore, are being implemented under the AMRUT (Atal Mission for Rejuvenation and Urban Transformation).
On completion of these projects next year, the city’s combined capacity to treat sewage would be enhanced to 986 million litres daily (mld) from 745 mld at present.
The new plants would treat sewage from the newly merged areas, the officials said. Trials are on at the 31-mld facility at Tiruvottiyur.
The water board had switched over to advanced sequential batch reactor (SBR) technology that requires less space in the new plants.
The quality of treated sewage was found to be better compared to the conventional technology such as the activated sludge process adopted in the existing facilities, they added.
For instance, the biological oxygen demand and total suspended solid levels, which determine the quality of treated sewage, would be reduced to less than 10 mg/litre adhering to new norms of the Central Pollution Control Board.
At present, the treated sewage discharged into waterbodies contains 30 mg/l and less than 100 mg/l.
Better technology
The old STPs are being refurbished and the ones at Kodungaiyur and Koyambedu are being dismantled to make way for the new ones. The capacity of two STPs at Kodungaiyur would be upgraded to 120 mld each. However, the existing STPs would adopt another biological process — moving bed biofilm reactor to efficiently remove pollutants. Officials said this was the best-suited technology to modify existing facilities which faced space constraints. The 54-mld Nesapakkam plant would be the first of the seven plants to be covered under the ₹170-crore project. “This process will provide the same quality of treated sewage as that of SBR. We will extend it to other existing plants after studying the results,” the official added. The entire project would be completed by 2023.
Meanwhile, residents wanted sewage pumping stations’ capacity to be improved to prevent sewage overflow and release of untreated sewage into rivers.
