CHENNAI: Even as Chennai Metropolitan Water Supply and Sewerage Board (Metro Water) is letting a major quantity of treated used water (TUW) from its sewage treatment plants into rivers, a study conducted by Tamil Nadu Green Climate Company (TNGCC) has suggested alternative uses of TUW will reduce the water stress of Chennai Basin in the future.
As per ‘Towards Climate-Resilient River Systems in Chennai - Assessing Risks at the Sub-basin level and Advancing a Circular Economy Approach’ report, prepared by TNGCC and Council on Energy, Environment and Water (CEEW), the total water demand for drinking and agriculture in the Chennai basin will rise 2,728 Million Cubic Metres (MCM) by 2050, driven by a 34% increase in population over the same period, under a business-as-usual (BAU) scenario.
The Chennai Basin covers Chennai, Chengalpattu, Kancheepuram, Tiruvallur and Ranipet districts and comprises six sub-basins such Adyar, Araniyar, Cooum, Gummidipoondi, Kovalam, and Kosasthalaiyar.
However, under a high population growth scenario, the total water demand will reach 2,939 MCM in 2050 and unmet water demand will rise to 754 MCM by 2050, further stressing water resources and jeopardising access for domestic and agricultural users, the report said. The report suggests the combined implementation of adoption of micro-irrigation and TUW reuse can reduce unmet water demand in the Chennai basin.
According to the estimates, scaling up micro-irrigation to 13% of the cultivated area and achieving 25% TUW reuse will reduce unmet water demand by about 52% by 2050. Increasing TUW reuse to 40% will further reduce unmet demand by about 63% by 2050. On the other hand, incorporating the climate change effect of increased water availability with micro-irrigation and TUW reuse will reduce unmet water demand by 93%.
Recommending interventions, the report added the Kosasthalaiyar sub-basin faces the highest water risk but also shows strong potential to mitigate it. The results indicate unmet water demand could be reduced by nearly 65% by 2050 by scaling up TUW reuse to 40% and micro-irrigation to 13%.
Similarly, investments and interventions in the Adyar sub-basin should prioritise decentralised, modular used water treatment plants near major demand centres to enable local reuse for non-potable domestic and industrial purposes apart from using TUW to recharge groundwater. Presently, Chennai has 12 STPs in Kodungaiyur, Koyambedu, Perungudi, Nesapakkam, Sholinganallur and Tiruvottiyur with a total waste water treatment capacity of 934 MLD (million litres per day).
Additionally, Metro Water releases about 10 MLD of treated used water into Porur lake to ensure groundwater recharge. On Tuesday (February 17), Metro Water supplied 1,233 MLD of drinking water, whereas it treated about 612 MLD of sewage.