CHENNAI: Setting off the alarm bells, government data reveal a staggering 15 to 18 crore litres of untreated sewage from the city is seeping into stormwater drains, reaching Cooum, Adyar or Buckingham Canal in the end. As per data from the Municipal Administration and Water Supply (MAWS) department, the city has an installed capacity to treat close to 1,000 million litres of sewage per day against the total sewage of 835 MLD (million litres per day) or 83.5 crore litres pumped into the STPs.
As per the MAWS report submitted with the National Green Tribunal (NGT), all of the city’s sewage is being treated before being let into the rivers and canals. But, of the nearly 835 MLD pumped into sewage treatment plants from pumping stations, only around 650 to 680 MLD reaches the STPs.
The remaining 150 to 180 MLD of sewage seeps into stormwater drains to reach the rivers, show Metro Water data. Chennai generates around 950 MLD of sewage, which is less than the pumped sewage. Several areas in Ambattur and in south Chennai that are not connected with underground sewage systems continue to let the sewage into stormwater drains and floodwater canals.
Sources at Metro Water said the underground pumping mains (sewage pipelines) in several parts of the city were laid decades ago. “The old pipelines are damaged over the years and sewage enters stormwater drains through cracks. We have more than sufficient capacity to treat sewage but the conveying system is faulty,” the source added.
The source further said an STP in Kodungaiyur is the worst affected among all. As per Metro Water data, only around 50% of the pumped sewage actually is being received at the STP. On July 6, the Kodungaiyur STP received only 179 million litres when a total of 324 million litres were pumped.
On the other hand, the water manager is mulling to adopt trenchless technology to fix damages and cracks in the underground sewer lines to replace conventional methods of digging trenches and fixing the damages. An official said the trenchless technology is the latest method using which Metro Water can avoid digging up roads.
“Cracks can be sealed without digging and, if adopted, about 500 metres of underground sewer lines can be repaired every day. Moreover, it can extend the life of pipelines by 40 years,” he said.
Under trenchless technology, a flexible resin tube will be inserted into the damaged pipelines and cured using hot water to form a new layer of pipeline within the existing pipeline. The proposal is awaiting board’s approval.
During the AIADMK regime, the Metro Water sent a proposal to repair the entire underground sewage system at a cost of `10,200 crore. However, the proposal was shelved after DMK government took charge.