New Delhi: With every flush in Delhi begins a long underground journey.In theory, sewage travels through sewers, reaches pumping stations, is treated at sewage treatment plants (STPs), and only then is safely discharged or reused.In reality, large volumes of untreated or partially treated waste still find their way into the Yamuna through stormwater drains, broken networks, and because of illegal dumping.Though recent Delhi Pollution Control Committee data shows some improvement in the quality of the river water compared with last year, the river’s fecal coliform levels — a key indicator of sewage contamination from human excreta — remain alarming: up to 620 times above the desired limit and 124 times higher than standards prescribed for outdoor bathing.How Delhi’s Sewage System WorksDelhi currently has an installed sewage treatment capacity of about 814 million gallons per day (MGD), while sewage generation has crossed 992 MGD, according to activists citing Economic Survey estimates. Even if the city achieves the planned expansion to 964.5 MGD by this Dec, experts say treatment alone will not solve the crisis.The city’s sewage is supposed to move through underground sewer lines into sewage pumping stations (SPS), from where it is diverted to STPs. At these plants, the sewage undergoes screening, sedimentation, biological treatment and disinfection before the treated water is released into drains or reused.But the system leaks at nearly every stage in the city.Unaccounted Sewage And Leaks“The main thing is that you are not capturing all the sewage, so some of it escapes the sewerage network,” said Prof A K Gosain of IIT-Delhi, pointing to unauthorised colonies and unsewered pockets where the waste directly enters drains.He said ageing infrastructure is another major problem. “There are networks where some sewer lines were intentionally punctured earlier to relieve choking. Unless you desilt and repair them, sewage will keep leaking into natural drains,” he said.According to Gosain, Delhi’s rapid vertical expansion — old houses are replaced by multi-storey apartments — has sharply increased sewage generation without matching upgrades in infrastructure. “Water supply, sewage handling and stormwater systems are interconnected. They must be tackled together,” he added.Septic Tank Waste And Untreated DrainsActivist Pankaj Kumar of Earth Warriors, a social enterprise, said large gaps remain outside the formal sewer network in Delhi. In several peripheral areas, including parts of Jaitpur and Kalindi Kunj, households still rely on septic tanks because sewer lines don’t exist.Recently, National Green Tribunal (NGT) ordered GPS tracking for tankers carrying septic waste. The problem, Kumar said, is what happens next. “Delhi doesn’t have fecal sludge treatment plants (FSTPs). Septage collected by tankers is often dumped illegally into stormwater drains or canals, and that is how it reaches the Yamuna,” he said.Kumar also questioned the functioning of the existing STPs. “They do not always operate properly. Even UV disinfection systems do not guarantee that bacterial contamination won’t be back once the treated water enters the drains,” he said.The result is a river that continues to carry the burden of a city whose sewage network remains incomplete, overloaded and leaking despite decades of expansion.
