Delhi’s STP plan under question: Treated water mixing up with drain effluents

At the Chilla regulator in East Delhi, a key point where treated sewage water from multiple treatment plants (STPs) is discharged into the Yamuna, treated clean water is again getting mixed up with untreated sewage from the Shahdara drain.

This entire blend of clean and polluted water is then reaching back into the Yamuna, raising concerns over the effectiveness of the Capital’s river clean-up efforts.

The visit also revealed that the stretch is choked with plastic waste, stagnant black water and foam-lined discharge points, blurring the distinction between a river and the Shahdara drain. During the ground visit, this correspondent saw huge quantity of solid waste accumulated beneath the regulator gates.

More significantly, at an outfall near the site, treated effluent from nearby STPs in the Kondli-Chilla belt was observed flowing back into the Shahdara drain which is already carrying untreated sewage.

The mixing was visible through foam formation and a noticeable change in water colour, indicating that treated water is being re-polluted before it reaches the Yamuna.

The finding signals the top challenge for the effectiveness of Delhi’s expanding sewage treatment infrastructure. According to official data, Kondli and Chilla STPs together have a treatment capacity of around 99 million gallons per day (MGD), forming a key part of the city’s strategy to reduce pollution load in the Yamuna. However, if treated effluent is routed into already contaminated drains, its impact on improving river water quality is significantly diluted.

For those living and working near the Chilla regulator, the condition of the river has long ceased to be surprising. Shubham Dwivedi and Shiva Kumar, who operate at the Noida-Delhi toll booth nearby, said they have never seen the Yamuna in a clean state. “We have been here for about a year, but have never seen the river in good condition,” they said.

Long-term residents point to a steady decline. Shiv Dutt (70), a resident of Ashok Nagar for over two decades, said the situation has worsened over time. “I have not seen it getting better in at least the last 10-15 years. It has deteriorated year after year,” he said.

The impact is not just visible but also palpable. Residents and commuters complain of persistent foul smell from both the drain and the river.

Haseena Khatun, who lives near Shani Mandir in Noida’s Sector 14-A and travels regularly through the area, said, “It smells very bad. I do not think it will ever get cleaned.”

For some, the degradation has affected livelihoods. Kishore (29), who occasionally fishes in the river, said catches have become rare. “We hardly find fish here now. The water is so black, it has chemicals and fish can’t survive in it,” he said.

The Chilla stretch, where the Hindon cut meets the Yamuna and the Shahdara outfall converges, remains one of the most polluted segments of the river in Delhi. While efforts have focused on increasing sewage treatment capacity, the issue of how treated water is conveyed to the river has emerged as a critical gap.

Talks going on: DJB

Responding to queries, Delhi Jal Board (DJB) CEO Kaushal Raj Sharma said treated effluent from four Kondli STPs and the Chilla STP is discharged into the Shahdara drain through designated channels before ultimately meeting the Yamuna. He said the drain, originally designed for stormwater and treated discharge, now also carries untreated sewage due to unregulated inflows over time.

Acknowledging the issue, Sharma said a proposal is under consideration to divert treated effluent directly into the Yamuna through a dedicated conduit, preventing it from mixing with polluted drain water. The plan also includes augmenting treatment capacity in the Kondli zone and intercepting untreated flows entering the Shahdara drain.

He said real-time monitoring systems were installed at STP outfalls. Also, drains themselves do not fall under the DJB’s jurisdiction. The Shahdara drain is managed by the Delhi’s Irrigation and Flood Control Department, while solid waste clearance is handled by the Municipal Corporation of Delhi (MCD).

Sharma further noted that some part of treated water is being reused for replenishing water bodies like Sanjay Lake and for non-potable purposes such as gardening. He also pointed out that a significant portion of pollution in the Shahdara drain originates upstream from Uttar Pradesh, with plans underway there to tap contributing drains for treatment.