37 Delhi sewage plants flunk central watchdog’s test — clear local pollution board’s bar

The inspection was conducted at all major treatment facilities of Rithala, Okhla, Kondli, Pappankalan, Yamuna Vihar, Nilothi, Keshopur and Coronation Pillar, among others.

According to the RTI reply, while all 37 failed in some or the other parameter, 36 plants failed to match Fecal Coliform’s permissible levels. The plants recorded levels as high as 4.7×10⁹ MPN/100 ml when the permissible limit is 230 MPN/100 ml. Others such as Vasant Kunj Phase I STP recorded 4.9×10⁶ MPN/100 ml while the figure at Pappankalan Phase I was 1.6×10⁷.

Even at plants where the DPCC recorded compliance, CPCB found bacterial contamination exceeding limits.

Ammoniacal Nitrogen, which indicates incomplete biological treatment, was above the limit of 5 mg/l at multiple facilities. According to the RTI reply, the CPCB recorded 37 mg/l at Mehrauli, 28 mg/l at Pappankalan Phase II, 26 mg/l at Yamuna Vihar Phase III and 13 mg/l at Yamuna Vihar Phase II. Elevated ammonia levels were also found at Okhla, Kondli and Nilothi, pointing to poor nitrification and inadequate aeration.

The CPCB data further shows that several plants discharged water with BOD and COD (Chemical Oxygen Demand) above permissible limits, which is a direct indication of untreated organic matter in the effluent. For instance, Yamuna Vihar Phase III recorded BOD at 88 mg/l and Molarband reported 36 mg/l.

In contrast, DPCC’s assessment report of June 30 — available on its portal — shows that many of the same plants met the permissible standards when samples were collected on June 5.

These plants are located in Akshardham, Chilla, Coronation Pillar Phase I and II, Delhi Gate Nallah Phase I and II, Najafgarh, Keshopur Phase II, Okhla Phase V and Rohini. A few plants, such as in Vasant Kunj, Mehrauli, Ghitorni, Kondli Phase II and Pappankalan (Old) were marked as “not meeting the standards”.

Further, the DPCC recorded “no flow” or “non-operational” status at Sonia Vihar and Molarband, while CPCB data showed active discharge with high levels of contamination at these plants.

The CPCB’s findings also contradict DPCC’s results in regard to several key facilities.

For instance, the DPCC report for Akshardham STP shows treated water within limits for BOD and Faecal Coliform, whereas CPCB recorded Faecal Coliform at 7.9×10⁴ MPN/100 ml, over 340 times the safe limit. Similarly, Najafgarh STP was marked compliant by DPCC at 81 MPN/100 ml, but the CPCB figure was 1.3×10⁵ MPN/100 ml. At Okhla Phase VI, DPCC recorded 210 MPN/100 ml, while CPCB reported 2.7×10⁵ MPN/100 ml.

A senior DJB official said that none of the plants met all the standards, attributing part of the variation to differences in the number of parameters tested. “The DPCC typically checks four or five parameters, while CPCB’s monitoring covered all of them,” the official said, adding that DJB’s own laboratories have lost NABL accreditation, making independent verification of DPCC’s results unreliable.

Repeated queries to DPCC officials did not elicit a response.

Officials in CPCB, meanwhile, said that this was the first time the Board carried out an independent assessment of all DJB plants in Delhi. “STP performance can fluctuate depending on inflow and load, but such large differences are unusual… If one agency finds compliance and another records multiple violations for the same outlet, that’s a cause for concern,” said a scientist from CPCB.

The reports also highlight a methodological difference. Both DPCC and DJB use the Nessler method for testing ammonia, a mercury-based technique that relies on colour comparison and was invalidated by the Bureau of Indian Standards in 2019 for being unsafe and error-prone. The CPCB instead uses spectrophotometric or ion-selective electrode methods, which are more precise and do not involve mercury.

With DJB claiming to treat over 4,000 million litres of sewage daily, the data suggests that a large portion of that volume remains inadequately treated before being discharged into the Yamuna and drains across Delhi.

Pankaj Kumar, a Yamuna activist, said the data clearly shows that Delhi’s STPs are not carrying out proper disinfection. “Fecal coliform levels are running into lakhs and crores. This contaminated water eventually flows into drains and the Yamuna, from where it’s often used for irrigating vegetables like cucumbers and radish, directly entering our food chain. Such water isn’t fit for human, animal, or even plant use. If these STPs were upgraded to keep coliform levels below 230 MPN, why is disinfection missing? Either chlorine dosing or UV systems aren’t functioning. High ammoniacal and total nitrogen levels also point to poor aeration,” he added.