3 min readJun 10, 2026 10:27 AM IST
First published on: Jun 10, 2026 at 10:27 AM IST
Ultraviolet disinfection systems installed across Delhi’s sewage treatment plants (STPs) are not effectively reducing biological pollution, the Delhi Pollution Control Committee (DPCC) has told the National Green Tribunal, with Researchers at IIT Delhi flagging the absence of key microbial data required to assess why the systems are underperforming.
In a response submitted to IIT Delhi and subsequently placed before the tribunal, the DPCC said that while it monitors compliance with prescribed standards, including faecal coliform levels, the Delhi Jal Board (DJB) tests microbial contamination only at the outlet of sewage treatment plants.
UV disinfection in wastewater treatment infrastructure is generally placed in the tertiary stage because pre-filtration is needed for turbid water to ensure effective disinfection. The wastewater flows through a UV reactive chamber and the process is faster, more efficient than chlorination technology. According to the US Environmental Protection Agency, the characteristics of the wastewater, UV radiation intensity and the amount of time the bacteria is exposed to the radiation, and the reactor configuration determine the effectiveness of a UV disinfection system.
IIT Delhi had pointed out that āa realistic assessment requires reliable microbial quality data at both inlet and outlet of the UV channelsā and noted that there was no data available on the effectiveness of UV disinfection systems installed at 14 STPs that had reported non-compliance with prescribed microbial standards.
āThe DPCC laboratory is conducting an analysis of fecal coliform only at the outlet of STPs of the DJB. Higher concentration of fecal coliform despite the STPs having UV disinfection system reflects the ineffectiveness (of the UV system),ā the pollution control body said.
The exchange forms part of information sought by IIT Delhi pursuant to an NGT order dated December 23, 2025, in a matter related to the performance of the cityās STPs and their role in the pollution of the Yamuna.
According to IIT Delhiās query reproduced in the DPCCās letter, āthere is no data available on the effectiveness of the UV Disinfection systems installed at these plantsā. The institute further observed that existing literature and manufacturer-certified data were āeither insufficient or unavailableā.
The DPCC, in its response, said it was āprimarily concerned with ensuring compliance with the prescribed standards for STPs of DJB including fecal coliformā. It noted that while standards have been prescribed for parameters such as pH, TSS, BOD, COD, ammoniacal nitrogen, total nitrogen, phosphate and faecal coliform, the Consolidated Consent and Authorisation format prepared by the Central Pollution Control Board suggests the adoption of āappropriate technology for disinfection of treated sewageā.
The affidavit, filed by Additional Director Dr Anwar Ali Khan, was submitted before the tribunal as part of an action taken report on directions issued by the NGT in August and December last year.
Separately, the DPCC informed the tribunal that it had issued directions for the imposition of environmental compensation of Rs 2.89 crore on the DJB and operators of 15 STPs for failing to meet prescribed standards between July and October 2025.
Delhi Jal Board (DJB) tests microbial contamination only at the outlet of sewage treatment plants. 
Share
