New Delhi, March 9 Untreated or partially treated sewage containing detergents is a key reason behind the recurring toxic foam in the Yamuna river, the Rajya Sabha was informed on Monday.
Responding to a question, Minister of State for Jal Shakti Raj Bhushan Choudhary said, The Central Pollution Control Board (CPCB) carried out monitoring on the Yamuna river at Kalindi Kunj, downstream of the Okhla barrage, in view of the foam formation in the Yamuna river in the years 2022-2024.
"The cause of the foam formation is due to the sudden drop in water level from the barrage; the agitation of foaming agents present in the wastewater, which forms foam that floats on the surface of the Yamuna river," he said.
"Surfactants in detergents are the main foaming agents present in untreated or partially treated sewage," the minister said.
He said that the 'Study on Yamuna Foam in Delhi', conducted by the Department of Environment, Government of NCT of Delhi, through The Energy and Resources Institute (TERI), found that the main cause of the event is the poor water quality of the river, which results from various factors such as effluent containing high ammonia and phosphate, released from anionic surfactants.
The government said that the main reasons for pollution in the Yamuna in Delhi include the discharge of untreated or partially treated sewage into the Yamuna river, the absence of common effluent treatment plants (CETPs) in some approved industrial areas, and delays in the completion of new projects and the rehabilitation and upgrading of sewage treatment projects.
As informed by the Delhi Pollution Control Committee (DPCC), the gap in sewage treatment in June 2025 was 645.55 million litres per day (MLD), the minister said.
Under the Namami Gange Programme in the state of Delhi, a total of 11 projects have been sanctioned at a cost of Rs 2,506 crores for the creation of 1,273 million litres per day (MLD) of sewage treatment capacity, he said.
Of these, nine projects, with a combined treatment capacity of 1,268 MLD, have been completed, he added.
According to the Delhi Jal Board (DJB), 37 sewage treatment plants (STPs) are operational in Delhi. Of these, 28 STPs, with a combined treatment capacity of 3,338 MLD, have been upgraded to meet the latest CPCB/DPCC standards, while the remaining nine are functioning according to old norms and design parameters, the minister added.
Thirteen CETPs, with a capacity of 212.3 MLD, have been provided to treat wastewater generated from industrial areas to control water pollution from industries in Delhi, the minister noted.