Treating untreated waste that flows into Yamuna

Only half of Delhi is connected to sewer lines, which means that the other half’s waste flows, untreated, into the Yamuna.

Though the Delhi Jal Board is constantly expanding its 7,200-km-long sewer network, rapid development has left large portions of the city without any alternative. A senior DJB official said: “We are trying our best to add more colonies to the network, but there is so much unplanned development.”

Recently, the DJB passed a proposal to construct 31 new sewage treatment plants (STPs), 27 sewage pumping stations and 600 km of sewer lines. It has expanded its treatment capacity from 613 million gallons per day (MGD) to 704 MGD.

But, its current STPs at 22 locations are working at 58 per cent of their installed capacity. It is also working on the ambitious interceptor sewer, which when completed is expected to reduce pollution in the Yamuna by decreasing the biological oxygen demand by 60 to 70 per cent.

Sushmita Sengupta, the deputy program director of the Centre for Science and Environment’s water unit, said more than new STPs, expanding the use of existing ones was more important.

“There is a need for decentralised treatment as urbanization will keep happening; more colonies will keep coming up,” she said.

Whatever Delhi is doing isn’t working well enough. The Union Environment Ministry’s annual report (2014-2015) says that the Central Pollution Control Board found the pollution level in the 40-km stretch of the Yamuna it studied unchanged over the years. The CPCB did find “gradual reduction in pollution load contributed by the major drains in NCT-Delhi.”

However, the report added: “This might be due to less availability of fresh water in the river, essential to maintain its self-purification capacity.”