Delhi to get interceptor sewers

Published: Thursday 15 November 2007

Down to EarthThe Delhi government has cleared a Rs 1,950-crore project to tap drains carrying sewage from colonies not connected to the city sewers. Interceptor sewers to be used for tapping is seen by the government as a temporary solution to the problem of untreated water reaching the Yamuna. The government plans to lay sewers throughout the city in the long run.

The project is a toned down version of a Rs 3,150-crore proposal first mooted by the Delhi Jal Board in 2006. It involves laying 50 km of interceptors, 2-3 metres in diameter, to intercept 150 small drains discharging into three major drains in the capital--Najafgarh, Supplementary and Shahadra. The three drains contribute 70 per cent of the discharge of 3,600 million litres a day (mld) of sewage into the Yamuna. Another 13 drains will be tapped into sewers under rehabilitation. Four drains including one near the Sarita Vihar bridge carrying about 690 mld finds no mention in the plan, which has been cleared without undertaking surveys directed by the supreme court.

The intercepted waste will be taken to a pumping station and then to a sewage treatment plant (stp). At places, the route is very circuitous. For example, sewage from a drain near the Yamuna Vihar stp would be sent to a distant pumping station, when pumping directly to the plant would have been prudent since, each kilometre of sewer costs almost Rs 20 crore. Also in monsoons the wastewater will bypass the interceptors into the Yamuna.

Delhi's stps can reduce sewage's biological oxygen demand to only 20mg/l (if they work); 3 mg/l will make the river fit for bathing. So the treated water will need more than six times dilution. But where's the water? The Yamuna lacks freshwater almost nine months a year.

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