Water

Reviving Delhi lake using constructed wetlands

Neela Hauz lake that’s spread over 10 acres used to serve as the biggest water body in south Delhi but rapid urbanisation turned it into a dump

 
Last Updated: Wednesday 09 January 2019

A lake that’s spread over 10 acres and is housed by Neela Hauz Biodiversity Park was being neglected and polluted for a long time, but not anymore.

Around four years ago, the Delhi Development Authority gave Environmental Management of Degraded Ecosystems (CEMDE), Delhi University, the responsibility to restore the lake. CR Babu, professor emeritus, CEMDE, was asked do the job using constructed wetland system (CWS).

Babu came up with an idea to use raw sewage water, discharged by a nearby village Kishangarh, and treat it with the help of a special kind of aquatic plant species. He made a CWS,which uses natural processes involving wetland vegetation, soil and microbes to improve water quality.

The lake, which is situated in the south central ridge, was once the largest fresh water body in the entire south Delhi and people used to use its water for drinking.But, extensive urbanisation gradually converted it into a dump site. When Delhi hosted the 19th Commonwealth Games in 2010, an over bridge was constructed over the lake and the debris was dumped there.

In 2012, the local residents filed a PIL in the Delhi high court seeking that the lake be revived. The court, in 2014, ordered the the DDA to take steps to restore the lake.

Treatment of water with the help of CWS is a two-step process. Step one involves storing the sewage water in an open pond for around 24 hours for oxidation. The aerobic bacteria breaks down the organic material in the raw sewage water. The treated water then flows through a channel, which has river pebbles. These pebbles filter out organic matter from the water.

The second step is to treat the sewage water in a wetland system, where 20 different kinds of aquatic plants like Typha, Pharagmites, Alternanthera, Ipomoea, Solanum etc. cleanse the water of its bio-toxins and ease it into the lake.

The aquatic plants do the cleansing of raw sewage. The water flows to the lake through natural gradient and no pumping is required. After the restoration of the lake, many birds also started coming back here.

CWS is not energy driven and can be easily replicated in other water bodies. For example, various sewage drainages, which discharge sewage water into the Yamuna River, can be converted into lakes. This will not only reduce the burden of sewage on the river, but also create numerous water bodies.

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