New Delhi, Dec 22 (PTI) Eleven constructed wetlands coming up on Yamuna floodplains near Kalindi Kunj will start cleaning around 1,500 million litres of sewage per day by mid-2021, experts said on Tuesday.

Currently, the wastewater from several unauthorised colonies in the area goes into the Yamuna directly and pollutes it. 

The constructed wetland ecosystem is part of the 115-hectare South Biodiversity Park being created underneath the Delhi-Noida Direct Flyway.

The first of the 11 wetlands became operational on Friday. It can treat 15-20 MLD wastewater.  

"It has been created using just boulders and plants," said ecologist CR Babu, who heads a 12-member team working on the project.

The Delhi Development Authority (DDA) is responsible for carrying out civil work.

"These wetlands, being created on a stretch spanning three kilometers -- from Kilokri to Batla House -- on the floodplains will treat around 1,500 MLD of sewage from around 25 drains that pollute the Yamuna," he said.

Maharani Bagh drain is the largest of them. It carries around 250-500 MLD wastewater.

The first constructed wetland near Kalindi Colony has oxidation ponds, a gradient channel with a mesh and boulders acting as filters, ridges and furrows having 25 aquatic plants that feed on organic matter in the wastewater.

"These constructed wetlands are an alternative to conventional sewage treatment plants in Delhi, which are either underutilised or do not treat wastewater properly. The quality of water flowing out of these constructed wetlands will be the same that of the Yamuna," Prof Babu told PTI.

"The remaining constructed wetlands will be fully functional by mid-2021. These will treat the sewage from unauthorised colonies such as Taimoor Nagar, Khizrabad, Zakir Nagar and Batla House that goes into the Yamuna directly," he said.

"We will plant more than 1 lakh saplings on the five kilometer-long embankment along the marginal bund and the islands we have created on the floodplains as part of the South Biodiversity Park," Babu said.

The work to remove water hyacinths from the existing natural wetlands will start in December-end. Thereafter, it will be full of birds, said Yasir Arafat, a scientist who is part of the 12-member team headed by Babu.

Wherever there are water hyacinths, the birds do not come, as the invasive aquatic plant restricts birds' access to water, Babu explained.

The work on the South Biodiversity Park began in May last year. The project costs Rs 2.5 crore and is expected to be completed in around five years.

The site, which is full of grass and water hyacinth, was being used as an illegal dump for construction debris and as an open defecation ground by slum dwellers, Arafat said.

A five-kilometer-long and seven-feet high wall is being constructed along this floodplain area to prevent illegal activities, he said.

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