August 22, 2021 11:53:42 am
The Delhi Jal Board (DJB) has set up ‘floating wetlands’ on a few lakes, including the Sanjay Van lake and Nangloi lake, as part of its lake restoration project, with the intention of improving the water quality of lakes.
Floating wetlands are foam platforms with plants over the surface of the lake – green islands of sorts that appear to float in the water. A DJB official said that the plants will absorb nutrient pollutants from the water since the surface of the roots will house bacteria that can remove organic waste from water. However, the plants themselves might be insufficient, and an aeration system has to be installed to provide oxygen in the water, the official added. The oxygen is then utilised by the bacteria to remove pollutants like ammonia and reduce biological oxygen demand levels in the water.
The plants themselves are expected to help remove around 10 to 12 per cent of nutrient pollutants in the water, he said. This is only during the growth phase. Once the plants have matured, their uptake of nutrients from the water will reduce further making aeration a crucial part of the system to aid the bacteria in consuming organic pollutants from water, he added.
While the floating wetlands were recently installed at Sanjay Van lake, the DJB had set them up earlier at the lakes at Nangloi and Rajokri. Aeration systems to provide oxygen in the water are still in the making. The wetlands are to come up in around ten lakes as part of the ‘City of Lakes’ project of the DJB, which aims to restore these lakes by improving their water quality, ensuring regular supply of water to these lakes, and landscaping and restoring the ecology of the surrounding area. The DJB will ensure the maintenance of these sites once the wetland systems are in place.
Plants that grow on the platforms include yellow and red canna, spider lily, elephant ear plants, pampas grass, and soft rush or bulrush plants. A single floating rafter, along with its maintenance, can cost between Rs. 8000 and Rs. 10,000, the official said. At Sanjay Van, a total of 597 such floating rafters were set up, while 1375 of them were installed at the Sonia Vihar Lake. They have also been used in the lakes at Jaffarpur Kalan and Rani Khera (150 rafters). A total of 401 such platforms are floating over the Nangloi lake.
The impact of such systems is debatable when the primary issues underlying the pollution in the lake have not been addressed, experts say. The use of floating wetlands is going to be negligible, said environmentalist Diwan Singh. “It diverts attention from the other things that need to be done like cleaning stormwater drains and ensuring that no sewage or other waste enters drains or the lake,” he said.
At Sanjay Van, the issue of a drain that contaminates the water in the lake has not yet been resolved, while the sewage draining into the Sonia Vihar lake has not yet been diverted, the DJB official admitted. The DJB plans on constructing a sewage treatment plant with a capacity of 7 MGD to handle the waste that finds its way to Sonia Vihar lake, and a consultant has been appointed for the project, he said.
Manu Bhatnagar, principal director of the natural heritage division of Indian National Trust for Art and Cultural Heritage (INTACH), said that very large numbers of such rafters would be necessary to make an impact. There could be other, certain ways of improving water quality like bioremediation and introducing fish species in large numbers, he said.
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