The Neela Hauz lake, a natural depression near Sanjay Van in south Delhi, once the source of drinking water for the locality , had turned into a dumping ground for malba and raw sewage from the surroundings. After its revival through entirely natural means, the lake is now the symbol of environmental regeneration at the Neela Hauz Biodiversity Park, Delhi Development Authority's latest addition to such green belts in the capital.
When local residents approached Delhi high court about the dismal condition of Neela Hauz, the area was handed over to DDA under its Delhi Biodiversity Foundation, and scientists and engineers started the revival process immediately . Within two years, the lake had been desilted to enable landscaping of the biodiversity park. Alongside, a wetland was constructed, which now treats close to a million litres of water every day through natural processes.
“No energy is being consumed for the process,“ said CR Babu, professor emeritus, Delhi University , and head of the Centre for Environmental Management of Degraded Ecosystems. “We are only using tanks and aquatic plants with special properties to clean the water.“
According to Babu, the process to design the constructed wetland took around two years. Just before the water enters the lake, it flows past a series of alternating troughs and gravel beds with aquatic plants growing on them. The professor explained that microbes generated by the 20 different types of aquatic plants cleansed the water of biotoxins, while sludge and fine particulates were removed via a gradual process of passing the water through layers of pebbles of varying sizes. “No sewage treatment plant in Delhi has proved this efficient in improving water quality , and we have achieved this through an all-natural process,“ said Babu.
When the scientists discovered that the water flowing into the lake was extremely high in phosphates and nitrates, an aquatic species called lemna was introduced. They not only naturally absorbed these compounds, but, as Yasser Arafat, who worked on the water body purification, narrated, “We used these nitrate and phosphate-rich lemna as fertilisers after collecting them from the water.“ The lake's biological oxygen demand (BOD) levels, along with the level of phosphates and nitrates, fell sharply. According to Faiyaz Khudsar, scientist in charge at DDA 's Yamuna Biodiversity Park, the revived water body at Neela Hauz is already attracting avian and aquatic species. “A dual purpose is being served through the constructed wetland system,“ said Khudsar. “The biodiversity park is producing plants that can be used as fertiliser, and at the same we are seeing the arrival of ducks there.“ Since its revival, 70 bird species have been sighted at Neela Hauz.
The regeneration model has proved so successful that officials have submitted the concept to Delhi Jal Board for implementation in other water bodies across Delhi. “We have shown the plan to the DJB. The water supply agency felt this system could be used in over 69 water bodies without the costs being very high because no additional energy would be consumed,“ said Babu.