A shroud of weeds covers the black sludge deposited through decades of unrelenting sewage flow. It will be hard to spot the ‘lake’ in Puttenahalli Lake in Yelahanka, which is currently the city’s only bird conservation reserve.
However, the embattled lake will get a facelift over the next three years as experts and officials seek to use a novel method to remove accumulated sewage in the lake.
On Wednesday, Forest Minister B. Ramanath Rai set in motion a ₹12.56-crore rejuvenation project that aims to restore the glory of the 34-acre lake.
The area, after all, continues to host up to 126 species of birds, many of which are migratory. “In the coming year, silt will be removed from the lake, a diversion channel created and walkways made to convert the lake into a spot where residents and visitors can see the birds,” said Dipika Bajpai, Deputy Conservator of Forests (Bengaluru Urban).
Plans also include the creation of spots for bird observations, gazebos and eventually include awareness programmes on the winged denizens of the lake. The plans, however, do not include a Sewage Treatment Plant (STP) which is stuck in a bureaucratic wrangle between two civic agencies.
According to H.N Chanakya from Centre for Sustainable Technologies at Indian Institute of Science, the inflow of sewage is between 2 million litres a day (MLD) and 10 MLD.
However, experts have found a way to work around this, relying on a technique that has not been tried on any other lake in the city. While a diversion channel will ensure raw sewage does not enter the lake, some part of the sewage will be “naturally” treated to replenish the water level.
Two ponds, with anaerobic bacteria and algae, will within 48 hours convert blackish water into life-sustaining greenish water.
Mr. Chanakya who helped design the system, said the lake needed just 1MLD a day in summers, and 0.3 MLD in winters.
“This water will be let out in the deep end to fill the lake which will naturally purify the entering water. This way, the shallow parts where birds perch and roost will continue to sustain the eco-system without any sewage,” he said. The system will not need maintenance for at least three years.
S.K. Sangunni, a retired IISc. professor and member of the Yelahanka Puttenahalli Lake and Bird Conservation Trust, said the sewage-filled lake was used by birds only to roost, while they would fly to nearby lakes to forage or hunt.
However, by allowing “nature to take care of itself”, the fish population at Puttenahalli lake was expected to rise. “This can become a model for other lakes that are now fed entirely by sewage. Instead of big-money projects, micro-level interventions like this can rejuvenate even Bellandur lake,” he said.
