Weeds, plastic pipes and bottles, usually the bane of most waterbodies, have come to the rescue of Puttenahalli lake.
In the past year, the 13-acre lake has seen the large-scale adoption of a low-cost technology that seems to have effectively dealt with the remnants of sewage in the recently rejuvenated lake. Using polyvinyl chloride (PVC) pipes and discarded one-litre PET (polyethylene terephthalate) bottles, ‘floating islands’ have been created on which various types of weeds are grown (vetiver, canna, colocasia, and alligator grass, among others).
These islands float around the lake, absorbing nutrients that form a part of the pollution of the lake that is sustained through treated water and rainwater. Since the introduction of the first floating platform in June 2016, residents have managed to craft over 50 more.
The effect? A drastic improvement in the lake’s health. Biological Oxygen Demand (BOD), which is an indicator of pollution, has decreased by over 67%, from 188 mg per litre to 62 mg per litre. Similarly, the nitrate content has fallen by nearly 60%, total solids by more than a third, and phosphates by 14%, according to an analysis by S.K. Srinivas, a biochemist who volunteers at the lake. He tested water samples from June 2016 and July 2017.
“There is still a long way to go before we reach the ideal BOD limit of less than 20 mg per litre. But this is a great step. We are experimenting with different types of platforms and weeds,” said Usha Rajagopalan, trustee of the citizen-driven Puttenahalli Neighbourhood Lake Improvement Trust (PNLIT), which conceived the project.
Each platform costs barely ₹4,000 and is financed through corporate funds under CSR.
The system is being tried to various degrees of success in Jakkur and Kaikondrahalli lakes, albeit in a smaller way.
S. Vishwanath, a water conservation expert and founder-director of Biome Solutions, said the system complements the existing wetlands. “The advantage is that these islands can be towed to areas that require a clean-up. The cleaning effect can be seen within a matter of minutes,” he said.
