BENGALURU: Bengaluru’s Bellandur Lake made international headlines for frothing and catching fire in 2015. This even made courts take note of the issue and issue a series of directions to the authorities. All this apart, the lake continues to froth every monsoon.
The issue also forced the state government to take up several measures to control the froth and fire. The National Green Tribunal formed a committee to resolve the issue.Scientists of Indian Institute of Science (IISc), Bengaluru, who have been monitoring the lake for the last four years, said three reasons led to foaming.
In their research report, they stated that a single type of surfactant commonly used in most households as detergents and shampoos played a dominant role in lake foaming.A team from Centre for Sustainable Technologies (CST) in IISc concluded that one of the reasons for foaming is untreated sewage entering the lake. “The pollutants in sewage take approximately 15 days to spread and a part of the organic material gets degraded in the absence of oxygen and settles down as sludge,” according to the report.
When more sewage enters the lake, the surface-active agent (surfactant) does not decompose and settles with the sludge. Chanakya HN, chief research scientist at CST and one of the authors of the study, said, “Imagine adding one full scoop of washing powder into a bucket of water. It will definitely foam given the right conditions.” Sometimes, the concentration of this sludge is 200 times more than what enters the lake.
The second cause is heavy rains bringing in large quantities of water from the city into the lake. Though pollutants should dilute with rainwater, the foam in the lake increases due to the rise in water level which reactivates the surfactant sludge and trapping air bubbles that turn into foam.
Lakshminarayana Rao, associate professor at CST, said, “This is an important phenomenon that converts the surfactant-laden water into foam.” Lastly, the research suggests that certain bacteria might be responsible for foam formation and stability, which the team will identify with more experiments.
‘Stop sewage flow’
The team studied the water samples from the lake every month in the last four years. It recreated a lab model to track changes in the chemical composition of surfactants in different regions of the lake. “I had to go to the lake every month to collect water and foam samples, and conduct experiments,” says Reshmi Das, PhD student at CST and first author of the study.
Scientists suggested that stopping the entry of untreated sewage into the lake is crucial to prevent the build-up of surfactants and sludge. Also, measures should be taken to remove the accumulated sludge from the lake before the onset of monsoon. According to the Karnataka State Pollution Control Board’s latest report, between April 2022 and March 2023, Bellandur Lake was classified five times under ‘D’ category and seven times under ‘E’ category.