Rainfall, untreated sewage water that enters the lake, and the possibility of suspended solids containing certain bacteria have been determined as the cause of heavy foaming in Bengaluru's Bellandur Lake.
A four-year-long study by researchers at the Centre for Sustainable Technologies (CST), the Indian Institute of Science (IISc) states that one of the reasons why foaming in the lake has puzzled the scientists is because it counterintuitively increases only after heavy rains, which are supposed to dilute pollutants in the lake that may be causing foaming.
However, a recent analysis by the team suggests that a single type of surfactant commonly used in most household washing powders and shampoos plays a dominant role in driving this foaming.
How to prevent foaming?
According to a release by IISc, one way to prevent foaming is to stop untreated sewage water from entering the lake. Apart from this, sludge also has to be removed that gets accumulated in lakes before monsoon.
How sludge accumulates?
Researchers at IISc found that a portion of the untreated sewage that was entering the lake was turning into sludge. "The first is untreated sewage that enters the lake. Because the lake is large, the sewage takes 10-15 days to disperse through the lake; during this time, a part of the organic material gets degraded in the absence of oxygen and settles down as sludge," researchers said.
Over the course of time, as more sewage flows into the lake, a part of it gets loosely attached to the sludge, which results in an increase in its concentration.
Heavy rainfall adds to this, because of which the surfactant gets dislodged from the sludge, making it foam-ready.
"To study the foam formation, the researchers collected water samples from the lake, analysed various parameters, and recreated a lab model to track the changes in the chemical composition of the surfactants across different regions of the lake as well as at different times of the year."
"I had to go to the lake every month over the years to collect water and foam samples, and conduct experiments on them,” says Reshmi Das, PhD student at CST and first author of the study. She took the help of officials from the Bangalore Water Supply and Sewerage Board (BWSSB) and Bangalore Development Authority (BDA) to collect the samples.