BENGALURU: A four-year long study by researchers at IISc has shown that there are three key aspects that are causing the foaming in the Bellandur lake. One, the rainfall itself, two, untreated sewage water that enters the lake, and three, the possibility of suspended solids containing certain bacteria.
But a recent analysis by the team suggests that a single type of surfactant (foam causing agent) commonly used in most washing powders at home, and shampoos may be a major reason for the foaming.
A study by researchers at Centre for Sustainable Technologies (CST), Indian Institute of Science (IISc), was published in the journal Science of the Total Environment.
One way of preventing the foaming, they say, is stopping untreated sewage from entering the lake, besides removing the sludge that is accumulated in lakes, before monsoon. This sludge should also be disposed of properly, they suggest.
How sludge accumulates
Researchers found that part of the untreated sewage that entered the lake was turning into sludge. "The first is untreated sewage entering 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," said IISc in a release.
Over time, as more sewage that flows in, a part of it gets loosely attached to the sludge. As a result, its concentration increases. "In some cases, up to 200 times the original concentration entering the lake," said Chanakya HN, Chief Research Scientist at CST and one of the authors of the study. He likened this to adding a scoop of washing powder into a bucket of water, and that giving rise to foam in the right conditions.
Adding to this is the heavy rainfall because of which the surfactant, which acts as a foaming agent, gets dislodged from the sludge and makes it foam-ready.
What Lakshminarayana Rao, associate professor at CST calls an important phenomenon that converts surface-laden water into foam, involves the following process: Firstly, there is a little foam deep in the lake. But when it rains, the water gushes along with a large concentration of surfactants into the lake, 25 feet deep. And during this inflow, air bubbles are trapped, causing foam to be formed.
Even though the mechanism needs to be validated, researchers also suggested that another factor could be at play in forming foam -- suspended solids containing certain bacteria.
How the water was studied
Water samples were collected from the lake, and were analysed for various parameters. A lab model was created to study the surfactants in the lake across the year. Reshmi Das, PhD student at CST and first author of the study recalls having gone to the lake each month to collect water and foam samples with help from BDA and BWSSB officials, to experiment on.