Surfactants in sewage main cause of Bellandur lake foam: Study

A study says foaming in Bellandur lake could be due to multiple factors, starting from the untreated sewage entering the lake to bacteria that might be responsible for the foam’s stability.

The study, ‘Unravelling the reason for seasonality of foaming in sewage-fed urban lakes,’ noted that foaming has puzzled scientists as it increases only after heavy rains. The phenomenon is counterintuitive as increased water flow is supposed to dilute pollutants in the lake.

Reshmi Das, Chanakya H N and Lakshminarayana Rao from the IISc’s Centre for Sustainable Technologies highlighted three factors key for foaming, and untreated sewage is the first one. Due to the lake’s large size, it takes over 10 days for the waste water to disperse during which organic material gets degraded in the absence of oxygen and settles down as sludge.

The surfactants settle down on the sludge with gradual increase in their concentration.

Chanakya, Chief Research Scientist at CST, said that in some cases the surfactant concentration was 200 times more than the original concentration entering the lake.

“Imagine adding one full scoop of washing powder into a bucket of water; it will definitely foam given the right conditions,” he explained.

Secondly, the run-off water during heavy rain churns up the surfactant-laden sludge, creating a conducive condition for foaming. The rise in the water level means the excess water spills over into the lake's outlet to depths of 25 feet, converting surfactant-laden water into foam.

Lastly, researchers suggested that a "certain bacteria" in suspended solids might be responsible for foam formation and stability, but said that the mechanisms involved need to be validated through further experiments.

The study said stopping the flow of untreated waste water was crucial to prevent foam formation.