Foam Composition and Surfactant Sources in an Urban Foaming Lake: A Comprehensive Analysis

Foaming of surface water bodies is a common concern of many major metropolitan cities globally. These hideous and persistent foams disturb aquatic ecosystems and also emit an obnoxious stench. These foams also overflow onto the surrounding roads, causing pedestrians discomfort and traffic disruption. Even though foaming of the aquatic system is a widespread phenomenon, it is not entirely scientifically understood yet. The central unexplored question in this domain is - what compounds make up a foam? To answer this question, it is vital to understand the physics of foaming, the properties of a compound that helps in foaming, and its chemical/physical influence on the distribution of other compounds and species in a water body.

 Foam is caused by surface-active compounds called surfactants. In aquatic environments, the surfactants may be either endogenous or anthropogenic in origin. In nutrient-rich waterbodies, decaying plants and microorganisms can be a potential endogenous source of surfactants. Commercially used surfactants in households and industries find their way into the aquatic ecosystem through untreated effluents discharged after anthropogenic activities. These foams, by the mechanism of foam fractionation, also tend to enrich many organic and inorganic compounds into the foam phase. Enrichment might lead to precariously high concentrations of surface-active contaminants in the foam phase, which would otherwise be within acceptable levels in bulk lake water. Thus, foam not only has surfactants but also has other enriched chemical compounds in it.

This work aims to identify those compounds in foam, focusing on sewage-fed Bellandur lake in India, which has been infamous for foaming for the past decade and understand their environmental implications. Bellandur Lake has anionic surfactant concentrations reaching up to 20 mg/l and surface tension as low as 45 mN/m. The Lake is eutrophied, with chlorophycean algae concentration reaching up to 13.8×10⁷ cells/mL of Lake water. The scope of this study is as follows:

• to assign relative flux to surfactants from various sources and identify the most significant contributor to foaming events;
• to estimate the relative difference in concentrations of contaminants in bulk liquid and foam phase and predict the possibility of an impending threat, if any.

This study thus provides an opportunity for a better understanding of the foaming pattern, which is essential to prevent the occurrence of such foaming events in future.