Foam in Urban Lake -Sources of Surfactant and Threshold Foaming Criteria

Recently, foaming waterbodies have become rampant globally. Mostly, foaming surface water results from a concoction of surfactants from different anthropogenic and naturogenic sources. The world has witnessed a population surge, urbanization, industrialization, and increased waste/wastewater generation trends. However, there has not been a simultaneous rise in the number of treatment plants and their penetration to localities. Therefore, surfactant-laden water, after its use in households and industries, ends up directly discharged into surface waters. This causes unaesthetic and pungent foams and undesirable changes in the aquatic ecosystem. Further, decaying plants and microbes (in water and sediment) can also be a source of surfactant.

Crucial unexplored questions related to foaming surface water are - i) the relative contributions of each surfactant source and ii) beyond what surfactant concentration, foaming becomes inevitable. To estimate threshold concentration, it is vital to identify the primary source of surfactant in the water body. The study area (foaming Bellandur Lake, India) received 243 MLD of untreated sewage out of 530 MLD total inflow. Anionic surfactant concentrations reached up to 20 ppm in Bellandur Lake and were primarily linked to household sewage. There are many such sewage-fed foaming waterbodies in developing countries, owing to a lack of treatment facilities. But threshold foaming concentration remains unknown.

This study aims to i) comprehensively analyze all the sources of surfactant in foam and ii) identify threshold foaming criteria, i.e., estimate a surfactant concentration beyond which foaming is probable. First, all the surfactants were identified and linked with their respective source. This study then hypothesizes that suspended solid and bacteria in wastewater are responsible for the biosorption/sorption of surfactants, rendering the water devoid of free/unbound surfactants. Once the surfactant concentration exceeds a limit, i.e., there exists free surfactant, the foaming sets in. Threshold surfactant concentration needs to be included as one of the monitoring parameters to discharge standards for inland surface water as a foam preventing criterion.