Foaming of Surface Waterbodies: A Comprehensive Study on Causes, Persistence, Seasonality, and Mitigation Strategies

Abstract

Foaming waterbodies have emerged as a significant global concern due to their adverse effects on aquatic ecosystems, offensive odour emissions, disruption of daily activities in nearby areas, and visual unpleasantness. Despite their widespread occurrence globally, the foaming phenomena in surface waterbodies have not received adequate scientific attention. This study focuses on Bellandur lake, located in Southern India, which experiences persistent foaming events since the past decade. The study emphasizes the urgent need to address the crisis of foaming waterbodies. The thesis investigates the sources and concentrations of surfactants, foam formation mechanisms and developing targeted strategies for effective foam mitigation. The study reveals that the primary source of pollution in Bellandur lake is untreated sewage, which contains surfactants. The anionic surfactant concentration in the lake water was measured at 17 ± 3 mg/L, with surface tension remaining below 50 mN/m, similar to the treatment plant inlet. Moreover, high phosphorus levels of 10 ± 3 mg/L were observed, primarily originating from feces and urine, indirectly impacting surfactant concentrations in the lake. Foam stability investigations highlight the crucial role of mixed filamentous bacteria, particularly the Flavobacteriia family, in contributing to foam stability. Furthermore, this research expands to explore the seasonality of foaming events and the sorption/desorption of surfactants onto sediment and suspended solids (SS) in foaming surface waters globally. The findings indicate that foaming lake sediment can contain up to 3.4 g of anionic surfactant per kilogram of dry sediment, correlating with organic matter content and surface area. The study also reveals the sorption capacity of SS in wastewater, which was measured at 53.5 ± 4 mg surfactant per gram of SS. In contrast, only a maximum of 5.3 mg surfactant was sorbed/g of sediment. The lake model analysis revealed that sorption is a first-order process and that surfactant sorption on SS and sediment is reversible. SS was found to desorb ∼73 % of sorbed surfactant back to the bulk water, while sediment desorbed 33–61 % of sorbed surfactants proportional to their Organic Matter. Contrary to common assumptions, rainfall does not dilute surfactant concentrations but instead increases the foaming potential through desorption from SS. The analysis of a foams demonstrates that surfactants originate from both anthropogenic and naturogenic sources, with anthropogenic surfactants comprising 96.5% of the total in foam. Linear Alkylbenzene Sulphonates (LAS) of various carbon chain lengths were identified as the most prevalent surfactants in the foam. Pseudomonas bacteria were found (>19.2 %) to be the primary surfactant producers in both the water and sediment of the lake. Modelling and field validation studies further elucidate the fate of LAS in the foaming lake, revealing limited degradation in the water and its presence in the sediment, due to low DO. The modelling further revealed that oxygenated water with a dissolved oxygen concentration of 3.5 mg/L has the capacity to degrade 90% of the surfactants within the residence time. Additionally, the process of desilting (by 1.5 m) contributed an additional 6% to the overall efficiency of surfactant removal. The lake receives a staggering 258 million litres of untreated sewage daily, accounting for 47% of its volume. The research demonstrates successful surfactant degradation of up to 90% within 30 h through controlled aeration at 3.5 mg/L DO. This insight guided the design of a customized inline treatment model for each sewage entry point of Bellandur lake, designed and optimized using BioWin for enhanced water quality. The approach, which includes recirculating sludge, achieved a 1/3rd reduction in treatment time while aligning with no-foam discharge limits. The first part of the study focuses on understanding the causes of stable and seasonal foaming. The findings in the final part offer a comprehensive blueprint for managing foam-related issues in waterbodies, encompassing design precision, stakeholder engagement, and process optimization.