Biofoam formation and defoamation in global wastewater treatment systems

Municipal wastewater treatment is largely based on activated sludge (AS) systems due to their ability to reduce biological and chemical oxygen demand (BOD/COD). They are similarly efficient in nitrification and denitrification. However, major drawbacks such as foaming associated with the prevalence of lipids (fats, oil, grease (FOG)) and proteinaceous material arise, which reduces AS efficiency – a focus of this review. Many strategies are employed for foam reduction in AS systems, where proliferation of foam-forming microorganisms can be challenging. To understand foam formation, prevention and deterioration, including destabilisation, a multidisciplinary mitigation approach is required, in which some bioprocess aspects such as foam destabilisation kinetics should be understood and quantified. This review reports on biological foam formation and source in wastewater treatment, defoaming strategies, and biofoam destabilisation kinetics as well as factors affecting foam stability.