Influence of microbial communities on foam fractionation of wastewater for PFAS removal

The occurrence of foaming in aerated bioreactors at wastewater treatment plants (WWTPs) presents an opportunity to integrate PFAS removal into WWTPs through foam fractionation. However, the influence of microbial communities on foam behaviour and consequently foam fractionation performance, as well as potential impacts on biological nutrient removal, need to be considered. In this study, we investigated the influence of microbial communities on foaming performance and their subsequent effects on PFAS enrichment and concentration reduction in foam fractionation. The presence of foam-forming bacteria, Gordonia and Microthrix, as identified by molecular analysis and supported by Gram-stained microscopic observations, was found to double the foam's delivered volumetric liquid fraction, leading to a significant decrease in long-chain PFAS enrichment factors (EFs). For example, the aqueous PFOA EF decreased from 50 to 18 in the presence of foam-forming bacteria. However, PFAS concentration reduction appeared unaffected by the presence of foam-forming bacteria. Interestingly, molecular analysis also revealed that key functional bacteria involved in nitrogen removal in aerated bioreactors, nitrifiers namely Nitrosomonas and Nitrospira, were negatively selected into the foam during foam fractionation. These findings support ongoing efforts to evaluate the integration of foam fractionation into aerated bioreactors as a potential strategy for PFAS removal.