Micro- and Nanobubbles Enhance the Abatement of Biodegradable Micropollutants in Aged Biological Activated Carbon Filters

Abstract

It has been demonstrated that the abatement of micropollutants in drinking water by biological activated carbon (BAC) filters with aged media deteriorates due to the decreased porosity and aerobic metabolism in dense biofilm. In this study, micro- and nanobubbles (MNBs) were introduced to the influent of young and aged BAC filters to potentially enhance the removal of micropollutants with various functional groups. Results showed that intermittent MNB introduction could enhance biodegradable micropollutant abatement in aged BAC filters. MNB introduction could yield a ∼10–70% relative increase in removal efficiencies of biodegradable micropollutants in 15-year BAC filters. Meanwhile, the cytotoxicity reduction in BAC filters was elevated from <60% to ∼80% due to the formation of less cytotoxic transformation products, as evidenced by mass spectrometry combined with a machine learning tool. Intermittent MNB introduction could induce localized reshaping of dense biofilm architecture, resulting in recovered pore structures in biofilm, which were pivotal for convective mass transfer. Correspondingly, abundances of Bacteroidota, Chloroflexota, and Acidobacteriota associated with aerobic metabolism of organic substances could be elevated in aged biofilm. However, continuous MNB introduction severely damaged biofilm integrity. The findings of this study support intermittent MNB introduction as a new approach to restore dense biofilm in aged BAC filters, resulting in enhanced biodegradation of micropollutants.