Self-regulating adaptability of biofilm microbiomes enhances manganese and ammonia removal in microbial electrochemical filters under dioxane exposure

Understanding the stability and assemblage of biofilm microbiomes under oligotrophic conditions is critical for improving groundwater bioremediation. In this study, a novel microbial electrochemical filter (MEF) was developed to explore the impact of weak electrical stimulation on functional adaptability of biofilms under oligotrophic and 1,4-dioxane exposure conditions. Under 20 mg/L 1,4-dioxane stress, the MEF achieved 94.72 % manganese removal and 27.27 % ammonia nitrogen removal, while the conventional biofilter exhibited 88.76 % manganese removal with negligible ammonia nitrogen removal. Metagenomics analyses revealed that dominant populations in the MEF included Nitrospira, Bradyrhizobium, and Nitrosomonas, with relative abundance of 6.23 −10.78 %, 5.81 −6.15 %, and 1.62 −5.58 %, respectively. Weak electrical stimulation enriched the manganese oxidation-associated genes cotA, mnxG, and mcoA, whose total relative abundances being 6.3 times that of the conventional biofilter before dioxane exposure and 2.0 times after exposure. Genes encoding ammonia monooxygenase (amoABC), hydroxylamine dehydrogenase (hao) increased by 2.4- and 1.9-fold, respectively, compared to the conventional biofilter. Additionally, genes involved in the reductive tricarboxylic acid cycle and nitrogen fixation were twice as abundant in the MEF than in the conventional biofilter, suggesting enhanced nutrients availability for heterotrophic bacteria during start-up. These findings demonstrated that weak electrical stimulation effectively regulated biofilm microbiomes and enhance pollutant removal in MEF under oligotrophic conditions.