Humic acid synergistic bioelectrochemical system for treating high-concentration ammonia nitrogen wastewater enriched with various antibiotics and microplastics

This study constructed a composite-polluted wastewater system containing high-concentration ammonia (5 g/L), multiple antibiotics (1 mg/L), and microplastics (10 mg/L) to simulate complex scenarios where emerging and conventional pollutants coexist in waste streams like sludge digestate and livestock effluent. Humic acid (HA, 10 mg/L) was integrated as a natural electron shuttle in coupled bioelectrochemical systems (BES) to enhance treatment. Results showed HA increased methane yield (9.89 %) and organic conversion, alleviated ammonia inhibition (11.96 %), and stabilized volatile fatty acids. It also effectively mitigated reactive oxygen species generation in microbial consortia and promoted extracellular polymeric substance formation, shielding cells against co-contaminant toxicity. HA stimulated the acetoclastic, dominated over the hydrogenotrophic, thereby promoting methane metabolism. Crucially, HA diminished the selective pressure of antibiotics, thereby suppressing antibiotic resistance genes (ARGs) proliferation and horizontal transfer, while enriching nitrogen metabolism genes. This confirms that HA-coupled BES enhances treatment resilience and microbial adaptability for complex wastewater.