Anaerobic granular sludge and biofilms in anaerobic wastewater fermentation remodeled by co-exposure to microplastics and antibiotics

Wastewater treatment plants are important areas for the concentration of antibiotics (ATBs) and microplastics (MPs), and anaerobic digestion (AD) is a green, efficient, and clean technology in wastewater treatment. Activated granular sludge (AGS) and biofilm methods are the two most critical biotreatment processes in the AD reactor; their differential response to complex pollutant exposure significantly affects wastewater treatment efficacy. However, differences regarding the response of the two sludge types to complex pollutants are not currently being explored. This study examines microbial adaptations to dual MPs (6 mg/L)-ATBs (1 mg/L) stress. Prolonged exposure reduced methanogenesis by 49.34 % and COD removal by 53.11 % while triggering microbial defense mechanisms: diminished cellular damage and enhanced antioxidant capacity, albeit at the cost of reduced electron transfer and energy metabolism efficacy. Extracellular polymeric substance secretion decreased, weakening structural integrity. Community restructuring featured declining Euryarchaeota and rising Actinomycetota, with biofilms enriching fermenters, acetogens, and electrogens versus AGS retaining more methanogens. Acetoclastic methanogenesis was dominated by upregulated acetate-to-acetyl-CoA genes (EC:2.7.2.1/2.3.1.8). Biofilms showed higher ARG loads but unchanged types, while AGS's granular structure conferred superior contaminant shielding. Enhanced denitrification gene expression contrasted with suppressed ammonium conversion, alongside elevated sulfide transformation potential (notably in biofilms). Biofilms demonstrated superior genetic-level resilience, cellular integrity, and energy generation. These findings yield mechanistic insights into AGS and biofilm responses during complex wastewater treatment scenarios.