Enhanced antibiotic removal in anaerobic hybrid reactors under hydraulic stress: Insights from granular activated carbon and polyurethane foam

This study examined the impact of support material type on the performance of anaerobic hybrid reactors treating antibiotic-laden wastewater under varying hydraulic retention times (HRT: 24 to 4 h). Two reactors with identical packing ratios (5.8% v /v) were operated for 182 days: one with granular activated carbon (R1 GAC ) and another with polyurethane foam (R2 PU ). Reducing HRT below 12 h impaired the performance of both reactors. Despite R2 PU retaining more attached biomass, R1 GAC achieved superior stability and removal of organic matter, antibiotics, and antibiotic resistance genes (ARGs) under hydraulic stress. On average, fluoroquinolone and sulfonamide removal in R1 GAC was approximately 26% and 10% higher than in R2 PU , respectively. At 4-hour HRT, R1 GAC outperformed R2 PU, removing antibiotics such as ciprofloxacin (43% vs. 32%), sulfamethoxazole (68% vs. 46%), and trimethoprim (81% vs. 75%). Batch adsorption showed that GAC had higher antibiotic affinity than PU, but its theoretical adsorption capacity would be exhausted within 13–129 days for most antibiotics. Sustained removal over 133 days of antibiotic exposure demonstrates that biodegradation was the dominant mechanism. Functional predictions suggested that GAC was associated with sustained co-metabolic activity under short HRTs. R1 GAC also reduced effluent ARG levels more effectively than R2 PU . Overall, GAC represents a promising strategy for robust anaerobic systems, enhancing antibiotic removal and mitigating ARG dissemination under hydraulic stress.