Impact and fate of ciprofloxacin on aerobic granular sludge: biological treatment, ciprofloxacin removal and biotransformation mechanisms

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Abstract
Ciprofloxacin (CIP) is commonly found in wastewater, posing challenges for biological treatment systems due to its persistence and inhibitory effects on microbial communities. This study examined the impact and fate of CIP on granular sludge in removing chemical oxygen demand (COD), ammonia-nitrogen (NH4+), and total phosphate (TP) under different redox conditions, as well as the degradation mechanisms of CIP. Results indicated that CIP impacts COD, ammonium and phosphorus removal by granular sludge in a dose-dependent manner. In aerobic conditions, COD removal by granular sludge was strongly inhibited (45-54% COD removal at 15 mg/L CIP) at higher CIP concentrations. Conversely, COD removal was at 66-62% in the presence of 15 mg/L CIP under anaerobic conditions, indicating lower impact of CIP. Ammonium and phosphate removals were higher under aerobic conditions as compared to anaerobic conditions, both impacted by CIP dosing. CIP removal by granular sludge was noticed under both aerobic and anaerobic conditions and at different initial CIP concentrations. CIP removal was highest at 85% under aerobic condition as compared to 60% under anaerobic condition for an applied 1 mg/L CIP dose. LC-MS analysis identified distinct biodegradation pathways with formation of 23 and 26 intermediates, respectively, under aerobic and anaerobic conditions. These findings highlight the importance of biosorption and biodegradation in CIP removal, and negative effects of CIP on COD and nutrient removal by granular sludge under different redox environments, offering insights for optimizing wastewater treatment strategies.

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