Biological conversion of sulfamethoxazole in an autotrophic denitrification system

Sulfamethoxazole (SMX) is a common antibiotic prescribed for treating infections, which is frequently detected in the effluent of conventional wastewater treatment plants (WWTPs). Its degradation and conversion in a laboratory-scale sulfur-based autotrophic denitrification reactor were for the first time investigated through long-term reactor operation and short-term batch experiments. Co-metabolism of SMX and nitrate by autotrophic denitrifiers was observed in this study. The specific SMX removal rate was 3.7 ± 1.4 μg/g SS-d, which was higher than those reported in conventional wastewater treatment processes. The removal of SMX by the enriched denitrifying sludge was mainly attributed to biodegradation. Four transformation products (three known with structures and one with unknown structure) were identified, of which the structures of the two transformation products (TPs) were altered in the isoxazole ring. Additionally, the presence of SMX significantly shaped the microbial community structures, leading to the dominant denitrifier shifting from Sulfuritalea to Sulfurimonas to maintain the stability of system. Collectively, the sulfur-based autotrophic denitrification process could effectively remove SMX in addition to efficient nitrate removal, and further polish the effluent from conventional WWTPs.