Effects of antibiotics on corncob supported solid-phase denitrification: Denitrification and antibiotics removal performance, mechanism, and antibiotic resistance genes

Solid-phase denitrification (SPD) has been used in wastewater treatment plant effluent to enhance nitrate removal, and antibiotics co-existing in the effluent is a common environ-mental problem. In this study, it was systematically investigated the effect of single trace sulfamethoxazole (SMX)/trimethoprim (TMP) and their mixture on microbial denitrification performance, the antibiotics removal, and antibiotics resistance genes (ARGs) in corncob supported SPD system. The average denitrification rate was improved by 46.90% or 61.09% with single 50 pg/L SMX or TMP, while there was no significant inhibition with mixed SMX and TMP. The abundance of dominant denitrifiers (Comamonadaceae family and Azospia) and fermentation bacteria (Ancalomicrobium) were consistent with the denitrification per-formance of different antibiotics groups. Single SMX and TMP achieved relatively higher denitrification gene and enzyme abundance. Mixed SMX and TMP improved the denitrifi-cation gene copies, but they reduced the key denitrification enzymes except for EC 1.7.7.2. Additionally, the removal efficiency of TMP (56.70% +/- 3.18%) was higher than that of SMX (25.44% +/- 2.62%) in single antibiotic group, and the existence of other antibiotics (i.e. SMX or TMP) had no significant impact on the TMP or SMX removal performance. Biodegrada-tion was the main removal mechanism of SMX and TMP, while sludge and corncob ad-sorption contributed a little to their removal. SMX had the risk of sulfanilamide resistance genes (SRGs) dissemination. Furthermore, network analysis indicated that Niveibacterium and Bradyrhizobium were the potential hosts of SRGs, which promoted the horizontal trans-mission of ARGs.(c) 2022 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

Automated summary

This study investigated the effects of single and mixed sulfamethoxazole (SMX) and trimethoprim (TMP) on microbial denitrification performance, antibiotics removal, and antibiotic resistance genes (ARGs) in a corncob supported solid-phase denitrification system. Single SMX or TMP significantly improved denitrification rate, while mixed SMX and TMP had no inhibition effect. The abundance of denitrifiers and fermentation bacteria corresponded to the denitrification performance of different antibiotics groups. The removal efficiency of TMP was higher than that of SMX, and the presence of other antibiotics did not significantly affect the removal performance of either TMP or SMX. Biodegradation was the main removal mechanism, and there was a risk of sulfanilamide resistance gene dissemination.