Effects of sulfamethoxazole/trimethoprim on corncob-supported solid-phase denitrification and removal performance: Microbial community, biotransformation pathways, and antibiotic resistance genes

[Display omitted] •0.05 and 2 mg/L sulfamethoxazole/trimethoprim could not inhibit nitrogen removal.•The genes related electron donor behaviours were not significantly affected.•The degradation pathways of sulfamethoxazole/trimethoprim were proposed.•The toxicity of intermediates tended to be lower than that of parent compounds.•The abundances and potential risks of antibiotic resistance genes were discussed. The widespread use of antibiotics inevitably results in their discharge into the water environment from the wastewater treatment plant (WWTP) effluents. Corncob-supported solid-phase denitrification (CC-SPD) has been identified as a promising technology for nitrogen removal of WWTP effluents. The effects of sulfamethoxazole (SMX)/trimethoprim (TMP) on nitrogen removal in up-flow CC-SPD reactors and the influencing mechanisms are studied at microbial and genetic levels, and the antibiotic removal performance, degradation pathways, and antibiotic resistant genes (ARGs) are also extensively investigated. Long-term experimental results indicated that 0.05 and 2 mg/L SMX/TMP, either individually or in combination, had no inhibition on nitrogen removal performance in CC-SPD reactors. The NO3–-N removal capacity was approximately 125.60–142.91 mg NO3–-N/g CC. Although the microbial community structure evolved to adapt to the 0.05 mg/L SMX/TMP, the relative abundances (RAs) of denitrification genes and genes related to electron donor behaviours did not significantly alter. Furthermore, SMX, with a higher removal efficiency of 42.17%, was more easily degradable compared to TMP, and the degradation products of SMX were more readily mineralized. Additionally, microorganisms degrade antibiotics through processes such as ring opening, hydrogenation, and bond cleavage, with the toxicity of intermediates often being lower than that of parent compounds. Moreover, 0.05 mg/L SMX/TMP did not significantly change the RAs of ARGs and movable genetic elements (MGEs). This study provides important basis for the antibiotic risk prevention in WWTP effluents and the practical application of SPD technology.