Short-Term and Long-Term Reduction of Sulfamethoxazole and Tetracycline in the Sewage Pipe

The sediments, biofilm, sewage, and upper space in the sewage pipe constituted the "primary reaction site" of pollutants. This study examined the short-term and long-term reduction of two common antibiotics, sulfamethoxazole (SMX) and tetracycline (TC), and disclosed their reduction mechanisms. The results showed that the removal pathways of antibiotics in sewage pipes were mainly sediments and biofilm adsorption, biodegradation, etc. In short term (72 h), TC was mainly removed by adsorption, while SMX relied more on biodegradation. Over longer periods (30 days), both antibiotics were adsorbed by sediments and biofilm, and the adsorption capacity of biofilm was greater. Under SMX and TC exposure, extracellular polymeric substance (EPS) secreted by microorganisms increased, and the surface charge of tightly bound EPS (TB-EPS) obviously decreased. TB-EPS transformed from lower molecular weight (< 1 kDa) to larger one and exposed more adsorption sites. For SMX, biodegradation was a more important pathway. It achieved through microorganism co-metabolism and denitrification and was positively correlated with relative abundance of Trichococcus, Sulfurospirillum, and norank_o__PeM15. Finally, the reduction rate of SMX in pipe effluent was in 65.60%-86.25%, and that of TC remained above 85%. This research could supplement the theory of pollutant migration and transformation in sewage systems.