In this study, the removal pathway of sulfadiazine (SDZ) and tetracycline (TC) and their roles in shaping microbial community were separately explored in two lab-scale membrane bioreactors (MBRs) operating in parallel with one control MBR. Results show that the MBR system eliminated more than 90% of TC in the feed, whereas removal efficiency of SDZ decreased from 100% to 40% with increasing SDZ concentrations (1-1000 μg/L). Based on batch tests, biodegradation and adsorption was the main removal route for SDZ and TC, following pseudo-first-order kinetic and pseudo-second-order kinetic model with a rate constant of 1.21 L/(g MLSS·d) and 1.91 h-1, respectively, in the acclimated sludge. As expected, the acclimated sludge possessed a higher removal potential for the antibiotics compared with unacclimated sludge. Notably, high-throughput sequencing revealed that the most abundant phylum Proteobacteria was resistant to TC (1-1000 μg/L), but was suppressed by SDZ (100-1000 μg/L). Members of the phylum TM7 were likely responsible for SDZ degradation. Overall, TC exhibited a stronger inhibitory effect on bacterial species and significantly reduced the biodiversity compared with SDZ, which could be strongly related to the persistent toxicity of TC to microbes resulting from its high adsorption potential on activated sludge.
Keywords: Sulfadiazine/tetracycline; antibiotics; bacterial community; membrane bioreactors; removal pathway.