Effect of antibiotic mixtures on the characteristics of soluble microbial products and microbial communities in upflow anaerobic sludge blanket

Two upflow anaerobic sludge blanket reactors (UASBs) were used to investigate the effects of three antibiotic mixtures (erythromycin, sulfamethoxazole, and tetracycline) on reactor performance, soluble microbial products (SMPs) composition and microbial community. One reactor (UASBantibiotics) was fed with antibiotic mixtures, whereas another reactor (UASBcontrol) was used as a control without the addition of antibiotic mixtures. Compared with those in UASBcontrol, UASBantibiotics show lower chemical oxygen demand removal efficiency and biogas content. A higher removal efficiency of antibiotic mixtures was obtained in first few stages in UASBantibiotics. The SMPs composition of effluent from the two reactors did not differ significantly, and the main components were protein-like substances, which produced higher fluorescence intensity in UASBantibiotics. Gas chromatography-mass spectrometry analysis revealed that the main compounds identified as SMPs (<580 Da) were alkanes, aromatics and esters, with only 20% similarity of SMPs between UASBantibiotics and UASBcontrol. Antibiotics had a significant effect on the microbial community structure. Notably, in UASBcontrol, hydrogenotrophic methanogens, key microorganisms in anaerobic digestion, had an obvious advantage at all stages compared with UASBantibiotics, whereas acetoclastic methanogen exhibited the opposite pattern. The above results demonstrated that antibiotic mixtures influenced the effluent quality during anaerobic treatment of synthetic wastewater, resulting in changes in the microbial community structure. This study clarified the effect of antibiotic mixtures on the operation of UASBs. It could contribute to identifying potential strategies for improving effluent quality in anaerobic treatment.