Effect of oxytetracycline on performance and microbial community of an anoxic-aerobic sequencing batch reactor treating mariculture wastewater

The performance and microbial community of an anoxic-aerobic sequencing batch reactor (SBR) treating mariculture wastewater were evaluated at different oxytetracycline (OTC) concentrations. The COD and nitrogen removal efficiencies decreased with the increase in OTC concentration from 0 to 12 mg L-1. No apparent NO3--N accumulation was found during the whole operational period, whereas NO2--N accumulation occurred at 12 mg L-1 OTC. The specific oxygen uptake rate (SOUR), specific ammonium oxidation rate (SAOR), specific nitrite oxidation rate (SNOR) and specific nitrate reduction rate (SNRR) decreased with increasing influent OTC concentration. The protein (PN) and polysaccharide (PS) contents in the loosely-bound extracellular polymeric substances (LB-EPS) and tightly bound EPS (TB-EPS) increased with the increase in OTC concentration from 0 to 12 mg L-1, respectively. The appearance of OTC in the influent could obviously affect the functional groups of the PN and PS in the LB-EPS and TB-EPS. X-ray photoelectron spectroscopy (XPS) illustrated that amino, carboxyl and hydroxyl groups in the EPS might be involved in the interaction between the EPS and OTC. The denaturing gradient gel electrophoresis (DGGE) profile indicated that some variations were found in the microbial community of the activated sludge with increasing OTC concentration. Some microorganisms were depleted or weakened with the increase in OTC concentration, whereas others became the predominant microorganisms due to their ability to adapt to the OTC toxicity.