Enhanced performance of tetracycline treatment in wastewater using aerobic granular sludge with in-situ generated biogenic manganese oxides.

Wastewaters containing tetracycline (TC) are produced in many industries, and biotechnology is an economic way to treat it. In this work, aerobic granular sludge (AGS) modified with in-situ generated biogenic manganese oxides (BioMnOx), named after manganese-oxidizing AGS (Mn-AGS), was used to treat TC in wastewater. Comparisons between Mn-AGS and AGS indicated that Mn-AGS showed superior TC resistance and treatment results than AGS. The activity of Mn-AGS was not inhibited by TC content as high as 20 mg/L. Wastewater TC could be removed stably and efficiently (95.2 ± 0.8%) in the Mn-AGS reactors after 119 days' acclimation. Furthermore, TC may be first adsorbed on Mn-AGS sludge and then degraded by both microbial community and BioMnOx. TC adsorption could be greatly improved by increasing solution pH, which can be attributed to the increase in negatively charged TC species at high pHs. The microbial community changed greatly after TC exposure and some TC-resistant bacteria, such as Flavobacterium, were enriched in the final sludge. Moreover, the antibiotic resistance genes (ARGs) tetA, tetG, and tetX largely increased and the microorganisms were TC-resistant through efflux pumps and antibiotic inactivation mechanisms. This work suggests a new biological-chemical coupling strategy, Mn-AGS, to treat antibiotics in organic wastewater with high efficiency and stability.