Influence of Elevated Salinity and the Presence of Cytostatic Drugs on Microbial Community in FO Anaerobic Membrane Bioreactors

Wastewater treatment using foward osmotic anaerobic membrane bioreactors (FO-AnMBR) has a number of advantages over traditional wastewater treatment approaches. Previous studies have investigated the overall performance of lab-scale FO-AnMBR in treating synthetic wastewater. During the operation of FO-AnMBR, it is expected that salinity gradually increases, which has also been shown experimentally. In addtion, emerging contaminants such as cytostatic drugs in wastewater would also be accumulated in the FO-AnMBR. Little has been known on whether and how the increased salinity and the presence of cytostatic drugs affect the microbial community in FO-AnMBR. The objective of this study was to investigate the influence of increased salinity and the presence of cytostatic drugs on the structure and function of the microbial community in FO-AnMBR through a metagenomics approach. A lab-scale FO-AnMBR was operated at 25 ^oC and fed with synthetic wastewater. Total DNA was extracted from sludge samples taken at pre-determined time points and sequenced using a HiSeq 2500 platform with 250-bp paired-end sequences. Based on the analyses of the sequences, structure and potential functions of the microbial communities were obtained. We found that the increased salinity in FO-AnMBR did not reduce the microbial diversity; however, the relative abunance of methane-producing archaea decreased significantly at high salinity condition, resulting in a reduced methane yield. The general metabolism did not differ significantly under low and high salinity conditions. Intriguingly, genes responsible for cell attachment and biofilm related signalling were enriched at high salinity condition. Transition of the gene clusters for assimilatory and dissimilatory nitrate reduction was also found. The presence of cytostatic drugs only slightly affected the microbial community composition. Biofilm-forming, multidrug resistant and siderophore-producing bacteria were found more dominant after the treatment with drugs.