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Antimicrobial resistance in a membrane enhanced biological phosphorus removal process Mohammadali, Mehrnoush


Coupling of membrane bioreactors with enhanced biological phosphorus removal (EBPR) processes increases the potential for low-yield sludge production by operating systems at long solids retention times (SRTs). However, biological foaming of anoxic mixed liquor in membrane EBPR (MEBPR) systems causes operational challenges (e.g. interference with the estimation of total suspended solids in the system). Hence, operating MEBPR systems by regular wastage of foam bacteria as a means to control SRT has gained increasing attention. The present research aims to evaluate the performance of MEBPR processes operating at long SRT (60 days) through estimation of the ARB release rates in foam, waste aerobic mixed liquor and effluent. The results indicated that, while superior antibiotic resistant bacterial (ARB) removal was achieved by membrane filtration in MEBPR systems (SRT= 60 and 25 days (control)), the proportions of sulfamethoxazole and trimethoprim resistant bacteria among mixed liquor heterotrophs exhibited statistically significant elevations relative to the influent. It was also demonstrated that extended SRT operations could achieve similar total daily release rates of ARB (amoxicillin, sulfamethoxazole, tetracycline) compared to those of the 25 day SRT train. In detail, waste aerobic mixed liquor and foam were found to be the major contributors to ARB release in the 25 and 60 day SRT trains, respectively. Data also showed that operating MEBPR systems at 25 and 60 day SRTs could reduce the total ARB release rates relative to the ARB inflow rates. It was also observed that the parallel trains significantly increased the relative abundances of the sul1 gene (normalized to 16S rRNA gene) in mixed liquor compared to those of the influent. Using an Illumina MiSeq platform, the taxonomic compositions of bacterial communities in influent and MEBPR environments were identified. Data analysis exhibited a shift in bacterial composition from influent to mixed liquor and then to treated effluent. A significant similarity was also found between mixed liquor and foam at the 25 day SRT train. Finally, PCR-based examination and functional screening of the fosmid library revealed the presence of nine antibiotic resistance genes conferring resistance to four classes of antimicrobials in the foaming compartment of the MEBPR process.

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