Evaluating performance of nitrogen and organic carbon removal in a single reactor by using A. faecalis strain NR aerobically

•An aerobic bioreactor inoculated with A. faecalis NR was successfully applied.•Simultaneous nitrogen and organic carbon removal were achieved.•The expression of key enzyme gene amoA for ammonium removal was determined.•Microbial community structure was analyzed.•Long-term operation with high NH4+-N loadings was assessed. The performance of nitrogen and organic carbon removal in a single reactor (R1) operating with A. faecalis strain NR aerobically was assessed. Under 150 mg/L influent NH4+-N, 91.3%, 71.4% and 90.9% of NH4+-N, TN and TOC were removed, presenting much higher efficiency than a control bioreactor inoculating activated sludge (R0). The amoA gene expression from strain NR in R1 was 7.8 times higher than that from activated sludge in R0, demonstrating the role of strain NR in removing NH4+. The analysis of microbial community composition revealed that strain NR was the dominant species and outcompeted ammonium oxidizing bacterium (AOB) under high organic carbon as well as ammonium. Simultaneous ammonium and organic carbon removal still maintained for a long-term operation with NH4+-N loadings of 300 and 450 mg/L in R1. Nitrogen balance showed that stripped NH3 only occupied a few percentages and aerobic denitrification played a significant role in nitrogen removal.