Variations of nitrogen-metabolizing enzyme activity and microbial community under typical loading conditions in full-scale leachate anoxic/aerobic system

Influent loading determines the performance of leachate treatment plant (LTP) facing the dynamic conditions, but enzyme expression in microbial community is unclear. Here, six nitrogen-metabolizing enzymes were detected during nitrification failures (NF), high loading (HL), low loading (LL), and low carbon/nitrogen (LCN) in a 500 m³/d LTP. Nitrogen removal in LL was 15 ± 5% higher than that in HL. The activity of hydroxylamine oxidoreductase decreased by 90% as the influent total nitrogen increased from 2450 mg/L to 3100 mg/L, which might be a critical enzyme causing the nitrification failure. Denitrifying enzyme abated by 1.3% as the carbon/nitrogen dropped by 1% in LCN. With the influent chemical oxygen demand decreased from 22000 mg/L to 12000 mg/L, the relative abundance of norank_f_Saprospiraceae dropped from 33.66% to 11.94%, and finally disappeared, which seems to be an indicator of the high load operation. These findings provide the basis for improving the efficiency of LTPs.