Nitrogen removal and N2O emission in subsurface wastewater infiltration systems with/without intermittent aeration under different organic loading rates

Nitrogen removal, N2O emission and nitrogen removal functional gene abundances in intermittent aerated (IA) and non-aerated (NA) subsurface wastewater infiltration systems (SWISs) under different organic loading rates (OLRs) were investigated. Aeration successfully created aerobic condition at 50 cm depth and did not change anoxic or anaerobic condition at 80 and 110 cm depths under OLR of 5.3, 10.9 and 16.5 g BOD/(m2 d). Meanwhile, aeration enhanced COD, NH4+-N, TN removal and the enrichment of nitrogen removal functional genes (amoA, nxrA, napA, narG, nirS, nirK, qnorB and nosZ) compared to NA SWIS. High COD removal rate of 91.6%, TN removal rate of 85.9% and low N2O emission rate of 32.4 mg/(m2 d) were obtained in IA SWIS under OLR of 16.5 g BOD/(m2 d). Intermittent aeration is a sensible strategy to achieve high OLR, low N2O emission, satisfactory organic matter and nitrogen removal performance for SWISs.