How do hydraulic load and intermittent aeration affect pollutants removal and greenhouse gases emission in wastewater ecological soil infiltration systems?

Abstract

This study investigated the effects of hydraulic load and intermittent aeration on matrix oxygen concentration, COD removal, NH4+-N removal, TN removal, TP removal, greenhouse gases (GHGs) emission and functional gene abundances in wastewater ecological soil infiltration systems (WESISs). Intermittent aeration created aerobic conditions above 40 cm depth and did not change anaerobic conditions below 70 cm depth, which enhanced the abundances of bacteria and functional genes related to organic matter and nitrogen removal and improved COD, NH4+-N, TN and TP removal compared with non-aeration. The pollutants removal efficiencies, CO2 conversion efficiency decreased and N2O conversion efficiency increased with hydraulic load increasing in the non-aeration WESIS. COD, NH4+-N, TP removal efficiencies and CO2 conversion efficiency decreased in the intermittent aeration WESIS when hydraulic load increased. As hydraulic load increased from 0.05 to 0.4 m/d, TN removal efficiency first increased and then decreased in the intermittent aeration WESIS. However, N2O conversion efficiency first decreased and then increased. Intermittent aeration WESIS achieved high removal efficiencies of 89.4%, 90.8%, 87.2%, 92.9% for COD, NH4+-N, TN, TP, high conversion efficiency of 92.8% for CO2 and low conversion efficiency of 0.19% for N2O at hydraulic load of 0.2 m/d. Intermittent aeration and hydraulic load had hardly any effects on CH4 emission.