Nitrogen removal in subsurface wastewater infiltration systems with and without intermittent aeration

• Organic pollutant loading did not affect pollutants removal in aerated SWISs.
• Microbial populations, NR and NIR activities increased in intermittent aeration.
• Intermittent aeration was effective in high organic pollutant loading SWISs.
• Intermittent aeration achieved high removal of COD, NH4+-N and TN.
• Intermittent aeration created aerobic conditions in upper matrix.

Matrix dissolved oxygen (DO) levels, organic pollutants and nitrogen removal performances in subsurface wastewater infiltration systems (SWISs) with and without intermittent aeration operated under different organic pollutant loadings were investigated. The intermittent aeration strategy not only significantly increased removal rates of organic pollutants and NH4+-N, but also successfully created aerobic conditions in the depth of 50 cm and did not change anoxic or anaerobic conditions in the depth of 80 and 110 cm resulting in high TN removal. Increasing organic pollutant loading did not affect the removal of organic pollutants and nitrogen in intermittent aerated SWISs. High removal rates of COD (95.68 ± 0.21%–98.41 ± 0.23%), NH4+-N (93.77 ± 0.39%–98.06 ± 0.16%) and TN (84.48 ± 0.57%–94.02 ± 0.25%) were obtained simultaneously in intermittent aerated SWISs for the organic pollutant loading from 7.4 to 29.1 g COD/(m2 d), and significantly higher than non-aerated SWISs. Intermittent aeration boosted the growth and reproduction of nitrifying bacteria and denitrifying bacteria. In the depth of 80 and 110 cm, nitrate reductase (NR) and nitrite reductase (NIR) activities with intermittent aeration were higher than that without aeration. The results suggest that intermittent aeration was a reliable option to achieve high nitrogen removal in SWISs, especially under high organic pollutant loading.