Organic pollutant and nitrogen removal performance of subsurface wastewater infiltration systems (SWISs) with and without intermittent aeration, and operated under different organic pollutant loadings, was investigated. The intermittent aeration strategy not only significantly increased removal rates of organic pollutants and NH 4 + -N, but also successfully created aerobic conditions at a depth of 50 cm and did not change anoxic or anaerobic conditions at a 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 (98.0%~98.4%), NH 4 + -N (93.8%~98.1%) and TN (84.5%~94.0%) were simultaneously obtained in intermittent aerated SWISs for organic pollutant loadings ranging from 7.4 to 29.1 g COD/(m 2 •d), and these removal rates were significantly higher than for non-aerated SWISs. The results suggest that intermittent aeration is a reliable option to achieve high nitrogen removal in SWISs, especially with high organic pollutant loading.
Dissolved oxygen (DO), were investigated. Aerobic conditions were effectively developed in 50 cm depth of the matrix and anoxic or anaerobic conditions were not changed in 80 and 110 cm depth by intermittent aeration, which encouraged nitrification. Increased influent COD/N ratio led to lower COD and nitrogen removal in conventional SWISs. Sufficient carbon source in high COD/N ratio influent promoted denitrification with intermittent aeration. High removal rates of COD (95.68 ± 0.21%), TP (92.02 ± 0.28%), -N (99.33 ± 0.05%), and - (89.65 ± 0.6%) were obtained with influent COD/N ratio of 12 in aerated SWISs. Under the COD/N ratio of 12 and 18, intermittent aeration boosted the growth and reproduction of nitrifying bacteria and denitrifying bacteria. Meanwhile, nitrate and nitrite reductase activities with intermittent aeration were higher than that without aeration in 80 and 110 cm depths.
Matrix dissolved oxygen, nitrogen removal and nitrogen functional gene abundances in two artificial aeration modes, continuous aeration (CA) and intermittent aeration (IA), in subsurface wastewater infiltration systems (SWISs) under different hydraulic loading rates (HLRs) were investigated. Aeration not only successfully created aerobic conditions at 50 cm depth, but also did not change anoxic or anaerobic conditions at 80 and 110 cm depths. Meanwhile, aeration significantly enhanced chemical oxygen demand, NH-N, and total nitrogen (TN) removal and the enrichment of nitrogen removal functional genes (amoA, nxrA, napA, narG, nirK and qnorB) compared to the non-aerated SWIS, especially for high HLRs. IA SWIS (79.7%-85.8%) had a better performance on TN removal compared with CA SWIS (73.8%-82.2%) when the HLRs ranged from 0.06 to 0.3 m/(m d). Intermittent aeration is a sensible strategy to achieve high HLR, good nitrogen removal performance and comparatively low operation cost for SWISs.
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