Effects of hydraulic loading rate and aeration mode on nitrogen removal and nitrogen functional gene abundances in subsurface wastewater infiltration systems

Abstract

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.

Effect of aeration and hydraulic loading rate on nitrogen removal by subsurface infiltration systems

“…() and Sun et al. () found that aeration was the most feasible method to ensure sufficient oxygen supply in SISs. The increase in HLRs resulted in decreased hydraulic retention time, and thus, ‐N removal efficiency decreased for IAM and NAM SISs.…”

“…Ye and Li (2009) reported greater rates of nitrification required DO concentrations above 1.5 mg/L. Jiang, Sun, Pan, Qi et al (2017) and Sun et al (2017) found that aeration was the most feasible method to ensure sufficient oxygen supply in SISs. The increase in HLRs resulted in decreased hydraulic retention time, and thus, NH + 4 -N removal efficiency decreased for IAM and NAM SISs.…”

“…Many studies have been conducted to improve HLRs of SISs by enhancing oxygen availability, one of the main limitations of these systems (Sun et al., ; Yang, Zhan, Wu, Kang, & Guo, ). Sufficient dissolved oxygen (DO) concentrations of SISs are necessary for effective pollutant removal.…”

“…However, NAM SISs can have low hydraulic loading rates (HLRs) and are ineffective at nitrogen removal. According to Li, Li, Sun, and Wang (2012) and Sun, Pan, Qi, and Fei (2017), nitrogen removal efficiencies Published online 19 February 2019 in Wiley Online Library (wileyonlinelibrary.com) Research Article of a conventional NAM SIS were 80%-85% under low HLRs (0.006-0.10 m 3 /[m 2 d]), but decreased to 70% with the HLR at 0.125 m 3 /(m 2 d). Low hydraulic loading and poor nitrogen removal restrict the widespread use of SISs.…”

Efficiencies of Nitrogen Removal in Slope-Constructed Wetlands

“…Because nitrification is a two-step process, inorganic ammonium nitrogen is oxidized to nitrite nitrogen by a bacterial group that is commonly referred to as Nitrosomonas [12]. This group functions in anoxic-anaerobic environments and in the presence of facultative biomass [13][14].…”