Effect of amended soil and hydraulic load on enhanced biological nitrogen removal in lab-scale SWIS

Effect of hydraulic loading rate on pollutant removal efficiency in subsurface infiltration system under intermittent operation and micro-power aeration

“…As shown in Table 1, HLR had obviously negative influence on the pollutants removal in the pilot system except for TN. inconsistent with previous studies, which declared that the average removal efficiency of TN will decrease with the increase of HLR (Li et al, 2012;Zou et al, 2009). It is probably due to the more available carbon source in the lower layer (TOC concentration in effluent A3) at 0.5 m 3 /m 2 d, which may lead to higher denitrification and result in lower effluent TN.…”

“…2, after the start-up period, the TN removal efficiency was nearly zero. After day 88, the average removal rate of TN increased to 13.8%, which was lower than the conventional SWIS (20-35%) and other modified SWIS (40-85%) (Zou et al, 2009;Pan et al, 2015). More than 65% TOC was biodegraded within the 0-35 cm substrate in the infiltration systems, leading to carbon source scarceness in the low layer for denitrification process (Table 1).…”

“…2, the purification processes were established over time, yielding comparatively stable purification efficiencies for organic matter after 1 week and for NH 4 + -N after 2 weeks. Compared to constructed wetlands and SWIS with lower HLR (Fan et al, 2013;Zou et al, 2009), the start-up period of the pilot system was significantly shortened, which could be ascribed to the growth of aerobic microbes boosted by the high pollutant loading and the sufficient oxygen supply. During the start-up period, COD, TOC, and NH 4 + -N in the effluent were gradually decreased, while TN showed contrary trend.…”

“…Substrate clogging is the inevitable consequence if this trend continuing. Accordingly, intermittent operation (Leuerenz et al, 2009;Li et al, 2012;Zhang et al, 2005), a special configuration with ring filter (Llorens et al, 2011), and using amended soil to replace original soil (Zou et al, 2009) have been developed to improve the oxygen availability. Intermittent operation allows for endogenous decay and desiccation to partially recover the filter porosity, leading to improvement of the removal efficiency of pollutants.…”

Nitrogen removal processes in deep subsurface wastewater infiltration systems

“…However, without denitrification, NO x À -N remains in solution and is transported in the percolate because it is not held by exchange reactions. Denitrification in the conventional SWIS is usually affected by the denitrifying biomass, temperature, soil characteristics, the carbon source and the carbon/nitrogen ratio (Sun et al, 1998;Xia et al, 2008;Yamaguchi et al, 1996;Zhang et al, 2005Zou et al, 2009. Furthermore, decomposition of organic matter and nitrification mainly occur in the upper portion, where oxygen is adequate.…”