Nitrogen Removal and N₂O Emission in Biochar‐Sludge Subsurface Wastewater Infiltration Systems

Abstract

Nitrogen removal and N2O emission of biochar-sludge amended subsurface wastewater infiltration systems (SWISs) with/without intermittent aeration under different organic surface loading rates (OSLRs) were investigated. Under OSLR, between 8.5 and 54.6 g COD/(m2 d), average chemical oxygen demand (COD), <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="00800-ilm01.gif"/>, and total nitrogen (TN) removal rates decreased with OSLR increasing in non-aerated SWISs amended with/without biochar-sludge; increasing OSLR hardly affected COD and <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="00800-ilm12.gif"/> removal in biochar-sludge amended SWIS with intermittent aeration; N2O emission rate decreased with influent OSLR increasing in the SWISs. Biochar-sludge amended SWIS with intermittent aeration obtained higher removal rates for COD (94.9 to 95.5%), <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="00800-ilm23.gif"/> (90.5 to 93.7%), TN (86.5 to 89.9%) and lower N2O emission rates [13.4 to 14.7 mg/(m2 d)] under high influent OSLR of 36.2 and 54.6 g COD/(m2 d) were compared with non-aerated SWISs with/without biochar-sludge. Furthermore, the abundances of amoA, nxrA, napA, narG, nirS, nirK, qnorB, and nosZ genes involved in nitrogen removal were enhanced under high influent OSLR in biochar-sludge amended SWIS with intermittent aeration.

Subsurface wastewater infiltration systems for nitrogen pollution control

“…In addition, anaerobic Fe ammonia oxidation may occur due to the coexistence of Fe 3+ and NH 4 + -N (Peng et al, 2020). Qi et al (2018) improved the NH 4 + -N removal efficiency and reduced N 2 O emission of the SWIS by adding 10% biochar and 10% sludge into the soil substrate (Table 4). Biochar, a C-rich solid product derived from the pyrolysis of agricultural biomass waste, exhibits high porosity, a large surface area, and significant cation exchange capacity.…”

“…Sludge is a complex mixture containing microorganisms, organic matter, colloids, and cations (Jiang et al, 2017). The biochar sludge exhibits high adsorption capacity and provides ample space for microbial growth and reproduction, thereby enhancing N removal efficiency and reducing N 2 O emissions (Qi et al, 2018). The start‐up cycle of SWIS was reduced by 30% through the utilization of dewatered sludge as microbial inoculum, leading to an enhancement in TN and NH 4 + –N removal rates to 77.1% and 91.6%, respectively (Jiang et al, 2017, Table 4).…”

Biochar application in biofiltration systems to remove nutrients, pathogens, and pharmaceutical and personal care products from wastewater

“…When influent N concentration increased from 67 to 160 mg N L −1 , the biochar‐amended CW (50%, v/v) showed stable TN removal performance (47.1 vs. 41.3%), whereas the TN removal efficiency decreased to 19.2–22.1% in 100% gravel CW (Saeed et al., 2019). When biochar was amended to a SWIS, improved TN removal (30–80%) and slightly lower N 2 O emissions (15–30 mg m −2 d −1 ) were observed, compared with conventional SWIS without biochar addition (20–70% TN removal and 18–34 mg m −2 d −1 N 2 O emission) (Qi et al., 2018).…”