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

This study investigated the effect of hydraulic loading rate (HLR) on matrix dissolved oxygen (DO), organic matter removal, nitrogen removal, N2 O emissions, and the abundances of functional genes participating in nitrogen removal in intermittent aerated mode (IAM) and nonaerated mode (NAM) subsurface infiltration systems (SISs). In contrast to NAM SISs, IAM SISs were able to create aerobic conditions in the upper matrix (above 50 cm depth) and anoxic or anaerobic conditions in the lower matrix (below 80 cm depth). Subsequently, this enhanced the abundance of functional genes related to nitrogen removal. Chemical oxygen demand (COD) and nitrogen removal performance were significantly higher under IAM SISs than with NAM SISs. Under a HLR of 0.3 m3 /(m2  d), the IAM SIS was able to achieve low N2 O emissions (12.6 mg/[m2  d]) along with removal efficiencies of 90.5%, 91.4%, and 85.7% for COD, ammonia nitrogen ( NH 4 + -N), and total nitrogen (TN), respectively. PRACTITIONER POINTS: Intermittent aeration successfully realized sequential aerobic and anaerobic conditions at 50 cm depth and at 80 and 110 cm depths of a subsurface infiltration system. Intermittent aeration reduced N2 O emissions and improved hydraulic loading rate and organic matter, nitrogen removal efficiencies. Intermittent aeration enhanced the abundances of amoA, nxrA, napA, narG, nirS, nirK, qnorB, and nosZ.

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

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), , 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 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%), (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.

Nitrogen removal and N2O emission by shunt distributing wastewater in aerated or non-aerated subsurface wastewater infiltration systems under different shunt ratios.

This study investigated matrix oxidation-reduction potential (ORP), nitrogen removal, N2O emission and nitrogen removal functional gene abundance in three subsurface wastewater infiltration systems (SWISs), named SWIS A (without aeration or shunt distributing wastewater), SWIS B (with shunt distributing wastewater) and SWIS C (with intermittent aeration and shunt distributing wastewater) under different shunt ratios. Aerobic conditions were produced at a depth of 50 cm and anoxic or anaerobic conditions were not changed at depths of 80 and 110 cm by aeration in SWIS C. High average removal rates of chemical oxygen demand (COD) (83.1% for SWIS B, 90.9% for SWIS C), NH3-N (74.3% for SWIS B, 90.8% for SWIS C) and total nitrogen (TN) (61.1% for SWIS B, 87.9% for SWIS C) were obtained under shunt ratios of 1:3 and 1:2 for SWIS B and C, respectively. The lowest N2O emission rate (28.4 mg/(m2 d)) and highest nitrogen removal functional gene abundances were achieved in SWIS C under a 1:2 shunt ratio. The results suggested intermittent aeration and shunt distributing wastewater combined strategy would enhance nitrogen removal and reduce N2O emission for SWISs.

Does influent COD/N ratio affect nitrogen removal and N2O emission in a novel biochar-sludge amended soil wastewater infiltration system (SWIS)?

Nitrogen removal and N2O emission of a biochar-sludge amended soil wastewater infiltration system (SWIS) with/without intermittent aeration under different influent COD/N ratios was investigated. Nitrogen removal and N2O emission were affected by influent COD/N ratio. Under a COD/N ratio between 1:1 and 15:1, average chemical oxygen demand (COD), NH4 +-N and total nitrogen (TN) removal rates decreased with COD/N ratio increase in non-aerated SWISs amended with/without biochar-sludge; an increasing COD/N ratio hardly affected COD and NH4 +-N removal in a biochar-sludge amended SWIS with intermittent aeration; the N2O emission rate decreased with COD/N ratio increase in the studied SWISs. The biochar-sludge amended SWIS with intermittent aeration achieved high COD (92.2%), NH4 +-N (96.8%), and TN (92.7%) removal rates and a low N2O emission rate (10.6 mg/(m2 d)) under a COD/N ratio of 15:1, which was higher than those in non-aerated SWISs amended with/without biochar-sludge. Combining the biochar-sludge amended SWIS with intermittent aeration enhanced the number of nitrifying bacteria, denitrifying bacteria, nitrate reductase activities, nitrite reductase activities, and improved the abundance of nitrogen removal functional genes under a high influent COD/N ratio. The results suggested that the joint use of intermittent aeration and biochar-sludge in a SWIS could be an effective and appropriate strategy for improving nitrogen removal and reducing N2O emissions in treating high COD/N ratio wastewater.

Organics removal, nitrogen removal and N2O emission in subsurface wastewater infiltration systems amended with/without biochar and sludge.

Organics removal, nitrogen removal, N2O emission and nitrogen removal functional gene abundances in four subsurface wastewater infiltration systems (SWISs), named SWIS A (no intermittent aeration without biochar and sludge), SWIS B (no intermittent aeration with biochar and sludge), SWIS C (intermittent aeration without biochar and sludge), SWIS D (intermittent aeration with biochar and sludge) were investigated. Intermittent aeration enhanced chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN) removal and the abundances of nitrogen removal functional genes (amoA, nxrA, napA, narG, nirS, nirK, qnorB and nosZ) compared to non-aerated SWISs. High COD (95.4 ±â€¯0.2%), NH4+-N (96.2 ±â€¯0.6%), TN (86.4 ±â€¯0.5%) removal efficiencies and low N2O emission rate (18.4 mg/(m2 d)) were obtained simultaneously in intermittent aerated SWIS amended with biochar and sludge. The results suggested that intermittent aerated SWISs amended with biochar and sludge could be an effective and appropriate method for improving treatment performance and reducing N2O emission.

Pollutants removal in subsurface infiltration systems by shunt distributing wastewater with/without intermittent aeration under different shunt ratios.

Matrix dissolved oxygen (DO), removal of COD, TP and nitrogen in subsurface infiltration systems (SISs), named SIS A (without intermittent aeration and shunt distributing wastewater), SIS B (with shunt distributing wastewater) and SIS C (with intermittent aeration and shunt distributing wastewater) were investigated. Aerobic conditions were developed in 50cm depth and anoxic or anaerobic conditions were not changed in 80 and 110cm depth by intermittent aeration. Under appropriate shunt ratios, shunt distributing wastewater improved denitrification and had little influence on COD, TP and NH3-N removal. Under the optimal shunt ratio of 1:2 for SIS C, high average removal rates of COD (90.06%), TP (93.17%), NH3-N (88.20%) and TN (85.79%) were obtained, which were higher than those in SIS A (COD: 82.56%, TP: 92.76%, NH3-N: 71.08%, TN: 49.24%) and SIS B (COD: 81.12%, TP: 92.58%, NH3-N: 69.14%, TN: 58.73%) under the optimal shunt ratio of 1:3.