Study On Enhanced Pollutants Removal In The Subsurface Wastewater Infiltration System By Biochar Addition

In this paper,two lab-scale subsurface wastewater infiltration systems?SWISs??1#with biochar,2#without biochar?were constructed to investigate the effect of biochar addition on nitrogen,phosphorus and organic matter removal and greenhouse gas emission under different operation parameters.Then,four pilot SWISs?SWIS A,non-intermittent aeration without biochar and sludge;SWIS B,non-intermittent aeration with biochar and sludge;SWIS C,intermittent aeration without biochar and sludge;SWIS D,intermittent aeration with biochar and sludge?were constructed to study the effect of biochar and sludge addition on nitrogen removal,organic matter removal,N₂O emission and functional gene abundances with/without intermittent aeration.The main conclusions are shown as follow:?1?The average removal efficiencies of NH₄⁺-N,COD and TP in 1#and 2#SWIS were the highest under hydraulic loading of 0.05 m³/?m²·d?,which were 93.4%and 92.7%,92.7%and95.1%,98.0%and 97.4%respectively.The average removal efficiencies of NH₄⁺-N in 1#and 2#SWIS were the highest under wetting-drying ratio of 3:1,which were 98.7%and 98.6%respectively.Under wetting-drying ratio of 2:1,the average removal efficiencies of NH₄⁺-N and TP in 1#and 2#SWIS were the highest,which were 95.5%and 91.3%,96.6%and 90.3%,respectively.By changing the quality concentration of COD in controlling C/N,the average removal efficiencies of TP in 1#and 2#SWIS were the highest under C/N of 6:1,which were94%and 88.2%respectively.The average removal efficiencies of COD in 1#and 2#SWIS were the highest under C/N of 3:1,which were 89.4%and 91.1%,respectively.The average removal efficiencies of TP in 1#SWIS and 2#SWIS were the highest when C/N were 12:1 and 9:1,respectively.The average removal efficiencies of NH₄⁺-N and TP in 1#SWIS were higher than those in 2#SWIS.By changing the quality concentration of NH₄⁺-N in controlling C/N,the average removal efficiencies of NH₄⁺-N and COD in 1#SWIS and 2#SWIS were the highest under C/N of 12:1,which were 97.0%and 97.9%,96.0%and 93.3%respectively.The average removal efficiencies of TP in 1#SWIS and 2#SWIS were the highest under C/N of 3:1,which were 94.7%and 90.1%,respectively.?2?Biochar addition promoted CH₄,CO₂,NH₃ and N₂ emission in the SWIS.When hydraulic loading was 0.05 m³/?m²·d?and wetting-drying ratio was 3:1,the emission rates of CH₄,CO₂,NH₃ and N₂ were the lowest.When C/N was 3:1 in changing the COD concentration,the emission rates of CH₄,CO₂ and N₂ were the lowest.When C/N was 12:1 by changing the NH₄⁺-N concentration,the emission rates of NH₃ and N₂ were the lowest.?3?High COD,NH₄⁺-N,TN removal efficiencies of 95.4±0.2%,96.2±0.6%,86.4±0.5%and low N₂O emission rate of 18.4 mg/?m² d?were obtained in intermittent aerated SWIS amended with biochar and sludge.Intermittent aeration enhanced the abundances of nitrogen removal functional genes compared with no-aerated SWISs.