Effects Of Influent Carbon Source And Operation Parameters On Subsurface Wastewater Infiltration System

Strengthening sewage treatment and rural ecological environment construction is one of the important contents in China’s 14th Five-Year Plan.In this paper,the current rural decentralized domestic sewage treatment is difficult.Taking the underground infiltration system as the research subject,the effects of different influent carbon sources and operating parameters on the purification of sewage by underground infiltration system are discussed.In this paper,two sets of subsurface wastewater infiltration system（SWIS）（1#-activated sludge,meadow brown soil,slag;2#-biochar,activated sludge,meadow brown soil,slag）were constructed to explore the effect of influent carbon source and different operational parameters（hydraulic load,C/N）on nitrogen removal,phosphorus removal and organic matter removal,gas emission and matrix microbial diversity in SWISs.The main conclusions are shown as follow:（1）The removal efficiencies of COD,NH₄⁺-N and TP in 1#SWIS and 2#SWIS decreased with the increase of hydraulic load.Hydraulic loading had no significant effect on NO₃^--N and NO₂^--N concentrations in the effluent（P>0.05）.Under hydraulic loading of 0.04 m~3/（m~2·d）,0.08 m~3/（m~2·d）,0.12 m~3/（m~2·d）and 0.16 m~3/（m~2·d）,the removal performances of 2#SWIS were better than that of 1#SWIS.The removal performances of SWIS with glucose as carbon source were better than that with sodium acetate.When hydraulic load was 0.04 m~3/（m~2·d）,average removal efficiencies of COD,NH₄⁺-N and TP in 1#and 2#SWIS were the highest.Average removal efficiencies of COD,NH₄⁺-N and TP in 1#and 2#SWIS were 87.56%and89.05%,94.17%and 95.46%,94.10%and 97.05%with glucose as carbon source,respectively.Average removal efficiencies of COD,NH₄⁺-N and TP in 1#SWIS and2#SWIS were 86.47%and 87.36%,94.45%and 96.21%,91.12%and 92.86%.（2）The removal efficiencies of COD,NH₄⁺-N and TP in 1#SWIS and 2#SWIS and the effluent concentrations of NO₃^--N and NO₂^--N increased first and then decreased with the increase of C/N.When C/N was 10:1,average removal efficiencies of COD,NH₄⁺-N and TP in 1#and 2#SWIS were the highest.With glucose as carbon source,average removal efficiencies of COD,NH₄⁺-N and TP in 1#and 2#SWIS were 88.97%and 90.05%,95.28%and 97.16%,95.97%and 97.05%,respectively.With sodium acetate as carbon source,average removal efficiencies of COD,NH₄⁺-N and TP in 1#and 2#SWIS were 88.61%and 89.11%,94.34%and 96.84%,93.56%and 94.34%,respectively.When C/N ratio was 5:1 and 10:1,the removal efficiencies of COD and NH₄⁺-N in SWIS with glucose as carbon source was higher than that with sodium acetate as carbon source.When C/N ratio was 15:1 and 20:1,the removal efficiencies of COD and NH₄⁺-N in SWIS with sodium acetate as carbon source was higher than that with glucose as carbon source.Under different C/N,TP removal efficiency in SWIS with glucose as carbon source was always higher than that with sodium acetate as carbon source.（3）With the increase of hydraulic load,the emission rates of CO₂,CH₄,NH₃and N₂in 1#SWIS and 2#SWIS gradually increased.At 0.04 m~3/（m~2·d）,0.08 m~3/（m~2·d）,0.12 m~3/（m~2·d）and 0.16 m~3/（m~2·d）hydraulic loading,the gas emission rate of 2#SWIS was higher than that of 1#SWIS.The optimal hydraulic loading of 1#SWIS and2#SWIS was 0.04 m~3/（m~2·d）.Under the optimal hydraulic load,when glucose was used as carbon source,the emission rates of CO₂,CH₄,NH₃and N₂in 1#SWIS were286.80 mg/（m~2·d）,30.28 mg/（m~2·d）,0.31 mg/（m~2·d）and 1.61 mg/（m~2·d）,respectively.The emission rates of CO₂,CH₄,NH₃and N₂in 2#SWIS were 330.90 mg/（m~2·d）,20.65 mg/（m~2·d）,0.32 mg/（m~2·d）and 1.63 mg/（m~2·d）,respectively.When sodium acetate was used as carbon source,the emission rates of CO₂,CH₄,NH₃and N₂in1#SWIS were 215.65 mg/（m~2·d）,28.35 mg/（m~2·d）,0.28 mg/（m~2·d）and 1.32mg/（m~2·d）,respectively.The emission rates of CO₂,CH₄,NH₃and N₂in 2#SWIS were 289.76 mg/（m~2·d）,22.15 mg/（m~2·d）,0.30 mg/（m~2·d）and 1.47 mg/（m~2·d）,respectively.With the increase of C/N,the emission rates of CO₂and NH₃in 1#SWIS and 2#SWIS first increased and then decreased,and the emission rates of CH₄and N₂gradually increased.At C/N of 5:1,10:1,15:1,20:1,the gas emission rates C/N of2#SWIS were higher than 1#SWIS.The optimal C/N of 1#SWIS and 2#SWIS was10:1.Under the optimal C/N,when glucose was used as carbon source,the emission rates of CO₂,CH₄,NH₃and N₂in 1#SWIS were 345.20 mg/（m~2·d）,24.56 mg/（m~2·d）,0.30 mg/（m~2·d）and 2.25 mg/（m~2·d）,respectively.The emission rates of CO₂,CH₄,NH₃and N₂in 2#SWIS were 367.30 mg/（m~2·d）,35.12 mg/（m~2·d）,0.31 mg/（m~2·d）and2.42 mg/（m~2·d）,respectively.When sodium acetate was used as carbon source,the emission rates of CO₂,CH₄,NH₃and N₂in 1#SWIS were 285.30 mg/（m~2·d）,23.42mg/（m~2·d）,0.27 mg/（m~2·d）and 1.86 mg/（m~2·d）,respectively.The release efficiencies of CO₂,CH₄,NH₃and N₂in 2#SWIS were 327.50 mg/（m~2·d）,32.76 mg/（m~2·d）,0.29mg/（m~2·d）and 1.97 mg/（m~2·d）,respectively.（4）Under different operational parameters（hydraulic load,C/N）,the relative abundance of 11 microbial species accounted for more than 95%in the matrix of two SWISs,which were Proteobacteria,Acidobacteria,Actinobacteria,Chloroflexi,Gemmatimonadetes,Bacteroidetes,Planctomycetes,Firmicutes,WPS-2,Verrucomicrobia,Nietrospira.The operating conditions（hydraulic load,C/N）and influent carbon source did not change microbial species in the matrix of two SWISs on phylum level.