| With the increasing problem of eutrophication in water,poor nitrogen removal in the subsurface wastewater infiltration system（SWIS）has been paid attention.Due to the limitation of structure,oxygen discharged into the substrate of the SWIS is seriously insufficient,which leads to anaerobic or anoxic state of the substrate and limits nitrogen removal in the SWIS.In this study,matrix dissolved oxygen,nitrogen removal and nitrogen functional gene abundances in continuous aerated（CA）,intermittent aerated（IA）and non-aerated（NA）pilot SWISs were investigated.The effects of influent COD/N ratio and organic loading on nitrogen removal,the number of microorganism and the activities of enzyme involved in nitrogen removal were also studied in the IA SWIS.This study will provide theoretical guidance for the optimization and application of aerated SWISs.The main conclusions are shown as follow:（1）Non-aerated SWIS was under anoxic or anaerobic conditions at 80 and 110 cm depths,and aerobic conditions were not good at 50 cm depth.Aeration not only successfully created aerobic conditions at 50 cm depth,but also did not change anoxic or anaerobic conditions at 80 and 110cm depths in aerated SWISs.Moreover,DO concentrations decreased with increasing hydraulic loading rates in NA,CA and IA SWISs.NA SWIS achieved COD removal rate of 86.1%,74.8%and 62.8%;NH4+-N removal rate of 72.4%,52.9%and 27.4%;TN removal rate of25.62%-53.24%under the HLR of 0.06,0.18 and 0.3 m3/（m2 d）,respectively.CA SWIS achieved COD removal rate of 98.2%,96.5%and 94.6%;NH4+-N removal rate of 94.5%,93.1%and 92.1%;TN removal rate of 73.8%-82.2%under the HLR of 0.06,0.18 and 0.3 m3/（m2 d）,respectively.IA SWIS achieved COD removal rate of 97.6%,93.1%and 91.4%;NH4+-N removal rate of 93.8%,92.5%and 91.4%;TN removal rate of 279.4%-85.8 under the HLR of0.06,0.18 and 0.3 m3/（m2 d）,respectively.TP removal rates were more than 90%in three SWISs.The effect of hydraulic loading rate on COD and NH4+-N removal of aerated SWISs were significantly less than non-aerated SWIS.TN removal rate of non-aerated SWIS decreases with the increasing of hydraulic loading rates.TN removal rate increases with the increase of hydraulic loading rate in aerated SWISs.TN removal rate of IA SWIS was higher than that of CA SWIS under the same hydraulic loading rate because of more carbon source obtained in IA SWIS.Aeration enhanced the enrichment of nitrogen removal functional genes（amoA,nxrA,napA,narG,nirK and qnorB）.Intermittent aeration is a reliable strategy to achieve low operation cost,and high hydraulic loading rate and TN removal for SWISs.The results suggest that the SWIS adopt intermittent aeration.（2）Under the influent COD/N ratio of 3,6,12 and 18,intermittent aeration not only successfully created aerobic conditions at 50 cm depth,but also did not change anoxic or anaerobic conditions at 80 and 110 cm depths.Under the influent COD/N ratio of 3,6,12 and 18,effluent COD concentration of IA SWIS was 2.52,7.66,20.75 and 36.28 mg/L,with removal rate of 98.4%,96.8%,95.7%and 94.9%;effluent NH4+-N concentration was 0.56,0.41,0.26 and1.14 mg/L,with removal rate of 99.3%,98.9%,98.5%and 97.0%;effluent TN concentration was 32.36,22.92,4.11 and 3.44 mg/L,with removal rate of 17.9%,42.3%,98.7%and 91.2%,respectively.TN removal rate increased with the increase of the COD/N ratio and high COD/N ratio was beneficial to TN removal in IA SWIS.Under the same COD/N ratio,TP removal rate of IA SWIS was slightly higher than that of NA SWIS.The number of nitrifying bacteria in IA SWIS decreased with the increase of depth,while the number of denitrifying bacteria increased with the increase of depth.COD/N ratio has no effect on the number of nitrifying bacteria,while the number of denitrifying bacteria at 80 cm and 110 cm increased with the increase of the COD/N ratio.The depth for nitrate reductase and nitrite reductase activities from high to low in sequence was 110,80 and 50 cm.Under COD/N of 12 and 18,the activities of nitrate reductase and nitrite reductase of IA SWIS at 80 cm and 110 cm depths were higher than those of NA SWIS.（3）Under influent organic pollutant loading of 7.4,14.8 and 29.1 g COD/（m2 d）,aerobic conditions were effectively developed at the depth of 50 cm and anoxic or anaerobic conditions were not changed at the depths of 80 and 110 cm by intermittent aeration.Under the influent organic pollutant loading of 7.4,14.8 and 29.1 g COD/（m2 d）,effluent COD concentration of IA SWIS was 2.16,7.89 and 20.95 mg/L,with removal rate of 98.4%,96.8%and 95.7%;effluent NH4+-N concentration was 0.85,1.53 and 2.31 mg/L,with removal rate of 98.1%,94.1%and93.8%;effluent TN concentration was 6.12,4.02 and 2.38 mg/L,with removal rate of 84.5%,89.9%和94.1%,respectively.TN removal rate increased with the increase of influent organic pollutant loading in IA SWIS.Under the same influent organic pollutant loading,TP removal rate of IA SWIS was slightly higher than that of NA SWIS.The number of nitrifying bacteria and denitrifying bacteria increased with the increase of influent organic pollutant loading.Under the same influent organic pollutant loading,the activities of nitrate reductase and nitrite reductase of IA SWIS at 80 cm and 110 cm depths were higher than those of NA SWIS.At the same depth,the activities of nitrate reductase and nitrite reductase of IA SWIS increased with the increase of influent organic pollutant loading.Intermittent aeration increased the number of microorganism and the activities of enzyme involved in nitrogen removal in the SWIS. |
PDF Full Text Request