Soil Enzyme Activities In Soil Filtration Assay Process Run

Soil infiltration treatment(SIT) is an ecologically in-situ wastewater treatment technology.During SIT process,pollutants are purified through integrated self-regulation mechanisms of the soil-microorganism-plant system.This study focused on the purification performance and soil enzyme activities through laboratory experiments.And the effects of operation conditions on soil enzymes were also carried out.The relationship between pollutant removals and enzyme activities,and the feasibility of soil enzymes being used as indicators for purification efficiency were finally discussed.SIT exhibited excellent removal efficiencies for COD,NH₃-N and TP,which were little affected by artificial soil compositions,influent organic loadings and COD/TN ratios,and nitrification inhibitor addition(Dicyandiamide,DCD)(p＞0.05). The influence of hydraulic loading rates was not the case.Under the conditions of higher hydraulic loading rate,the effluent quality from SIT tended to be worsen, which is not favorable for the consideration of groundwater safety.The results indicated that artificial soil C/N ratios had greater influence on nitrogen removal of SIT,compared with other influent characteristics.Higher nitrogen removals could be observed in the systems with high C/N ratios(C1,C2,and C4)(p＜0.05).The effect of DCD addition on nitrogen removal depended on soil compositon of the system,which mainly contributed to the different performences of the soil systems(C1,C2,and C3) being investigated in this study.The determination of some soil biochemical properties was also carried out.The results indicated that extracellular polysaccharide in soil matrix had no significant correlations with soil infiltrability,and its content remained stable during investigation period(p＞0.05).Catalase activities had no significant spacial difference(p＞0.05),and increased with the elevation of hydraulic loadings.While urease varied in quite a different way(p＜0.05),and its activity increased with the increase of influent organic loadings.The activities of nitrate reductase(NAR) and nitrite reductase(NIR) were less affected by hydraulic loadings(p＞0.05).Soil enzyme activities were depressed under lower temperatures.DCD had inhibition effects on catalase and urease activities,and showed stimulation or inhibition effects on NAR and NIR activities of the soil systems,depending on soil compositons. The correlations between soil enzyme activities and purification efficiencies were also analyzed.Soil enzyme activities had no significant relationship with influent organic and hydraulic loadings(p＞0.05).However,some positive relationship could be found between influent COD/TN and NAR and NIR activities, which was significant at the middle soil layer of C2 and the bottom soil layer of C3(p＜0.05).Some significant relations were obtained between urease activities and nitrogen removal performances for the systems composed of campus soil(p＜0.05), while the relationships were not so remarkable between NAR and NIR activities and TN removal.A significant negative relationship only existed between NIR of bottom soil layer and effluent TN concentration in system C1(p＜0.01),which could not be found in systems C2 and C3(p＞0.05).In addition,the correlations between soil enzyme activities and the purification efficiencies of organic substances and phosphorus were not very noticeable(p＞0.05).