Study On Nitrogen Removal Performance Of Enhanced Soil Infiltration System

As an effective ecological system, soil infiltration system performs well in purifying decentralized domestic sewage. It has great theoretical value and practical significance to further enhance the nitrogen removal ability of soil infiltration system in purifying the sewage with high NH4+-N concentration (70mg/L-150 mg/L). Therefore, four soil infiltration systems, including three enhanced systems and a untreated system, are constructed in this study, the aims are to investigate the effect of start-up time, inflow mode and external carbon source on the nitrogen removal performance of the soil infiltration systems; to reveal the change rules of NO2--N concentration in enhanced systems; and to put forward some reference proposals for the exploration of the coexistence among nitrogen removal pathways in soil infiltration systems. The main results of this study are as following:After 18 days operation, four soil infiltration systems were successfully started up and became more stable. During the stable stage, the removal efficiencies of NH4+-N and COD were more than 97% and around 90%, respectively.Moreover, diffluent inflow mode could promote pollutants removal of soil infiltration systems. In particular, by using diffluent inflow mode, the average COD concentrations in effluent of four soil infiltration systems (from reactor 1# to reactor 4#) were 28.52 mg/L,29.65 mg/L,25.43, mg/L and 28.58mg/L, respectively, which was less than that of start-up and stable stage period. Accordingly, the average removal efficiencies of NH4+-N were 98.20%,98.39%,99.52% and 98.03%, respectively, and the average removal efficiencies of TN were 20.97%,53.48%、 16.47%、 64.42%, respectively. Through comparison and analysis, it can be conclude that increasing temperatures can promote the removal of COD, NH4+-N and TN; external biological matrix can improve the process of nitrification; and the amount of soil is one of the main influence factors on the NH4+-N removal of soil infiltration system.Under the condition without external carbon source added in inflow, the NH4+-N removal efficiencies of reactor 1#, reactor 3# and reactor 4# were still around 90%, Additionally, cycle fluctuation of effluent NO2--N concentration was observed in four reactors, the period of a cycle fluctuation was not constant but was in the range of 2-9 days, and the NO2--N concentration in effluent of reactors 4# was higher than that of three other reactors.The average NH4+-N concentrations in effluent of four soil infiltration systems (from reactor 1# to reactor 4#) were low, however, NO3--N concentrations were high, which means four soil infiltration systems had a enhanced ability of nitrification, But a poor ability of denitrification.The reason remain to be found.