| Subsurface wastewater infiltration system (SWIS) is a sewage purification technique combined manual work with sel-purification. It has merits including low cost、high quality discharge、light effects from climate、no power needed、without order、easy management、no sludge produced etc, which is a kind of living creature, ecosystem engineering technique that have the vast development foreground.In this paper, the traditional constructed SWIS on the basis of improvements in the analysis of previous studies, four experimental systems of septic system for domestic wastewater treatment was set up. Preparation of the substrate was mainly studied. Under different hydraulic loading rates, water samples were taken for analysis of CODcr, ammonia, total nitrogen and total phosphorus concentrations. The influence of start-up period on the treatment effect of the system was analyzed for different dry/wet ratios、modified soil and increasing aeration device. Mechanism of contamination removal were explored initially. The main conclusions are:A set of subsurface wastewater infiltration system was designed. Analysis of the subsurface and inner environment was easy with the side sampling points. At the lower of the system was the water collection area. The wastewater flowed through the cross distribution pipe to the infiltration area. As then, the distribution of the wastewater was uniform.The experimental results of the substrate for enhancing pollutants removal effects showed that, improvement material such as ceramicite and turf soil were compared and ceramicite was chosen as the improvement material of sandy soil. The bio-substrate was made of activated sludge, sandy soil, slag and turf soil with the proportion of 1:14:2:3. The porosity, infiltration rate and organic matter content of the bio-substrate were raised greatly compared to the sandy soil.In the normal condition, the effect of pollutants removal was not very good, when increasing aeration device, the system significantly within the SWIS. With a hydraulic loading rate of 10cm/d, dry/wet ratio of 2:1, the system reached the mature state after 22 days. The average removal efficiencies was 88.28% for CODCr,44.5% for NH4+-N and 92.5% for total phosphorus. There is great effect of SWIS on dry/wet ratio in start-up period, when increasing the number of bio-substrate, the system significantly enhanced removal of pollutants.This study investigated the effect of SWIS at different dry/wet ratio of 1:2,1:1, 2:1 and 3:1. The experimental investigation shows that, in stable operation period, pollutants removal first increases then decreases with the heighten dry/wet ratio, the optimal dry/wet ratio was 1:1. The average outflow concentration was 13.86mg/L, 1.58mg/L,6.39mg/L,0.54mg/L. The average removal efficiencies was 89.17% for CODCr,90.87% for NH4+-N,68.02% for total nitrogen and 86.86% for total phosphorus.Under different hydraulic loading rates of 6cm/d,8cm/d, 10cm/d and 12cm/d, it was found that when the loading rate increases, the system removal efficiency decreased for CODCr, NH4+-N, total nitrogen and total phosphorus. But the effluent quality meets the first level Acriteria specified in Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 19818-2002), therefore SWIS has stronger anti-shock loading capability. |
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