Removal Of Urban Runoff Contaminants By Two-stage Mixed-media Soil Infiltration System

The pollution of rainwater runoff has become the main source of urban non-point pollution. A two-stage mixed-media soil infiltration system was developed, which strengthened the system of nitrogen removal performance and enhanced removal efficiency of each pollutant in runoff. It had important theoretical and practical guiding significance for the centralized treatment of urban rain water utilization. The research results were as follows:(1) During start-up period the biofilm completed in about 20-25 days. During stable period effluent COD concentrations maintained below 40 mg/L, met the surface water class V water quality standard, and the average removal rate was 87.82%.Effluent concentrations of NH4+-N most days were below 1.5 mg/L, met the surface water class IV water quality standard. The average removal rate reached 96.50%.During stable period NO3--N effluent concentrations were lower than 0.6 mg/L, the average removal rate reached 89.67%. Effluent NO2--N concentrations were lower than 0.1 mg/L, kept a high NO2--N average removal rate of 99.50%. Effluent TP concentrations most days were below 0.4 mg/L, met the surface water class V water quality standard. Stable average removal rate was 79.48%.(2) Under different hydraulic load of 0.48, 0.32, 0.24 and 0.16 m/d, the removal rate of COD were 85.82%, 92.60%, 88.06% and 94.34%, basically followed that the removal rate of high hydraulic load is low. The removal rate of NH4+-N were 96.50%,95.93%, 95.88% and 96.16%, all higher than 95%. Hydraulic load had little effect on NO3--N, NO2--N and TP. The smaller the hydraulic load, the higher the removal rate,which were stable at above 79%, 98% and 77%. Under different wet-dry ratio of 1:1,1:2, 1:5, the removal rate of COD were 92.60%, 95.53% and 97.02%. The longer the drying time, the higher the removal rate. The removal rate of NH4+-N were 95.93%,94.61% and 94.07%. Drying time had little effect on the removal rate, 1:1 was the best condition for NH4+-N. Likewise, the removal rate of NO3--N were 79.41%,80.48% and 73.89%. Under the conditions of 1:1 and 1:2, the nitrogen removal can be carried out smoothly. The removal rate of NO2--N were 97.97%, 98.29% and 98.12%.The removal rate of TP were 78.61%, 78.12% and 78.15%. Wet-dry ratio had little effect on them.(3) The effluent concentrations of COD in the roof runoff and road surface runoff were lower than that of 15 mg/L and 10 mg/L. The average removal rate was86.44% and 92%, which met the surface water class I water quality standards. The effluent concentrations of NH4+-N in the roof runoff and road surface runoff were lower than that of 1 mg/L, which met the surface water class III water quality standards. The overall removal rate was 94.21% and 92.66%. The effluent concentrations of NO3--N in the roof runoff and road surface runoff were lower than that of 0.47 mg/L and 0.7 mg/L. The total removal rate reached 98.07% and 95.73%.The effluent concentrations of NO2--N was lower than that of 0.02 mg/L, the total removal rate reached 94.88% and 94.84%. The effluent concentrations of TP was0.33~0.37 mg/L, met the surface water class V water quality standard.