| Mountainous urban terrain not only includes the mountains and hills, but also with the river, thegulf and other complex terrain combinations. This uniquegeographical feature makes the surface runoff in mountain city has the characteristics of wide area, strong randomness and complex causes. And it effects more obvious at the beginning of the runoff, more remarkable in early stage of runoff, which can obviously affect the quality of urban surface runoff.This paper selected the typical mountain city of Chongqing as the test point and it designed a set of combination process with ecological pond-surface flow constructed wetland-gravel filter strip. The process could analyze the reduction of main pollutants including COD (chemical oxygen demand), TP (total phosphorus), TN (total nitrogen), NH4+-N (ammonia nitrogen) and NO3--N (nitrate nitrogen) in simulation and rainfall runoff. The simulated runoff experiments were divided into two parts:static and dynamic. Static experiments had been made to compare the characteristics of pollutants removal under simulated runoff in ecological pond and subsurface constructed wetland. Dynamic experiments analyzed the influence of HRT (hydraulic retention time), influent COD concentration and nitrogen composition on the removal of the efficiency in the simulation runoff with continuous flow. Actual runoff experiments including stormwater runoff and sunny runoff analyzed the wetland combination of rainfall runoff and sunny runoff treatments. The results showed:The removal efficiency of COD was similar to the ecological pond and the surface flow constructed wetland in the condition of simulating runoff. The surface flow constructed wetland had obvious advantages in degradation removal of TN and TP. However, both treatments of the NH4-N removal efficiency needed be improved; The reduction rate of COD and TP increased while the reduction of TN and NH4+-N increased first and then decreased, but the reduction of NO3--N steadily increased with the hydraulic retention time prolonging; The increase of COD concentration in influent was beneficial to the removal of TN and especially NO3--N, but it decreased the reduction rate of NH4+-N. The removal rate of TP increased first and then decreased with the influent COD concentration increasing. When the COD concentration was 200 mg/L, the removal rate of TP was the highest; Nitrogen forms in runoff affected the removal of COD and TN, but it had no obvious influence on TP reduction. The increase of NO3--N ratio could increase the reduction of TN and COD, while the increase of NH4+-N ratio was not conducive to the reduction of both of them; With rainfall intensity increased, the concentration of COD, TP, TN, NH4+-N and NO3--N increased in rainfall runoff. And the average reduction of each pollutant was 54%,77%,56%,36%,81% after treatment. When the pollutant concentration was low in sunny day, the combined wetland could achieve further removal, and the removal rate was 36%～60%,24%～43%,42%～51%,25%～43% and 41%～65%. |
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