Characteristics Of Pollutant Accumulation And Migration In Urban Surface-pipe System

Recently,urban surface pollution has gradually become the main source of water pollution.Understanding the occurrence and migration characteristics of non-point source pollutants is of great signifi cance for formulating corresponding control measures and improving urban water environment.This paper select the Baishi harbor as the target area,reveals the spatial distribution of common non-point source pollutants in surface runoff and sediment,as wel l as the correlation of pollutants in the transport process;The exchange characteristics of pollutants at sediment-water interface of rainwater pipes were discussed through laboratory simulation experiments.The grain size of the surface sediments in Zhuz hou city is unimodal,and the grain size less than 250μm accounts for more than 65%of the total accumulation.When the drought days reached 12 days,the surface sediment accumulation in the industrial area was 1.22～3.95 times that of other areas.The COD,Cu,Cr and Ni of each functional area showed moderate variation.TP,NH₄⁺-N,NO₃^--N,Zn,Pb and Cd showed strong variation.The surface pollutants are mainly concentrated in the sediments with the particle size of 75～150μm.The power function model can better describe the accumulation process of surface sediment and pollutants in rainless period,and R² value is greater than 0.800.The EMC value of pollutants in runoff is generally similar to the distribution law of surface pollutant accumulation before r ain in each functional area.The MFF₃₀calculation results show that when the cumulative runoff rate is 30%,the cumulative pollutant load rate in the industrial area is 35.16%-78.25%,except for the strong initial scour effect in the industrial area,whic h only shows a moderate initial scour effect.Combined with the calculation results of the gap function,it ca n be considered to control 30%～50%of the surface runoff,so as to achieve effective control of the surface runoff pollutants.The spatial distribution characteristics of the pollutants were similar to those of the surface pollutants.The main component and Pearson correlation analysis showed that the surface accumulation process of pollutants in rainless period was influenced by the main sources of pollutants and the total amount of sediment accumulation.On the whole,the surface sediment accumulation was significantly correlated with C OD and heavy metal accumulation.The content of pollutants in runoff is mainly affected by the accumulation of surface pollutants,and there is a significant correlation between SS and all pollutants in runoff.There is a good correlation between surface sediment and surface runoff,the correlation coefficient is greater than 0.900,and the correlation between other environmental media is weak.Heavy metals were always strongly correlated with each environmental medium,and the correlation coefficients were all greater than 0.850.The main microorganisms in the sediment of rainwater pipelines in the study area were facultative anaerobes,and the dominant bacteria were ammoniating,denitrifying and phosphorus-accumulating functional bacteria.The results show that the decrease of DO,the increase of temperature and disturbance intensity can increase the pollutant exchange flux.When the temperature is 25℃and the disturbance intensity is 300 r·min^-1,the NH₄⁺-N exchange flux is 1.630 mg·（m²·h）^-1,the SCOD is 36.218mg·（m²·h）^-1,and the DTP is 0.049 mg·（m²·h）^-1.There are differences in the optimal fitting curve types between environmental factors and different pollutant exchange fluxes.