Analysis Of The Whole Process Of Combined Non-point Source Pollution And Research On Its Control Measures

The non-point source pollution caused by rainfall erosion in urban areas has become increasingly harmful to receiving water,with the control of point sources pollution and the improvement of urban sewage treatment and collection systems.At present,the scope of urban non-point source pollution is relatively small,but it brings about the urban black odor caused by nutrient salt and oxygen-consuming organic matter.Therefore,a comprehensive and scientific understanding of non-point source pollutant transport path and source apportionment in combined sewer systems is essential for managing and improving urban water environment.Previous studies have investigated transport and sources of road deposited sediments（RDS）and sewer sediments individually,and most of these studies focused on stormwater pollution in combined sewer overflow.However,studies about pollutant transport and source apportionment of the entire urban non-point source pollution process in combined sewer systems are lacking.This limited the systemic and direct of pollution management.This study analyzed build-up and wash-off process of pollutants on road surfaces and in sewer within a catchment of combined sewer systems in a typical old district in Zhuhai.Besides,source apportionment of the entire urban non-point source pollution was investigated using the mass conservation method.Based on the outcomes,several suggestions were given for taking measures to control non-point source pollution in combined sewer systems.The outcomes as flows:（1）The build-up load of road deposited sediments in the study area was28.81±10.69 g·m^-2.The average wash-off load of road deposited sediments during five different rainfall events was 19.27±10.90 g·m^-2 and the wash-off percentage was52.69±13.3%.The event mean concentrations of suspended solids（SS）in road runoff were 52-109 mg·L^-1,The average wash-off load of RDS during five different rainfall events was 19.27±10.90 g·m^-2（2）The build-up load of total organic carbon（TOC）,total nitrogen（TN）and total phosphorus（TP）in sewer sediments were 2.34±1.07 kg·m^-1,0.15±0.07 kg·m^-1,0.10±0.05kg·m^-1 respectively in light rain and moderate rain;The average wash-off load of TOC,TN and TP were1.32±1.03 kg·m^-1,0.08±0.06 kg·m^-1,0.06±0.04 kg·m^-11 in heavy rain,and the event mean concentrations of SS in sewer runoff were 68-158 mg·L^-1,and the event mean concentrations of SS in sewer runoff were 68-158 mg·L^-1.（3）Source apportionment analysis showed that road runoff,domestic wastewater and sewer sediments contributed 39%-72%,<20%,and 13%-56%to SS,respectively.The thickness of sewer sediments increased by 1-14 cm during light and moderate rains,and decreased by 7-17 cm during heavy rains.The contribution of pollution from road runoff,domestic sewage and sewer sediments in combined sewer systems were 2%-52%,9%-65%,and 8%-81%,respectively.（4）Under the process of non-point source pollution,this study proposes two aspects plan from both engineering and non-engineering.Among them,the engineering measures suggest intercepting 12 mm runoff depth;for the entire drainage zone,it is recommended that intercepts the 25 mm runoff in final discharge of the pipeline to control 80%pollutants in the runoff pollution.