城市面源污染特征及排放负荷研究--以内江市为例

城市面源污染已引起国内外的重视，研究城市面源污染特征及排放负荷，为城市面源防治提供借鉴有重要意义。在内江市将城市下垫面按照水文效应和面源污染特性不同划分为屋面，庭院，交通道路，城市水环境四类，每类下垫面中选取一定数量的点进行监测，根据选取的典型点位的监测结果，研究城市面源污染特征及污染物负荷，结果表明：（1）各类下垫面中，交通干道污染质量浓度普遍较高，屋面污染物质量浓度相对较低，交通干道 COD、悬浮物、总磷、氨氮、总氮平均质量浓度分别为215.31 mg·L-1、280.20 mg·L-1、0.35 mg·L-1、2.29 mg·L-1、4.06 mg·L-1；屋面COD、悬浮物、总磷、氨氮、总氮平均质量浓度分别为85.56 mg·L-1、117.25 mg·L-1、0.13 mg·L-1、2.03 mg·L-1、3.63 mg·L-1。（2）不同材质屋面中，沥青屋面的污染物质量浓度普遍较高，陶瓦屋面的污染物质量浓度相对较低。沥青屋面 COD、悬浮物、总磷、氨氮、总氮平均质量浓度分别为73.4 mg·L-1、56.0 mg·L-1、0.181 mg·L-1、2.529 mg·L-1、5.254 mg·L-1；陶瓦屋面COD、悬浮物、总磷、氨氮、总氮平均质量浓度分别为30.8 mg·L-1、45.4 mg·L-1、0.106 mg·L-1、2.099 mg·L-1、4.167 mg·L-1。（3）单次降雨COD污染负荷在34.6~73.7 t之间，相当于整个城区城镇生活污水不加处理排放1天；根据3次降雨监测结果估算全年COD、悬浮物、总磷、氨氮、总氮排放量分别为2177.1 t、2778.3 t、3.855 t、41.410 t、69.133 t，城市面源COD污染负荷是城镇生活源的近20%。（4）各类下垫面中，屋面的污染物排放负荷贡献率最大，其次为庭院、交通干道、一般道路、城市水环境，一次典型降雨中，屋面对COD污染负荷的贡献率为30.9%，庭院为28.7%，交通干道为24.7%，一般道路为14.9%，城市水环境仅为0.8%。（5）各类下垫面中，交通干道的初始冲刷效应最明显，其次为一般道路、庭院、屋面。根据分析得出结论：城市面源中COD、悬浮物的污染不容忽视；不同下垫面呈现不同的污染特征，屋面的污染物质量浓度较低，但由于面积贡献率大，污染物负荷贡献率较高，均在25%以上，交通干道、一般道路五类污染物由于质量浓度较高，各污染物负荷贡献率均超过其面积贡献率，可作为城市面源防治的重点；截留和处理城市降雨初期径流对于城市面源污染处理非常重要。

Study on the characteristics of urban non-point source pollution and its discharge load：a case study for Neijiang,Sichuan province

More and more concerns have been raised to urban non-point source pollution and it is of much importance for the study on its characteristic and discharge load in view of the corresponding measures for preventing and controlling. A case study on the characteristic of urban non-point source pollution and its discharge load was carried out in Neijing, Sichuan Province. Underlying surface of Neijing was divided into four categories including roof, courtyard, road, and urban water according to the hydrology effect and non-point source pollution characteristic. Several sampling spots were designed in each underlying surface for the monitoring. The results indicated that pollution concentration of major roads was highest among four categories, while that of roofs was comparatively lower. The average concentrations of COD, suspend matter, total phosphours, ammonia nitrogen and total nitrogen of major roads and roofs were215.31 mg·L-1, 280.20 mg·L-1, 0.35 mg·L-1, 2.29 mg·L-1, 4.06 mg·L-1 and 85.56 mg·L-1, 117.25 mg·L-1, 0.13 mg·L-1, 2.03 mg·L-1, 3.63 mg·L-1, respectively. Among roofs with different materials, asphalt roof had highest pollution levels, while terra-cotta one had the lowest. The average concentrations of COD, suspend matter, total phosphours, ammonia nitrogen and total nitrogen of asphalt and terra-cotta roofs were 73.4 mg·L-1, 56.0 mg·L-1, 0.181 mg·L-1, 2.529 mg·L-1, 5.254 mg·L-1 and 30.8 mg·L-1, 45.4 mg·L-1, 0.106 mg·L-1, 2.099 mg·L-1, 4.167 mg·L-1, respectively. COD load in each rainfall was in the range of 34.6~73.7 t, which equaled to urban daily sewage discharge. It was estimated that annual discharge loads of COD, suspend matter, total phosphours, ammonia nitrogen and total nitrogen were 2177.1 t, 2 778.3 t, 3.855 t, 41.410 t, 69.133 t according to three times’ the typical rainfall monitoring, Annual COD load of urban non-point source accounted for nearly 20%of city life pollution. Among the discharge loads in one typical rainfall from all underlying surfaces, that from the roofs was highest which accounted for 30.9%. The following came as courtyard, major loads, general roads and urban water, contributing 28.7%, 24.7%, 14.9% and 0.8%, respectively. The initial flush effect is most obvious on the major roads among all the underlying surfaces. The general roads came the second. The courtyard and roofs came the third and fourth. Accordingly, much attention should be paid to COD and suspend matter pollution from urban non-point sources. Different pollution characteristic exhibited in different underlying surfaces. The pollution concentration from the roofs was low, but the discharge load was high due to its large area. It is essential to take it as one of the most important urban non-point pollution sources. Interception and treatment of the initial runoff from the urban rainfall is the critical to control urban non-point pollution sources.