城市垃圾焚烧发电项目烟气中重金属干沉降对土壤的影响

Influence of heavy metal dry deposition on soil in flue gas of municipal solid waste incineration power generation project

焚烧炉烟气中重金属沉降造成的土壤污染是城市垃圾焚烧发电项目环境影响评价及环境保护管理工作关注的重点。以某城市垃圾焚烧发电项目为例,在确定焚烧炉排放源强及气象数据等资料的基础上,采用AERMOD模型预测焚烧烟气中Pb、Hg、Cd的沉降特征和对项目所在区域土壤环境质量的影响。结果表明:土壤中污染物浓度随离源距离的增加均呈现出先上升后下降的趋势,其中Hg的占标率最大为27.2%,其次Cd为21.8%,Pb的占标率最小为4.7%,预测的重金属浓度均满足《土壤环境质量标准》(GB 15618—1995)二级标准限值要求;污染物分布与风密切相关,利用污染系数衡量风对污染物扩散传输的影响,可知污染扩散距离北向大于南向、东向大于西向,南北向大于东西向,污染系数与污染物沉降量分布一致。研究可为气体涉重金属污染物扩散沉降对土壤环境影响相关领域的科研、应用工作提供参考和借鉴。

Background,aim,and scope Soil pollution caused by heavy metal deposition in flue gas of incinerator from municipal solid waste incineration power generation project is the focus of environmental impact assessment and environmental protection management.Materials and methods A municipal solid waste incineration project was selected as an example.Based on determining the incinerator emission intensity and meteorological data,the AERMOD was used to predict the settlement characteristics of Pb,Hg and Cd in incineration flue gas and the influence on the soil environmental quality in the area of the project.Results The cumulative concentrations of Pb,Hg,Cd were 16.35 mg.kg^-1,0.2720 mg.kg^-1,0.1310 mg.kg^-1 and the corresponding concentration standard rates were 4.7%,27.2%,21.8%respectively.The annual settlement of Pb,Hg,Cd in the downwind direction all increased first and then decreased with the distance from the source and the corresponding peaks were 8.06 mg.m^-2(d=400 m),0.13 mg.m^-2(d=400 m),0.04 mg.m^-2(d=300-500 m).The pollution coefficient which was related to wind direction,wind frequency,wind speed was used to measure the influence of wind on the diffusion of pollutants,and the larger pollution coefficient meant the farther distance of corresponding equal settlement.Pollution coefficient was greater in the south than in the north,the west was greater than the east and the north-south was greater than the east-west.Discussion Although the cumulative concentrations of Pb,Hg,Cd all met the secondary standard limits of Soil Environmental Quality Standard for Soils(GB 15618-1995),it should be paid attention to in view of its harmfulness.The settlement of pollutants increased first and then decreased with distance from the source.The distribution of pollutants had a good consistency with the pollution coefficient.The pollution diffusion distance of the north was greater than that of the south,the east was greater than the west and the north-south was greater than the east-west.Conclusions Heavy metal in incineration flue gas from municipal solid waste incineration power generation project would enter the soil with atmospheric deposition.Therefore,predictions on the impact of heavy metal deposition on the soil environment was necessary when carrying out environmental impact assessment of such projects.In this research,the relevant departments should pay attention to the emission of pollutants from waste incineration especially Hg and Cd,although the sedimentation of heavy metal pollutants in incineration flue gas had not exceeded the standard.Recommendations and perspectives This research would provide reference for the research and application work related to effects of gas with heavy metal pollutants on soil environment.