重庆市城市污泥中的重金属及其农用环境容量

Content,speciation of heavy metal in sewage sludge and its environmental capacity for agricultural use in Chongqing

城市污泥农用的环境风险取决于城市污泥中的污染物含量及土壤理化性质。该文分析了重庆市10个城市污水处理厂污泥中的Cu,Zn,Pb和Cd含量及形态,根据土壤环境容量及氮肥施用量计算了重庆主要旱地土壤的最大施用量和年施用量。结果表明,重庆市城市污泥中的Zn、Cu、Pb和Cd含量分别为362.12～725.32mg/kg,69.84～170.22mg/kg,21.25～107.24mg/kg和1.26～4.25mg/kg。污泥中不稳定态Zn、Cu、Pb和Cd的比例分别为42.89%～44.74%,2.69%～9.45%,0.95%～12.06%和61.05%～79.91%。根据土壤重金属的静态容量,计算出重庆主要旱地土壤紫色土和黄壤城市污泥的一次性最高施用量分别为384.62t/hm2和98.90t/hm2。根据土壤重金属动态容量,以15、20、50为年限,计算出的城市污泥的年施用量,紫色土为66.10,60.91和55.71t/(hm2·a),黄壤为30.32,28.99和27.53t/(hm2·a)。根据作物的需氮量计算城市污泥的年施用量为3.04～6.40t/(hm2·a),该施用量低于根据土壤环境的动态容量计算的施用量,按此用量施用城市污泥更安全。

The environmental risks for agricultural use of sewage sludge depend on the contents of pollutants in sewage sludge and the properties of soils. Sewage sludge was collected from ten urban wastewater treatment plants located in Chongqing. The contents and distributions of Cu, Zn, Pb and Cd were analyzed. The maximum application rates and annual application rates of sewage sludge were calculated on the basis of soil environmental capacity and the application of nitrogen fertilizer. The results showed that the contents of Zn,Cu, Pb and Cd were 362.12--725.32 mg/kg, 69.84--170.22 mg/kg, 21.25--107.24 mg/kg and 1.26--4.25 mg/kg, respectively. The proportions of unstable Zn, Cu, Pb and Cd in sewage sludge were 42.89%--44.7%, 2.69%--9.45%, 0.95%--12.06% and 61.05%--79.91%, respectively. According to the static environment capacity, the maximum application rates of sewage sludge were 384.62 t/hm^2 for purple soil and 98.90 t/hm^2 for yellow soil. The annual application rates calculated on the dynamic environment capacity were 66.10, 60.91 and 55.71 t/hm^2 for a 15, 20 and 50 application year terms for purple soil, respectively, and were 30.32, 28.99 and 27.53 t/hm^2 for a 15, 20 and 50 application year terms for yellow soil. The annual application rate of sewage sludge calculated on nitrogen fertilizer application was 3.04--6.40 t/（hm^2.a）, which is safer due to the lower heavy metal input than that calculated on the dynamic environment capacity.