施用污泥对土壤中重金属含量的影响

随着城市污水处理厂数量的迅速增加,污泥的处置及其环境影响受到越来越多的关注。污泥土地利用因具有处理费用低廉及高效性的特点,已成为重要的污泥处理方式。然而污泥中的重金属元素是限制其大规模农田利用的重要因素。施污土壤中重金属的形态研究可以用来评价土壤中重金属的生物有效性以及它们在土壤中的移动性。用修正BCR三步连续提取法进行分步提取研究了施污后的水稻田土壤中Cu、Pb、Cd、Zn的形态分布状况。与对照相比,在直接施用污泥的水稻田土壤中Cu、Pb、Cd、Zn的含量显著增加。但即使是在施污60t/hm2的土壤中,Cu、Pb、Zn的含量亦远低于中国土壤环境质量标准。在施污的水稻田土壤中4种重金属元素的形态分布规律为:残渣态>可氧化态>可还原态>可交换态和弱酸溶解态。这些重金属元素在水稻田土壤中相对稳定性顺序为Zn>Cu>Cd=Pb。

The Effect of the Application of Sludge on Content of Heavy Metal in the Soil

With the rapid increase of sewage treatment plants,the disposal and the environmental impact of sewage sludge have been paid more and more attention.Land application of sewage sludge has become an important way for sludge disposal due to its lower cost and higher efficiency.But heavy metals contained in sludge are important confined factor to sludge application on agricultural land on a large scale.The investigation of speciation of metals both in sludge-amended soil and in sludge itself may help to assess the bioavailable metal fractions and the possibility of mobilization of these metals in soil.The modified three-step sequential extraction procedure proposed by the BCR was used to predict Cu,Pb,Cd,Zn fractional distribution in rice soil amended with composted sludge.There is significant increasing on Cu,Pb,Cd,Zn contents in rice soil amended with sludge application as compared with that in the reference soil.The total contents of Cu,Pb,Zn were much lower even in soil applied with sludge at doses of 60 t/hm2 than national soil environmental standards.The fractional orders of four heavy metal elements in rice soil amended with sludge was followed:residual>oxidizable>reducible>exchangeable and weak acid soluble.The stable orders of these metals in rice soils was followed:Zn>Cu>Cd=Pb.