硫化物对城市污泥中重金属的形态分布与生物有效性影响

以合肥市某污水处理厂污泥为研究对象,研究了Na_2S、(NH_4)_2S改良剂对污泥重金属形态、生物有效性的影响。结果表明:硫化物改良剂可以提高污泥pH值,添加Na_2S和(NH_4)_2S改良剂后的污泥pH值比对照pH值最大升高分别为3.1和1.0;改良剂对污泥中重金属Cu、Zn、Cd、As均有显著钝化作用,利用Tessier连续提取法分析污泥重金属化学形态,2种改良剂均有效降低了污泥中重金属可交换态的质量比,使其向碳酸盐结合态、铁锰氧化物结合态等稳定态转化,可交换态Zn、Cd比对照最大降低程度分别达98.8%和98.6%;硫化物处理显著降低了污泥中重金属有效态质量比,硫化物添加量越多,重金属有效态降低幅度越大,其中对有效态Cu、Cd的作用效果更为明显,Cu、Cd有效态最大降低幅度分别为87.3%、52.6%;T3型发光菌发光量试验表明,添加硫化物改良剂后污泥中重金属毒性降低;盆栽试验结果显示,硫化物钝化污泥后青菜地上部和根部重金属积累量大大降低,地上部As、Cd、Cu、Zn最大降低量分别为51.6%、31.2%、17.5%、20.7%,根部As、Cd最大降低程度分别为19.5%、58.1%。

Effect of the sulfide amendment on the speciation distribution and bioavailability of heavy metals in municipal sludge

The article is intended to make an investigation of the effects of the sulfide amendment on the speciation distribution and bioavailability of heavy metals in the municipal sludge treating methods by taking Hefei City Sewage Plant as a case study sample.For this purpose,we have investigated Na2S and(NH4)2S for their effects of amendment on the above mentioned distribution and bioavailability of the heavy metals in the sludge.The results of our investigation have shown that it is possible and useful to raise the pH value of sludge by adding sulfide,for the effect of Na2S treatment on the pH value turns to be greater than that of (NH4)2S.As compared with the control group,the pH units of the sludge in treating Na2S and(NH4)2S has increased to 3.1 and 1.0,respectively.What is more,the sulfide amendment has made significant retardation effect on the heavy metals of Cu,Zn,Cd,and As in the sludge.Based on the study of the heavy metal distribution regularity and the chemical speciation by Tessier sequential extraction procedure,we have managed to reduce the exchangeable content of the heavy metals in the sludge and increased the carbonate bound and the status in-situ of the iron manganese oxide of the heavy metals when Na2S and (NH4)2S were added to the sludge.The exchangeable contents of Zn and Cd in the sulfide treatment have thus maximally been reduced by the rates of 98.8％ and 98.6％,respectively,as compared with the controlled group.Thus,it can be seen that the sulfide amendment we have done proves to have significantly reduced the available content status in situ of the heavy metals in the sludge,with the result that,with the increase of the sulfide addition,the existing content of the heavy metals in the soil has been diminished.The retardation effect for sulfide treatment on the content of Cu,Cd in the sludge proves more significantly than on the contents of other heavy metals with the fact that the maximum reduction rates for Cu and Cd turn to get by the respective rates of 87.3％ and 52.6％,while the available content of heavy metals proves to be negatively correlated with the dosage of sulfide.Furthermore,the tests for the toxicity of the heavy metals to Photobacterium phosphoreum T3 also suggest that the sulfide amendment can also help to alleviate the toxicity of the heavy metals in the sludge.The results of the pot experiments we have done also indicate that the accumulation of heavy metals in the upper level and in the roots of Brassica chinensis L.has also promoted the reduction of the sulfide amendment to the sludge.For example,the contents of Cu and Cd in the roots have been found maximally reduced to the respective rates of 19.5％ and 58.1％,whereas those of As,Cd,Cu and Zn in the upper level had maximally reduced by 51.6％,31.2％,17.5％ and 20.7％,respectively.