污泥富磷堆肥前后重金属赋存形态及释放能力变化

Changes in Heavy Metal Speciation and Release Behavior Before and After Sludge Composting Under a Phosphate-rich Atmosphere

市政污泥富含有机质和N、P等营养元素,经堆肥稳定化处理后可成为矿山废弃地复垦的良好基质,但市政污泥中含有的重金属成为限制其土地利用的主要瓶颈.以磷尾矿为辅料进行污泥堆肥处理,既可利用其中磷酸盐固定市政污泥中的重金属,又可实现磷尾矿和市政污泥的协同资源化利用.以磷尾矿渣为辅料,采用高温好氧堆肥工艺,研究污泥堆肥前后重金属As、Cr、Cu、Ni、Pb、Cd和Zn的赋存形态以及不同pH条件下的重金属浸出特性,探讨污泥富磷堆肥处理对堆肥中重金属迁移转化的影响.结果表明,污泥添加磷尾矿渣经过堆肥处理,促进了重金属由不稳定形态向稳定形态转化,降低了重金属在土壤自然pH范围(6~8)内及强碱性条件下的潜在释放风险,有利于污泥的土地利用.

Sewage sludge is rich in organic matter,N,and P and could be used as a soil amendment to improve the status of soil organic matter,soil structural characteristics,and soil water retention capacity after aerobic composting.However,heavy metals in sewage sludge have become the main bottleneck limiting its land application.In addition,with the large-scale exploitation of phosphate rock resources in our region of interest,a large amount of phosphate tailings needs to be disposed and a large area of abandoned mining lands needs to be reclaimed.Phosphate tailings could be auxiliary materials for sewage sludge composting to immobilize heavy metals,and the compost could be applied for revegetation of the abandoned mining lands.The contents of As,Cr,Cu,Ni,Pb,Cd,and Zn were measured,and a successive extraction procedure was used to investigate the change in speciation of heavy metals in the sludge before and after the phosphate-rich composting.pH-dependent leaching tests were carried out to further evaluate the immobilization effects of composting on heavy metals and the release potential under different pH conditions.The results showed that the contents of heavy metals in the compost satisfied the corresponding threshold for land reclamation.Adding phosphate tailings greatly improved the stability of heavy metals during the composting process.The portion of stable residues of Pb,Cd,As,and Zn in the phosphate-rich compost was 84.00%,58.00%,68.50%,and 30.93%,respectively,compared with 68.10%,30.50%,40.32%,and 16.48%for the control,compost without adding the phosphate tailings.Meanwhile,the maximum leaching potential of As,Ni,Pb,Zn,and Cu in the phosphate-rich compost decreased from 3.692 mg·kg（-1）,0.903 mg·kg（-1）,0.217 mg·kg（-1）,7.225 mg·kg（-1）,and 8.725 mg·kg（-1） to 0.684 mg·kg（-1）,0.586 mg·kg（-1）,0.071 mg·kg（-1）,2.603 mg·kg（-1）,and 6.935 mg·kg（-1） in the control,respectively,for pH 6-8.It could be concluded that the addition of phosphate tailings in the sludge composting lowered the risk of heavy metals in sewage sludge compost to make it favorable for beneficial use in abandoned mining land reclamation.