剩余污泥厌氧消化过程重金属形态转化及生物有效性分析

Analysis of Chemical Speciation and Bioavailability of Heavy Metals in Waste Activated Sludge During Anaerobic Digestion

为研究污泥厌氧消化过程中物理化学性质的变化对典型重金属形态转化的影响,对其农用的可行性及生物有效性进行评估,对取自某城市污水处理厂的剩余污泥进行了序批式厌氧消化实验,在试验过程中测定了污泥理化学性质,采用Tessier分步提取法提取了污泥样品中的典型重金属,并采用电感耦合等离子发射光谱仪(ICP-OES)测定各形态重金属含量及总量。结果表明,厌氧消化过程中重金属的形态发生了显著变化,由不稳定态向比较稳定的残渣态和有机结合态转变,某些重金属形态与污泥理化性质如pH、碱度、VS/TS及氨氮显著相关。厌氧消化可以有效地降低污泥中重金属的潜在迁移能力和生物有效性,经厌氧消化后污泥可以更好地进行土地利用。

The major limitation of land application of sewage sludge is the total heavy metal contents and their bioavailability to the soil-plant system. This study was conducted to determine the heavy metal speciation and the influence of changing the physical-chemical properties of the medium in the course of anaerobic digestion on the concentrations, bioavailability or chemical forms of Cu, Zn, Cr and Ni in sewage sludge.Principal physical and chemical properties of sewage sludge during anaerobic digestion were investigated. The total metal contents in digested sludge were higher than that in raw sludge but lower than the limit values of land application. Furthermore, it was observed by using Tessier sequential extraction procedure in sludge during anaerobic digestion that heavy metal distribution and bioavailability show some changes depending on the metal itself and the physical-chemical properties of the medium. Bioavailable fractions of all elements tend to de- crease. Cu and Cr present more affinity to organic and residual fractions, while Zn and Ni seem to be preferentially bound to all fractions ex- cept exchangeable. Significant degrees of correlation were found between certain heavy metal fractions and changes of some selected vari- ables（e.g, pH, VS/TS, alkalinity and ammonia） during the course of anaerobic digestion.