城市污泥重金属在高级厌氧消化工艺系统中的迁移转化及风险评价

采用改进的BCR连续提取法，研究了4座再生水厂高级厌氧消化系统中热水解和厌氧消化对污泥所含重金属(As、Cd、Cr、Cu、Hg、Ni、Pb、Zn)赋存形态的影响，并利用风险评价指数法(RAC)和潜在生态风险指数法(PERI)评估了消化产物进行土地利用时的重金属迁移风险和潜在生态风险。结果显示，4座再生水厂热水解污泥中的Cr、Cu、Pb、Ni、Cd、Zn的不稳定态向稳定态转化了0.9%~24.9%；消化污泥中Cr、Cu、Pb、Ni、Cd、Zn重金属的残渣态增加了1.0%~19.2%。RAC评价结果表明，消化污泥中重金属Cu、Hg、Pb、Cr、Cd、Zn的迁移风险指数均小于5%，处于无迁移风险或低迁移风险水平。以北京市土壤背景值和北京市大兴区土壤实测值作为参比值进行PERI评价，结果表明，消化产物中生物可利用态与潜在可利用态重金属均处于较低风险水平。高级厌氧消化有利于污泥中其它形态重金属逐渐向残渣态转化，从而降低其迁移性与生态风险。

Migration and transformation of heavy metals in sewage sludge during advanced anaerobic digestion process and risk assessment

The study was carried out to investigate the effects of thermal hydrolysis and anaerobic digestion on the form distribution of heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb, Zn) in the sludge of four reclaimed wastewater treatment plants with the modified BCR continuous extraction method. Meanwhile, the migration risk and potential ecological risk of heavy metals in the digested products for land use were evaluated by the risk assessment code (RAC) and potential ecological risk index (PERI) methods. The results showed that 0.9%~24.9% of the unstable states of Cr, Cu, Pb, Ni, Cd and Zn in the thermal-hydrolyzed sludge of four reclaimed wastewater treatment plants were transformed to the stable states. Meanwhile, the proportion of residual state of Cr, Cu, Pb, Ni, Cd and Zn in digested sludge was increased by 1.0%~19.2%. The RAC results showed that the risk indexes of heavy metals Cu, Hg, Pb, Cr, Cd and Zn in digested sludge were all less than 5%, which was at the level of no migration risk or low migration risk. Furthermore, with the background value of Beijing soil and the measured value of Daxing District soil in Beijing as reference values, the PERI results showed that the bioavailable and potentially available heavy metals in digested products were at a lower risk level. These results indicated that advanced anaerobic digestion process was conducive to the gradual transformation of other forms of heavy metals to the residual state, reducing their mobility and ecological risk.