中温厌氧消化与高温厌氧消化对污泥重金属风险及稳定性的影响

通过分析中温厌氧消化+机械脱水以及热水解预处理+高温厌氧消化工艺过程中重金属含量与形态的变化，研究了中温厌氧消化与高温厌氧消化工艺对污泥重金属风险、形态及稳定性的影响.结果表明，中温厌氧消化工艺增加了污泥中Cd、Cr、Cu、Ni和Zn的含量，重金属污染等级和潜在生态风险增强.高温厌氧消化工艺降低了污泥Cd和Cr的含量，重金属污染等级和潜在生态风险降低.其中，N厂污泥主要致污染金属为Cd和Zn，S厂污泥主要致污染金属为Cd；Cd是6种重金属风险系数最高的，是污泥潜在生态危害的最大贡献者.中温厌氧消化后，污泥中Cd、Ni、Pb和Zn的可还原态和可氧化态所占质量分数之和降低；Cd、Cr、Cu和Ni的残渣态所占质量分数降低.可见，中温厌氧消化后，污泥重金属的潜在毒性和稳定态向直接毒性转化.高温厌氧消化后，污泥Cd、Cr、Cu、Pb和Zn的可交换态所占质量分数降低；Cd、Cr、Cu、Ni、Pb和Zn的残渣态所占质量分数亦降低，可见，高温厌氧消化后，重金属的直接毒性和稳定态向潜在毒性转化.

Effects of Mesophilic Anaerobic Digestion and Thermophilic Anaerobic Digestion on the Risk and Stability of Heavy Metals in Sludge

Anaerobic digestion is widely used for sewage sludge stabilization. Different anaerobic digestion methods have different impacts on the speciation and stability of heavy metals in sludge. This study investigated the response of the speciation and stability of heavy metals in sludge to the treatment of mesophilic anaerobic digestion-mechanical dewatering and thermal hydrolysis pre-treatment-thermophilic anaerobic digestion. The results showed that the process of mesophilic anaerobic digestion increased the contents of Cd, Cr, Cu, Ni, and Zn in the sludge, increasing its contamination level and potential ecological risks. In contrast, the thermophilic anaerobic digestion process increased the contents of Cd, Cr, and Pb in the sludge, reducing the level of heavy metal contamination and potential ecological risks. It was found that the main contaminated metals were Cd and Zn in Plant N and Cd in Plant S. Cd has the highest risk factor and is the highest risk contributor to the potential ecological risk of all the types of sludge. The sum of reducible and the exchangeable fractions of Cd, Ni, Pb, and Zn reduced, and the residual fraction of Cd, Cr, Cu, and Ni decreased after mesophilic anaerobic digestion. This indicated that the process of mesophilic anaerobic digestion changed the proportion of potential toxicity and steady state of the heavy metals into direct toxicity. After thermophilic anaerobic digestion, the exchangeable proportion of Cd, Cr, Cu, Pb, and Zn decreased, and the steady state of Cd, Cr, Cu, Ni, Pb, and Zn decreased. After the thermophilic anaerobic digestion process, the proportions of bio-availability and mobility of heavy metals therefore decreased, and the proportions of steady state also reduced. The potential toxicity increased.