JINXiao,WUYun-sheng,YINZheng-yi,et al.Heavy Metal Speciation Transformation and Ecological Risk Assessment in a Sludge Pyrolysis and Carbonization Project[J].China Water & Wastewater,2025,41(19):60-65.
污泥热解炭化工程重金属形态变化及生态风险评价
- Title:
- Heavy Metal Speciation Transformation and Ecological Risk Assessment in a Sludge Pyrolysis and Carbonization Project
- Keywords:
- sludge pyrolysis and carbonization; heavy metal; speciation transformation; ecological risk assessment
- 摘要:
- 以某市政污泥热解炭化工程中的脱水污泥和污泥炭产物为研究对象，对炭化过程中Cd、Cr、Pb、Ni、Zn、Cu、As、Hg等8种重金属的总量及形态（弱酸提取态F1、可还原态F2、可氧化态F3和残渣态F4）迁移转化特征进行分析，并采用风险评价准则法（RAC）对重金属生态风险等级进行评价。结果表明，脱水污泥和污泥炭中8种重金属的总量均未超过现行国家标准限值，热解炭化过程对污泥中重金属Cr、Pb、Ni、Zn、Cu、As有不同程度的富集作用。该工程采用中高温热解炭化（550~650 ℃），可以促使重金属从较高生物有效性形态（F1、F2）迁移转化为较高稳定性形态（F3、F4），污泥炭中重金属的F3+F4形态占比高低顺序为CrPbNiCuZnAs≈CdHg，其中Cr、Pb、Ni、Cu的F3+F4形态占比高达94%以上，Zn的F3+F4形态占比显著增加至87.09%，As和Cd的F3+F4形态占比在84%左右。RAC风险评价结果表明，脱水污泥中重金属Zn和Cd的潜在生态风险等级较高，而污泥炭中重金属均已呈现为低风险或无风险等级（As、Hg除外），污泥炭的合法合规资源化利用基本没有潜在的环境风险。
- Abstract:
- This study analyzed the migration and transformation characteristics of eight heavy metals (Cd, Cr, Pb, Ni, Zn, Cu, As, and Hg) from the dewatered sludge and its derived carbonized products during the carbonization process of a municipal sludge pyrolysis and carbonization project, with a focus on both their total contents and chemical forms (weak acid extractable fraction F1, reducible fraction F2, oxidizable fraction F3, and residual fraction F4). The risk assessment code (RAC) method was employed to evaluate the ecological risks associated with these heavy metals. The total contents of eight heavy metals in dewatered sludge and sludge-based biochar (SBB) did not exceed the permissible limits specified by the current national standards. The pyrolysis and carbonization process resulted in varying degrees of enrichment of the heavy metals Cr, Pb, Ni, Zn, Cu, and As present in the sludge. This project employed medium-and high-temperature pyrolysis and carbonization (550-650 ℃), which facilitated the migration and transformation of heavy metals from high bioavailable fractions (F1 and F2) into relatively stable forms (F3 and F4). The decreasing order of the proportion of F3 and F4 forms of heavy metals in SBB was as follows: Cr, Pb, Ni, Cu, Zn, As/Cd, and Hg. Specifically, the proportions of F3 and F4 forms for Cr, Pb, Ni, and Cu exceeded 94%, while that of Zn increased significantly to 87.09%. The proportions of F3 and F4 forms for As and Cd were approximately 84%. The results of RAC indicated that the heavy metals Zn and Cd in dewatered sludge exhibited relatively high potential ecological risk levels, whereas the heavy metals present in SBB were predominantly categorized as low?risk or non?risk, with the exception of As and Hg. Therefore, the legal and compliant utilization of SBB is unlikely to pose significant environmental risks.
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