Li Zhiwei, Yu Di, Liu Xuejiao, Wang Yin
CAS Key Laboratory of Urban Pollutant Conversion, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China.
University of Chinese Academy of Sciences, Beijing 100049, China.
Toxics. 2023 May 9;11(5):447. doi: 10.3390/toxics11050447.
Pyrolysis is an emerging and effective means for sludge disposal. Biochar derived from sludge has broad application prospects, however, is limited by heavy metals. In this study, the fate of heavy metals (HMs) in pyrolysis coupling with acid washing treatment for sewage sludge was comprehensively investigated for the first time. Most of the HMs redistributed in the pyrolyzed residues (biochar) after pyrolysis, and the enrichment order of the HMs was: Zn > Cu > Ni > Cr. Compared with various washing agents, phosphoric acid presented a superior washing effect on most heavy metals (Cu, Zn, and Cr) in biochars derived at low pyrolysis temperature and Ni in biochars derived at high pyrolysis temperature. The optimal washing conditions for heavy metals (including Cu, Zn, Cr, and Ni) removal by HPO were obtained by batch washing experiments and the response surface methodology (RSM). The total maximum HM removal efficiency was 95.05% under the optimal washing specifications by HPO (acid concentration of 2.47 mol/L, L/S of 9.85 mL/g, and a washing temperature of 71.18 °C). Kinetic results indicated that the washing process of heavy metals in sludge and biochars was controlled by a mixture of diffusion and surface chemical reactions. After phosphoric acid washing, the leaching concentrations of HMs in the solid residue were further reduced compared with that of biochar, which were below the USEPA limit value (5 mg/L). The solid residue after pyrolysis coupling with acid washing resulted in a low environmental risk for resource utilization (the values of the potential ecological risk index were lower than 20). This work provides an environmentally friendly alternative of pyrolysis coupling with acid washing treatment for sewage sludge from the viewpoint of the utilization of solid waste.
热解是一种新兴且有效的污泥处理方法。源自污泥的生物炭具有广阔的应用前景，然而，却受到重金属的限制。本研究首次全面考察了污水污泥热解耦合酸洗处理过程中重金属的归宿。热解后，大部分重金属重新分布在热解残渣（生物炭）中，重金属的富集顺序为：锌＞铜＞镍＞铬。与各种洗涤试剂相比，磷酸对低温热解生物炭中的大多数重金属（铜、锌和铬）以及高温热解生物炭中的镍具有更好的洗涤效果。通过批量洗涤实验和响应面法（RSM）获得了磷酸去除重金属（包括铜、锌、铬和镍）的最佳洗涤条件。在磷酸最佳洗涤条件（酸浓度为2.47 mol/L，液固比为9.85 mL/g，洗涤温度为71.18℃）下，重金属的总最大去除效率为95.05%。动力学结果表明，污泥和生物炭中重金属的洗涤过程受扩散和表面化学反应的混合控制。与生物炭相比，磷酸洗涤后固体残渣中重金属的浸出浓度进一步降低，低于美国环境保护局的限值（5 mg/L）。热解耦合酸洗后的固体残渣在资源利用方面具有较低的环境风险（潜在生态风险指数值低于20）。从固体废物利用的角度来看，这项工作为污水污泥热解耦合酸洗处理提供了一种环境友好的替代方法。
