Saffari Mahboub, Moazallahi Masomeh, Mashayekhi Rezvan
Department of Environment, Institute of Science and High Technology and Environmental Sciences, Graduate University of Advanced Technology, Kerman, Iran.
Institute of Science and High Technology and Environmental Sciences, Graduate University of Advanced Technology, Kerman, Iran.
Sci Rep. 2025 Jan 23;15(1):2986. doi: 10.1038/s41598-025-87169-3.
Co-pyrolysis is an efficient approach for municipal sewage sludge (SS) treatment, facilitating the production of biochar and promoting the stabilization and removal of heavy metals, particularly when combined with chlorinated materials. This study explores the impact of pyrolysis temperatures (400 °C and 600 °C) and chlorinated additives (polyvinyl chloride (PVC) as an organic chloride source and ferric chloride (FeCl) as an inorganic chloride source) at 10% and 20% concentrations, on the yield, chemical speciation, leachability, and ecological risks of arsenic (As), chromium (Cr), and zinc (Zn) in biochar derived from SS. The results revealed that increasing the pyrolysis temperature from 400 to 600 °C significantly reduced biochar yield due to enhanced volatilization of organic components, as well as the removal of heavy metals in interaction with chlorinated materials. Chlorinated additives distinctly influenced heavy metal behavior. PVC treatments at 600 °C effectively reduced the total concentrations of As and Zn by 60% and 88.3%, respectively, while FeCl reduced Cr concentrations by up to 72.5%. Chemical speciation analysis showed that PVC treatments increased the residual fractions of As and Zn, reducing their bioavailability and environmental risk. In contrast, FeCl promoted the transformation of Cr into oxidizable fractions, enhancing its stability. TCLP results confirmed the effectiveness of both additives in reducing heavy metal leachability, with PVC at 600 °C demonstrating superior performance for As and Zn, and FeCl excelling in Cr stabilization. Ecological risk index assessments revealed that PVC treatments consistently resulted in lower RI values at both temperatures and concentrations, keeping them below the low-risk threshold. In contrast, FeCl treatments exhibited elevated risk levels, especially at higher concentrations and temperatures, reaching moderate to considerable risk categories. Overall, PVC treatment at 600 °C proved to be the most effective strategy for reducing As and Zn leachability and enhancing biochar stability. While FeCl demonstrated better performance in Cr stabilization, these findings highlight the importance of selecting appropriate chlorinated additives based on the target heavy metal for optimizing biochar production and minimizing environmental impacts effectively.
共热解是一种处理城市污水污泥（SS）的有效方法，有助于生物炭的生产，并促进重金属的稳定化和去除，特别是与含氯材料结合使用时。本研究探讨了热解温度（400℃和600℃）以及浓度为10%和20%的含氯添加剂（作为有机氯源的聚氯乙烯（PVC）和作为无机氯源的氯化铁（FeCl））对SS衍生生物炭中砷（As）、铬（Cr）和锌（Zn）的产量、化学形态、浸出性和生态风险的影响。结果表明，将热解温度从400℃提高到600℃会显著降低生物炭产量，这是由于有机成分挥发增强以及与含氯材料相互作用导致重金属去除。含氯添加剂对重金属行为有明显影响。在600℃下进行PVC处理分别有效降低了As和Zn的总浓度60%和88.3%，而FeCl使Cr浓度降低了72.5%。化学形态分析表明，PVC处理增加了As和Zn的残留分数，降低了它们的生物可利用性和环境风险。相比之下，FeCl促进了Cr向可氧化态的转化，提高了其稳定性。毒性特征浸出程序（TCLP）结果证实了两种添加剂在降低重金属浸出性方面的有效性，600℃下的PVC对As和Zn表现出卓越性能，而FeCl在Cr稳定化方面表现出色。生态风险指数评估表明，在两个温度和浓度下，PVC处理始终导致较低的风险指数（RI）值，使其低于低风险阈值。相比之下，FeCl处理表现出较高的风险水平，特别是在较高浓度和温度下，达到中度至相当高的风险类别。总体而言，600℃下的PVC处理被证明是降低As和Zn浸出性以及提高生物炭稳定性的最有效策略。虽然FeCl在Cr稳定化方面表现更好，但这些发现凸显了根据目标重金属选择合适的含氯添加剂以优化生物炭生产并有效最小化环境影响的重要性。
