Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, P. R. China.
College of Grassland, Resources, and Environment, Inner Mongolia Agricultural University, Hohhot 010018, P. R. China.
Environ Sci Technol. 2024 Sep 10;58(36):16186-16195. doi: 10.1021/acs.est.4c04266. Epub 2024 Aug 27.
Metal(loid)s in sewage sludge (SS) are effectively immobilized after pyrolysis. However, the bioavailability and fate of the immobilized metal(loid)s in SS-derived biochar (SSB) following land application remain largely unknown. Here, the speciation and bioavailability evolution of SSB-borne Cr and Zn in soil were systematically investigated by combining pot and field trials and X-ray absorption spectroscopy. Results showed that approximately 58% of Cr existing as Cr(III)-humic complex in SS were transformed into Fe (hydr)oxide-bound Cr(III), while nano-ZnS in SS was transformed into stable ZnS and ferrihydrite-bound species (accounting for over 90% of Zn in SSB) during pyrolysis. All immobilized metal(loid)s, including Cr and Zn, in SSB tended to be slowly remobilized during aging in soil. This study highlighted that SSB acted as a dual role of source and sink of metal(loid)s in soil and posed potential risks by serving a greater role of a metal(loid) source than a sink when applied to uncontaminated soils. Nevertheless, SSB could impede the translocation of metal(loid)s from soil to crop compared to SS, where coexisting elements, including Fe, P, and Zn, played critical roles. These findings provide new insights for understanding the fate of SSB-borne metal(loid)s in soil and assessing the viability of pyrolyzing SS for land application.
在热解后，污水污泥（SS）中的金属（类）物质被有效地固定。然而，在土地应用后，SS 衍生生物炭（SSB）中固定的金属（类）物质的生物有效性和归宿仍然很大程度上未知。在这里，通过结合盆栽和田间试验和 X 射线吸收光谱，系统地研究了 SSB 携带的 Cr 和 Zn 在土壤中的形态和生物有效性演变。结果表明，SS 中约 58%的以 Cr(III)-腐殖质络合物形式存在的 Cr 被转化为 Fe（氢）氧化物结合的 Cr(III)，而 SS 中的纳米 ZnS 则在热解过程中转化为稳定的 ZnS 和铁氢氧化物结合的物质（占 SSB 中 Zn 的 90%以上）。在土壤老化过程中，所有固定的金属（类）物质，包括 Cr 和 Zn，在 SSB 中都倾向于缓慢地重新释放。本研究强调，SSB 在土壤中既是金属（类）物质的源又是汇，当应用于未污染的土壤时，它作为金属（类）物质源的作用大于作为汇的作用，从而构成潜在的风险。然而，与 SS 相比，SSB 可以阻止金属（类）物质从土壤向作物的迁移，其中共存的元素，包括 Fe、P 和 Zn，发挥了关键作用。这些发现为理解 SSB 携带的金属（类）物质在土壤中的归宿以及评估热解 SS 用于土地应用的可行性提供了新的见解。
