Dewatering is an indispensable link in sludge treatment, but its effect on the microplastics (MPs) remains inadequately understood. This study investigated the physicochemical changes and leaching behavior of MPs during the mechanical dewatering of sludge, as well as the impact of MP leachates on activated sludge (AS). After sludge dewatering, MPs exhibit rougher surfaces, decreased sizes and altered functional groups due to the addition of dewatering agents and the application of mechanical force. Meanwhile, plastic additives, depolymerization products, and derivatives of their interactions are leached from MPs during sludge dewatering process. The concentration of MP-based leachates in sludge is 2–25 times higher than that in water. The enhancement of pH and ionic strength caused by dewatering agents induces the release of MP leachates enriched with protein-like, fulvic acid-like, and soluble microbial by-product-like substances. The reflux of MP leachates in sludge dewatering liquor to the wastewater treatment system negatively impacts AS, leading to a decrease in COD removal rate and inhibition of the extracellular polymeric substances secretion. More importantly, MP leachates cause oxidative stress to microbial cells and alter the microbial community structure of AS at the phylum and genus levels. These findings confirm that MPs undergo aging and leaching during sludge dewatering process, and MP leachates may negatively affect the wastewater treatment system.

中文翻译：

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污泥机械脱水过程中微塑料的浸出行为及其对活性污泥的影响


脱水是污泥处理中不可或缺的环节，但人们对其对微塑料 （MP） 的影响仍不充分。本研究调查了污泥机械脱水过程中 MPs 的物理化学变化和浸出行为，以及 MP 渗滤液对活性污泥 （AS） 的影响。污泥脱水后，由于添加脱水剂和施加机械力，MP 表面更粗糙，尺寸减小，官能团发生变化。同时，塑料添加剂、解聚产物及其相互作用的衍生物在污泥脱水过程中从 MP 中浸出。污泥中 MP 基渗滤液的浓度比水中高 2-25 倍。脱水剂引起的 pH 值和离子强度的增强会诱导释放富含蛋白质样、黄腐酸样和可溶性微生物副产品样物质的 MP 渗滤液。污泥脱水液中 MP 渗出液回流到废水处理系统对 AS 产生负面影响，导致 COD 去除率降低并抑制细胞外聚合物物质的分泌。更重要的是，MP 渗滤液对微生物细胞造成氧化应激，并在门和属水平上改变 AS 的微生物群落结构。这些发现证实，MP 在污泥脱水过程中会发生老化和浸出，MP 渗滤液可能会对废水处理系统产生负面影响。