School of Environmental and Chemical Engineering, Organic Compound Pollution Control Engineering, Ministry of Education, Shanghai University, Shanghai 200444, PR China.
School of Environmental and Chemical Engineering, Organic Compound Pollution Control Engineering, Ministry of Education, Shanghai University, Shanghai 200444, PR China.
Water Res. 2022 Aug 15;222:118876. doi: 10.1016/j.watres.2022.118876. Epub 2022 Jul 17.
Sewage sludge is an important source for microplastics (MPs) entering into environment. Hydrothermal treatment has been considered a promising method for reducing MPs in sewage sludge. However, MPs degradation characteristics and mechanism during sludge hydrothermal treatment are not fully understood. In the study, three common MPs, i.e. polyethylene (PE), polystyrene (PS) and polyethylene terephthalate (PET) were used to explore the effect of hydrothermal treatment on the properties of MPs in sewage sludge. The hydrothermally-treated (HT) MPs in sludge feature more broken and rougher surfaces with higher O-containing functional groups in the sludge than those in water. The dissolved leachates from the HT MPs in the sludge show higher concentrations than the counterparts, implying that certain components in sludge serve to promote the MP degradation and leaching during hydrothermal treatment. Three model components in the sludge, including protein, carbohydrate, and SiO, were further investigated for their individual effects on the hydrothermal degradation of MPs. Compared with those in water, the HT MPs in the protein and carbohydrate solutions show greater changes in the surface micro-morphologies and carbonyl index, and generate more leachates. However, the SiO solution results in similar difference in the MPs changes with the water solution, indicating that organic components of sludge play a more critical role in the enhanced MPs hydrothermal degradation than inorganic components. The HT PET leads to more pronounced changes in the physicochemical and leaching characteristics than the HT PE and PS, possibly due to more susceptible hydrolysis of the PET. Hydrothermal degradation of the MPs is found to be mainly driven by depolymerization of the polymer and leaching of the plastics additives. The findings imply that the sludge organic components significantly promote the MPs aging and degradation during hydrothermal treatment, and potential changes in the environmental risk of the treated MPs upon their subsequent land applications.
污水污泥是进入环境的微塑料（MPs）的重要来源。热水处理被认为是减少污水污泥中 MPs 的一种很有前途的方法。然而，污泥热水处理过程中 MPs 的降解特性和机制尚不完全清楚。在这项研究中，使用了三种常见的 MPs，即聚乙烯（PE）、聚苯乙烯（PS）和聚对苯二甲酸乙二醇酯（PET），来探索热水处理对污泥中 MPs 特性的影响。与水中的 MPs 相比，污泥中 HT-MPs 的表面更破碎、更粗糙，且含有更多的含氧官能团。污泥中 HT-MPs 的溶解浸出液的浓度高于水中的 MPs，这表明污泥中的某些成分有助于促进 MP 在热水处理过程中的降解和浸出。进一步研究了污泥中的三种模型成分，包括蛋白质、碳水化合物和 SiO2，以研究它们各自对 MPs 热水降解的影响。与水中的 MPs 相比，蛋白质和碳水化合物溶液中的 HT-MPs 的表面微观形貌和羰基指数变化更大，且浸出液更多。然而，SiO2 溶液对 MPs 变化的影响与水相似，这表明污泥中的有机成分比无机成分在增强 MPs 热水降解方面发挥更关键的作用。与 HT-PE 和 PS 相比，HT-PET 导致 MPs 的物理化学和浸出特性发生更显著的变化，这可能是由于 PET 更易发生水解。MPs 的热水降解主要是由聚合物的解聚和塑料添加剂的浸出驱动的。研究结果表明，污泥中的有机成分在热水处理过程中显著促进了 MPs 的老化和降解，以及处理后的 MPs 在随后的土地应用中环境风险的潜在变化。
