State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
Water Res. 2022 Aug 1;221:118825. doi: 10.1016/j.watres.2022.118825. Epub 2022 Jul 5.
According to extensive in situ investigations, the microplastics (MPs) determined in current wastewater treatment plants (WWTPs) are mostly aged, with roughened surfaces and varied types of oxygen-containing functional groups (i.e., carbonyl and hydroxyl). However, the formation mechanism of aged MPs in WWTPs is still unclear. This paper systematically reviewed MP fragmentation and generation mechanisms in WWTPs at different treatment stages. The results highlight that MPs are prone to undergo physical abrasion, biofouling, and chemical oxidation-associated weathering in WWTPs at different treatment stages and can be further decomposed into smaller secondary MPs, including in nanoplastics (less than 1000 nm or 100 nm in size), suggesting that WWTPs can act as a formation source for MPs in aquatic environments. Sand associated mechanical crashes in the primary stage, microbes in active sewage sludge-related biodegradation in the secondary stage, and oxidant-relevant chemical oxidation processes (light photons, Cl, and O) in the tertiary stage are the dominant causes of MP formation in WWTPs. For MP formation mechanisms in WWTPs, external environmental forces (shear and stress forces, UV radiation, and biodegradation) can first induce plastic chain scission, destroy the plastic molecular arrangement, and create abundant pores and cracks on the MP surface. Then, the physicochemical properties (modulus of elasticity, tensile strength and elongation at break) of MPs shift consequently and finally breakdown into smaller secondary MPs or nanoscale plastics. Overall, this review provides new insights to better understand the formation mechanism, occurrence, fate, and adverse effects of aged microplastics/nanoplastics in current WWTPs.
根据广泛的现场调查，当前污水处理厂（WWTP）中确定的微塑料（MPs）大多是老化的，表面粗糙，具有不同类型的含氧官能团（即羰基和羟基）。然而，WWTP 中老化 MPs 的形成机制仍不清楚。本文系统地综述了 WWTP 不同处理阶段 MP 破碎和生成机制。结果表明，MP 在 WWTP 的不同处理阶段容易经历物理磨损、生物污垢和与化学氧化相关的风化，并进一步分解为较小的二次 MPs，包括纳米塑料（尺寸小于 1000nm 或 100nm），这表明 WWTP 可以作为水生环境中 MPs 的形成源。初级阶段与砂相关的机械崩解、二级阶段与活性污水污泥相关的生物降解中的微生物、以及三级阶段与氧化剂相关的化学氧化过程（光量子、Cl 和 O）是 WWTP 中 MP 形成的主要原因。对于 WWTP 中 MP 的形成机制，外部环境力（剪切和应力、UV 辐射和生物降解）首先会诱导塑料链断裂，破坏塑料分子排列，并在 MP 表面产生大量的孔隙和裂缝。然后，MP 的物理化学性质（弹性模量、拉伸强度和断裂伸长率）随之发生变化，最终破碎成较小的二次 MPs 或纳米级塑料。总体而言，本综述提供了新的见解，以更好地理解当前 WWTP 中老化微塑料/纳米塑料的形成机制、发生、命运和不良影响。
