Wastewater treatment plants (WWTPs) efficiently retain microplastic particles (MPs) generated within urban areas. Among the wastewater treatment steps, disinfection has not been characterized for its potential MPs retention activity, although it has been reported that processes used to abate the bacterial load could also affect MPs concentration. For this reason, we evaluated the MPs concentration across the overall wastewater treatment process and before and after the disinfection step in four small/medium WWTPs located in the north of Italy. Most of the MPs found in the samples were fibers or fragments, smaller than 500 μm, mainly composed of polyethylene, polypropylene, or polyethylene terephthalate. The retention efficiency at the outlets was higher than 94% in all the plants analyzed. More interestingly, the disinfection treatments adopted by the different WWTPs reduced MPs concentration from a minimum of 9.1% (UV treatment) to a maximum of 67.6% (chlorination), promoting a further increase of the overall retention efficiency of the WWTPs from 0.4 to 0.7%. Quantitatively, the disinfection contributes to the MPs reduction in the outlets by retaining 0.5–6.7 million MPs per day, in WWTPs that discharge 2.7–12 million MPs per day. The results of the present work underline the importance of a careful choice of the steps that constitute the wastewater treatment, including disinfection, in order to minimize MPs discharge into the natural ecosystems.

污水处理厂 (WWTP) 有效地保留了城市地区产生的微塑料颗粒 (MP)。在废水处理步骤中，消毒尚未因其潜在的 MPs 保留活性而被表征，尽管据报道，用于减少细菌负荷的过程也可能影响 MPs 浓度。出于这个原因，我们评估了位于意大利北部的四个中小型污水处理厂在整个废水处理过程中以及消毒步骤前后的 MPs 浓度。样品中发现的大多数 MPs 是纤维或碎片，小于 500 μm，主要由聚乙烯、聚丙烯或聚对苯二甲酸乙二醇酯组成。在所分析的所有工厂中，出口处的保留效率均高于 94%。更有趣的是，不同污水处理厂采用的消毒处理将 MPs 浓度从最低 9.1%（紫外线处理）降低到最高 67.6%（氯化处理），促进污水处理厂的整体截留效率从 0.4% 进一步提高到 0.7%。从数量上看，在每天排放 27-1200 万个 MPs 的污水处理厂中，消毒通过每天保留 5-670 万个 MPs 有助于减少出口的 MPs。目前工作的结果强调了仔细选择构成废水处理（包括消毒）的步骤的重要性，以尽量减少 MPs 排放到自然生态系统中。4% 到 0.7%。从数量上看，在每天排放 27-1200 万个 MPs 的污水处理厂中，消毒通过每天保留 5-670 万个 MPs 有助于减少出口的 MPs。目前工作的结果强调了仔细选择构成废水处理（包括消毒）的步骤的重要性，以尽量减少 MPs 排放到自然生态系统中。4% 到 0.7%。从数量上看，在每天排放 27-1200 万个 MPs 的污水处理厂中，消毒通过每天保留 5-670 万个 MPs 有助于减少出口的 MPs。目前工作的结果强调了仔细选择构成废水处理（包括消毒）的步骤的重要性，以尽量减少 MPs 排放到自然生态系统中。