Retention of microplastics (MPs) at the third largest wastewater treatment plant (WWTP) in Sweden was investigated. The plant is one of the most modern and advanced of its kind, with rapid sand filter for tertiary treatment in combination with mechanical, biological, and chemical treatment. It achieved a significantly high treatment efficiency, which brought the MP concentration in its discharge on par with concentrations measured in marine waters of the same region. This novel data shows that properly designed modern WWTPs can reduce the MP content of sewage down to background levels measured in the receiving aquatic environment. Opposite to current understanding of the retention of MP by WWTPs, a modern and well-designed WWTP does not have to be a significant point source for MP. MPs were quantified at all major treatment steps, including digester inlet and outlet sludge. MPs sized 10–500 µm were analyzed by a focal plane array based micro-Fourier transform infrared (FPA-µFTIR) microscopy, a hyperspectral imaging technique, while MPs above 500 µm were analyzed by Attenuated Total Reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Mass was estimated from the hyperspectral images for MPs <500 µm and from microscope images >500 µm. The overall treatment efficiency was in terms of MP counts 99.98 %, with a daily input of 6.42 × 10 and output of 1.04 × 10 particles. The mass removal efficiency was 99.99 %. The mechanical part of the treatment, the pre-treatment, and primary stages, reduced both the MP counts and mass by approximately 71 %. The combined biological treatment, secondary settling, and final polishing with rapid sand filtration removed nearly all the remaining 29 %. MPs became successively smaller as they passed the different treatment steps. The digester inlet received 1.04 × 10 MPs daily, while it discharged 9.96 × 10 MPs, causing a small but not significant decrease in MP counts, with a corresponding MP mass reduction of 9.56 %.

中文翻译：

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将废水中的微塑料处理至与附近海水相当的水平

对瑞典第三大废水处理厂 (WWTP) 的微塑料 (MP) 滞留情况进行了调查。该工厂是同类工厂中最现代化、最先进的工厂之一，采用快速砂滤器进行三级处理，结合机械、生物和化学处理。它实现了显着高的处理效率，使其排放中的 MP 浓度与同一地区海水中测量的浓度相当。这一新颖的数据表明，正确设计的现代污水处理厂可以将污水中的 MP 含量降低至接收水生环境中测得的背景水平。与目前对污水处理厂保留 MP 的理解相反，现代化且设计良好的污水处理厂不一定是 MP 的重要点源。对所有主要处理步骤（包括消化池入口和出口污泥）的 MP 进行了量化。尺寸为 10–500 µm 的 MP 通过基于焦平面阵列的微傅里叶变换红外 (FPA-µFTIR) 显微镜（一种高光谱成像技术）进行分析，而大于 500 µm 的 MP 通过衰减全反射傅里叶变换红外 (ATR-FTIR) 进行分析）光谱学。根据 <500 µm 的 MP 的高光谱图像和 > 500 µm 的显微镜图像估计质量。总处理效率以 MP 计数计为 99.98%，每日输入 6.42 × 10 个颗粒，输出 1.04 × 10 个颗粒。质量去除效率为99.99%。治疗的机械部分、预处理和初级阶段使 MP 计数和质量减少了约 71%。生物处理、二次沉降和最终抛光与快速砂滤相结合，几乎去除了所有剩余的 29%。随着通过不同的处理步骤，MP 逐渐变小。消化池入口每天接收 1.04 × 10 MPs，同时排出 9.96 × 10 MPs，导致 MP 计数小幅但不显着减少，相应的 MP 质量减少了 9.56%。