污水处理厂中微塑料的去除效能与全流程分析——以北京某下沉式三级污水处理厂为例

污水处理厂排放是微塑料进入自然环境的重要途径之一，本研究对北京某下沉式三级污水处理厂八个工艺单元中微塑料的赋存特征和去除效能进行全流程分析.研究表明该厂赋存微塑料主要形态为纤维，主要成分为聚丙烯、聚酯和聚乙烯，尺寸≤500μm的微塑料影响最为显著.该厂对微塑料的整体去除率为91.7%，主要依靠沉淀和截留过滤去除.双层平流沉淀池（二沉池）的去除效能最高，而生化处理单元没有明显去除效果.整体上，微塑料呈现从污水向污泥迁移的趋势.该厂最终出水中微塑料浓度为1.3n/L，成分为聚酯纤维，出水排放没有引起周边受纳水体中微塑料浓度升高，但干扰了下游地表水体中微塑料的成分，深度处理单元是降低受纳水体微塑料污染风险的重要保障.

Removal efficiency and whole process analysis of microplastics in a wastewater treatment plant: Taking an underground tertiary wastewater treatment plant in Beijing as an example

The effluents from wastewater treatment plants (WWTPs) is one of the important pathways for microplastics entering natural environments. This study analysed the occurrence characteristics and removal efficiencies of microplastics in eight processes of an underground tertiary WWTP in Beijing. The results showed that microplastics in this WWTP were mainly in form of fiber, with major compositions of polypropylene, polyester and polyethylene and the primary size ≤500μm. The overall removal efficiency of microplastics in this WWTP was 91.7%, which mainly benefits from interception, filtration and sedimentation units. Among all the processes, the double-deck horizontal sedimentation tank (the secondary sedimentation tank) showed the highest removal efficiency of microplastics, and biochemical treatment processes did not present significant removal efficiency. As a whole, the microplastics showed a migration trend from wastewater to sludge. In the effluent of this WWTP, the microplastic concentration was 1.3n/L with the composition of polyester fiber. The effluent discharge did not increase the microplastic concentrations in surrounding water body, but affected the microplastic compositions in downstream surface water. The results indicate that advanced treatment processes are necessary guarantees to control the pollution risk of microplastics in surrounding water.