Characteristics and removal efficiency of microplastics in sewage treatment plants in typical northern cities

This study focused on six wastewater treatment plants in Handan City, a typical industrial city in northern China with a population equivalent of ≥100,000, addressing the issue of “high industrial wastewater content leading to prominent microplastic (MPs) loads.” The study employed FTIR-microscopy combined identification (double-blind testing with κ=0.87) and ANCOVA covariance correction to systematically evaluate the occurrence characteristics and removal efficiency of MPs in tertiary treatment processes (A²O, oxidation ditch, V-type filter). The main results are as follows: the log-normal distribution of inlet MPs abundance ln(MP) = N(3.81, 0.32²), with a 15.2% linear increase in abundance for every 10% increase in industrial wastewater proportion (β = 1.52, R² = 0.93, p<0.001); the main components were PE and PP, accounting for 60–70% of the total; particle sizes were concentrated in the 0–500 μm range, accounting for >50%. The average removal rate for primary treatment is 38.5 ± 18.2% (mean ± standard deviation), and the removal rate for secondary treatment significantly increases to 62.8 ± 9.7%. This study provides important data support for understanding and optimizing the efficiency of wastewater treatment plants in reducing microplastic pollution, and has significant implications for developing effective environmental management strategies and reducing environmental emissions of microplastics.