The Pollution Characteristics and Fate of Microplastics in Typical Wastewater Treatment Systems in Northern China

Abstract

This study focuses on the occurrence status and removal efficiency of microplastics in wastewater treatment plant processes. Analysis of effluent and sludge samples from the Wulongkou and Shuangqiao wastewater treatment plants in Zhengzhou revealed an overall microplastic removal efficiency of 95.64% and 92.53%, respectively, indicating the effectiveness of wastewater treatment plants in reducing microplastic emissions. Microplastics primarily exist in forms such as fiber, fragment, floc, film, and grain. Fibers are predominant in the effluent of the Wulongkou plant, while fibers and films predominate in the effluent of the Shuangqiao plant. Moreover, microplastics are predominantly sized below 500 μm, with larger microplastics (2–5 mm) exhibiting higher removal efficiencies after secondary treatment. Analysis of microplastic types revealed that PE is the most common type in the effluent of the Wulongkou plant, while the Shuangqiao plant predominantly contains PE and PA66. The abundance of microplastics in sludge samples was found to be 6.4 ± 0.8 items/g and 11.3 ± 2.3 items/g, highlighting sludge as an important sink for microplastics. Surface analysis of microplastics revealed characteristics such as wrinkles and cracks, with energy-dispersive spectroscopy indicating significant adsorption of heavy metal elements such as Zn, Hg, and Pb onto microplastic surfaces in sludge. These findings underscore the importance of microplastic removal in wastewater treatment processes and provide scientific evidence for the control and management of microplastic pollution in the future.