Morphology, distribution and removal of microplastics in municipal wastewater plants by traditional oxidation ditch technology

In order to investigate the morphological characteristics and removal patterns of microplastics in urban wastewater plants in China, especially oxidation ditch process wastewater plants, the presence patterns and removal efficacy of MPs in each treatment unit of a two-phase project of an oxidation ditch process wastewater plant in Handan City were thoroughly analyzed. The results showed that the main shape of MPs was fibrous, accounting for 56.5%, followed by fragments and films, with particles accounting for the smallest proportion at only 4.0%. The particle size range was mainly between 150 and 5000µm, with MPs in the 150~500µm range accounting for the highest proportion at 43.0%. The main types were polyethylene, polyester, and polypropylene, accounting for 28.9%, 17.3%, and 22.5%, respectively. The analysis of the effect of shape and particle size on removal efficacy revealed that fibrous MPs were the most difficult to remove, and as particle size decreased, the difficulty of removal increased. The overall removal rates for the first phase of the plant and the expansion project were (92.0 ± 2.5)% and (83.6 ± 1.6)%, respectively. The analysis of removal rates for each process level and treatment unit showed that the key roles in removal were played by secondary treatment and deep treatment, with the treatment unit being the oxidation ditch sedimentation tank. The main mechanisms were physical sedimentation and retention in the filtration tank. © 2024 Chinese Society for Environmental Sciences. All rights reserved.