Occurrence, characteristics, and removal of microplastics in wastewater treatment plants located on the Moroccan Atlantic: The case of Agadir metropolis

Wastewater treatment plants (WWTPs) are some of the main sources of microplastics (MPs) in the environment. How-ever, studies on the occurrence and removal efficiency of MPs in WWTPs are still scarce, especially in African countries. Thus, the aim of this work was to study the abundance of MPs in the influent and effluent of two WWTPs (Aourir and M'zar) from the Agadir metropolis (Moroccan Atlantic). The two WWTPs receive different wastewater inputs (domes-tic and industrial). In addition, the impacts of seasonality on the fate and removal efficiency were investigated. The results showed that the MPs abundance in the wastewater decreased from 188 MPs/L in the influent to 50 MPs/L in the effluent for Aourir WWTP (domestic inputs); while the abundance was greater in the M'zar WWTP (urban and in-dustrial inputs) recording a mean value of 519 MPs/L and 86 MPs/L in the influent and effluent, respectively. MPs col-lected in the Aourir WWTP ranged from 290 to 3200 mu m, while MPs from the M'zar WWTP, ranged from 330 to 4200 mu m. Overall, the size range of 100-500 mu m was the most abundant for both WWTPs. Fibers were the highest MPs morphotype found, followed by fragments. MP colors were mainly red, black, blue, and transparent for both treatment plants. Additionally, FTIR spectroscopy showed the presence of eight different polymers, mainly polyethylene (PE), polypropylene (PP), and polystyrene (PS). Seasonal variation analysis showed that MPs abundance in summer was sig-nificantly higher compared to other seasons. However, the comparison of the removal efficiency (RE) between the dif-ferent seasons indicated that the winter season (74 %) recorded the highest RE for Aourir WWTP. Conversely, spring (87 %) recorded the highest RE for M'zar WWTP. SEM/EDX micrographs showed different degrees of weathering and chemical elements adhering to the surface of the MPs. The findings of the current study will serve as a baseline for fu-ture considerations about management strategies, wastewater reuse, as well as the understanding of the occurrence of microplastic pollution along the marine ecosystems of Morocco.

Automated summary

Wastewater treatment plants are important sources of microplastics in the environment, but there is limited research on their occurrence and removal efficiency, especially in African countries. This study investigated the abundance of microplastics in the influent and effluent of two wastewater treatment plants in Morocco and found that the abundance was higher in the plant receiving urban and industrial inputs. Fibers were the most common type of microplastics, and the main polymers identified were polyethylene, polypropylene, and polystyrene. The study also found that the abundance of microplastics varied with seasons, with higher levels in summer. The findings of this study have implications for wastewater management and understanding microplastic pollution in marine ecosystems.