Microplastic characterization and assessment of removal efficiency in an urban and industrial wastewater treatment plant with submarine emission discharge.

Wastewater treatment plants (WWTPs) are significant contributors to microplastic (MP) pollution in marine ecosystems when they are inefficient. This study aimed to evaluate the effectiveness of microplastic removal from the effluent of the Anza WWTP (Morocco), which processes industrial and urban wastewater using a lamellar decantation system combined with a submarine emissary for treated water discharge. Additionally, this study investigated the presence of microplastics in the Atlantic seawater where treatment plant effluent is released. Microplastics were collected and extracted from wastewater and seawater samples to assess their abundance, shape, size, polymer type, and removal rates in the treatment plant. The findings revealed an average MP concentration of 1114 ± 90 MPs/L in the influent and 607 ± 101 MPs/L in the effluent, indicating a removal efficiency of 46 %. Seasonal analysis revealed the highest MP concentrations during the summer, with 2181.33 MPs/L in the influent and 1209 MPs/L in the effluent. Seawater samples from the discharge zone of the submarine emissary had an average MP concentration of 1600 MPs/m. Characterization of the MPs revealed that fibers were the most common form of MPs in all the samples. The 500-100 μm size fraction was predominant in the WWTP samples, while MPs smaller than 1 mm were more abundant in the seawater samples. Seven polymer types were identified using attenuated total reflection fourier transform infrared spectroscopy (ATR-FTIR), with PET, PE, PVC, PA, PS, PP, and EVA being the most prevalent. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX) revealed various degrees of weathering and chemical elements adhering to the MP surfaces. The results of this study provide valuable insights into the effectiveness of conventional treatment systems in removing microplastics and offer a reference for developing management strategies to mitigate MP pollution in Morocco's marine ecosystems.