Microplastic removal efficiency and polymer characterization in coastal wastewater treatment plants using FTIR spectroscopy

Microplastic (MP) pollution in wastewater is a growing concern due to its environmental persistence and ecological toxicity. However, critical data on MPs in the Gulf Coast region of the United States is lacking. This study assessed MP concentrations, polymer types, and removal efficiencies in four wastewater treatment plants (WWTPs) with distinct treatment technologies in the Gulf Coast region. Influent and effluent samples were collected from facilities in Alabama, Mississippi, and Florida, and processed using sequential filtration, peroxide digestion, density separation, and analyzed using Fourier-transform infrared (FTIR) microscopy. Results revealed that total MP concentrations ranged from 3,472 ± 2,012 particles/m³ in influent to 1,372 ± 1,740 particles/m³ in effluent, with the wide variability reflecting differences among treatment systems and seasonal sampling conditions. Polyethylene terephthalate (PET) 37% and Polystyrene (PS) 27% were the most abundant polymers identified, followed by Polyethylene (PE) 21% and Polypropylene (PP) 13%. Polymer-specific removal varied by density and the treatment plant’s removal technology. PET and PS showed high removal (>80%) at sites with advanced filtration or lagoon-wetland systems, whereas PE and PP exhibited lower removal efficiencies (<60%). Seasonal trends showed higher loads and weaker removal in winter, while summer had lower loads, with over 90% removal. This study highlights the influence of polymer type and treatment technology on MP removal and underscores the importance of tailored strategies for MP removal. • Microplastic (MP) concentrations and polymer compositions were investigated across four Gulf Coast wastewater treatment plants. • Average influent and effluent concentrations were 3,472 and 1,372 particles·m⁻³, with ~60% overall removal efficiency, with the observed differences depending on the type of treatment configuration. • PET and PS dominated, while low-density PE/PP showed poor removal, indicating buoyancy-driven persistence. • Advanced BNR and disk filtration achieved the highest and most stable MP removal among all treatment systems.