Microplastic Removal Efficiency in Natural Stabilization Wastewater Treatment Plant

ABSTRACT Microplastics (MPs) have emerged as a persistent global pollutant, primarily driven by the exponential increase in plastic usage. Wastewater treatment plants (WWTPs) play an important role in removing a significant amount of microplastics. To date, microplastic removal efficiency in the natural stabilization wastewater treatment plant in Hetuada Industrial District (HID), Nepal, is not known. To establish Microplastics baseline levels and evaluate microplastics removal efficiency in the wastewater treatment system, six components of wastewater treatment were selected for evaluation. Composite samples were collected from the raw influent, after the screening chamber, the Grit chamber, the anaerobic lagoon, the aerobic lagoon, and the oxidation stair/effluent. MPs were quantified by stereomicroscope and sorted by color, shape, and size. The abundance of MPs in the WWTPs was highest at the inlet (256 MPs/L) and lowest at the outlet (32 MPs/L). The study found considerable variability in the color, shape, and size of microplastics entering and leaving the WWTPs. The color spectrum varied extensively, including blue, red, green, transparent, white, and black, as blue MPs were most frequent at the inlet (44.2%), and the shapes were fibers (53.1%) and fragments (46.9%) in the influent. The treatment plant showed the successive removal of microplastic concentration from one treatment stage to the next, with an overall removal efficiency of up to 87.5%. These results suggest the potential for future research focusing on modifying WWTP processes and integrating advanced treatment techniques to capture nearly all microplastics, thereby improving environmental protection.