Characterization of Microplastics at a Large Wastewater Treatment Plant

Microplastics are widely detected in the marine environment, however their sources and pathways are less well understood. Studies have shown that Wastewater Treatment Plants (WWTPs) serve as a pathway for microplastics to enter marine environments despite relatively high removal rates. Our objective is to characterize microplastics throughout different treatment processes at a large WWTP located in Southern California while estimating removal rates in an effort to better understand how to mitigate environmental discharges of microplastics. Samples were collected at multiple primary and secondary stages throughout the treatment process, including influents, effluents, sludges, and biosolids. Samples were digested, size fractionated (45 – 125 μm, 125 – 300 μm, and 300 – 1,000 μm), and filtered before quantification and characterization using brightfield and fluorescence microscopy. Advanced analytical techniques were used to confirm a subset of suspected microplastic particles, using Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy (ATR-FTIR). Qualitative analysis confirmed the presence of various morphological forms of microplastics such as films, foams, microspheres, fragments, and fibers with fragments being the most prevalent. Preliminary results indicate that > 90% removal occurs throughout the treatment process, particularly through the retention of microplastics in primary sludges and biosolids. While research in this area is increasing, more research is required to better understand how WWTPs may mitigate microplastic pollution contributions to marine, freshwater, and terrestrial ecosystems. This study will inform our understanding of the environmental fate and management of microplastics in WWTPs, receiving waters, and biosolids for land application.