Fate of Microplastic-Like Particles in Wastewater Treatment and the Role of Commercial Laundry

The goal of this study was to assess whether a large-scale commercial laundry contributes microplastics to the receiving wastewater treatment plant and to compare microplastic-like particle content in samples from three plants with varying industrial inputs and infiltration/inflow over 12 months. Suspected microplastic (MP) counts, morphology, and sizes were determined using a modified ASTM D8333-20 digestion method and fluorescence microscopy. Samples from a large commercial laundry were collected to determine the impact of laundering synthetic fabrics on MP content in wastewater influent. Influent and effluent samples were collected from each plant, and at one plant intermediate samples were collected before and after sand filtration to assess its role in MP abatement. Domestic wastewater heavily influenced MP-like particles in wastewater. Fibers released in laundering, domestic or commercial, constituted a minor part of overall particle counts. While fiber morphology in laundry wastewater accounted for up to 13% of total suspected MPs (4.7% average), it represented only 0.1–2.2% (0.8% average) of particles in influent at the two plants receiving industrial inputs and 0.2–1.7% (0.6% average) at the plant treating strictly domestic wastewater. On average, MP-like particle counts in commercial laundry water were four times lower than counts in wastewater influent. All three plants effectively removed MP-like particles, with average removals of 91.0, 95.4, and 97.1%. Most removal occurred after secondary treatment, presumably via enmeshment in residual solids, with sand filtration offering little additional benefit. The majority of particles were 10–50 μm, which may explain limited filtration capture. While effective, wastewater treatment plants remain major pathways for MP entry into the environment, and more research is needed to identify and address MP sources in wastewater.