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Influence of Treatment Technology and Sampling Methodology on Microplastic Abundance and Characteristics: A Comparative Study of Three Sewage Treatment Plants in Penang, Malaysia
Summary
Researchers compared microplastic removal across three Malaysian sewage treatment plants and found all achieved high removal efficiencies (92–99%), though treatment technology and sampling methodology significantly influenced measured concentrations, polymer types, and particle morphology in both influent and effluent samples.
Microplastics (MPs) enter sewage treatment plants (STPs) primarily through domestic wastewater, yet their removal is often incomplete and strongly influenced by treatment processes, making these facilities important pathways for MP release into the environment. This study quantifies MP concentrations, characteristics, and evaluates removal efficiencies across all treatment units of three STPs in Malaysia employing extended aeration (STP-1), a sequencing batch reactor (STP-2), and a mechanized oxidation ditch system (STP-3). Across facilities, influent MP concentrations varied significantly between plants and sampling methods (Kruskal–Wallis test, p < 0.05), with volume-reduced samples, yielding higher values: 10.33 ± 1.53, 10.24 ± 3.86, and 5.67 ± 3.29 MPs/L in STP-1, STP-2, and STP-3, respectively. Effluent concentrations were uniformly low, ranging from 0.06 ± 0.02–0.13 ± 0.13 MPs/L (STP-1), 0.01 ± 0.01–0.08 ± 0.14 MPs/L (STP-2), and 0.03 ± 0.02–0.21 ± 0.07 MPs/L (STP-3), with no significant differences among plants (Kruskal–Wallis test, p > 0.05), indicating comparable overall performance. Removal efficiencies were highest in STP-2 (99.07–99.92%), followed by STP-1 (97.06–99.42%) and STP-3 (92.49–99.53%), underscoring the influence of treatment technology. Fibers, fragments, and foams were the dominant MP shapes, while polymers such as polypropylene, acrylonitrile butadiene styrene, low-density polyethylene, styrene acrylonitrile, polyethylene terephthalate, high-impact polystyrene, high-density polyethylene, water-soluble polyurethane, and polystyrene reflected diverse community‑level plastic usage. Catchment characteristics influenced MP concentration, morphology, and polymer distribution, whereas sampling methodology exerted strong and systematic effects on all measured parameters, with volume-reduced sampling consistently capturing higher concentrations and greater shape and polymer diversity.