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Source fingerprints, process fate, and risk redistribution of microplastics in a full-scale wastewater treatment plant receiving e-waste dismantling wastewater
Summary
Wastewater from an e-waste recycling plant in China contained extremely high levels of microplastics—far more than typical city sewage—loaded with chemical additives like phthalates and flame retardants. While treatment removed most microplastics from the water, they didn't disappear; they simply piled up in the leftover sludge, which is often used as fertilizer or disposed of on land. This means the pollution isn't eliminated, just relocated, raising concerns about microplastics and their chemical hitchhikers re-entering soil, water, and potentially our food supply.
Microplastics (MPs) from industrial activities remain far less understood than those from municipal sources, particularly in wastewater systems serving e-waste dismantling. Here, a full-scale wastewater treatment plant (WWTP) dedicated to e-waste dismantling wastewater in Guiyu, China, was investigated through four seasonal sampling campaigns covering its two parallel treatment trains, namely an anaerobic-anoxic-oxic (A/A/O) oxidation ditch-secondary clarification train and an A/A/O oxidation ditch-membrane bioreactor (MBR) train. MPs were quantified and characterized by micro-Raman spectroscopy, and their process fate, source-related fingerprints, co-occurrence with phthalate esters (PAEs) and organophosphate esters (OPEs), and screening-level hazard redistribution were systematically evaluated. The raw influent contained 6637.3 ± 927.4 MPs/L, far exceeding typical levels reported for municipal WWTPs and reaching the upper range of industrial wastewater systems. Although both treatment trains reduced aqueous MP concentrations by 2-3 orders of magnitude, the removed particles were largely transferred to sludge rather than eliminated. E-waste-related engineering polymers dominated the MP assemblage, accounting for 65.7% in the influent and 69.6% in dry sludge. Angular fragments with sharp edges and regular outlines were also consistently abundant, contributing 59.8% and 66.1% of MPs in the influent and dry sludge, respectively. Together with significant positive associations between e-waste-related MPs and multiple high-molecular-weight PAEs and OPEs, these polymeric, morphological, and pollutant-co-occurrence features support an integrated source-fingerprint-based inference for e-waste-related MPs in this WWTP. Screening-level hazard assessment further suggested that wastewater treatment lowered the hazard-weighted MP burden in the aqueous phase but redistributed the dominant burden to sludge. This study provides a process-oriented understanding of MP behavior in a dedicated e-waste wastewater treatment system and highlights that integrated source fingerprints and sludge-phase accumulation should be explicitly considered in the assessment and control of industrial MP pollution.