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Stormwater runoff treatment using magnetite-based ballasted flocculation targeting tire-wear particles removal
Summary
Rain runoff from city streets picks up tiny tire particles—a type of microplastic that's been linked to health and environmental harm—and washing this water is tricky because these particles are hard to filter out. Researchers found that adding magnetic mineral particles (magnetite) to the water speeds up clumping and removal of these tire particles, clearing the water in just 15 seconds and removing most of the pollutants, including 94% of cloudiness-causing debris. This fast, compact treatment method could make it safer and more practical for cities to clean and reuse stormwater instead of letting it carry microplastic pollution into rivers and dr
Urban stormwater runoff is increasingly recognized as a valuable alternative water source, yet its reuse is hindered by emerging pollutants such as microplastics. Among these, tire-wear particles (TWP) represent a major concern due to their ubiquity and potential toxicity. This study explores ballasted flocculation (BF) as a compact and high-rate physicochemical treatment for the targeted removal of TWP from urban runoff. Natural magnetite was selected as ballast material, as it enhances floc density and settling while offering magnetic properties that enable easy separation and recovery for reuse, supporting a circular treatment approach. To simulate stormwater conditions, aged TWPs were prepared in the laboratory by oxidative aging (UV/PMS). BF experiments demonstrated faster clarification compared to conventional flocculation, exhibiting nearly two-fold higher apparent first-order clarification rate constants and achieving up to 94% turbidity removal within 15 s when using magnetite fraction of 32–50 μm. Operational parameter analysis confirmed robust performance across variations in coagulant dose, ballast concentration, and TWP levels, while pH adjustment to neutrality proved crucial. Under these conditions, effluent turbidity was reduced to 2.3 NTU and particle size analysis of the effluent revealed a clear shift toward particles <50 μm, confirming effective removal of the added TWP (~130 μm). Additional removal of bulk organic matter was evidenced by reductions of 61% TOC and 44.5% UV 254 . Zeta potential measurements showed a change from −20.30 mV to −6.50 mV, indicating charge neutralization and floc consolidation. BF process produces compact sludge and clarified effluent, supporting decentralized stormwater treatment under short effective treatment times.