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Upcycling Microplastic-Laden Spent Adsorbents to Mitigate Secondary Pollution: Insights into the Drivers, Pressures, State, Impacts, Responses (DPSIR) Framework
Summary
When microplastics are removed from water using adsorption materials, the resulting plastic-laden spent adsorbents create a secondary waste problem. This study applied the DPSIR (Drivers-Pressures-State-Impacts-Responses) environmental management framework to this issue and tested whether pyrolyzing spent adsorbents at 600°C could convert them into useful circular carbon materials (CCM) while destroying the embedded microplastics. The pyrolysis approach achieved about 60% polystyrene microplastic removal and produced a porous carbon material with useful surface properties for further water treatment. The work highlights that microplastic remediation technologies need to account for their own waste streams to avoid simply shifting pollution from one form to another.
The Driver, Pressure, State, Impact, Response (DPSIR) framework was applied to assess microplastic pollution and the risk of secondary contamination from microplastic-laden spent adsorbents. Key driving forces include increasing plastic production, widespread polymer consumption, and growing reliance on adsorption technologies for microplastic remediation. These drivers impose pressures through the continuous release of polystyrene microplastics (PS-MPs) into aquatic systems and the accumulation of spent adsorbents after treatment. The resulting state is characterized by microplastic-contaminated water and spent adsorbents that pose secondary pollution risks if unmanaged. Circular carbon material (CCM), produced via pyrolysis of spent adsorbents at 600 °C for 2 h, achieved approximately 60% PS-MP removal and exhibited a surface area of 108–137 m2/g and showed a Type II isotherm. The associated impacts include limited recovery efficiency and potential microplastic remobilization. As a response, CCM was upcycled into magnetic circular carbon (MCC) via co-precipitation of iron oxide nanoparticles, improving removal efficiency to ~89%, enhancing mesoporosity and producing a Type IV–H3 isotherm (enhanced mesoporosity), and enabling easy magnetic separation. Overall, DPSIR analysis demonstrates that spent-adsorbent upcycling offers a stabilization and risk-mitigation pathway for microplastic-laden residues, reducing their environmental mobility and supporting circular-economy-based microplastic remediation, while highlighting the need for future emissions characterization to fully quantify net environmental benefits.