Making waves: Overcoming toxicity and deactivation challenges in polymerization-based wastewater treatment

Polymerization-based oxidation processes (PBOP) present a promising alternative to chemical and energy-intensive advanced oxidation processes (AOPs) for removing emerging pollutants in water treatment. By reducing oxidant consumption and minimizing carbon emissions, PBOP offers a more sustainable solution. However, the polymerization products generated in these processes pose significant sustainability challenges, including potential toxicity and catalyst deactivation. Firstly, the polymeric products formed during PBOP exhibit increased hydrophobicity (higher K_ow), which correlates strongly with enhanced bioconcentration potential (K_B) and aquatic toxicity. Residual dissolved polymers, or those reentering the environment, present ecological risks through non-specific narcosis (due to their lipophilic nature) and potential specific toxicity arising from retained functional groups, such as benzene rings. Secondly, in heterogeneous catalytic systems, these polymeric byproducts tend to adsorb onto catalyst surfaces via hydrophobic interactions and van der Waals forces. Over time, this deposition blocks active sites, impairs reactant adsorption and activation, potentially repels oxidants, and disrupts electron transfer, ultimately leading to catalyst deactivation. This mechanism, which was often previously attributed to "degradation intermediates," is now understood to be driven by the accumulation of polymeric products. Several strategies have been proposed to address these challenges and ensure the sustainable implementation of PBOP. These include coupling PBOP with energy-efficient microfiltration or coagulation processes to remove polymeric byproducts effectively and develop efficient and environmentally friendly catalyst regeneration technologies. Promising approaches involve in-situ electrochemical regeneration or the transformation of polymers into catalytic sites, which also enable resource utilization. A comprehensive understanding of the environmental toxicity of polymeric products, coupled with insights into the mechanisms of catalyst deactivation, is essential for advancing PBOP technology in an environmentally responsible manner.