The Electrochemical reactor: a sustainable approach of microplastics separation: Microplastics Separation: Perspective

The gradual accumulation of microplastics (MPs) in the aquatic environment has become a major concern all over the world. Plastics particles with the size of <5mm are considered as MPs [1]. The small-sized MPs can easily be swallowed by various organisms, especially aquatic animals that exist at low trophic levels. In consequence, it resulting irreversible damage to the food chain. Research has been found that more than 690 marine species have encountered tiny plastic debris [2]. These plastic particles are degrading very slowly and thus, 60% of floating debris in the ocean is made of plastics [3]. Different polymeric MPs are available in the water while polyethylene, polypropylene, polystyrene, and polyamides-based MPs are mostly notable [4]. As a result, varieties of MPs separation systems have already been established to tackle MPs including membrane filtration, adsorption, magnetic extraction, coagulation, chemical oxidation, etc. But these advanced approaches can’t confirm the long-term sustainability due to the formation of secondary MPs (after extraction from water) [1]. So complete mineralization of MPs is inevitable. In this phenomenon, advanced oxidation systems like photocatalytic degradation, Fenton/photo Fenton systems, and hydrogen peroxide oxidation can perform to decompose MPs into carbon dioxide (CO2) and water. But these approaches are embroiled with several problems like the bulk of chemicals requirements, more expensive, toxic bi-products formation, lower degradation rate, etc. which are leading to environmental hazards [5]. To overcome these drawbacks, electrochemical oxidation is becoming prominent as a green approach to mineralize MPs without leading to secondary pollution. This oxidation system can break the long alkanes/olefin chains of MPs via the generation of oxidizing radicals like hydroxyl/sulfate radicals (•OH/SO4•-) and ultimately produce less harmful products (CO2 and water) [6]. Although the research community is experimenting electro-oxidation system for MPs removal but it has lower removal efficiency (58 ± 21%) within 1 h duration [7]. It may happen due to the lack of materials optimization including anode material, electrolyte type, current intensity, and electrolyte concentrations. Moreover, anode fouling and mutual contaminates interaction may also inhibiting the process efficacy. So it’s inevitable to reduce anode fouling along with mutual contaminations to generate reactive oxygen species within full scale. With such a viewpoint, the fabrication of a hybrid electrochemical reactor should initially consider electro-sorption before going to the electro-oxidation at the final stage of the MPs separation system (Fig. 1). Because this approach can reduce fouling contaminates along with MPs adsorption to a greater extent via adsorption mechanism and may reduce the processing load on oxidation system. It’s also noteworthy to mention that the water baffle can also be used between adsorption and oxidation chamber to use the gravitational force in the form of MPs sedimentation. Moreover, experimentation with different anode materials, electrolytes types as well as concentrations, and current intensity should be carried out to make optimization for maximum MPs mineralization. However, the produced CO2 from the reactor can also be used as feedstock gas for the preparation of commercially valuable products. Thus the coupling of electro-sorption and electro-oxidation can remove MPs from water without jeopardizing the environment and may ensure long-term sustainability with maximum efficiency. Fig. 1: Design of microplastics separation reactor using electrochemical technology.