Electrocoagulation for Polystyrene and Polyethylene Microplastic Removal: Particle Size Effects, Mechanisms, and Floc Characterization

Abstract

Microplastics (MPs) have emerged as a critical environmental issue, with electrocoagulation showing promise as an efficient technology for MP removal in wastewater treatment. However, there is a limited understanding of how the electrocoagulation process parameters influence removal efficiency across different MP types and sizes. This study addresses this gap by investigating the effects of the MP type and particle size (43–125 μm) on MP-floc aggregate evolution and their interactions, which affect the mechanism and efficiency of removal, using a batch reactor with a sacrificial iron anode under galvanostatic conditions (16.7 A m–2). MP removal efficiencies reached up to 81% for polystyrene (85–105 μm) and 79% for polyethylene (106–125 μm). Samples were collected at discrete intervals to monitor the process through multi-image capture and analysis. The work elucidates how the MP surface hydrophilicity and molecular structure govern interactions with coagulants, affecting dominant removal mechanisms (polystyrene: sweep flocculation; polyethylene: charge neutralization) and energy requirements. Zeta potential and FTIR analyses revealed surface modifications and electroactive species formation. Floc characterization showed that polystyrene forms compact, elongated flocs, whereas polyethylene produces more spongy, symmetrical aggregates. Floc size correlated positively with MP size. These mechanistic insights advance the understanding of MP–coagulant interactions and provide a framework for optimizing reactor design.