Parametric study on electro-coagulation for efficient removal of microplastics from reverse osmosis wastewater

Flowchart of a lab-scale electrocoagulation study for microplastic removal from wastewater, showing sample collection from membrane treatment units, operating conditions, electrocoagulation mechanism, optimization criteria, and target outcomes including over 95% removal and reduced energy and sludge production. Reverse osmosis is an advanced treatment technology, which shows high removal efficiencies for emerging pollutants; however, during the removal process, concentrate containing pollutants such as microplastics (MPs) is generated. Electro-coagulation (EC) offers lower chemical use, less sludge, and better removal efficiency when it comes to removing MPs. This study evaluated various EC conditions to optimize the removal of MP particles identified in the reverse osmosis wastewater exceeding 1,000 ea/L, with 14 types of MP polymers. Through EC batch experiments, the effects of inter-electrode distance, current density, and initial pH on turbidity and MPs removal were analyzed according to reaction time. Considering energy consumption as a priority, 95% removal rate of MPs was achieved under optimal conditions, which included an inter-electrode distance of 10 mm, a current density of 3 mA/cm2, and an initial pH of 5. Under these conditions, MPs were removed by flotation or sedimentation, depending on their density and size. Polypropylene, polyethylene, polystyrene, polymethyl methacrylate, polyurethane, polycarbonate, polyvinyl alcohol, and polyvinyl chloride were removed 100%, showing the best performance. This study suggests that EC treatment is an effective method for removing MPs and a promising treatment technology to alleviate the problem of MP pollution in wastewater treatment systems.