Synergistic Removal of Microplastics and Organic Matter in Desalination by Ferrous Iron/peracetic Acid System

Microplastics (MPs) have become an emerging pollutant in the oceans. We found that in seawater with both MPs and humic acids (HA), the Modified Fouling Index (MFI) values were much greater than the superposition of MPs only and HA only, and that MPs and HA formed a synergistic fouling of the ultrafiltration (UF) membrane. Therefore, this work proposes a ferrous iron/peroxyacetic acid (Fe2+/PAA) advanced oxidative coagulation system as a novel pretreatment technology for seawater reverse osmosis (SWRO) when the ocean is heavily polluted. Fe2+/PAA significantly reduces the negative charge of microplastic-containing seawater compared to conventional coagulation techniques, resulting in improved coagulation that allows for more effective removal of MPs, turbidity, and organics. In addition, Fe2+/PAA contributes to the rapid formation of flocs, and the floc particle size is much larger than that of conventional coagulation systems. It is worth noting that the Fe2+/PAA system significantly reduces the dosage of chemicals. The optimal dosage of Fe2+/PAA is 0.2 mM/0.1 mM, which greatly reduces the dosage of chemicals compared to conventional coagulation (0.4–0.5 mM of Fe3+). In this context, Fe2+/PAA will provide a high-performance, low-cost pretreatment technology for desalination plants.