Enhanced removal of polyethylene microplastics from water through polymeric ferric sulfate with laminarin

Abstract

Coagulation has been demonstrated as an effective method for eliminating microplastics from water. However, based on the existing literature, the use of a single coagulant has not yet yielded satisfactory results in microplastic removal. Hence, it is crucial to investigate the potential of enhanced coagulation techniques. In this study, laminarin (LA) was used as a novel coagulant aid to investigate its enhanced coagulation performance in the removal of polyethylene (PE) microplastics using polymeric ferric sulfate (PFS). The coagulation mechanism was investigated through zeta potential, Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The results demonstrated that the coagulation efficiency of PFS on PE microplastics could be improved by adding an appropriate amount of LA. The removal rates of PE microplastics by single PFS and PFS-LA reached 48.5% and 93.8%, respectively, when the dosages of PFS and LA were 250 mg/L and 5 mg/L. The coagulation mechanisms of PFS and PFS-LA on PE microplastics were found to be the same, with the addition of LA significantly enhancing the effects of charge neutralization, adsorption bridging, and sweep flocculation of PFS. Various experiments conducted under different pH levels, microplastic particle sizes, coexisting ions, humic acid coexistence, and real water conditions demonstrated that the PFS-LA complex coagulation system exhibited better environmental adaptability.