Coagulative removal of polyethylene microplastics using polyaluminum chloride in conjunction with laminarin

Abstract

As emerging pollutants in water, microplastics pose potential risks to aquatic organisms and human health. Previous studies have shown that traditional metal coagulants are effective in removing microplastics from water, but they come with drawbacks such as high chemical dosage and metal residues. Therefore, it is important to explore more efficient coagulation systems. This study utilized laminarin (LA) as a coagulant aid in combination with polyaluminum chloride (PAC) to investigate its enhanced coagulation performance on polyethylene microplastics in water. The performance of coagulation systems for the removal of microplastics was evaluated for different agent dosages, pH, anion and HA content. Experimental results demonstrated that the compounded system (PAC-LA) significantly improved the removal efficiency of PE microplastics compared to the single PAC system, achieving a removal rate of 91.5% while reducing the dosage of PAC. The enhanced coagulation mechanism of LA was analyzed using various techniques including scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and zeta potential analysis. The results indicated that charge neutralization and sweep flocculation were the primary coagulation mechanisms in the presence of PAC alone. The effect of charge neutralization and adsorption was strengthened with the introduction of LA. The coagulation system of PAC-LA showed higher removal rates of PE microplastics under different environmental conditions such as varying pH levels, co-existing anions, and humic acid, suggesting a promising application for microplastic control in water.