Removal behavior of microplastics using alum coagulant and its enhancement using polyamine-coated sand

Abstract

In recent years, microplastics (MPs) smaller than 100μm have been reported to be abundant in bulk water samples from drinking water treatment plants (WTPs). In this study, the removal behavior of MPs for different sizes (10–100μm), shape and surface morphology were investigated using alum coagulant and alum combined with cationic polyamine-coated (PC) sand. For identification and quantification, MPs were stained with Nile Red dye and observed under a laser scanning fluorescent microscope. The removal of MPs increases with increasing doses of alum up to 30mgL–1 (70.7%). Further increases in the doses resulted in a sharp decrease in the removal of MPs. The analysis for different sizes showed lower removal of smaller MPs (10–30μm) for all doses of alum. PC sand (500mgL–1) combined with 20mgL–1 of alum dose showed the highest removal (92.7%) of MPs. The removal was enhanced by 26.8% when compared with alum alone. The removal of MPs followed the behavior of elongated-rough (ER)>elongated-smooth (ES) >spherical-rough (SR)>spherical-smooth (SS) and was supported by a flocculation kinetic study. This study revealed that size, shape and surface morphology of MPs play important roles in the removal of MPs from drinking WTPs.