Removal Behaviors and Mechanism of Polystyrene Microplastics By Coagulation/Ultrafiltration Process: Co-Effects of Humic Acid

Abstract

Microplastics (MPs) have been detected in drinking water, of which could threaten the water quality, and absorb or accumulate humic acid (HA). Coagulation-ultrafiltration (CUF) is a common drinking water treatment technology, but the behavior and mechanism of MPs/MPs-HA removal by CUF remain to be further explored. In this study, the removal mechanism of polystyrene (PS)-MPs coagulated by Al/Fe based salts with or without HA was investigated to optimize CUF process. The results showed that Al-based salts was better than Fe-based salts in removal efficiency of PS or HA, and the optimal coagulants dosage of PS-HA composite system (12 mg·L-1) was higher than that of the individual PS system (9 mg·L-1). Moreover, the coagulation mechanism was studied by Fourier transform infrared spectroscope (FTIR) and X-ray photoelectron spectroscopy (XPS), showing that the oxygen group in PS/PS-HA was the main binding site of Al/Fe hydrolysate, and the effects of charge neutralization, adsorption bridging and sweep flocculation became weaker in turn at the optimal dosage. In addition, the cake layer formed by coagulation and the presence of HA alleviated the irreversible membrane fouling by intercepting flow and re-adsorption. This study provides guidance for the improvement of the traditional drinking water treatment process to remove MPs.

Keywords: polystyrene microplastics, Humic acid, coagulation, Ultrafiltration