Ultrafiltration membrane fouling by microplastics with raw water: Behaviors and alleviation methods

Abstract

It is well accepted that microplastics (MPs) exist in freshwater that is used as a key source for production of drinking water. Because of the potential health effects from MPs, it is necessary to remove the MPs during the water treatment. Among various technologies, membrane technology plays a dominant role. The integrated ultrafiltration membrane-based system has attracted considerably high attention for water treatment due to its cost-effectiveness. In this study, the ultrafiltration (UF) membrane fouling by the MPs was investigated. The results indicated that the UF membrane fouling was enhanced due to the synergistic effect of MPs and the existing substance in raw water. The transmembrane pressure (TMP) was positively correlated with the loading of MPs; the MPs with an averaged size of 1 μm caused the most severe fouling among the tested sizes. The aluminum-based flocs (Al-flocs) were injected and the loose cake layers were formed on the membrane surface, leading to a reduction in the TMP by almost 85% at the Al-flocs total dosage of 26 mM. A further fouling alleviation was achieved by the membrane module reciprocating rotation or helical rotation, which regulated the thickness of the loose cake layers. The three-dimensional computational fluid dynamics (CFD) modeling analysis indicated the flow in the tank was in the transition from laminar flow to turbulent flow. The results also showed that the shear stress had the maximum value when the module started to rotate regardless of the rotation duration, indicating the main regulation induced at the beginning of the rotation. In this work, the findings illustrated how MPs practically affect the UF membrane fouling and advocated the applicability of the dynamic integrated process to alleviating the fouling caused by the MPs.