Dynamic regulation of Al-based floc cake layers by spiral rotation during ultrafiltration in drinking water treatment

Abstract

Integrated ultrafiltration (UF) membrane-based processes are promising drinking water treatment technologies. However, the membrane module always remains static, resulting in membrane fouling through the gradual formation of a thick cake layer. As floc-based cake layers are loose, in the present study, a membrane module spiral rotation was introduced with the aim of regulating the cake layers. The cake layer thickness readily decreased and the UF membrane fouling was alleviated. The results showed that Al-based flocs were not easily removed from the membrane surface during rotation due to its low density; as a result, the likelihood of humic acid (HA) reaching the membrane surface was low. Computational fluid dynamics indicated that a strong shearing force was generated with high rotation height. Thus, the cake layer thickness was easily regulated, and the UF membrane fouling was further alleviated. However, the floc-based cake layer could be broken by strong shearing forces, thereby allowing HA molecules to directly reach the membrane surface and further aggravating membrane fouling. In comparison to alkaline condition, the UF membrane performed better under acidic conditions, particularly in terms of HA removal, due to the smaller floc size and higher positive charge. Additionally, excellent UF membrane performance was also observed when treating raw water, indicating the potential application.