Enhanced ultrafiltration membrane fouling alleviation by module rotation with Fe-based flocs. Issue 5 (October 2021) - Miao, Rui
Abstract: The modules of ultrafiltration (UF) membrane always occupy a fixed position during filtration. This results in a gradual aggravation of membrane fouling because of the continuous pollutants deposition. However, it is known that the cake layer is composed of loosely hydrolyzed flocs. Therefore, in this study, the rotation concept of membrane-module was investigated in conjunction with the integrated floc (Fe-based)-UF process. We found that the Fe-based flocs can be easily peeled off the membrane surface during rotation, and the UF membrane fouling was alleviated, particularly with spiral module rotation because of the strong shearing force induced. The fouling behavior after spiral module rotation was similar for different floc dosages because of the looseness cake layer formed. The applied computational fluid dynamics model showed that a greater spiral rotation height corresponded to a larger water velocity distribution and stronger shearing force in the membrane tank, and this resulted in a reduction in the fouling degree due to the thinner cake layer formed. Moreover, in comparison with alkaline conditions, a slightly more severe fouling degree was observed under acidic conditions because of the induced denser cake layer with smaller Fe-based floc sizes; however, a significantly higher humic-acid removal efficiency was observed. In addition, UF membrane performed well with river water samples taken from the South-to-North water diversion project in China (Beijing), thereby indicating the rotating module potential application in membrane-based drinking water treatment. Graphical Abstract: ga1 Highlights: The cake-layer thickness was significantly reduced after rotation. The outer cake layer was more easily regulated than the inner layer. Spiral rotation achieved better fouling mitigation than horizontal rotation. Laminar flow was not the main flow regime in the membrane tank after rotation. Fe-based flocs are more easily peeled off the membrane surface than those of HA.