Enhanced alleviation of ultrafiltration membrane fouling by regulating cake layer thickness with pre-coagulation during drinking water treatment

Abstract

Ultrafiltration (UF) membrane modules are static in membrane tanks; thus, result in the continuous development of a cake layer and serious membrane fouling. Thickness regulation is the most convenient method to solve this owing to the looseness induced by flocs. Recently, integrated membrane technology is increasingly being applied due to its high pollutant removal efficiency and low space requirements. Herein, with the injection of Fe-based flocs, the UF membrane performance was investigated with module rotation in the presence of humic acid (HA) and south-to-north water in China. The obtained results showed that the outer cake layer was easily shed away owing to the strong flow shear force. The thickness of the cake layer decreased and membrane fouling was significantly alleviated. The faster the rotation speed, the thinner the cake layer and the lower the membrane fouling was. However, the reduction rate of the cake layer thickness decreased as the rotation speed increased owing to the high density of the inner cake layer. Although both the rotation speed and rotation time played an important role in reducing the membrane fouling, the removal efficiency of HA remained constant, and the cake layer tended to be the main fouling mechanism; thus, indicating that module rotation is beneficial to the integrated technology. Owing to the smaller particle size and higher positive charge of flocs formed under an acidic condition, more negatively charged HA molecules were adsorbed, and the UF membrane performance was superior to that in an alkaline condition. Raw water experiments further confirmed the excellent UF membrane performance. Based on this, the proposed technology has great potential for wide applications in rural areas, particularly with the rapid development of clean energy (e.g., solar energy) and intelligent water services.