A strategy to alleviate membrane fouling by optimizing the structure of the cake layer formed by flocs deposited directly on the membrane in the ultrafiltration process through coagulation and nanoscale Fe3O4/Fe3O4@SiO2 load

Abstract

Membrane fouling has always been a problem hindering the practicability of ultrafiltration. Direct regulation of the structure of the cake layer formed by rapid deposition of flocs as a “secondary barrier” in the in-line coagulation ultrafiltration (C-UF) process has acquired importance as a research topic in comparison to membrane modification and standard coagulation ultrafiltration. In this study, membrane fouling was controlled in the C-UF process via coagulation/nano-scale Fe3O4 load (C/FL-UF) and coagulation/nano-scale Fe3O4@SiO2 load (C/FSL-UF). The promotion effects of these two processes (C/FL-UF and C/FSL-UF) on the reduction of membrane fouling and improvement of water quality were systematically studied employing simulated surface water. Floc characteristics, XDLVO theory, and the Hermia model, etc were employed to explain the optimization of cake layer. For coagulation/Fe3O4 load, the floc size was large and loose, whereas, for coagulation/Fe3O4@SiO2 load with high recoverability., the floc size was slightly loose. The newly constructed cake layer had improved porosity, structural stability and capacity of water transport. Meanwhile, decrease of unit adhesion free energy and secondary minimum depth along with the substantial increase of energy barrier between the reconstructed cake layers and membranes or colloids explained the mechanism of reduced membrane fouling from the surface energetics. The gradual decrease of water contact angle and the optical images proved that the affinity of the cake layer was significantly reduced. Hermia model further validated the accuracy of this study in controlling membrane fouling by regulating the formation of the cake layer. Finally, the study concluded by analyzing the practicability and efficacy of the procedure to further elucidate the applicability of this research.