Mitigation mechanism of ozonation in the casein fouling of ultrafiltration membranes: Possible application in dairy wastewater treatment

Abstract Membrane fouling control is one topic of concern during the application of ultrafiltration in dairy wastewater treatment. Casein is abundant in dairy wastewater; thus, in this work, preozonation for the casein solutions were carried out, and the membrane fouling behavior was investigated before and after preozonation. To reveal the effect mechanism of preozonation in casein fouling of ultrafiltration membranes, we explored the changes in casein's interfacial forces at the membrane surface, fouling layer structures, and its properties after pre-ozonation. Results showed that the casein molecules without ozonation could hold together tightly to form larger micelles, which were retained on the membrane surface to form a gel scale with poor fluidity and permeability, and also caused the most serious membrane fouling. By contrast, once preozonation occurred, the hydrophobic forces and the hydrogen bonds between membrane and casein, and between casein molecules were disrupted, which not only mitigated the adsorption/deposition of ozone-treated casein onto the membrane surface, but also destroyed the micellar structures of stable casein and resulted in a more open-and-loose fouling layer. Eventually, the membrane showed less fouling. Therefore, preozonation could effectively mitigate casein fouling of ultrafiltration membranes.