A new linear growth theoretical model of protein reversible fouling layer in protein wastewater ultrafiltration: fouling mechanism prediction for different proteins and pressures

Ultrafiltration shows promise for treating protein-rich wastewater; however, the decreased flux and increased operating costs due to protein fouling constrain its practical application. Therefore, it is crucial to investigate the fouling mechanism. Although reversible protein fouling significantly affects the ultrafiltration process, there is a relative lack of theoretical modeling studies on this subject. To solve this problem, a reversible-fouling-layer theoretical model is proposed in this study, which could help to design and optimize the ultrafiltration treatment process for wastewater containing different proteins. In this model, the reversible fouling layer has a constant specific resistance during the stable stage and its thickness increases linearly with the permeate volume per unit membrane area ( V ), and proteins in the reversible fouling layer is converted to irreversible fouling on the membrane surface. The validation of the linear relationship between reversible resistance and V in the transmembrane resistance test of three protein solutions (bovine serum albumin [BSA], ovalbumin, and γ-globulin), as well as the pressure sensitivity test, demonstrated the accuracy of the model in predicting the fouling mechanism. A complementary description of the irreversible fouling mechanism was completed by establishing an empirical formula for irreversible resistance and characterizing fouling using SEM, AFM, and particle size distribution. Finally, a coupled theoretical-empirical model that can be used for fouling and flux prediction in low irreversible fouling conversion systems was presented.