Modeling of membrane fouling in ultrafiltration of skim milk

Many models are proposed to predict flux decline in membrane ultrafiltration, but since these models have limiting assumptions, they are not applicable to all solutions. The present study modeled fouling in skim milk concentration process using proposed equations for the main mechanisms of fouling, including complete blocking mechanism, intermediate blocking mechanism, standard blocking mechanism and cake filtration mechanism. These models then were compared with experimental data at 50, 100, 150, 200 and 250 kPa trans-membrane pressures to investigate the effect of trans-membrane pressure on flux decline. Based on the results obtained here, it was found that predictions of cake filtration model were in good agreement with experimental data, while those of standard blocking model were in poor agreement. Complete blocking mechanism was not capable of predicting flux data using CurveExpert Professional. With decreasing trans-membrane pressure, the differences between experimental data and models decreased. The results also showed that the second mechanism responsible for flux decline was intermediate blocking model. In fact, cake filtration mechanism and intermediate blocking mechanism are the two main mechanisms responsible for fouling in skim milk concentration process. Moreover, the results obtained from modeling of resistance showed that the cake layer resistance was the main resistance to flow, which was in accordance with what we had expected from accumulation of protein and fat molecules on the surface of the membrane. All in all, the cake filtration mechanism is the main mechanism for predicting flux decline, and it is expected that this model in combination with intermediate blocking model, would result in the best prediction of fouling phenomena in milk concentration process.