Ultrafiltration of orange press liquor: Optimization for permeate flux and fouling index by response surface methodology

A Box-Behnken design of response surface methodology (RSM) was used to analyze the performance of polysulphone ultrafiltration (UF) hollow fiber membranes in the clarification of orange press liquors. A regression model was developed for permeate flux, fouling index and blocking index as a function of transmembrane pressure (TMP), temperature and feed flow-rate. The experimental operating conditions were selected within the following ranges: TMP 0.2–1.4 bar, temperature 15–35 °C, and feed flow-rate 85–245 L/h. A total of 30 experiments was performed according to the total recycle configuration. Based on the lack-of-fit test, the analysis of variance (ANOVA) showed the regression model to be adequate. From the regression analysis, the permeate flux, fouling index and blocking index were expressed with quadratic equations of TMP, temperature and feed flow-rate. Quadratic terms of TMP, temperature and feed flow-rate showed a significant influence on the performance of the UF membrane. A strong interaction effect of temperature and feed flow-rate was observed on the permeate flux while interactions TMP-temperature and TMP-feed flow-rate were found to be less significant. In the case of fouling index, interactions TMP-temperature and TMP-feed flow-rate produced a significant effect. In order to maximize the permeate flux and minimize the fouling index, the desirability function approach was applied to analyze the regression model equations. The optimized operating variables were found to be 1.4 bar, 15 °C and 167.7 L/h for a maximum desirability of 0.76. Experimental data of permeate flux and fouling index, obtained in optimized operating conditions, resulted in a good agreement with the predicted values of the regression model.