Ultrafiltration of Moroccan Valencia orange juice: juice quality, optimization by custom designs and membrane fouling

Abstract

The growing demand for healthy foods has forced researchers to develop processes capable of concentrating or clarifying fruit juices while producing high quality products and the most promising techniques are membrane techniques. However, the obstacle of these techniques is the fouling problem. The objective of this study is to clarify Moroccan Valencia orange juice by ultrafiltration (UF) using two plate membranes characterized by different membrane materials (polyether sulfone (PES) and polysulfone (PS) with a molecular weight cutoff (MWCO) of 30 and 20 k Da respectively. The performance of these membranes was studied in terms of selectivity and productivity in respect to parameters describing juice quality. In the first part of this work, the response surface method (RSM) based on custom designs (CD) was used to model and optimize the UF process. The independent variables of the RSM method are transmembrane pressure (TMP) and feed flow rate (FF), while permeate flux is considered as a response. Secondly, Hermia model and resistance model were applied to describe and to identify the fouling mechanism.

According to the results, the two membranes kept the original composition while the total suspended solids (SS) and the pectin content were completely removed. Both factors (TMP) and (FF) influence significantly the permeate flux. A TMP of 1,99-2 bar and FF of 229,99-330 L/h for PES and PS respectively were obtained. ANOVA of the regression model showed that both models are highly significant with R² > 0,95. However, the PES membrane exhibits a permeate flux which is greater than the PS membrane. The rejection rates of the monitored parameters were lower than those obtained by the PS membrane. The concentration polarization is the main cause of the flux drop and it appears that, for both membranes, the fouling is due to surface fouling mechanisms which is a cake formation.