Fouling of reverse osmosis membrane in sugar mill condensate purification under sub- and super-boundary flux conditions

Abstract

The sugar production process, inherently water-intensive, is characterized by pronounced condensate formation during the evaporation and boiling phases. Given the environmental and resource implications, there is a scholarly emphasis on the potable reuse of such condensate by reverse osmosis (RO) in sugar mills. However, membrane fouling presents a significant challenge to the consistent operation of the RO process. This research examines the influence of operating parameters, namely transmembrane pressure and crossflow velocity, on the performance and fouling tendencies of an RO membrane during the purification of sugar mill condensate. The boundary flux theory was employed to model the permeate flux throughout this process. A boundary flux (5.92 L h−1m−2) and its corresponding operating pressure (10 bar) were determined. Moreover, a comparative analysis of the fouling mechanisms and the composition of the foulant layer under both sub-boundary and super-boundary conditions was undertaken. Under sub-boundary conditions, the fouling mechanism was identified as cake-intermediate blocking, while the super-boundary condition exhibited intermediate blocking. Under both conditions, organic fouling emerged as the primary fouling type. The TOC of surface contaminants ranged from 1.07 to 1.86 g/m2. Within this, proteins (484.0 to 850.3 mg m−2) and polysaccharides (201.5 to 379.2 mg m−2) were the dominant components. However, when operating conditions surpassed the boundary, there was a noticeable rise in inorganic fouling such as Ca (from 44.95 to 149.43 mg m−2) and Fe (from 4.40 to 112.09 mg m−2), which is likely due to the co-deposition of organic materials with inorganic ions. This research contributes to a more nuanced understanding of how operating conditions influence fouling mechanisms and provides foundational insights for addressing fouling challenges in sugar mill condensate purification.