Biofouling in sugarcane juice refining by nanofiltration membrane: Fouling mechanism and cleaning

An integrated membrane process for green sugarcane juice purification is promising but its application is limited by serious membrane fouling, especially biofouling. For the first time, this work investigated the effect of pH, temperature and sugar concentration on the growth of L. mesenteroides subsp. dextranicum, which is a main bacterium consisting in cane juice leading to serious biofouling during decoloration of cane juice by nanofiltration (NF). It was found that acidic pH, lower temperature and sucrose concentration increased bacterial growth, and more dextran was produced at faster bacterial growth, resulting in severer fouling during membrane filtration. Biofouling behavior and enzymatic/chemical cleaning efficiency were compared in dead-end and cross-flow filtrations of synthetic solution or cane juice (in virtue of membrane fouling resistance, permeate flux decline, permeability recovery, surface morphology and chemistry characterizations), showing that dextran was not only the main foulant but also the adhesive among the other foulants as well as between foulants and membrane. Moreover, a compact dextran layer would cover or enwrap other foulants such as protein, pigments, cell debris and bacteria, protecting them from chemical cleaning. Therefore, the dextranase degradation followed by an alkaline cleaning with surfactant was the most effective strategy to remove the biofouling layer and recover the membrane permeability. This work not only elucidated the fouling mechanisms during decoloration of cane juice by NF, but also offered an effective cleaning strategy for biofouling control in the practical application.