Deconstruction and reconstitution of fouling layer in decolorization of cane juice by nanofiltration membrane

Abstract

Ubiquitous membrane fouling is a knotty problem in membrane-based sugar-making process, which limits productivity and sugar quality. Especially during decolorization of sugarcane juice by nanofiltration (NF), fouling mechanism is still obscure and the fouling formation is difficult to control effectively. Herein, based on the analysis of the real fouling layer residue, seven components are served as model solutes and foulants to study their NF separation performance and fouling behavior. We found that the coexistence of polysaccharides and proteins had no synergistic enhancement on membrane fouling, yet attenuated fouling layer because the formation of large complex produced more shear-enhanced back diffusion. Chlorogenic acid (CA), as a phenolic pigment and main pore foulant, aggravates the polysaccharides or proteins fouling owing to its bridging effect between membrane and large foulants, especially polysaccharides with high hydrophilicity. Laccase can catalyze oxidation and self-polymerization of CA, not only reducing its accessibility to block the pores and the bridging effect, but also in-situ forming a hydrophilic coating layer on the membrane surface, which is regarded as an effective pretreatment strategy for fouling control. During the cross-flow filtration of real sugarcane juice, the average permeate flux increases by 67.1% and irreversible fouling decreases by 21.2%, showing great application potential due to its biocompatibility and considerable economic benefits. This work not only elaborately elucidates the fouling mechanism among components in cane juice decolorization by NF, but also proposes an innovative approach to reconstitute fouling layer for improving membrane antifouling performance in practical application.