Sustainable utilization of cane molasses by an integrated separation process: Interplay between adsorption and nanofiltration

摘要

Molasses-based fermentation produces a large amount of wastewater with high salinity and recalcitrant pigments, and thus alternative strategies to efficiently utilize molasses are required. In this study, the clarified molasses were treated by nonpolar resin adsorption to recover caramel pigments, and this operation also greatly alleviated fouling formation on loose nanofiltration (NF) membranes used for molasses decolorization, especially the polyethersulphone (PES) membrane. PES1 membrane (molecular weight cut-off similar to 1000 Da, AMFOR) was selected as a substitute for NF5 membrane (340-460 Da, self-made) with a polyamide (PA) separation layer thanks to its stronger long-term chlorine resistance than NF5. The short-term chlorine cleaning at pH 12 could improve the hydrophilicity of PES1 and mitigate its irreversible fouling formation, but such effect decreased color retention by PES1 because the fouling-induced pore narrowing was weakened. The decolorized molasses (the PES1 permeate) were further treated by a tight NF and ion exchange resin adsorption, and the tight NF could not only separate sucrose and reducing sugar, but also retain most divalent ions and residual pigments lessening the burden of the subsequent resin adsorption. The sucrose-rich liquid could be used for sugar crystallization while the desalted reducing sugar was expected to be concentrated to produce syrup. This work offered a complete technological route for green and sustainable utilization of cane molasses from practical application point of view.