Evaluation of cellulose tubing membranes for dialysis-based recovery of biosurfactants from corn steep water

Dialysis is a promising downstream processing technique for purifying valuable metabolites like biosurfactants from agri-food streams. Compared to conventional membrane technologies, this approach offers the advantages of using biodegradable membranes while maintaining product integrity. However, several challenges must be addressed before industrial implementation, particularly concerning the long-term durability of cellulose membranes in high-microbial-load environments. In this study, dialysis for processing corn steep water (CSW), a biosurfactant-rich stream, was evaluated in terms of operational temperature (22 °C and 4 °C), membrane cellulose structures (regenerated cellulose (RC) and cellulose ester (CE)) and molecular weight cut-offs (MWCO) of tubing membranes (1 kDa, 3.5–5 kDa, 6–8 kDa, and 8–10 kDa). The membrane that provided the best performance for desalination of CSW and purification of biosurfactants was the 6–8 kDa RC membrane working at 4 °C ensuring consistent reproducibility and maintaining long-term durability after multiple dialysis cycles. Optical Interferometric Profilometry (OP) and Atomic Force Microscopy (AFM) analysis aligned with Scanning Electron Microscope (SEM) morphology images showed that RC membranes exhibited a smoother topography, and a more uniform shape compared to the Biotech CE membranes. Specifically, RC membranes demonstrated significantly lower roughness values, ranging from 5.44 to 29.29 nm vs 28.43 to 317.06 nm for Biotech CE membranes, which agrees with the better performance observed for RC membranes. Additionally, nanoindentation tests revealed that Biotech CE membranes are comparatively more rigid than RC membranes, the latter having shown better elastic recovery, favourable for dialysis operated under lower-pressure conditions. Moreover, it was observed for RC membranes that Young's modulus (E) decreased with the increase of MWCO. The experimental results highlight the strong potential of 6–8 kDa regenerated cellulose membranes for sustainable biosurfactant downstream process of CSW, with this study providing critical insights for future scale-up efforts.