Xylitol is a sugar alcohol used as a sweetener in the food industry. Xylitol can be produced from D-xylose using a fermentation process, but it then needs to be separated from the other components of the fermentation broth (e.g., metabolic products, residual substances, biomass cells, and mineral salts), before being purified as xylitol crystals. Therefore, to obtain high purity xylitol, various separation processes are required. One very promising downstream processing method is membrane separation. This study evaluated membrane-based processes for the separation of biomass cells and other impurities, determined the concentration of xylitol produced from Debaryomyces hansenii yeast fermentation broth, and proposed a polysulfone ultrafiltration (UF) membrane for biomass-cell separation followed by polyamide nanofiltration (NF) to remove low-molecular-weight compounds (e.g., acetic acids) from sugars. The effects of operating pressure were examined using a fermentation broth model solution. The results showed that a higher pressure caused a higher permeate flux; however, the permeate flux's rate flow decreased over time due to concentration polarization, and fouling in the UF and NF membranes. Nevertheless, at all pressures, UF achieved a 99% rejection of biomass cells. In addition, microscope analysis showed that no biomass cells were detected in the permeates of UF. The resulting NF concentrates revealed high xylitol retention and a beneficially lower concentration of acetic acids. The operating pressures of the UF test conditions were 1 barg and 1.5 barg, illustrating that, at a pressure of 5.5 barg, the experiments achieved reasonably high xylitol retention (above 90%) indicating negligible losses of sugar in the permeate port. Moreover, this was proven to be a feasible way to concentrate xylitol up to three times from the initial concentration of the model fermentation broth (MFB). Therefore, the results demonstrated that a two-stage combination of UF and NF is a promising system for the downstream processing of microbial xylitol production.

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The combination of chitosan and metal oxides was utilized as an addition to improve the fouling resistance of polyethersulfone (PES) ultrafiltration membranes. Pure water flux, membrane hydrophilicity by the contact angle, scanning electron micrographs, and Fourier-transform infrared spectra were used to characterize the membranes. With the addition of metal oxides, the modified membrane’s water flux increased. The PES membrane with 0.25% wt chitosan and 2.0% wt AgNO3 had the highest flux and antibacterial activity among the membranes tested. Because of its potential to improve membrane hydrophilicity, the water flux increased with the addition of chitosan and AgNO3. Because of the improved hydrophilicity, the contact angle reduced as chitosan and Ag loading was increased. The PES–chitosan–Ag2O (from AgNO3 2.0% wt) membrane had high antibacterial activity against Escherichia coli and Staphylococcus aureus, whereas the PES–2.0% wt Ag membrane did not show the same result. Finally, the addition of chitosan in the PES–Ag membrane increased the membrane’s antibacterial activity substantially.

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This study evaluated the performance of nanofiltration (NF) membrane for the treatment of hand-drawn batik wastewater containing synthetic dyes as well as real batik wastewater. Three commercial NF membranes (NF270, TS40 and XN45) were used. The effect of transmembrane pressure, NF membrane types, synthetic dyes concentration, and solution types on flux and rejection were investigated. The results showed that the use of all NF membranes could reach dye removal of ca. 99%. NF270 membrane exhibited the highest flux, 2-3 times higher than that of TS40 and XN45 membranes. NF270 membrane was further used for treating real batik wastewater. The results showed high rejections in terms of total suspended solids (TSS), chemical oxygen demand (COD), and total dissolved solids (TDS) were obtained. The practical applicability of NF270 membrane for real handdrawn batik wastewater treatment fulfilled the quality standards in terms of TSS, COD, and BOD parameters. Overall, the NF270 membrane showed favorable performance for batik effluent treatment.