Desalination performance of a forward osmosis membrane from acetylated nata de coco (bacterial cellulose)

Abstract

Forward osmosis (FO) membrane was fabricated from acetylated nata de coco (NDC). Acetylation of NDC was done by subjecting it to dissolution by 2 concentrations (1% and 2%) of methylene chloride for 72-hours prior to solvent evaporation to form the FO membrane. Membranes were characterized in terms of thickness, hydrophilicity, morphology, and tensile strength. A laboratory-scale FO system was used to test the performance of modified NDC FO membrane in desalination by determination of water flux, salt flux, and salt rejection. The FO system employs three kinds of feed solutions (deionized (DI) water, 0.6 M NaCl, and seawater) and 2M sucrose as draw solution. The water permeability coefficient was also determined. The dried unmodified NDC sheet was used as control to check if the modified NDC can function as FO membrane. The DI water fluxes of 1.19 L/m2-h (LMH) and 0.67 LMH were recorded for 1% and 2% modified-NDC membranes, respectively. These values are lower compared to the 6.24 LMH observed with the dried unmodified NDC sheet. Water fluxes of 0.6 M NaCl solution and seawater are similar for both 1% and 2% modified-NDC membranes that ranges from 0.51 to 0.56 LMH. High salt rejections were observed for all feed solutions ranging from 91% to 97.9%. The tensile strengths of the membranes are 54.30 and 117.88 N/mm2 for the 1% and 2% modified-NDC membrane, respectively. These suggest that the modified FO-NDC membrane is suitable for FO process.