Semi-permeable membranes of binary polymer blends of cellulose triacetate (CTA) and chitosan (CS) were produced to harvest microalgal biomass for biofuels. Relatively thick membranes of polymer blends containing more than 70% CTA were prepared via solution blending in formic acid. Various characterization methods revealed that both polymers are immiscible at the molecular level at room temperature. However, they were macroscopically compatible and exhibited uniform physical properties due to the molecular interactions between CTA and CS with the same cellulosic backbone containing two linear polysaccharides through a -1,4 glycosidic bond. Careful visual inspection revealed that these membranes are transparent and their light transmittance was greater than 90% at all blend compositions. All membranes showed excellent tensile strength at all compositions and the maximum tensile strength was 52.4 MP from the membrane with a CTA/CS weight ratio of 9:1. The NO3- permeability of these blend films increased with increasing CS content and the maximum value was 44.28 mg/m(2)/day. To improve the NO3- permeability or transfer rate of the CTA/CS membranes, the porous CTA/CS membranes were also prepared using various amounts of silica nanoparticles. POLYM. ENG. SCI., 58:192-197, 2018. (c) 2017 Society of Plastics Engineers