Harvesting microalgae Chlorella vulgaris sp. using cellulose triacetate/acetate forward osmosis membranes

Forward osmosis (FO) has potential for microalgal harvesting because it enables biomass concentration without externally applied hydraulic pressure; however, membrane permeability, selectivity, and fouling remain important considerations for its application. This study investigated cellulose triacetate/cellulose acetate (CTA/CA) blend membranes with CTA/CA ratios of 1:2, 1:3, and 1:4 for FO-based concentration of Chlorella vulgaris. The membrane formulations were evaluated in terms of porosity, water contact angle, water flux, specific reverse salt flux (SRSF), microalgal rejection, and flux recovery ratio (FRR). The optimized membrane was further characterized using field-emission scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, atomic force microscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. Among the investigated formulations, the CTA/CA (1:2) membrane exhibited the most favorable performance under the tested conditions, achieving the highest water flux (8.38 ± 0.35 L m⁻² h⁻¹), 100% apparent microalgal rejection, low SRSF (0.069 ± 0.002 g L⁻¹), and the highest FRR (97.25%), with statistically significant differences among membrane formulations (p < 0.05). The CTA/CA (1:2) membrane also exhibited the highest porosity and lowest water contact angle among the formulations, while further characterization revealed an asymmetric morphology and suitable thermal stability. During a 7-h short-term continuous filtration experiment, the optimized membrane achieved a volume reduction factor of 1.9 while maintaining measurable water flux throughout the filtration period. Overall, the results demonstrate that CTA/CA blend composition influences membrane physicochemical and filtration characteristics, with the CTA/CA (1:2) membrane showing potential for FO-based C. vulgaris concentration under the investigated conditions.