Alternating tangential flow millifluidic device for forward osmosis: mitigation of concentration polarization

• Forward Osmosis setup for low volumes, high-value uses, runs without pump. • Reliable tool to evaluate membrane performance in automated mode. • Modeling analysis reveals limitations due to concentration polarization. • Alternated cross flow and bubbles mitigate concentration polarization. • New membrane shows flux 4 times higher than commercial ones . Forward osmosis (FO) is recognized as a promising technique for gentle concentration of high-value products. However, conventional FO setups often require large fluid volumes and pumping systems, which limit their applicability to fragile or scarce samples. To overcome this limitation, we developed a cross-flow millifluidic FO device that operates without a pump and enables precise testing of membrane performance under low-volume conditions. Its originality lies in combining alternated tangential flow and bubble injection to mitigate concentration polarization, while offering a versatile platform for automated operation. Comparison between model predictions and experimental results highlights the role of concentration polarization as a major performance-limiting factor. The use of alternating flow and bubble generation in the draw solution is shown to reduce this limitation and enhance mass transfer. The device proves to be a reliable tool for membrane testing, producing results consistent with those reported in the literature for commercial membranes. When coupled with newly developed membranes, the system delivered markedly improved performance, achieving water fluxes up to 4 times higher than those of commercial references selected. The developed set-up is used to concentrate proteins up to 3-times and the effect of operating conditions is analyzed. This demonstrates not only the suitability of the device for systematic membrane characterization, but also its technological potential for FO process concentration of biological fluids. .