Membrane transport behavior characterization method with constant water flux in pressure-assisted forward osmosis

In this study, a new membrane transport behavior characterization method using constant water flux in a pressure-assisted forward osmosis (PAFO) was developed. The constant water flux was realized by superimposing a hydraulic pressure on the concentration gradient to follow the target water flux. The pump adjusts its hydraulic pressure automatically to compensate for the target flow rate (water flux) which is insufficient by the concentration gradient itself. The constant water flux makes the method relieve the complex correlation between the water flux and the concentration gradient in theoretical models. Using the developed method, we characterized various properties that correlate with membrane transport behavior, such as mass transfer coefficient, structure parameter, diffusion coefficient, and reverse salt flux. The biggest advantage of the method is the continuous measurement of various membrane transport behavior properties by changing solution concentration with acceptable accuracy. In most cases, validation experiments showed that the proposed method can estimate the various membrane transport behavior properties under ±10% error (<5% in case of diffusion coefficient) in a wide range of concentrations. In conclusion, the proposed method can be utilized as a continuous, multifunctional, and less laborious method for membrane transport behavior characterization.