A novel empirical method for predicting concentration polarization in forward osmosis for single and multicomponent draw solutions

Concentration polarization is one of the inherent problems in forward osmosis membrane process. A quantitative evaluation of concentration polarization is therefore vital to understand its impact on the performance of the forward osmosis. Limited data in the literature exists for the diffusion coefficient of mixed electrolyte or multicomponent solutions, which makes the calculation of mass transfer coefficient and solute resistance to diffusion in forward osmosis complicated. Therefore, an empirical method based on a limited set of well-defined experiments for evaluating and predicting the concentration polarization, water flux, and reverse solute flux is presented for single and mixed, or multi-ions draw solutions. The proposed method does not rely on the hydrodynamic conditions and flow regime in the system and provides an approach to measure and predict concentration polarization, water flux, and reverse salt flux when the diffusion coefficient of a feed solution (FS) or draw solution (DS) is challenging to determine. The developed numerical method is two steps method to measure internal and external concentration polarization using different concentrations of the draw and feed solutions. Experimental work was carried out with a single, and highly soluble sodium chloride (NaCl) DS and a mixture of NaCl and magnesium sulphate (MgSO₄) were used as a selected multicomponent DS. The results showed a 95% to 99% agreement with the experimental data.