Influential analysis of concentration polarization on water flux and power density in PRO process: Modeling and experiments

Pressure retarded osmosis (PRO) is a potential technology for harvesting renewable energy from the salinity gradients. However, the PRO performance can be dramatically influenced by concentration polarizations and reverse salt flux (RSF) of the forward osmosis membrane. A mathematical PRO model considering dilutive external concentration polarization (DECP), concentrative internal concentration polarization (CICP), concentrative external concentration polarization (CECP) and the RSF was developed to predict the water flux of the PRO, from which we predicted the power density achieved by the membrane. Experimental verification of the model was carried out by using a bench-scale PRO system. The experimental results demonstrated a good agreement with the actual model scenarios of the water flux and the power density. This study also quantitatively analyzed the proportions of the osmotic pressure drop caused by different factors. It was showed that the proportions of CICP rose from 7.7% to 50.4%, as the feed solution concentration increased from 0 M to 1.5 M under a constant osmotic pressure difference (0.5 M), which also led to a reduction in water flux from 11.55 L m− 2 h− 1 to 1.40 L m− 2 h− 1. Results also indicated that, at higher solution concentrations, the osmotic pressure drop caused by CECP is as notable as that of DECP.