Characterization of internal and external concentration polarizations during forward osmosis processes Original Research Article

Forward osmosis (FO) is an emerging technology showing promising future in fields of water/wastewater reclamation, desalination and energy production. However, the efficiency of such process can be adversely affected by internal concentration polarization (ICP), which is usually characterized by the structural parameter, S value. In this work, we established three independent testing methods in reverse osmosis (RO) mode to evaluate the S value, namely the Jv-method, the Rs-method and the Rt-method, relying on the measurements of RO water flux, salt rejection and trace contaminant (boron in this work) rejection, respectively. S values achieved by three methods showed good agreement with that obtained by the conventional FO water flux fitting method. Among the three approaches, the Rs-method exhibited a much smaller deviation and it was demonstrated successfully that this method can be used to estimate the value of the solute permeability graphically at the same time. In addition, the Rs-method showed the feasibility to study ICP and external concentration polarization (ECP) interpretively.