Evaluation of apparent membrane performance parameters in pressure retarded osmosis processes under varying draw pressures and with draw solutions containing organics

The performance of pressure retarded osmosis (PRO) membrane, characterized by water and solute permeability (A and B) and the structural parameter (S), was analyzed by a new method designed to simulate the PRO process more closely. Compared to conventional approaches to membrane characterization using reverse osmosis (RO)/forward osmosis (FO), the newly developed method using a single PRO experiment better predicted PRO process performance, particularly when high pressure was applied on the draw side. It was clearly demonstrated that apparent B value increased with increasing draw pressure. This characterization method was also used to evaluate PRO membrane performance in the presence of organic matter, such as alginate or xanthan, in draw solutions. Organic matter in draw solutions reduced the apparent B value, which could result in less draw solute loss in PRO processes. Our experimental observations clearly suggested that PRO membrane processes should be analyzed and predicted by methods like the one presented which simulate actual PRO operating conditions, particularly the hydraulic pressure applied to draw solutions.