A Standard Methodology for Evaluating Membrane Performance In Engineered Osmosis

Osmotically driven membrane processes (ODMP) such as forward osmosis and pressure retarded osmosis are extensively investigated for utilization in a broad range of applications. In ODMP, the operating conditions and membrane morphology play more critical roles in mass transport and process performance than in pressure-driven membrane processes. Search of the literature reveals that ODMP membranes, especially newly developed ones, are tested under different temperatures, draw solution compositions and concentrations, flowrates, and pressures. In order to be able to compare different membranes, it is important to develop standard protocols for testing of membranes for ODMP.

In this study we propose a standard methodology for testing of ODMP membranes based on experience gained and operating conditions used in FO and PRO studies in recent years. A round-robin testing of two membranes in seven independent laboratories revealed that water flux and membrane permeability coefficients were very similar when all groups performed the experiments and calculations using the same protocols. Thin film composite membranes have higher water permeability, but results are more scattered due to the technical difficulties to test these membranes. 

Further conclusions reiterate that at least three experiments for each parameter must be conducted under the same condition and with different membrane samples in order to obtain reliable results. It is also important that manufacturers of ODMP membranes use unique naming and numbering of their manufacturing batches and that they provide minimal characteristics parameter of their membranes, similar to the specifications provided for established commercial pressure-driven membranes.