Development of a versatile testing apparatus for measuring hollow fiber membrane flux and permeance

Despite the widespread adoption of hollow fiber membranes for water and wastewater treatment applications, there remains few available methods of reliably determining the flux and permeance of individual hollow fiber membranes for both for outside-in and inside-out operation. We present a new apparatus that can measure the flux and permeance of individual or multiple hollow fiber membranes in both the outside-in and inside-out orientations, partnered with a python-based open-source permeance analysis software. Firstly, we demonstrate the reliability of the instrument in two different configurations. We compare the difference between testing 3 individual membranes and 3 sets of 3 membranes with their permeance combined through manifolds, in dead-end mode. Secondly, the practical utility and advanced capabilities of the apparatus are demonstrated through a series of case studies examining the compaction and fouling behaviors of hollow fiber membranes in both outside-in and inside-out orientation in dead-end mode. We observed significant behavior differences depending on the membrane orientation. For the studied ultrafiltration (UF) membranes, there was not a significant difference in performance depending on orientation, however for the microfiltration (MF) membranes, severe compaction-induced flux loss was observed for the inside-out orientation, with no significant compaction observed in outside-in orientation. Additionally, the orientation of liquid flow significantly affected the flux and permeance measurements of fouled MF membranes. We related the difference in flux and permeance to the differences in structure, as characterized by SEM and liquid-liquid porometry. Deviation in results between the two orientations demonstrates the importance of being able to test hollow fiber membranes in both outside-in and inside-out orientations. This newly designed apparatus will be used to further investigate fundamental mechanisms that affect hollow fiber membrane flux and permeance.