Rotating reverse osmosis for water recovery in space: influence of operational parameters on RO performance

Rotating reverse osmosis (RO), which is based on Taylor-Couette flow, offers a means to minimize flux decline due to concentration polarization and membrane fouling. However, the operating conditions play a significant role in determining the effectiveness of the system. In this study, the effect of operating conditions on system performance was explored using a theoretical model. Flux, rejection, recovery, and theoretical power consumption were calculated for a wide variety of operating parameters including transmembrane pressure, rotational speed, and concentrate flow rate. Flux and rejection increase with increasing transmembrane pressure and rotational speed. Operating in the vortical flow regime enhances the filtration performance. Higher concentrate flow increases flux, but decreases recovery. The power consumption for rotating RO is similar to that for conventional RO except at very high rotational speeds.

The following conclusions can be drawn from this work: 1. The model calculations show that flux and rejection increase with increasing transmembrane pressure and rotational speed. Our previous analyses and experiments showed similar results [10,17], but these results were for dead-end dynamic filtration, for which there was no concentrate flow (Qconc = 0). This current model, which includes the effect of the concentrate flow rate, demonstrates that higher concentrate flow increases flux, but decreases recovery. 2. It is possible to predict the operating parameters necessary to achieve certain filtration requirements. In particular, using Fig. 3, the Rotational speed (rpm) 2500 2000 (a) Transmembrane pressure, ∆P (kPa) Transmembrane pressure, ∆P (kPa) Qconc (mL/min) (b) Fig. 8. Contours of membrane module volume (cm3) to produce the daily water requirements for one person in space. (a) At different pressures and rotational speeds (Qcon c= 3 mL/min); (b) At different pressures and concentrate flow rates (ω = 100 rpm).