Rotating reverse osmosis and spiral wound reverse osmosis filtration: A comparison

Wastewater produced by the crew members on a long-term space mission needs to be recovered as potable water. Reverse osmosis (RO) has long been in use as a physical membrane separation technology for wastewater treatment. However, membrane fouling and concentration polarization have limited the efficiency for high recovery reverse osmosis systems. An advanced high pressure rotating RO device was designed to minimize these problems by the rotation of the cylindrical RO filter producing shear and Taylor vortices in the annulus of the device. We compare the performance of the rotating RO device to a standard spiral wound RO module using a commercially-available RO membrane under conditions of very high recovery and similar permeate flux. The studies were conducted using 0.01N sodium chloride solution and biological water processor effluent (BWPE) as model wastewaters. The results for 100% recovery of water from 0.01N sodium chloride solution show that the spiral wound RO has poor rejection (<5%) compared to more than 75% rejection for the rotating RO over a period of 2 days. Similar differences in rejection were observed for BWPE for a 5-day test at high recoveries. The overall ion rejection, dissolved organic carbon (DOC) rejection, and ammonium ion rejection from BWPE was typically two times higher for the rotating RO system than for spiral wound RO at 70-80% recovery. Thus, while rotating RO is a more complicated system than spiral wound RO, it provides better rejection of contaminants at very high recoveries.