Nonlinear Behavior of Permeate Flux in Full-Scale Reverse Osmosis Processes

Abstract

Permeate flux is a key design and operating parameter for the reverse osmosis (RO) process. It has been widely observed from laboratory studies that permeate flux is linearly related to transmembrane pressure, but it has been noted that such a simple linear relationship may not be strictly applicable to a typical full-scale RO process where a long membrane channel is employed. A pilot-scale RO system with a 4-m-long membrane channel was used in this study to investigate the behavior of permeate flux under various operating conditions. It was noted that the linear relationship between the average permeate flux and transmembrane pressure was only true when the RO system was operating at low transmembrane pressure or recovery. The average permeate flux deviated substantially from the linear relationship as the transmembrane pressure increased. It was speculated that thermodynamic equilibrium between the osmotic pressure in the membrane channel and the transmembrane pressure of the RO process might become the limiting factor of RO processes under certain circumstances.