Performance limitation of the full-scale reverse osmosis process

The mechanisms controlling the performance of a full-scale reverse osmosis (RO) process (typically a pressure vessel holding six 1 m long modules in series) under various operating conditions are carefully examined in this study. We demonstrate that thermodynamic equilibrium imposes a strong restriction on the performance of a full-scale RO process under certain circumstances. This thermodynamic restriction arises from the significant increase in osmotic pressure downstream of an RO membrane channel (owing to the phenomenon of salt accumulation within the RO channel as a result of permeate production). The behavior of the full-scale RO process under thermodynamic restriction is much different from that of the process when it is controlled by mass transfer. The conditions for an RO process to shift from mass transfer-controlled regime to thermodynamically restricted regime are delineated and discussed.