How RO membrane permeability and other performance factors affect process cost and energy use: A review

Abstract

Reverse osmosis (RO) technology has progressed steadily over the last few decades. Those gains were achieved through improvements in both RO membrane element performance and energy recovery technologies. However, some recent literature indicates that RO membrane water permeability is approaching performance limits imposed by transport processes and thermodynamic constraints. This paper reviews how RO membrane element performance affects the cost of RO processes, especially the specific energy consumption. RO membrane performance encompasses water permeability, salt permeability, and other some characteristics of the RO element. This paper considers not only conventional RO processes, but also the recently proposed closed-circuit RO and batch RO processes. Even if the membrane water permeability increases, little additional effect is found when the membrane water permeability exceeds around 3 LMH/bar for seawater RO and 8 LMH/bar for brackish water RO in conventional single-stage RO. Increasing membrane water permeability has the potential to decrease membrane surface area and associated costs. A major limitation of most existing literature is that performance is evaluation on in terms of the initial operating conditions. Chronological changes, such as result from fouling, must also be considered to accurately validate how membrane element performance affects RO cost.

A Review of CFD Modelling and Performance Metrics for Osmotic Membrane Processes

“…The main challenges currently faced by hybrid RO desalination systems that increase energy consumption are fouling, internal and external concentration polarisation, all of which reduce solvent flux. Therefore, some strategies for dealing with these problems are the development of anti-fouling membranes [ 137 , 138 , 139 ], increased membrane permeance [ 107 , 140 , 141 ] and improved spacer design [ 52 , 55 , 56 , 57 , 58 ], particularly for the FO and PRO units.…”

“…A 3D CFD model consisting of several unit cells or several millimetres in length, for instance, would require several tens of millions of discretised elements to resolve the local flow and mass transfer precisely [ 46 ]; hence, the detailed modelling of a full-scale module would be thousands of times that size. To overcome this challenge, the performance of module-scale RO can be evaluated using a multi-scale approach in which correlations for mass transfer and pressure drop obtained by data fitting the results of small-scale models are used [ 46 , 141 ]. With respect to temporal scales, models can be categorised into either steady (aiming to selecting best module design) or transient flow simulation (aimed at understanding how the solutes or fouling components interact with the membrane surface).…”

Nanocomposite Membranes for Liquid and Gas Separations from the Perspective of Nanostructure Dimensions

“…Ultrafast water transport is the ultimate goal of all liquid separation processes. Increasing membrane water permeability can potentially decrease the membrane surface area requirement and the associated costs [ 130 ]. The water permeability of membrane has also been associated with the specific energy consumption of a pressure-driven membrane process such as reverse osmosis [ 131 ].…”

Membrane and Electrochemical Processes for Water Desalination: A Short Perspective and the Role of Nanotechnology

“…In past decades, most research has focused on improving the TFC RO membranes’ performance from ~1 LMH/bar to 5.77 LMH/bar without sacrificing the salt rejection ( Table 1 ) [ 22 , 23 , 24 , 25 ]. Nevertheless, the application of highly permeable membranes to commercial-sized existing modules could increase the extent of CP within the module and accordingly makes process optimization difficult [ 19 , 26 ]. Thus, developing a new module with shorter vessel length could take advantage of a highly permeable membrane.…”

“…Subsequently, several important aspects of currently studied electrochemical cells are described. Because detailed research or review articles for each desalination process have been published recently [ 14 , 15 , 16 , 17 , 18 , 19 ], this perspective attempts to introduce several major findings from each study. A performance evaluation matrix of theoretical (or practical) energy consumption with an emphasis on thermodynamic energy efficiency is introduced based on the characteristics of the representative membrane (RO) and electrochemical (CDI) processes.…”