Two-phase flow in membrane processes: A technology with a future

Worldwide, the application of a (gas/liquid) two-phase flow in membrane processes has received ample scientific deliberation because of its potential to reduce concentration polarization and membrane fouling, and therefore enhance membrane flux. Gas/liquid flows are now used to promote turbulence and instabilities inside membrane modules in various membrane processes such as microfiltration, ultrafiltration, nanofiltration, reverse osmosis, membrane distillation, electrodialysis, and membrane bio-reactors. This paper provides a comprehensive and critical literature review of the state of the art in this research area. A total of 205 scientific papers published in peer-reviewed journals from 1989 to 2013 were collected. The data in 195 of these papers (published up to 2011) were compiled and analyzed. These data were analyzed and normalized based on gas and liquid superficial velocities, gas/liquid ratio and feed types, trans-membrane pressure and membrane module type in order to make a fair comparison and identify general characteristics. The objective was to identify key factors in the application of two-phase flows in aqueous separation and purification processes, deliver new insights in how to optimize operations for implementation of this technology in the industry, discuss the importance of energy saving, provide a brief overview of current commercial applications and suggest future directions for research.