Treatment technologies for reverse osmosis concentrate volume minimization: A review

Reverse osmosis (RO) is a well-established technology for treatment of impaired water sources and production of potable water. One of the major drawbacks with RO is the volume of concentrate (reject) produced during the process. Several technologies and process configurations, which are available for further treatment of RO concentrate, reduce the reject volume. In this paper, a comprehensive review of treatment technologies for treating RO concentrate from municipal and industrial sites to enhance the overall feed water recovery is presented. Treatment technologies are discussed according to their classification as membrane-based, thermal-based, or emerging technologies. All categories are capable of reducing RO concentrate volume, and in combination, can achieve zero liquid discharge. Membrane-based technologies are less energy intensive when compared to thermal-based technologies, but when the concentrate water quality is complex, such as with industrial effluents, the use of membrane-based technologies is restricted. Thermal-based technologies are capital intensive, consume a significant amount of energy and are not suitable for large flow rates. This review also addresses emerging technologies, such as forward osmosis (FO) and membrane distillation (MD) that show promise to efficiently treat RO concentrate, but these technologies are still under development and operational data on large scale facilities are limited. Selection of the best available technology for concentrate volume minimization will depend on several factors including the treated water quality, energy consumption, costs and technological development stage.