Recent Trends in Membrane Processes for Water Purification of Brackish Water

Abstract

Naturally occurring brackish water, normally containing 500–10,000 mg/L of total dissolved solids, is not safe for direct consumption due to its salinity. The salinity level needs to be reduced to a level below 500 mg/L to make it drinkable as per recommendations of the World Health Organization (WHO). Reverse osmosis (RO) process for water desalination purposes is currently considered to be the most effective, economical, efficient, and optimized method dominating the water purification market. An extensive research has been carried out in the field of membrane-based brackish water reverse osmosis (BWRO) process to improve its desalting performance. Various aspects of a BWRO process system such as nature and type of membrane material, module design parameters, process configuration, energy recovery devices, operating parameters, economical aspects are reviewed in this chapter. Theoretical background of a BWRO process, transport mechanism through BWRO membranes, and desalination performance of BWRO membranes are considered here. An updated review of different commercially available BWRO membranes, membrane modules, and process configurations is also provided. In addition, major components of a typical BWRO plant such as pretreatment unit, pumping system, membrane module section, and post-treatment unit are also described in this review. General process considerations, economic aspects, energy recovery options, and process optimization of a BWRO system are discussed here. High-performance BWRO membranes prepared from polymeric and thin-film composite materials are inserted in commercial spiral wound modules to make the desalting process economically efficient. Concentrated brine rejected from a BWRO plant can be economically treated by installing solar stills at sunlit places. A double-stage membrane process can enhance water recovery of BWRO plants from the usual range of 85–90% to about 95–98%. Brackish water can be purified by BWRO process at reduced cost by using high rejection membranes, installing larger pressure vessels, and adopting hybrid membrane design.