Hybrid configurations for brackish water desalination: a review of operational parameters and their impact on performance

Abstract

ABSTRACT The remote villages in arid and semi-arid inland regions of Rajasthan state in India and many other countries are dependent on brackish groundwater for potable uses. Generally, community RO (Reverse Osmosis) plants are installed for brackish water treatment in rural agglomerations where the MLD (Minimal liquid discharge) scheme is followed which includes pre-treatment and pre-concentration technologies, that consumes relatively low energy than thermal technologies for ZLD (Zero liquid discharge). This paper discusses the application of hybrid processes involving MLD technologies such as IEX (Ion Exchange), NF (Nanofiltration), RO, FO (Forward Osmosis) and UF (Ultrafiltration). for brackish water treatment. The impact of feed water quality and operational parameters such as flux, feed flow rate and transmembrane pressure are discussed. Further, performance indicators such as salt rejection, recovery, energy consumption and scaling propensity are discussed to evaluate the feasibility of various configurations. The findings of this review indicate NF as impressive membrane technology for conjunction with IEX, RO and UF. Further, the use of FO or NF as a pre-treatment for RO has been found to reduce the scaling propensity of RO membranes; and the use of UF as a pre-treatment for NF has been found to reduce the propensity of organic fouling on NF membranes. Also, IEX as a pre-treatment can be coupled with low-pressure RO/NF to remove the scale-causing divalent ions and enhance recovery along with an option of reusing RO/NF reject water for regeneration of IEX column.