High recovery membrane desalting of low-salinity brackish water: Integration of accelerated precipitation softening with membrane RO: Fid-Bau Portal

High recovery membrane desalting of low-salinity brackish water: Integration of accelerated precipitation softening with membrane RO

Rahardianto, Anditya / Gao, Junbo / Gabelich, Christopher J. / Williams, Mark D. / Cohen, Yoram

Abstract

The integration of membrane RO (reverse osmosis) desalting and APS (accelerated precipitation softening) was evaluated for achieving high product water recovery of > 95 % from desalting of mildly brackish surface water. A systematic approach that included laboratory RO demonstrations, membrane scaling diagnostics, and mineral solubility analysis was undertaken to develop an effective physical/chemical APS strategy for reducing the concentration of scale-forming ions in the PRO (primary RO) concentrate. APS demineralization, as an inter-stage process, between the PRO and SRO (secondary RO) desalting, involved alkaline pH adjustment and calcite crystal seeding of the PRO concentrate, followed by microfiltration and pH reduction by acid dosing to avoid calcite scaling in the SRO stage. A Colorado River water desalting case study demonstrated that, at 90% PRO recovery, the PRO concentrate stream contained barite, calcite, gypsum, and silica above their solubility limits by factors of 122, 47, 1.1, and 0.8, respectively. Further desalting was not feasible with traditional scale-control strategies, like pH reduction and antiscalant addition. APS demineralization enabled significant concentration reduction of calcium > 90 %, barium > 95 %, and strontium about 78 % and moderate reduction of 10 to 20 % of magnesium and silica. APS kinetics were favorable even in the presence of antiscalant carryover from the PRO stage. High recovery desalination of up to 98 % is feasible with the PRO-APS-SRO sequence, which reduces the limitations imposed by membrane scaling.