Optimize Brackish Groundwater: Treating RO Brine to Increase Recovery and Reduce Disposal Volume

Abstract

The Eastern Municipal Water District in Perris, Calif., recently completed brine treatment studies for the California Department of Water Resources and the US Department of Interior, Bureau of Reclamation. The studies investigated the cost of alternative process treatment trains to recover usable water from primary reverse osmosis (RO) brine and significantly reduce brine volume or achieve complete zero-liquid discharge. The studies included pilot-scale, bench-scale, and desktop evaluations of established and emerging technologies for brine treatment. Chemical softening of primary RO brine followed by a second RO process or electrodialysis reversal (EDR) is an established technology. Emerging technologies investigated included membrane distillation (MD), forward osmosis (FO), and seeded RO. A 50-gpm chemical softening process was operated for six months and provided feedwater to RO and EDR pilot units. MD and FO were tested at bench scale, and seeded RO was operated in a batch pilot plant. Capital and operations and maintenance cost estimates were established for several treatment configurations that also included brine concentration, crystallization, and pond evaporation. The configurations were then compared. Overall, total annual costs for 14 treatment train combinations were generally within about 10 percent of each other. Treatment for removing and recovering salable salt by-products was, however, more costly, probably because of capital costs associated with selective precipitation and washing and processing of salts. Treatment trains that included a third concentration step (the seeded RO process) ahead of thermal mechanical evaporation appeared to have slightly lower overall costs. This is attributed to the reduced size of the thermal evaporation process. Additional work on MD, FO, and seeded RO processes is needed.