High recovery, low fouling, and low energy reverse osmosis

Abstract

Desalination and water reuse using reverse osmosis (RO) are viable new water supply resources; however, traditional RO systems often create excess brine waste, do not fully utilize source water supplies, and consume too much energy. Newly emerging closed-circuit RO processes improve RO performance and reduce its cost by increasing recovery, reducing fouling and scaling, and reducing energy consumption. This performance has been documented in dozens of RO installations in a range of applications. In particular, a closed-circuit RO unit operated on groundwater with a silica concentration of 59 ppm at recovery rates of up to 93.5%, producing brine silica concentrations exceeding 900 ppm. This recovery rate was sustained at neutral pH, with modest anti-scalant dosing and no scaling-related CIP requirements. A traditional RO system operating in feedwater with this concentration of silica would be limited to 76% recovery or less, corresponding to more than 3 times the production rate of brine concentrate. At another site, seawater with a total dissolved solids content of 35,329 ppm was desalinated with 5.5 kWh/1,000 gal (1.45 kWh/m3) of RO pump energy. This represents the lowest energy consumption ever reported for seawater RO at a comparable recovery rate and flux.