ABSTRACT Conceptual diagram depicting key trends in closed-circuit reverse osmosis performance with seawater augmentation at potable reuse facilities, including system pressure and energy changes, permeate quality, and concentrate composition. Seawater-augmented potable reuse at an advanced water purification facility can provide additional water supplies without significant increases in infrastructure. Operational flexibility in the reverse osmosis (RO) process was conceptually analyzed using closed-circuit RO simulations. Feedwater-shortage and increased-production scenarios were compared with a baseline scenario with no seawater augmentation. Seawater augmentation increased the feedwater total dissolved solid (TDS) concentrations but diluted the wastewater constituents (organics and nutrients), and thus decreased the likelihood of RO membrane fouling. Maximum recovery rates, determined using pressure and solubility criteria, decreased from 90 in the baseline to 77% when blended with 30% seawater. The reduced recovery rates required increased RO feedwater flowrates and resulted in increased RO concentrate flowrates. With 30% seawater augmentation, the concentrate flowrate is ∼2.7 times higher, with a TDS ∼4.5 times higher than the baseline; this may require modifications to outfall infrastructure. On the other hand, nutrients in the concentrate to be discharged were diluted, which could reduce impacts on aquatic life and human health. Specific energy consumption increased from 1.36 in the baseline to 4.20 kWh/m3 with 30% seawater augmentation; however, low-pressure energy recovery devices can be implemented to mitigate energy penalties. Modifications to piping may also be required to increase corrosion resistance.
Dahdah et al. (Fri,) studied this question.