Comparison of Energy Consumption of Osmotically Assisted Reverse Osmosis and Low-Salt-Rejection Reverse Osmosis for Brine Management

Abstract

Minimum and zero liquid discharge (MLD/ZLD) are emerging brine management strategies that attract heightened attention. Although conventional reverse osmosis (RO) can improve the energy efficiency of MLD/ ZLD processes, its application is limited by the maximum hydraulic pressure (ΔP max ) that can be applied in current membrane modules. To overcome such limitation, novel RO-based technologies, including osmotically assisted RO (OARO) and low-salt-rejection RO (LSRRO), have been proposed. Herein, we utilize process modeling to systematically compare the energy consumption of OARO and LSRRO for MLD/ZLD applications. Our modeling results show that the specific energy consumption (SEC) of LSRRO is lower (by up to ∼30%) than that of OARO for concentrating moderately saline feed waters (<∼35,000 mg/L TDS) to meet MLD/ZLD goals, whereas the SEC of OARO is lower (by up to ∼40%) than that of LSSRO for concentrating higher salinity feed waters (>∼70,000 mg/L TDS). However, by implementing more stages and/or an elevated ΔP max , LSRRO has the potential to outperform OARO energetically for treating high-salinity feed waters. Notably, the SEC of both OARO and LSRRO could be 50% lower than that of mechanical vapor compressor, the commonly used brine concentrator in MLD/ZLD applications. We conclude with a discussion on the practicability of OARO and LSRRO based on membrane module availability and capital cost, suggesting that LSRRO could potentially be more feasible than OARO.

Drivers, challenges, and emerging technologies for desalination of high-salinity brines: A critical review

“…Therefore, OMRO can desalinate the effluents to concentrations beyond conventional RO limits (57,000-90,000 ppm TDS), while requiring substantially less energy (≈4-29 kWh e /m 3 ) [11,214] than traditional distillation processes. Various configurations of OMRO include counter-flow/ osmotically assisted reverse osmosis (CF/OARO), cascading osmotically mediated reverse osmosis (COMRO), and low salt rejection reverse osmosis (LSRRO) [215,216]; the distinct features and advantages of each configuration were discussed in previous studies [11,212,217,218]. A pilot-scale demonstration of CF/OARO was reported in 2018, and a 5000 m 3 /d (1.3 × 10 6 gal/d) CF/OARO plant is currently being built in Saudi Arabia to enhance water recovery from seawater desalination concentrate [219].…”

“…7. Specific energy consumption as a function of feed salinity for alternative and emerging methods, where robust data is available [9][10][11][13][14][15]218,228,231,245,246,[255][256][257]259,260,268,275,277,278,285,291,296,299,308,311,324,327,330,352,375,377,394,395,414,416,417,. Filled, dotted, and open symbols denote data from industrial operations, bench-and pilot-scale experiments, and modeling studies, respectively.…”

Making Waves: Zero Liquid Discharge for Sustainable Industrial Effluent Management

“…A full-scale ZLD system installed at Changxing power plant in Zhejiang, China applies FO process (with use of NH 3 /CO 2 as the thermolytic draw solute) to concentrate RO brine to >220 g/L [24], which is then fed to a crystallizer for final treatment. More recently, novel RO technologies that can overcome the hydraulic pressure limit of conventional RO are proposed, including osmotically assisted RO and low-salt-rejection RO [25]. These innovative technologies can highly concentrate industrial wastewaters under moderate operating pressures.…”

Multistage Surface-Heated Vacuum Membrane Distillation Process Enables High Water Recovery and Excellent Heat Utilization: A Modeling Study

“…9 From a brine concentration or "minimal liquid discharge (MLD)" perspective, the brine volume and disposal cost are minimized. When zero liquid discharge (ZLD) is the goal, the concentrated brine is required to exceed 250,000 ppm TDS 10,11 before being fed into a thermal crystallizer. 12,13 Membrane distillation (MD) is capable of converting high-TDS brines into distillate quality product water in a single pass, 14−16 and MD can desalinate waters of higher TDS than reverse osmosis (currently limited to ∼100,000 ppm TDS); MD also may offer a lower capital cost (particularly in applications <500 m 3 day −1 ) than the traditional thermal distillation process.…”

“…From a brine concentration or “minimal liquid discharge (MLD)” perspective, the brine volume and disposal cost are minimized. When zero liquid discharge (ZLD) is the goal, the concentrated brine is required to exceed 250,000 ppm TDS , before being fed into a thermal crystallizer. , …”