Osmosis-Assisted Reverse Osmosis: A Promising Brine Desalination Technology

Overview

Osmosis assisted reverse osmosis (OARO) is a promising membrane process for brine management and desalination. It offers a high recovery rate and energy efficiency even when dealing with highly saline brine. OARO has been tested for brine feed with salinity of 150,000 mg/l [1].

OARO Mechanism

OARO combines the working principles of Forward Osmosis (FO) and Reverse Osmosis (RO). Unlike the traditional RO process, a saline solution is pumped through the permeate side to reduce the osmotic pressure gradient across the membrane. This allows for operation at lower pressures, making it suitable for treating highly concentrated brines without exceeding the membrane’s burst pressure [2]. However, the draw solution requires additional treatment to reach desired salinity levels. 

OARO Process Flow 

A series of OARO stages can be used in sequence to reduce the concentration of the feed, then a traditional RO process to obtain the final permeate as shown in the figure below. Brine is used as a feed solution in the first stage, where a lower salinity permeate stream sweeps the membrane. In subsequent stages, the permeate from the previous stage becomes the feed solution for the next membrane cell, further reducing its salinity. If the salinity of the diluted permeate is higher than the desired permeate quality, another closed stage can be used for further dilution. The number of stages depends on the initial salinity and desired product quality [3]. The final stage is a traditional RO process used to reduce the salinity to the desired limit.

Research and Development Opportunities 

Currently the OARO process and membranes are under research and development. OARO membranes must ideally have low solute permeability and high-water permeability [4]. In addition to manufacturing a tailored membrane for OARO, the current research effort is focused on evaluating the scaling of membranes when using highly saline brine and evaluating the economic feasibility of the process. We offer a wide selection of FO and RO membranes that could be a starting point and a valuable resource for your OARO research and development.

Designing membrane cells for OARO is still under development with a particular emphasis on membrane support from the permeate side. The cell must provide physical support for the membrane against the applied pressure and allow for the draw solution sweep flow at the same time. 

Our experts would be glad to be part of the development journey and answer your technical inquiries about Osmosis Assisted Reverse Osmosis.

References:

[1] G. P. Thiel, E. W. Tow, L. D. Banchik, H. W. Chung, and J. H. Lienhard, “Energy consumption in desalinating produced water from shale oil and gas extraction,” Desalination, vol. 366, pp. 94–112, Jun. 2015, doi: 10.1016/j.desal.2014.12.038.

[2] T. V. Bartholomew, L. Mey, J. T. Arena, N. S. Siefert, and M. S. Mauter, “Osmotically assisted reverse osmosis for high salinity brine treatment,” Desalination, vol. 421, pp. 3–11, Nov. 2017, doi: 10.1016/j.desal.2017.04.012.

[3] B. H. M. Beigi, S. Gadkari, and J. Sadhukhan, “Osmotically assisted reverse osmosis, simulated to achieve high solute concentrations, at low energy consumption,” Scientific Reports, vol. 12, no. 1, Aug. 2022, doi: 10.1038/s41598-022-16974-x.

[4] C. D. Peters and N. P. Hankins, “Osmotically assisted reverse osmosis (OARO): Five approaches to dewatering saline brines using pressure-driven membrane processes,” Desalination, vol. 458, pp. 1–13, May 2019, doi: 10.1016/j.desal.2019.01.025.