Exploring the Limitations of Osmotically Assisted Reverse Osmosis: Membrane Fouling and the Limiting Flux

Abstract

Osmotically assisted reverse osmosis (OARO) has shown great potential for low-cost and energy-efficient brine management. However, its performance can be significantly limited by membrane fouling. Here, we performed for the first time a comprehensive study on OARO membrane fouling, explored the associated fouling mechanisms, and evaluated fouling reversibility via simple physical cleaning strategies. First, internal membrane fouling at the draw (permeate) side was shown to be insignificant. Flux behavior in short-term operation was correlated to both the evolution of fouling and the change of internal concentration polarization. In long-term operation, membrane fouling constrained the OARO water flux to a singular, common upper limit, in terms of limiting flux, which was demonstrated to be independent of operating pressures and membrane properties. Generally, once the limiting flux was exceeded, the OARO process performance could not be improved by higher-pressure operation or by utilizing more permeable and selective membranes. Instead, different cyclic cleaning strategies were shown to be more promising alternatives for improving performance. While both surface flushing and osmotic backwashing (OB) were found to be highly effective when using pure water, a full flux recovery could not be achieved when a nonpure solution was used during OB due to severe internal clogging during OB. All in all, the presented findings provided significant implications for OARO operation and fouling control.

Reject brine management: Denitrification and zero liquid discharge (ZLD)—Current status, challenges and future prospects

“…OARO is a membrane-based process for desalination of high-salinity brines. This technology has a high recovery rate and is energy-efficient (Peters et al, 2022). OARO combines both the FO and RO working principles (Fig.…”

Electrified Solar Zero Liquid Discharge: Exploring the Potential of PV-ZLD in the US

“…24,25 However, membrane-based methods for the treatment of high-salinity brine had particular challenges related to fouling, which restricts water flux. 26 Combining freeze desalination, membrane distillation, and crystallization can reach ZLD levels and use renewable energy as an energy source. However, energy consumption is greater than RO-based systems.…”

“…Hybridization reduces the total specific energy consumption by combining the most efficient technologies for a particular feeding salinity in series. , There are numerous alternative hybrid methods based on membranes to concentrate brine, but none are in the commercial state. The use of osmotically assisted reverse osmosis (OARO) and low salt rejection reverse osmosis (LSRRO) systems can decrease the specific energy consumption by 50% compared to traditional brine concentration systems. , However, membrane-based methods for the treatment of high-salinity brine had particular challenges related to fouling, which restricts water flux …”

Electrified Solar Zero Liquid Discharge: Exploring the Potential of PV-ZLD in the US

“…The use of osmotically assisted reverse osmosis (OARO) and low salt rejection reverse osmosis (LSRRO) systems can decrease the specific energy consumption by 50% compared to traditional brine concentration systems 22,23 . However, membrane-based methods for the treatment of high-salinity brine had particular challenges related to fouling, which restricts water flux 24 . Combining freeze desalination, membrane distillation, and crystallization can reach ZLD levels and use renewable energy as an energy source.…”