Energy efficient assisted forward osmosis

Leader

Challenge

Forward osmosis (FO) has been demonstrated as a promising technology capable of producing fresh water with a low energy requirement. Although this and other osmosis processes have been extensively studied in the last few years, the full potential of osmotic-based processes to dilute seawater before reverse osmosis (RO) treatment has not been fully investigated. The potential of a novel mode of osmosis operation, called assisted forward osmosis (AFO), may be an opportunity for reducing the high energy requirements of sea and brackish RO plants, whereby hydraulic pressure is used as an additional driving force to enhance water permeation flux. An initial assessment indicates a potential energy saving of up to 12.5% when the FO is operated at 50% recovery. The potential of the concept is significant, and could greatly increase the viability of future desalination projects.

Investiation

Experimentally and theoretically demonstrate the potential of the use of AFO to significantly reduce energy consumption of sea and brackish water treatment by RO membranes. Evaluate the limitations to improving flux in FO through (1) the use of new commercially available thin film composite thin film composite (TFC) FO membranes and (2) the implementation of hydraulic pressure or pressure-assisted osmosis (AFO or PAO).

Outcomes

The PAO-NF concept was demonstrated using different commercially available nanofiltration (NF) membranes and all outperformed the conventional FO membrane. As expected NF membranes were much more responsive to the hydraulic pressure driving force, resulting from their higher water permeability.

Fouling tests demonstrated the low fouling behaviour often associated with FO was due to operation at low permeation fluxes. With higher initial fluxes, fouling was found compacted on the membrane surface and consequently flux decline was observed over time. At similar initial fluxes, fouling was more severe when a moderate hydraulic pressure (4 bar) was applied. Osmotic backwashing was an effective cleaning strategy. Interestingly, novel FO membranes demonstrated improved rejection across the range of tested trace organic contaminants by steric rejection. Operation in PAO mode led to a general decrease of rejection, as a result of membrane deformation and less reverse salt diffusion.

The economic model demonstrated the benefits of using NF membranes in the PAO process due to the savings in required membrane surface area and thus CAPEX costs. In additional to the savings in CAPEX, the energy needs for RO step could also be reduced due to the osmotic dilution. Indeed, the energy modelling demonstrated that the overall PAO-NF/RO hybrid could be beneficial for process economics; reducing up to 31% of the energy needs for RO as a result of osmotic dilution. The economic analysis also highlighted that further flux improvement is needed (>30 L.m-2.h-1) to lower investment costs down to an economically acceptable level for the FO-RO hybrid to become beneficial compared to standalone seawater RO.

Future Direction

One avenue of interest would be to develop or modify existing NF membranes with thinner mechanical support layers in order to perform better in osmotic-based process and also in PAO. This alternative operation of PAO-NF operation will allow the future research focus on new FO configurations and operations, and membrane material development.

Technology Readiness

This technology is protected by PCT patent application WO2015/157818. Industrial  partners are being sought to work with the Principal Investigator to explore the applications of the technology. 

Partners 

       


 

Total Value: $673,500 (cash and in-kind contributions)

Principal Investigator: Associate Professor Pierre Le-Clech

Title: Assisted forward osmosis for energy savings in reverse osmosis desalination

Length: 54 months

Personnel: 7 collaborators contributing 4.4 FTE

Further Information

FR3 UNSW Le-Clech (Energy) Summary Poster

Project Summary Poster – AFO

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