Forward Osmosis: Current Status and Perspectives

Study Shows Forward Osmosis Desalination Not Energy Efficient

Forward osmosis (FO) is a natural process for water transfer through a selectively permeable membrane driven by the osmotic pressure difference across the membrane. Starting from Sidney Loeb's pioneering work in pressure-retarded osmosis (PRO) three decades ago published in the first issue of the Journal of Membrane Science (January, 1976), there has been a resurgence of interest in various osmotic processes in recent years. The renewed attention comes from the potential to either reduce energy consumption in wastewater treatment, water purification and seawater desalination, or produce energy from salinity-gradient energy harvesting, etc.

However, there are a number of technical barriers that impede FO's industrial applications. The major challenges to be overcome include (i) the lack of an ideal draw solution that exhibits high osmotic pressure and can be easily regenerated to produce pure water; and (ii) the lack of an optimized membrane that can produce a high water flux, comparable to commercial RO membranes, with low salt transmission, and possessing effective anti-fouling properties. In addition, a suitable module design is required to maintain long-term system performance for specific applications, etc. This virtual special issue of the Journal of Membrane Science provides the state-of-the-art of FO technology, including the contributions from the membrane community to address the above-mentioned challenges over the period from 1976 to June 2012.

Concluding remarks

Osmotically driven membrane processes are remarkable new and green technologies and have attracted extensive studies in recent years. Considerable R&D outcomes for FO have been published in the Journal of Membrane Science, in its role as the premier journal in the membrane field. The research activities are mainly focused on novel FO/PRO membrane development (28%), exploration of various applications of osmotic processes (24%), fundamental understanding of concentration polarization and modeling (21%), membrane fouling control (10%), invention of new draw solutes (8%) and module design (7%). The people most actively involved in this field currently include Elimelech's group, Cath and Childress's groups and McCutcheon's group in the United States, Chung's group and the Wang-Tang-Fane group in Singapore.

It is anticipated that the efforts from the membrane community will continue to achieve technology breakthroughs in novel FO membranes and draw solute developments in the near future. This virtual special issue is expected to provide a platform for easy access to state-of-the-art FO technology so as to facilitate further FO technology development.

Appendix: List of forward osmosis papers published in Journal of Membrane Science up to June 2012

Source: Elsevier

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Taxonomy

• Desalination
• Forward Osmosis

1 Comment

1. Forward Osmosis (FO) is not new and it has limited ability to yield total energy savings - likely 10 to 30 % of that needed conventional SWRO desalination. Similar to reverse osmosis, FO is limited by the energy needed to break the the chemical bonds of salts and water or other soulite in which the salts are dissolved. State of the art SWRO technologies and membranes available today allow to desalinate water at not more than 70 to 80 % of this minimum theroetical energy and therefore, whatever technology we use cannot yield much more than 70 to 80-% savings theoretically. Since we can never recover 100 % of this difference (in seawater desalination we can only recover 40 to 50 %), the maximum theoretical savings are proportionally smaller. When we consider the much higher fouling potential of state of the art FO membranes as compared to SWRO membranes , their higher trans-membrane pressure and energy needed to pump the water between the FO system components which are more complex than RO system components, the overall maximum savings go down very fast. FO requires lower energy to drive water movement through a membrane, but is does not produce fresh water directly - it just drives it from one solution with high osmotic pressure (i.e. seawater) to another solution with high osmotic pressure (solute -.i.e., ammonium bicarbonate). Getting the water out of the solute still needs energy; more energy is also needed to pump the water between the separation and recovery components, etc.- so in total, the savings are practically limited.