Forward Osmosis
"Forward Osmosisis an osmotic process that, like reverse osmosis uses a semi-permeable membrane to effect separation of water from dissolved solutes. The driving force for this separation is an osmotic pressure gradient, such that a "draw" solution of high concentration (relative to that of the feed solution), is used to induce a net flow of water through the membrane into the draw solution, thus effectively separating the feed water from its solutes. In contrast, the reverse osmosis process uses hydraulic pressure as the driving force for separation, which serves to counteract the osmotic pressure gradient that would otherwise favor water flux from the permeate to the feed. The simplest equation describing the relationship between osmotic and hydraulic pressures and water flux is:
where Jw is water flux, A is the hydraulic permeability of the membrane, Δπ is the difference in osmotic pressures on the two sides of the membrane, and ΔP is the difference in hydrostatic pressure (negative values of Jw indicating reverse osmotic flow). The modeling of these relationships is in practice more complex than this equation indicates, with flux depending on the membrane, feed, and draw solution characteristics, as well as the fluid dynamics within the process itself." (Wikipedia, Forward Osmosis, 3/9/2011)
Recent Journal Articles
Hydrophilic Superparamagnetic Nanoparticles: Synthesis, Characterization, and Performance in Forward Osmosis Processes
(382–388) Industrial & Engineering Chemistry Research 50 #1 (2011)
Ge et al of theNational University of Singapore, China and King Abdullah University of Science and Technology, Saudi Arabia synthesized a series of poly(ethylene glycol)diacid-coated (PEG−(COOH)2-coated) magnetic nanoparticles MNPs with different size distributions have been synthesized by means of the thermal decomposition method resulting in nanospheres with narrow size distribution, and a mean size from 4.2 to 17.5 nm depending on the ratio of the two starting materials of PEG−(COOH)2 to ferric triacetylacetonate (Fe(acac)3). The as-prepared PEG−(COOH)2 MNPs exhibit good dispersibility and generate high osmotic pressures in aqueous solutions. Water fluxes of >10 L m−2 h−1 are achieved across Hydration Technologies Inc. flat sheet membranes when deionized water is used as the feed solution. The MNPs can be easily recovered from draw solutions by applying a magnetic field. The MNPs remain active after nine runs of recycle but with a total water flux decrease of 21% due to slight aggregation. Results have demonstrated that using PEG−(COOH)2 MNPs as draw solutes is feasible in the FO process. (RDC 2/14/2011)