A point of additional interest with such bags is that they may be readily used to recycle urine, greatly extending the ability of a backpacker or soldier to survive in arid environments. Typically, the draw solutes are sugars such as glucose or fructose, which provide the additional benefit of nutrition to the user of the FO device. The diluted draw solution may then be ingested directly. With sufficient contact time, such water will permeate the membrane bag into the draw solution, leaving the undesirable feed constituents behind. This allows, for example, the ingestion of water from surface waters (streams, ponds, puddles, etc.) that may be expected to contain pathogens or toxins that are readily rejected by the FO membrane. One example of an application of this type may be found in "hydration bags", which use an ingestible draw solute and are intended for separation of water from dilute feeds. The forward osmosis process is also known as osmosis or in the case of a number of companies who have coined their own terminology 'engineered osmosis' and 'manipulated osmosis'. Depending on the concentration of solutes in the feed (which dictates the necessary concentration of solutes in the draw) and the intended use of the product of the FO process, this step may be all that is required. The membrane separation of the FO process in effect results in a "trade" between the solutes of the feed solution and the draw solution. For instance the loss of draw solution may affect the feed solution perhaps due to environmental issues or contamination of the feed stream, such as in osmotic membrane bioreactors.Īn additional distinction between the reverse osmosis (RO) and forward osmosis (FO) processes is that the permeate water resulting from an RO process is in most cases fresh water ready for use.
![reverse osmosis pro ii simulation reverse osmosis pro ii simulation](https://0.academia-photos.com/attachment_thumbnails/42284677/mini_magick20190217-5556-p1wyuk.png)
Clearly these phenomena have consequences in terms of the selection of the draw solution for any particular FO process.
![reverse osmosis pro ii simulation reverse osmosis pro ii simulation](https://i.ytimg.com/vi/zePth0V9iYM/mqdefault.jpg)
This does two things the draw solution solutes may diffuse to the feed solution and the feed solution solutes may diffuse to the draw solution.
![reverse osmosis pro ii simulation reverse osmosis pro ii simulation](https://ars.els-cdn.com/content/image/1-s2.0-S0376738819332004-fx1.jpg)
In FO processes we may have solute diffusion in both directions depending on the composition of the draw solution and the feed water. This is well known in reverse osmosis where solutes from the feedwater diffuse to the product water, however in the case of forward osmosis the situation can be far more complicated. It is clear from this governing equation that a solute will diffuse from an area of high concentration to an area of low concentration. J s = B Δ c is the trans-membrane concentration differential for the solute.