Forward osmosis ( FO ) is an osmotic process which, like reverse osmosis (RO), uses a semi-permeable membrane to separate water from dissolved solutes. The driving force for this separation is the osmotic pressure gradient, so that a "balanced" solution of high concentration (relative to the feed solution) is used to induce the net flow of water through the membrane into the lottery solution, thereby effectively separating the feed water from the solute. In contrast, the reverse osmosis process uses hydraulic pressure as the driving force for separation, which serves to counter the osmotic pressure gradient which would otherwise support the water flux from permeate to feed. Then significantly more energy is required for reverse osmosis compared to the osmosis to the front.
Persamaan paling sederhana yang menggambarkan hubungan antara tekanan osmotik dan hidraulik dan fluks air (pelarut) adalah:
di mana adalah fluks air, A adalah permeabilitas hidrolik dari membran, ?? They smell the bones of the osmotik, and the kedua sisi membran, dan? P adalah perbedaan dalam tekanan hidrostatik (nilai negatif menunjukkan aliran osmotik balik). Pemodelan hubungan ini dalam prakteknya lebih kompleks daripada persamaan ini menunjukkan, dengan fluks tergantung pada membran, umpan, dan menarik karakteristik solusi, serta dinamika fluida dalam proceso itu sendiri.
Flux zat terlarut ( ) untuk setiap solut individu dapat dimodelkan oleh Fick's Law
Di mana adalah koefisien permeabilitas terlarut dan adalah diferensial konsentrasi trans-membran untuk zat terlarut. Jelas dari persamaan yang mengatur bahwa zat terlarut akan menyebar dari area konsentrasi tinggi ke area konsentrasi rendah. Ini dikenal dalam reverse osmosis di mana zat terlarut dari air umpan menyebar ke air produk, namun dalam kasus osmosis ke depan situasinya bisa jauh lebih rumit.
In the FO process, we may have dissolved diffusion in both directions depending on the composition of the aqueous solution and the feed water. It does two things; the solvent agitation solution can diffuse into the feed solution and the solution solution solution can diffuse into the lottery solution. Obviously this phenomenon has consequences in terms of selection of lottery solutions for each particular FO process. For example the loss of withdrawal solutions may affect the bait solution may be due to environmental problems or contamination of the feed stream, as in osmotic membrane bioreactors.
An additional difference between the reverse osmosis (RO) and forward osmosis (FO) processes is that the water absorbs the results of the RO process in many cases fresh water is ready for use. In the FO process, this does not happen. Membrane separation from the FO process in effect produces a "trade" between the solute of the feed solution and the draw solution. Depending on the concentration of solute in the feed (which determines the solute concentration required in the draw) and the purpose of product use of the FO process, this step may be all that is needed.
The process of advanced osmosis is also known as osmosis or in the case of a number of companies that have created their own engineering osmosis terminology and manipulated osmosis.
Video Forward osmosis
Apps
The emergency drink
One example of this type of application can be found in the "hydration bag", which uses ingestion drawing solutes and is intended for the separation of water from the aqueous feed. This allows, for example, the consumption of water from surface water (rivers, ponds, pools, etc.) which may be expected to contain pathogens or toxins easily rejected by the FO membrane. With sufficient contact time, such water will penetrate the membrane bag into the lottery solution, leaving unwanted feed constituents behind. The solvent recall solution can then be digested directly. Typically, the balancing agent is a sugar like glucose or fructose, which provides additional nutritional benefits for users of FO devices. An additional point of interest with such a bag is that it can be used to recycle urine, greatly extending the ability of a backpacker or warrior to survive in a barren environment. This process may also, in principle, be used with highly concentrated salt water feed sources such as seawater, as one of the first uses of FO with edible solutes is to survive in a marine life raft.
Desalination
Water desalination can be generated from diluted/osmotic stirring solution, using a second process. This may be by membrane separation, thermal method, physical separation or a combination of these processes. This process has a low fouling feature due to the first step forward osmosis, unlike the conventional reverse osmosis desalination plant where fouling is often a problem. Modern water has deployed osmotic-based desalination plants ahead in Gibraltar and Oman. In March 2010, National Geographic magazine cited forward osmosis as one of three promising technologies for reducing desalination energy requirements.
Evaporative cooling tower - make-up water
One other application developed, in which only a step forward osmosis is used, is in evaporative makeup water. In this case cooling water is a lottery solution and water lost by evaporation is replaced only by water produced by osmosis forward from suitable sources, such as seawater, brackish water, waste treated waste or industrial wastewater. So compared to other desalination processes that can be used for make-up water, energy consumption is a fraction of this with the added advantage of a low fouling tendency of the osmosis process going forward.
Waste Treatment of TPA
In cases where the desired product is fresh water containing no solute, a second separation step is required. The first separation step of the FO, driven by an osmotic pressure gradient, does not require significant energy input (only stirring without pressure or pumping of the solutions involved). The second separation step, but usually requires energy input. One of the methods used for the second separation step is to use RO. This approach has been used, for example, in the treatment of landfill leachate. Separation of membrane FO is used to extract water from leachate feed into brine (NaCl). The diluted salt water then passes through the RO process to produce fresh water and reusable salt water concentrate. The advantage of this method is not the energy savings, but rather the fact that the FO process is more resistant to fouling than the leachate feed than the RO process alone. Similar FO/RO hybrids have been used for the concentration of food products, such as fruit juice.
Brine Concentration
Brine concentration using forward osmosis can be achieved by using a solution of high osmotic pressure with the means to restore and regenerate. One such process uses a process of ammonia-carbon dioxide advanced osmosis originally developed at Yale University and commercialized by Oasys Water. Because ammonia and carbon dioxide readily dissociate into gases by heat, interesting solutes can be effectively recovered and reused in closed-loop systems. Salt concentrations are currently used in the oil and gas industry for treating water produced in the Permian Basin area of ​​Texas.
Feed water' softening '/pre-treatment for thermal desalination
One application that is not exploited is to 'soften' or pre-treat the feedwater to a multi-stage flash (MSF) or plant multiple effect distillation (MED) by osmotically diluting saline water recirculating with cooling water. This reduces the concentration scale of calcium carbonate and calcium sulphate formation compared with the normal process, thereby allowing the increase in the temperature of the upper brine (TBT), the output and the resulting output ratio (GOR). Darwish et al. showed that TBT can be raised from 110 ° C to 135 ° C while maintaining the same scale index for calcium sulphate.
Osmotic Strength
In 1954 Pattle suggested that there was an untapped source of energy when a river mixed with the sea, in terms of lost osmotic pressure, but not until the mid-70s where practical methods of exploiting selectively use membe permeable by Loeb. and independently by Jellinek outlined. This process is referred to by Loeb as a pressure retarded osmosis (PRO) and a simple implementation is shown opposite. Some situations that can be considered for exploiting it are using differential osmotic pressure between low brackish rivers that flow into the sea, or saltwater and seawater. The worldwide theoretical potential for osmotic power is estimated at 1,650 TWh/year.
Recently a large amount of research and development has been undertaken and funded by Statkraft, the Norwegian state energy company. A prototype factory built in Norway produces gross output between 2 - 4 kW; see the Statkraft osmotic power prototype at Hurum. A much larger factory with a 1 to 2 MW output at SunndalsÃÆ'¸ra, 400 km north of Oslo is considered but subsequently declined. The New Energy and Technological Energy Development Organization (NEDO) in Japan is funding work on osmotic forces.
Maps Forward osmosis
Research
A current research area in FO involves the direct removal of drawing solutes, in this case by means of a magnetic field. Small magnetic particles (nanoscale) are suspended in solution that creates sufficient osmotic pressure for water separation from the aqueous feed. Once the lottery solutions containing these particles have been diluted by the flux of FO water, they can be separated from the solution by using a magnet (either against the side of the hydration bag, or around the in-line pipe in the steady state process). ).
References
Further reading
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Cath, T; Childress, A; Elimelech, M (2006). "Forward osmosis: Principles, apps, and current developments" (PDF) . Journal of Membrane Science . 281 : 70-87. doi: 10.1016/j.memsci.2006.05.048. Archived from the original (PDF) in 2006-09-13. - Duranceau, Steven (July 2012). "The Appearance of Osmosis Processes to the Front and Osmotic Pressures for Drinking Water Treatment" (PDF) . Florida Water Resources Journal : 32-36 . Retrieved June 14 2013 .
- Nicoll, Peter G. "Forward Osmosis - Brief Introduction" (PDF) . http://idadesal.org/publications/invited-white-papers/. International Desalination Association . Retrieved November 13 2014 .
Source of the article : Wikipedia
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