Osmosis, forward

Nevertheless, research is continuing along the lines of pure FO, if not PRO. The membranes used for successful FO require the following  

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An interesting alternative development is that of forward osmosis. Whereas in reverse osmosis a high pressure is required to oppose the natural tendency of freshwater to move across such a membrane via osmosis to dilute the seawater, in forward osmosis the system takes advantage of this natural tendency. Here, salt water sits on one side of the membrane, but the freshwater on the opposite side is transformed into a high-concentration solution by adding NH3 and CO2. Water naturally flows from the salt water to what is now the draw solution, which can have a solute concentration as high as 10 times that of the salt water. There is no need for an external pressure. The diluted draw solution is then heated to evaporate off the CO2 and NH3 for reuse, leaving behind freshwater. (See Patel-Predd, 2006). 

Hybrid processes are also being considered more seriously than ever [84]. There are hybrid processes, such as pretreatment by UF and NF to provide RO feedwater and RO treatment of boiler water for the distillation process, and those are already in practice. Combining RO with the emerging membrane separation processes such as MD and forward osmosis (FO) will become more important to decrease the amount of effluent from the RO desalination plant. As drinking water production by the desalination of seawater and brackish water increases, iuCTease in the quantity of salty RO effluent will become more of environmental concern. The RO hybrid process with MD and FO may become the answer to solve the problem. 

A.K. Ghosh, R.C. Bindal, S. Prabhakar, P.K. Tewari, Concentration of ammonium diuranate effluent by reverse osmosis and forward osmosis membrane processes. Desal. Water Treat., 2013, 52(1-3), 2014. http //dx.doi.org/10.1080/ 19443994.2013.808449. 

R.L. McGinnis, M. Elimelech, Energy requirements of ammonia-carbon dioxide forward osmosis desahnation. Desalination 2007, 207, 370-382. 

A. AchUh, T.Y. Cath, E.A. Marchand, A.E. ChUdress, The forward osmosis membrane bioreactor A low fouling alternative to MBR processes. Desalination 2009, 239, 10-21. 

E.R. Comelissen, D. Harmsen, K.P. de Korte, C.J. Ruiken, J.-J. Qin, H. Oo, L.P. Wessels, Membrane fouling and process performance of forward osmosis membranes on activated sludge. Journal of Membrane Science 2008, 319, 158-168. 

C.R. Martinetti, A.E. ChUdress, T.Y. Cath, High recovery of concentrated RO brines using forward osmosis and membrane distiUation, Journal of Membrane Science 2009, 331, 31-39. 

S. Zhao, L. Zou, C.Y. Tang, D. Mulcahy, Recent developments in forward osmosis Opportunities and chaUenges. Journal of Membrane Science 2012, 396, 1-21. 

G.T. Gray, J.R. McCutcheon, M. Elimelech, Internal concentration polarization in forward osmosis Role of membrane orientation. Desalination 2006, 197, 1-8. 

V. Sant Anna, L. Damasceno Ferreira Marczak, I.C. Tessaro, Membrane concentration of liquid foods by forward osmosis Process and quality view. Journal of Pood Engineering 2012, 111,483 89. 

C.H. Tan, H.Y. Ng, Revised external and internal concentration polarization models to improve flux prediction in forward osmosis process. Desalination 2013, 309,125-140. 

A number of alternatives to reverse osmosis are being considered. Two promising alternatives are membrane distillation [97] and forward osmosis [98]. Membrane distillation relies on vapor pressure differences across a membrane, arising from a temperature difference, to drive water transport. The process utilizes low temperature heat sources and operates at low pressure which can reduce operating costs relative to reverse osmosis. Forward osmosis relies on water permeation across a water selective membrane to a draw solution - the reverse of reverse osmosis. The water must then be separated from the draw solution but this may be less expense than reverse osmosis because the process operates at low pressure. 

To summarise, the development and remarkable success of commercial membrane processes for Uquid separations — RO, nanofiltration (NF), UF, and MF — would not have been possible without the discovery and subsequent development of high-flux, extremely thin (skinned) CA membranes by Srinivas Sourirajan and Sidney Loeb at UCLA, culminating in the development of TFC PA membranes by John Cadotte. Membrane technologies such as NF, PV and GS got the impetus from the work on RO in the 1950s and 1960s. These successes have led to the development of newer membrane processes such as membrane distillation (MD) and forward osmosis (FO). 

Forward osmosis (FO) is a membrane-separation process that uses osmotic pressure difference between a concentrated draw solution and a feed stream to drive water across a semipermeable membrane [63]. The basis of FO is osmosis, a natural and spontaneously occurring process. It is strictly direct osmosis across an RO membrane. A draw solute of high osmotic pressure, e.g., ammonium carbonate passes across one side of the FO membrane, and a high salinity solution, e.g., seawater flows across the other side of the membrane, as shown in Figure 1.17. Water transfers from the seawater to the draw solute side due to osmotic flow. It is then necessary to regenerate the draw solute and recover the water transferred by the FO process, e.g., in a distillation unit. The primary challenge is... 

Figure 1.17 Schematic flow diagram of a forward osmosis system with ammonia carbon dioxide draw solution (https //www.google.com/search q=cellulose+acetate+membrane). Source [63].

Another useful application of FO is the so-called osmotic backwash for cleaning RO membranes [62]. TFC membranes cannot be backwashed because the top thin layer can get detached. However, since forward osmosis transfers pure or fresh water through an RO/NF membrane under osmotic pressure, it can be used to backwash and clean the membrane with the permeate without the risk of damaging the membrane. One process operation is described below ... 

Reverse osmosis is widely used in the field of desalination technology. Reverse osmosis is displacing conventional thermal technologies, as well as other technologies such as membrane distillation, electrodialysis, and forward osmosis [91]. 

In contrast to a neutral membrane, the positively charged forward osmosis membrane provides double electric repulsions to the salt transfer through the membrane in the active layer facing feed water configuration. This results in a reduction of the salt penetration, while in the active layer facing draw solution config-... 

Setiawan L, Wang R, Li K, Fane AG. Fabrication of novel poly(amide-imide) forward osmosis hollow fiber membranes with a... 

Application of Forward Osmosis to Reduce Produced Water Injection Volumes... 

Keywords Produced water, forward osmosis, thermal brine, volume reduction 1. Introduction... 

Forward Osmosis (FO) is an emerging membrane technology for water treatment that typically involves two steps ... 

Flux J is defined as the volumetric flow rate of a permeating solvent or solute through a unit area of a membrane. The general form of solvent permeating flux, for forward osmosis, pressure-retarded osmosis, and reverse osmosis is given as... 

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