Reverse Osmosis and Nanofiltration

The MWCO of NF and RO is in the 100 to 1000 Da range with pores 1 nm in diameter. Organics rejection is therefore expected to be high. According to van der Bruggen et al. (1999), differences in rejection between membranes are clearly visible for compounds which exhibit about 50% rejection. Taylor and Mulford (1995) found TOC removal in NF to be sieving-controlled, and, thus independent of pressure and recover. The rejection of inorganic solutes was diffusion limited. 

In summary, key parameters to ion rejection are the membrane pore size, charge, pH, ion charge and size, flux and pressure, concentration, solute-solute interactions, composition of mixtures, and speciation. While models have been successful in explaining some results, the entire rejection mechanism is still poorly understood. 

Rejection of oiganics may be determined by size and charge as well as the same parameters that govern ion rejection. In addition, factors such as molecular conformation and stmeture may play a role. 

Mallevialle et al (1996) summarised the following trends in organics rejection by RO as follows. 

In summary, NF and RO achieve extremely high natural organics rejection compared to MF and UF. The compliance of NF with surface water requirements appears unproblematic. However, the rejection mechanisms are not well understood. Solution chemistry, organic characteristics, membrane charge, and the presence of inorganics, seem to be major factors. 

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In the field of membrane filtration, a distinction is made based upon the size of the particles, which are retained by the membrane. That is micro-, ultra-, nanofiltration and reverse osmosis. Figure 4.8 shows a schematic picture of the classification of membrane processes. The areas of importance for application with homogeneous catalysts are ultra- and nanofiltration, depicted in gray. 

Radjenovic J, Petrovic M, Ventura F, Barcelo D (2008) Rejection of pharmaceuticals in nanofiltration and reverse osmosis membrane drinking water treatment. Water Res 42 3601-3610... 

Beier S, Koster S, Veltmann K, Schroder HFr, Pinnekamp J (2010) Treatment of hospital wastewater effluent by nanofiltration and reverse osmosis. Water Sci Technol 61 1691-1698... 

Poly(ethersulfone) (PES) is widely used for the preparation of membranes, including ultrafiltration, nanofiltration, and reverse osmosis membranes (88). However, PES lacks hydrophilic groups and the membrane material must be therefore modified. 

Nanofiltration Compared to microfiltration and ultrafiltration, nanofiltration and reverse osmosis are more expensive and susceptible to fouling (Shih, 2005, 95). Most of the expenses result from the high densities of the membranes, which require high pressures (0.34-6.9 MPa) and a considerable... 

Ultrafiltration Filtration for the treatment of water that removes suspended particles with diameters that are greater than about 0.01 pm (compare with filtration, microfiltration, nanofiltration, and reverse osmosis). 

Comparison between nanofiltration and reverse osmosis operations 60... 

COMPARISON BETWEEN NANOFILTRATION AND REVERSE OSMOSIS OPERATIONS... 

Concentration Units. Typical concentrators for rinsing solutions are membrane filtration units, which split the feed into diluate and concentrate streams, meaning purification and recovery, respectively [106], Both nanofiltration and reverse osmosis might be applied, depending on the physico-chemical properties of the solutes. 

What is the Difference Between Nanofiltration and Reverse Osmosis ... 

Many industrial activities, such as gas production [81-83], catalysis [84], and fuel cells [83], require gas separation. Fouling in gas separation processes, however, is less severe than in microfiltration, nanofiltration, and reverse osmosis where it is the main cause of permanent flux decline and loss of product quality [81],... 

Membranes may be hastily classified according to the driving force at the origin of the transport process (1) a pressure differential leads to micro-, ultra-, nanofiltration, and reverse osmosis (2) a difference of concentration across the membrane leads to diffusion of a species between two solutions (dialysis) and (3) an electric potential difference applied to an ion-exchange membrane (lEM) leads to migration of ions through the membrane (electrodialysis, membrane electrolysis, and... 

Some areas of application are the nuclear industry and the treatment of radioactive liquid wastes, with two main purposes reduction in the waste volume for further disposal, and reuse of decontaminated water. Pressure-driven membrane processes (microfiltration, ultrafiltration, nanofiltration, and reverse osmosis [RO]) are widely used for the treatment of radioactive waste. 

Ko3mncu, I. and Yazgan, M., Application of nanofiltration and reverse osmosis membranes to the salty and polluted surface water, J. Environ. Sci. Health, A 36(7), 1321, 2001. 

Ion Transport under Nanofiltration and Reverse Osmosis Conditions... 

Separate and Concentrate Lactic Acid Using Combination of Nanofiltration and Reverse Osmosis Membranes... 

Abstract The processes of lactic acid production include two key stages, which are (a) fermentation and (h) product recovery. In this study, fiee cell of Bifidobacterium longum was used to produce lactic acid from cheese whey. The produced lactic acid was then separated and purified from the fermentation broth using combination of nanofiltration and reverse osmosis membranes. Nanofiltration membrane with a molecular weight cutofif of 100-400 Da was used to separate lactic acid from lactose and cells in the cheese whey fermentation broth in the first step. The obtained permeate from the above nanofiltration is mainly composed of lactic acid and water, which was then concentrated with a reverse osmosis membrane in the second step. Among the tested nanofiltration membranes, HL membrane from GE Osmonics has the highest lactose retention (97 1%). In the reverse osmosis process, the ADF membrane could retain 100% of lactic acid to obtain permeate with water only. The effect of membrane and pressure on permeate flux and retention of lactose/lactic acid was also reported in this paper. 

An alkali acid treatment method was applied to the membrane system (both nanofiltration and reverse osmosis separation) in the following steps (a) fully open the recirculation and permeate valves, (b) flush with tap water for 5 min, (c) circulate 2 L of 4% phosphoric acid for 10 min, (d) rinse with tap water for 5 min, (e) circulate 2 L of 0.1 N NaOH solution for 10 min, and (f) rinse with 10 L of D1 water for 5 min. 

Combined nanofiltration and reverse osmosis membranes could successfully separate and concentrate lactic acid from cheese whey fermentation broth. Nanofiltration membrane could retain about 97% of lactose to obtain permeate mainly containing lactic acid and water. The highest lactose retention of 97% was obtained with the HL membrane. The tested reverse osmosis membranes successfully separated lactic acid from water. Nearly 100% of lactic acid retention was obtained with the ADF membrane. 

These systems were designed for up to 20 MPa in nanofiltration and reverse osmosis experiments. The cell volume is 190 mL. The magnetic stirrer is purchased from Amicon. The drawing is shown in Figure A2.3. 

Clair D.H., Adams P.V., Shreve S. (1997), Microfiltralion of a high-turbidity surface water with posttreatment by nanofiltration and reverse osmosis, Proc. AWWA Membrane Technology Conference, New Orleans, Feb. 97, 23.3-268. 

Hofman J.A.M.H., Beerendonk E.F., Kruithof J.C. (1995), Modelling of the rejection of organic micropollutants by nanofiltration and reverse osmosis systems, Proc. AWWA Membrane Technology Conf, Reno, Nevada, Aug 95, 733-746. 

Membrane operations in water treatment processes include (in order of decreasing pore size) microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. In general, microfiltration and ultrafiltration would have little effect on the removal of transformation products due to their relatively large pore... 

P. Dydo, M. Turek, J. Ciba, J. Trojanowska, and J. Kluczka, Boron removal from landfill leachate by means of nanofiltration and reverse osmosis. Desalination 185 (2005) 131-137. 

Tremendous opportunity exists for hybrid processes consisting solely of membrane processes or a combination of membrane and non-membrane processes. Of the large number of potential combinations, studies of several are reported in the literature including nanofiltration with reverse osmosis [99] nanofiltration with electrodialysis [100] ultrafiltration with nanofiltration and reverse osmosis [101] ultrafiltration with membrane distillation [102] nanofiltration with reverse osmosis and a microfiltration membrane-based sorbent [103] microfiltration with flotation [104] microfiltration and ultrafiltration with ozone and activated carbon adsorption [105] and membrane processes with photocatalysis [106-107]. Despite the activity in this area, a comprehensive approach to designing hybrid systems does not exist future work would benefit from the development of such a design framework. 

Sulfonated polysulfone seems to also play an important role in nanofiltration and reverse osmosis membranes commercialized by Desal. According to Petersen [34] the Desal-5 membrane appears to consist of three layers a microporous polysulfone, a sulfonated overlay and a top ultrathin layer based on polypipera-zineamide. 

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