Brackish water membranes

Brackish water membranes are designed to treat lower-salinity feed waters, up to about 4,000 to 5,000 ppm (TDS). Maximum operating pressure for brackish water membranes is typically 600 psi. These membranes are typically tested at the following conditions  

As with seawater membranes, there is no one uniform test condition for all brackish water membranes of the same type. Thus, a direct comparison between manufacturers requires a close look at the test conditions. 

Brackish water membranes also come in various types with different performance ratings. These specific types are discussed below. 

Manufacture Seawater Membrane Permeate Flow gpd Rejection (%) 

Low-fouling membranes are available from some manufacturers. These membranes can be modified is several ways to reduce the potential for fouling them with contaminants in the feed water. Chapter 4.2.3 describes these modifications. 

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Fig. 1. Water flux and NaCl rejection of several membrane types (10), where (D) represents seawater membranes, which operate at 5.5 MPa and 25°C ( ), brackish water membranes, which operate at 1500 mg/L NaCl feed, 1.5 MPa, and 25°C and (SSI) nanofiltration membranes, which operate at 500 mg/L NaCl feed, 0.74 MPa, and 25°C. A represents cellulose acetate—cellulose triacetate B, linear aromatic polyamide C, cross-linked polyether D, cross-linked fully aromatic polyamide E, other thin-film composite membranes F, asymmetric membranes G, BW-30 (FilmTec) H, SU-700 (Toray) I, A-15 (Du Pont) J, NTR-739HF (Nitto-Denko) K, NTR-729HF (Nitto-Denko) L, NTR-7250 (Nitto-Denko) M, NF40 (FilmTec) N, NF40HF (FilmTec) O, UTC-40HF (Toray) P, NF70 (FilmTec) Q, UTC-60 (Toray) R, UTC-20HF (Toray) and S, NF50 (FilmTec). To convert MPa to psi,...

Parameter Seawater membrane (SW-30) Brackish water membrane (CA) Nanofiltration membrane (NTR-7250)... 

For 8-inch diameter, brackish water membrane modules Microfiltration pore size < 0.5 microns. 

Table 9.2 Recommended feed water flow rate as a function of feed water source for brackish water membranes, as adapted from Dow Water and Process Solutions.1...

Brackish water membranes can be shipped from the manufacturer wet or dry. Wet membranes have been performance tested at the factory. However, testing is usually conducted for shorter (hours) versus longer (days) periods. As noted in Figure 14.2 (Chapter 14.3.2), there is a period of time after start up during which membrane performance is not stable due to compaction. Flux and rejection both decrease during this period. Unless a membrane is wet tested until stable performance is achieved, the performance specifications for that membranes based on the wet test are not accurate.7... 

Brackish Water Membrane—The flux and rejection of the membrane is determined when the membrane is tested on a feedwater of an aqueous sodium chloride solution with a concentration of... 

Figure 15. Permeate flow rate per unit membrane area (gallons/day/ft ) and NaCl rejection of brackish water membranes offered by GE (<>), FilmTec/Dow (x), Koch (o), Toray (a), Trisep (+), andNitto Denko/Hydranautics (Is). All values taken from the manufacturers web sites. Test conditions for all membranes were 2000 ppm NaCl feed concentration, 225 psi feed pressure, 77 F feed temperature, and 15% permeate recovery. Feed pH for test conditions varied slightly in the tests from 6.5-8. Note that a 1500 ppm NaCl feed was used to obtain the Nitto Denko/Hydranautics values normalization to 2000 ppm NaCl reduces permeability by S%.

Production of high-purity water, concentration of food and heavy metal recovery from well water, river water, lake water, or industrial waste water Lower pressure brackish water membrane Ideal for small drinking water systems due to low energy consumption... 

S.V. Cabibbo, D.B. Guy, A.C. Ammeralaan, A. Ko, R. Singh, Parametric study on brackish water membrane desalting plants, NWSIAJ,July (1979) 17-36. 

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