Environmental Engineering Reference
In-Depth Information
(a)
Separation method
Operating pressure (psi)
Particles removed
Tu rbidity, algae, giardia,
cryptosporidia, bacteria
Macromolecules, asbestos,
virus
Organic chemicals, hardness,
color, radionuclides
Metal ions, salt
Metal ions, salt
Metal ions, salt
10-30
Microfiltration
15-35
Ultrafiltration
80-150
Nanofiltration
Electrodialysis reversal
Brackish reverse osmosis
Seawater reverse osmosis
80-100
150-300
500-900
(b)
Microfiltration
Ultrafiltration
Nanofiltration
EDR and RO
0.0001
0.001
0.01
0.1
1
10
Particle size (µm)
FIGURE 27.6
Membrane selectivity and operation information. (a) Operating pressure and particle removal by separation
method. (b) Particle size range removed by separation process. (From Nath, K.,
Membrane Separation Processes
.
Prentice Hall: New Delhi, 2008; and American Membrane Technology Association.
Application of Membrane
Technologies.
Available from: http://www.amtaorg.com/wp-content/uploads/1_applicationofmembranetech
nologies.pdf, 2007.)
Concentrate
discharge
Saline
feed
Pretreatment
Freshwater
FIGURE 27.7
Simple schematic representation of the RO process showing essential unit processes. (Based on Trieb, F., ed.
Concentrating Solar Power for Water Desalination
. ed. G.A.C. [DLR] and I.O.T. Thermodynamics. Federal Ministry
for the Environment, Nature Conservation and Nuclear Energy: Stuttgart, Germany, 2007.)
the pressure requirements for brackish water desalination are much lower (15-25 bar) than
the pressure requirements of seawater desalination (54-80 bar) [23]. It should be noted that
although the osmotic pressure of seawater is approximately 25 bar [28], higher operating
pressures are required to achieve practical lows as well as balance the increasing salinity
of the feedwater and overcome concentration polarization across the membranes as the
desalination process progresses [1,23,29].
