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Demineralization
Types of membrane processes:1
1. RO Reverse Osmosis2. ED Electrodialysis
3. EDR Electrodialysis Reversal
4. UF Ultrafiltration5. NF Nanofiltration
Electrodialysis (ED)
Should be not operated when feedwater contains any of the
following: 3
1. Chlorine residual of any concentration
2. Hydrogen sulfide of any concentration
3. "Calgon" or any other hexametaphosphate in excess of 10
mg/L
4. Manganese in excess of 0.1 mg/L
5. Iron in excess of 0.3 mg/L
Reverse Osmosis (RO)
Cellulose Acetate 4 Thin Film Composite 5
Psi: 400 Psi: 200pH: 4-6 pH: 3-10
Max. Cl2:
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Rate of hydrolysis is at a minimum at pH of about 4.7 6
Brine valves are NEVER to be fully closed. 7
Scale inhibitor most frequently used is sodium
hexametaphosphate. 8
It also prevents the scaling of Ca(SO4)2 on RO membranes.16
To remove inorganic precipitates, use an acid flush of citric
acid. 10
The recovery rate is determined or limited by two things: 9
1. Desired product water quality
2. Solubility limits of minerals in the brine.
The most common and serious problem resulting from
concentrationpolarization, is the increasing tendency for the
precipitation of sparingly
soluble salts and the deposition of particulate matter on the
membrane
surface. 11
Definitions:
Concentration polarization Buildup of retained particles on the
membrane
surface, due to dewatering of the feed closest to the membrane.
The
thickness is controlled by the flow velocity across the
membrane. 13
Demineralization Treatment process that removes dissolved
minerals
(salts) from water. 14
Flux Flow 14
Hydrolysis Chemical reaction in which a compound is converted
into
another compound by taking up water. 13
Polarization Concentration of ions in the thin boundary layer
adjacent to a
membrane or pipe wall. 12
Total Dissolved Solids (TDS) All of the dissolved solids in a
water. 15
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