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| Dissolved Gases |
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Dissolved gases found in water can be natural in the raw water source or generated as a result of chemical reactions in the water purification process.
Dissolved gases contribute mainly to the corrosion problems in water
lines. |
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| Carbon
Dioxide (CO2) |
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Naturally found or a result of acid addition to raw water during
pretreatment to condition the water for membrane treatment. Forms
carbonic acid, lowers water pH and causes corrosion. |
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| Oxygen
(O2) |
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Naturally available in raw water, especially surface water. Can
cause corrosion problems in water lines. |
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| Hydrogen
Sulfide (H2S) |
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Naturally available in raw water, especially in ground water. Can
contribute to corrosion in water lines. It can also form
elementary sulfur, causing serious fouling problems in the membrane
elements. |
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| Chlorine
(Cl2) |
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Introduced to the treated water for the purpose of disinfection, e.g.
municipal water. Can contribute to corrosion in water lines.
It can also oxidize the Thin Film Composite (TFC) Membrane Elements,
causing loss of rejection and irreversible membrane damage. |
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| Gas Removal |
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Gases can be removed by stripping or adsorption. |
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| Stripping |
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Most common technique to remove dissolved gases is by stripping in a Packed
Column. Air is normally used as the stripping gas in the mass
transfer process, where a forced air draft is allowed to flow counter
current to falling water in a packed column. Special
packing is randomly placed in the column for the purpose of maximizing
the transfer efficiency by increasing the surface area of contact
between the gas-liquid phases. |
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| Adsorption |
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Sometimes used to remove gases from water. Activated Carbon
Filters are normally used, mostly in small installations e.g.
residential or commercial RO systems where chlorinated feed water is
treated prior to entering the system. |
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