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Recognize Membrane Foulants

Pretreating feedwater can lengthen the life of membrane elements, improve the quality of the water produced and reduce the amount of maintenance and cleaning a system requires.


Membrane fouling occurs when materials from the feed stream collect on or near the membrane surface and restrict water permeation. Fouling may occur as layers of deposition on the surface of the membrane (cake fouling), a hardened layer on the membrane surface (scale), particle insertion into the pore channel or entrance (pore blockage), or chemical attachment of particles to the membrane (adsorption).



Foulant

Effects

Action

Inorganic Salts

Reduced permeate flow

Remove hardness via pretreatment and softening

Scale formation on membrane surface

Add antiscalant or dispersant

Increased salt passage

Decrease feed pH

Increased differential pressure

Clean with an acid cleaner

Organics

(oils, grease)

Decreased permeate flow

Optimize pretreatment

Increased salt passage

Install an activated carbon filter

Clean with suitable detergent

Iron

Stains membrane surface

Remove iron with pretreatment

Rapid reduction in permeate flow

Clean with chelating agent

Silica

Decreased permeate flow

Evaluate recovery and pH

Slight increase in salt passage

Optimize pretreatment for colloidal removal

Biological

Foul odor or taste

Perform routine sanitizing

Slime

Reduced permeate flow



Employ continuous operation

Slime formation

Increased differential pressure


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