There are various symptoms that can be associated with membrane damage:

  1. Loss in permeability that doesn’t recover even after aggressive cleaning: This is usually a sign of irreversible damage.  It can occur as a result of membrane dehydration, exposure to certain solvents that cause pore collapse, cationic polymers or surfactants which irreversibly bind to the membrane, or oxidation by halogens like iodine which impact permeability through steric effects.
  2. Dramatic increase in permeability coupled with an increase in conductivity: This is usually a sign of halogenation by chlorine or oxidation by permanganate or chlorine dioxide. The presence of transition metals (such as Iron, manganese, cobalt, etc.), can accelerate this damage wherever the metals have deposited and make more membrane-safe oxidizers such as peroxides or peracetic acid cause membrane surface damage. Severe delamination would also exhibit similar symptoms. Membrane probing can determine whether an increased permeate conductivity is simply due to leakage at the permeate tube interconnectors (damaged O-ring), but such leakage would not exhibit a severe increase in permeability.
  3. Increase in differential pressure (ΔP) in combination with increased conductivity: Continuing to operate a system while experiencing a high differential pressure will cause telescoping and/or feed spacer migration.  The movement of membrane media will result in membrane abrasion and an irreversible loss in permeate quality. This will be exacerbated by any deposits that were trapped at the feed spacer contact points.
  4. Increase in conductivity with no significant increase in permeability: This is usually due to minor delamination caused by a leaking check valve or CIP performed with the permeate valve closed.  Other causes can be due to abrasion, or exposure to oxidizers in the presence of small amounts of locally deposited transition metals.

As mentioned above, membrane probing can identify O-ring damage. Inspection of the exterior of a membrane can identify severe telescoping/feed spacer migration. A membrane autopsy can typically determine the cause of any failures internal to the membrane. Full element performance tests will determine the performance of the membrane as compared to specifications. Inspection of the membrane once opened can identify delamination, or the presence of particulates. Fujiwara testing coupled with X-ray Photoelectron spectroscopy (XPS) can identify halogenation. Dye tests will highlight any surface damage as high molecular weight dye passes through the membrane staining the permeate side. The location and pattern of the stains offer clues as to the nature and cause of the physical membrane damage. These dye tests can even be scaled up to full element tests allowing the entire membrane element to be inspected for any physical damage.

For examples, please see the blog titled Membrane Autopsy: Damage from Permeate Backpressure athttps://www.membranechemicals.com/membrane-autopsy-damage-from-permeate-backpressure/

See also:

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