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RO Membrane Fouling Symptoms, Causes, and  Corrective Measures

Permeate Flow Salt Passage Different Pressure Direct Cause Indirect Cause Corrective Measure
Increase Increase Unchanged Oxidation Damage Free Chlorine, Ozone, KMnO4 Replace Element.  Check Carbon or Sodium Bisulfite Injection Pretreatment.
Increase Increase Unchanged Membrane Leak Permeate backpressure or
Replace Element & Check System Design
Replace Element & Check Sediment Filtration Pretreatment
Increase Increase Unchanged O-Ring Leak Improper Installation Check and/or Replace O-Rings
Increase Increase Unchanged Leaking Product Tube Damaged During Element Loading Replace Element
Decrease Increase Increase Scaling Insufficient Hardness Removal or
System Recovery too High
Clean or Replace Element
Check Water Softener or Antiscalant injection.  
Lower System Recovery
Decrease Increase Increase Colloidal Fouling Insufficient Pretreatment Clean or Replace Element, Improve Pretreatment
Decrease Unchanged Increase Biofouling Contaminated Raw Water, Insufficient Pretreatment Clean or Replace Element, Disinfection, Improve Pretreatment
Decrease Unchanged Unchanged Organic Fouling Oil; Cationic Polyelectrolytes Clean or Replace Element, Improve Preatreatment
Decrease Decrease Unchanged Compaction Water Hammer Replace Element or Add Elements

*Items in red = Main Symptom

Common Foulants and Their Associated Symptoms

Foulant Symptoms

Cleaning Solution, per Membrane Type

Biological Growth Element may have strong odor, possible mold growth on the scroll end.  Element will likely exhibit low permeate flow, but salt rejection will usually be as good if not better than the original test. Alkaline Cleaner
TF:  AM-22
CA: AM-33
Carbonate Scale Usually on tap water or brackish water elements only.  The element may be noticeably heavier than normal.  Element will exhibit low permeate flow and poor salt rejection. Acid Cleaner
TF:  AM-11
CA:  AM-44
Iron Fouling Rust coloring seen on the end of the scroll.   Possibly some large rust flakes from iron plumbing.  Element will exhibit low permeate flow and poor salt rejection.  Rust colored reject water may be seen on start of baseline test. Acid Cleaner
TF:  AM-11
CA:  AM-44
Silt or Carbon Fines Brown or black material on scroll end.  Low flow, good rejection in early stages.  High flow and very poor rejection in later stages due to the abrasive effects of the material on the membrane.


RO Membrane Fouling Troubleshooting

How quickly did the fouling take place? Possible causes Solution for possible cause
Overnight Fouling Clay, Silt, Oils, Etc. 
Clean with Alkaline Cleaner (TF:  AM-22, CA:  AM-33)
Intermediate Length Fouling
(5 to 10 Days)
Microbiological Sources.  Prefilters will show a slimy deposit. Use biocide flush followed by alkaline cleaning (TF:  AM-22, CA:  AM-33).  Regular sanitization may be necessary.
Slow Fouling Most common and most difficult to identify. Follow regular membrane cleaning sequence:
  1. Flush
  2. Acid Cleaning (TF:  AM-11, CA:  AM-44)
  3. Flush
  4. Alkaline Cleaning  (TF:  AM-22, CA:  AM-33)
  5. Flush

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 Operating Do's & Don'ts System Recovery Membrane Foulant Identif. System Troubleshooting Res. RO Troubleshooting Operation Parameters Record Keeping Pre-Start-up Check System Shut-Down Flocon Antiscalant Selection

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All Content on this site is  intended for informational purposes for experienced water treatment professionals only.  Applied Membranes, Inc. does not assume any liability for any damages caused by the misapplication or misinterpretation of any of the information contained on this website.
Applied Membranes, Inc. 2007