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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 |
¹ Permeate backpressure or
² Abrasion |
¹ Replace Element & Check System Design
² 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 |
¹ Insufficient Hardness Removal or
² System Recovery too High |
Clean or Replace Element
¹ Check Water Softener or Antiscalant injection.
² 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. |
AM-55 |
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:
- Flush
- Acid Cleaning
(TF: AM-11, CA: AM-44)
- Flush
- Alkaline
Cleaning (TF: AM-22, CA: AM-33)
- Flush
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