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Membrane Cleaning Questions & Answers

How often should I clean my membranes?

In normal operation, the membrane in reverse osmosis membrane elements can become fouled by suspended solids, microorganisms and mineral scale. These deposits build up during operation and cause loss in water output or salt rejection, or both. Membrane elements should be cleaned whenever the normalized water output rate drops by 15% from its initial flow rate (the flow rate established during the first 24 to 48 hours of operation) or when salt content in in the product water rises noticeably.

It should be noted that the water output rate will drop if feedwater temperature decreases (see Temperature Correction). This is normal and does not indicate membrane fouling.


Is is necessary to heat our RO cleaning solution when the temperature of our well water is already relatively warm and does not change much throughout the year?

If your cleaning solution temperature is at least 20 deg C, then you do not need a heating element. Also, as you recycle the water there will be further rise in temperature, which should be kept below 50 deg C.

What is the proper sequence to follow when cleaning my membranes?

Membrane Cleaning Sequence
  1. Acid Cleaning
  2. Flush
  3. Alkaline Cleaning
  4. Flush
  5. Sanitizing
  6. Flush


What should the flow rate be for proper membrane cleaning?

Membrane Type Medium Flow (MF) High Flow (HF)
4" x 40" 4 10
4" Magnum 4 10
6" x 40" 12 20
8" x 40" 25 35
8" Magnum 25 35


Estimate of Total Flow Required for Membrane Cleaning


  • HTF = High Total Flow

  • MTF = Medium Total Flow

  • NV = Number of Vessels in Parallel

  • HF = High Flow from Flow Table

  • MF = Medium Flow from Flow Table

How much cleaning solution will I need to clean my membranes?

Membrane Type Chemical Solution Volume, Gallons (Vol)
4" x 40" 2.5
4" Magnum 3.5
6" x 40" 4.0
8" x 40" 6.0
8" Magnum 8.5


Estimate of Cleaning Solution Volume

V = El Vol 5

  • El = Number of Elements

  • Vol = Volume of one element from Flow Tables


Which Membrane Cleaner Should I Use?

The membrane cleaner required will depend on the type of fouling the membrane has been exposed to. Visit the below page to troubleshoot:
Click Here

In Mongolia we are using RO elements Dow/Hydranautics BW30LE-4040, treating groundwater high in TDS (no organics). For CIP, can we use HCl as a cleaning agent? We do not have Cirtic Acid and shipping will take a long time (getting through Chinese Border). If we can use HCl, what dosage or solution strength should we use?

Yes, you can use HCl. Add acid to water very slowly and carefully while stirring (mixing) till you have a pH of 3 (do not go below 2). Use this water and circulate for cleaning.

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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