Increase in Trans-Membrane Pressure (TMP) in RO

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What could be the possible cause of increase in Trans-Membrane Pressure (TMP) in RO. My team did CIP the TMP is increasing 3 days post the CIP.

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10 Answers

  1. This is purely anecdotal, however, we have one RO bank where some unknown "foulant" apparently got on the membrane surface, both 1st permeate pass, and 2nd permeate pass.  The transmembrane pressure went up by minimum of 60%, but oddly no increase in the differential pressure across vessels.  Salt rejection also increased (which seems counterintuitive).   For a water supply with reactive silica in the 20 ppm range, and approximately 1600 microsiemen/cm conductivity, the second pass permeate is normally below 2 conductivity, and the silica is less than 10 ppb.  Alkaline surfactant cleanings did nothing to remove the foulant at all.  Although the feed pressure is now near the vessel limit on the 2nd pass, we are at least able to operate the unit, and the water quality is surpassing.

    Any ideas?  I had thought perhaps this was oil fouling, but how would that stay put indefinitely on the membranes?

  2. First of all, need to confirm the effectiveness of CIP such as feed pressure before/after CIP, then recheck the incoming water quality. I suspect CIP is not done perfectly.

  3. Hello friends,

    An important thing to remember is that the  improper  selection  of  a cleaning  chemical,  or  the  sequence  of  chemical  introduction,  can make the foulant worse.

    Please send us:
    1. Raw water analysis.
    2. List the chemicals you used to wash (for example HCl 0.2 % (w) and...)
    3. Membrane cleaning arrangement? ( was first done? Acid or Base cleaning)
    4. A general explanation of how to CIP.
    I think with this data we can find the problem of your work.

    Thanks.

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  4. The best you can do is to carry out an analysis of the feed water to determine its composition before you do the CIP . Pressure drop is used in ROs to check the intergrity of the membranes. Check for both organic and inorganic contaminants. This will give an indication of what could be blinding the membranes and gives you the best pretreatment to embark on and  the subsequent CIP to do.

  6. Tmp is used for MBR where the suction pressure will be noted at time of Pump's running and stopping. The difference of both  is TMP.

    The problem you are telling is  increse of feed pressure. 

    For membrane we know 2 type of fouling  1_ bio fouling or colloidal foul.

    Make cip by caustic soda and increse time  of soaking. And after caustic soda make cip by Hcl  and keep its pH 2.4 

  7. Le Chartelies principle when 2 membranes separates a chemical reaction or non such as in RO.

  8. If you are referring to pressure drop along the axis of each element of spiral wound membrane, then your CIP protocol was only effective in shifting the location of the foulants (typical of biofouled membranes to result in an increase in dP in the next few operating days.  Clean again with a more stringent high pH cleaning this time.

  9. Just to confirm, by TMP you mean Trans Membrane Pressure, the pressure difference between the feed and the permeate sides of the membrane?

    Has the flow (either feed or permeate) changed? Has the temperature changed? Has the TDS of the water changed?

    If none of the above have changed, it is likely that you have a fouling or scaling issue going on. Typically this would not be an SDI type issue as that would normally result in greater element differential pressure (feed to concentrate ends of the element), but rather something that is adhering to the surface of the membrane. 

    Have you seen this before after CIP? How do you determine when to run the CIP? Has the feed water changed in any way?

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  10. Did you perform an SDI on the incoming water? Silt density index indicates how much particulate is in the water and how fast the membrane will bind over

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