High TDS after cleaning RO membrane

Published on by in Technology

Hi,

I have BW-30 400 RO membrane which I am using for 2 years now, couple of months back I had to clean it because Permeate flow drops significantly, I used citric acid followed by caustic (NaOH) cleaning but after cleaning my permeate TDS are gone high to 80TDS while it was 30-35 TDS for whole previous use.

Can Anyone please guide me  how to restore it to original performance.

I shall be thankful.

Regards,
Mudabir Iqbal

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9 Answers

  1. Hi

    In my experience, you should go for NaOH first and then go for acid washing. this way after a quick CIP you will have a neutralized surface of the membrane. check the permeate pH also. You may have to start over the alkaline and acid washing sequence with proper rising time in between and a CIP before turning the system into service mode. Use Iron-free HydroChloric acid in proper portions.

    Good Luck.

  2. Mudabir  

    You are using Filmtec  Element system best in performance. You have to provide detail information of your System and Operating data with feed water detail analysis test report to give you perfect solution. Filmtec elements give 7 to 10 years assured performance. CIP suggestion can be given by any operator. System design and maintaining operating condition is the Key of Filmtec Membrane performance

    Regards

    Amdy

    mtplimited@gmail.com

  3. Is you permeate flow better ? if Yes ,it sounds that you probably done a good clean. It needs to operate for a while it will clean up. Monitor TDS for 1-2 days. Why you use citric acid ?? 

    1 Comment

    1. Thanks Sir, permeate flow is as original as of first day two years back,  I monitored it for more than 30 days now but it still the same, I use citric acid because I read it on google , kindly recommend me generic cleaning chemicals and procedures for proper cleaning, I shall be thankful to you

  4. Dear Sir,

     

    I confirm what other people have written. It is not unusual to see an increase in permeate TDS after a cleaning. If you want to avoid or minimize this effect you could use a neutral pH cleaner. Please contact me by email if you would like to know more about the product(s) we can offer in this perspective.

     

    As a side note; it is generally recommended to first do a high pH clean before a low pH clean. The opposite has a higher probability to leave fouling or scale in your system after the cleaning cycle. In addition, the negative impact on the salt rejection of the membranes (causing the increased permeate TDS after a CIP) is mainly caused by the high pH clean. Finishing with a low pH clean can help restore the salt rejection and prevent or lower the increased TDS effect in the permeate after CIP.

     

    1 Comment

  5. Hi. You should do the basic CIP before the acidic to remove firstly the biofouling and after the scaling

  6. This is normal to see increase TDS after CIP. Wait 24 to 48 hours run time after CIP before making comparison. If TDS is still too high, you can try running the RO "harder" to squeeze the membranes. Try increase feed flow and/or higher recovery. Also try another acid clean after the caustic clean, this can tighten the membranes and improve rejection.

    1 Comment

    1. Thanks Robert, but now its ,more than 30 days and still the same TDS,I will try your suggestion in next CIP

  7. Concerning TDS data, I suppose that chemical cleaning was performed using higher concentration of chemicals comparing to guidelines causing membrane fouling, which is non reversible.

    If after chemical cleaning permeate flow is raised to normal or start-up value and pressure drop is droped accordingly, it shows that cleaning was succesful, but membrane structure is damaged causing higher salt passage.

    1 Comment

    1. Thanks sir, I strictly follow the guidelines regarding chemical ,but unfortunately didnt get the required result.

  8. Hi mudabir
    If you have done the cleaning procedure correctly and based on the manufacturer`s guide lines, this situation is normal and its due to the chemicals effects on the membranes surface during the cleaning. Based on the cleaning chemicals and cleaning each steps duration this situation could stand for 2 days.
    I suggest you to keep the system on the operating for this period and determine the TDS changes during this days. I wish your permeadity get back even earlier, otherwise you will need to shut the system off immediately and check its condition more closely.

    1 Comment

    1. Thanks Mohammad, its now more than 30 days and condition is the same, would you suggest me to go for CIP alkaline first and then acidic .

  9. Put the membrane in DI water for a few days...

    1 Comment

    1. Dear Robert its really hard for me to put the membrane out of service, if you have any other suggestion kindly tell me.