RO Membrane Giving High Output TDS

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We own a 2000 ltr/h water treatment plant and it was working fine till two days ago. We were  getting < 100 mg/l TDS with 2500 TDS of raw water and ~4000 mg/l TDS of wastage water.

Now all of sudden the RO membrane (DoW made BW30-400) is giving high output TDS of ~200 mg/ltr while the raw water is still having same TDS. Output wastage water TDS is now around 3000; it was around 4000 previously.

What could be the reason for this sudden increase in TDS?  I don't think membrane can stop working all of sudden.

I tried cleaning the membrane and it gave 130 TDS for 2 minutes and started increasing after that to 200 again. Please suggest what to do? 

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26 Answers

  1. hope your problem might have been solved... as you are using 2 nos of 8040 membranes for 2000 lph plant... pls check for maximum recommended recovery and also min membrane flow required.

    1 Comment

    1. From where should I get it? User guide doesn't says anything about recovery though!

  2. One thing you must do is testing your raw water quality thoroughly. Measuring raw water TDS in not enough. You need to measure hardness, Iron and Chlorine content of your raw water. Then you can find a appropriate method to pre-treat your water.

  3. No Guys checked everything and 'O' ring was absolutely in shape and no chance of leaking from there. Looks like membrane was damaged.

    So I have changed both of 2 membranes with 2 new ones. it's the same DoW BW30-400 IG membranes and now I am facing another problem.

    When I installed these 2 membranes and even in past when we installed this plant, I was getting ~2300 liter/hr flow rate with same set of inputs i.e. 12.5KG pressure and with 2600 mg/l TDS but now after 10 days of use, this flow rate is decreased to 1800 liter/hr.

     permeated water TDS is excellent around 25 mg/liter but flow is lesser.

    Could someone help?

    What could be the reason of such decrement in permeate flow in just 10 days??

    Some solution please?

     

    Regards,

    Dharmendra

    9958728104

     

    1 Comment

    1. Guys can someone answer to my latest query that why the new membrane's permeated watsr flow is decreased just after 5 days from 2300 lyrics/hr to 1800 ltr/hr?

      6 Comment replies

      1. You should check your water especially for Hardness, Silica and free chlorine.

        Send the test report to your antiscalant supplier and choose the antiscalant accordingly.

      3. Dharmendra;
        You mentioned having a 2 micron filters before the HP pump. To me it seems overkill to have such a small filter and pressure differentials on  2 micron filters are greater than a 5 or 10 micron. My recommendation is to have a 5 or perhaps a 10 micron filter. Do you have pressure differential gauges on your 2 micron filter? 
        What is the DPSI on your 2 micron filter?
        What is the reason for having the carbon filter for pre-treatment? Do you have oxidation prior to this carbon filter?

      4. Thank you Andrew and Pierre....yes that's what I was also thinking about.

        So I have now changed my anti-scaling chemical and now using a chemical which is supposed to be used till 5k TDS raw water treatment plant.

        Inlet water temperature is around 30°C and there is no pre-treatment plant  as such except sand,carbon and 2 micron filters before high pressure pump.

        How would I know whether I need some kind of pre treatment for my raw water?

        Should I get it tested in lab?

      5. Dharmenda

        I would have to agree with Andrew and add a possibility of flow restriction on your pre-treatment if you have one. (Filters being plugged) You did not mentioned if you have scale inhibitor injection(s). You may want to look at your chemical injection system(s) to make sure you have a proper dosage for your anti scalant, sulfuric acid etc....

        Also, you did not mentioned anything about your influent temperature. Lower temperature require more power to produce same flow through your membranes than higher temperature. 

      6. Hi Dharmendra,

        May I ask if you have any pre-treatment for your membrane?

        When you replaced the membrane did you notice excessive bio-fouling or scaling issues?

        A rapid formation of a biofilm colony or scale development is usually the answer for the decrease in flow rate. In this case, you will need to look at adequate pre-treatment for your membranes to maximize their efficiency.

        I specialise in RO pre-treatment in Asia and Australia, please email me at andrew@waterandoilsolutions.com.au and I'll be happy to see if I can help.

         

  4. I could be wrong but this honestly sounds very much like a broken seal between your membranes or a membrane failure. A couple questions:  1. How often do you probe your RO membranes for conductivity in the permeate stream...I make sure that this is done monthly on all our plants and is the absolute fastest way to determine which membrane unit is causing your failure 2. Do you have an ORP (oxidation reduction potential) sensor in front of your high pressure pumps because this type of sudden failure sounds like a non-dissolved particle or oxidant was allowed into your RO units and repuptured one of them.    If you've done these 2 already I can ask more specific questions but in would start with probing and find the culprit membrane and remove and replace it immediately.    Kurt

  5.  Mr. dharmendra, Nice talking to you regarding below matter & our mutual discussion I have colleague from Ex Pentair , Kindly do call on my no. 9213073095

  8. Dear Please first check Water Quality of each vessel &  do probing test to find out the each membrane condition, its simple to find out which vessel or membrane's O-ring or inter connector oring missed placed. its very easy.

    2 Comments

    1. No Dear Probing is simple,

      Probing If one pressure vessel shows a significantly higher permeate concentration than the other vessels of the same stage, then this vessel should be probed. The procedure allows locating a problem within a pressure vessel while Plant in operation without unloading elements. Probing involves the insertion of a plastic tube (approx. 1/4 inch (6 mm) in diameter) into the full length of the permeate tube  in order to measure the permeate conductivity at different locations inside the pressure vessel.

      For example, 

      01. Open Vessel permeate pipe connector, check water Quality ,

      02. Arrange 1/4 inch (6 mm) or 1/3 inch plastic semi flexible tube Mark point as per membrane length 40'',

      03. insert the tube in permeate pipe,

      04. take water sample form each membrane & check result 

      Again.

      Probing must be performed while the reverse osmosis system is operating. The tubing is worked through various fittings to the other end of the vessel. It is then gradually pulled back or enter forward as diverted water samples are tested. Sufficient time (30 seconds) should be allowed between samples to be sure that water from the new sampling location has completely displaced the water within the tubing.

       

       

    2. So You are saying I can open the membrane housing by my own and can check the seal by myself only? How the probe test is done?

  9. good list Prem!

    Answered on by

  10. Thanks a lot guys.

    So after reading all the answers I feel I should be able to solve the issue. Now let me answer some of people's questions about fault in measuring the TDS and flow inputs.

    Well I have checked these TDS with correct TDS meters.

    Well most important thing is that wastage flux TDS is decreased (fom 4000 to 3200 mg/l) while the inlet water TDS is increased from 2300 to 2800 while treated output water TDS from 80 to 180 mg/l. This can only happen when some amount of inlet water is directly purring to the wastage flux water and in my that could be due to broken/damage 'O' ring between 2 membranes. And almost all the answers I got are emphasizing to the same fact so I believe broken O ring would be a common issue.

    Also I would mention one more point here is that we did membrane wash with 'Namak ka acid' (a diluted acid which is mainly concentrated with salt) and that might be the cause of O seal ring damage. 

    This 'Namak ka acid' was recommended by the guys who commissioned the plant and to be more precise they have used it before 1.5 year back (the plant was commissioned around 2.3 year back) in the same plant when we reported low treated water output flow issue to them.

    So I need one suggestion now, should I check the O ring by my own or should it be checked by some mechanic? I am not sure how much easy/difficult it would be to re-inserting the membranes inside the housing.

    Regards,

    Dharmendra

     

    1 Comment

    1. Dear Dharmendra Sharma , The easy way to find out where excactly there is a leakage is to take a sample of purified (produced) water from each membrane housing outlet. Comparing the TDS or Conductivity measurments, you can find out where the leakage comes from.  After that, you can open only the membrane housing it needs to replace o-rings and/or connectrors.

      Membrane fitting is very easy. Many people without specific knowledge have done it succesfully. There is only need to have enough space (1.5 m) from each side of the membrane housing.

  11. Dear Dharmendra,

    The following points may check.

    1. Sealing system of the RO membrane (gasket looseness/damaged) to be checked.
    2. By passing of the membrane.
    3. Check connection of water IN/OUT
    4. Check damaged of membrane, due to uneven pressure
    5. Have your composite membranes been exposed to chlorine or any other strong oxidant? The exposure may have damaged the membranes.
    6. Have your cellulose acetate (CAB) membranes been exposed to pH extremes? The exposure may have damaged the membranes. Likely causes of pH extremes are faulty metering pumps, acid tanks that have gone dry, loss of prime to the metering pump, or flushing/storage in non-acidified water.
    7. Is the instrumentation accurate? Verify that all of your instruments are calibrated properly.
    8. Do the elements look discoloured or damaged? Inspect the RO elements for foulants or physical damage.

  12. I think there is a possibility that the membrane will work with water. Over time the washing process reduces the amount of soluble salts, so I recommend you should test the water and storage utensils and to ensure water safety

  13. Check each membrane housing out tds. Their would b some damage on membrane or interconnecter.

  14. Ok we are Naarvi group can assist you, we also represent most reputed PEntair brand in  water project , pl. do call on 9213073095

  15. what is the age of the membrane? .. was there any increase in any other raw water constituents? .. perhaps, the membrane wasn't cleaned long enough .. Bob Hennes  

  16. How did you do your CIP? increase in TDS is normally due to failed seal, damaged membranes or aggressive fouling & scalling.

    If the seal is not faulty, take one membrane for a destructive test. All the best.

  17. Another possibility is chlorine damage to the RO membranes.  Chlorine damage will initially result in a reduction in flux, followed by an increase in both flux and TDS concentrations in the permeate.  So, an apparent increase in flux could be a failed seal or failed membrane.  Comparing the current flux rate with your previous flux rate won't help clarify the problem as both result in similar outcomes (increased flux and TDS).  Get your equipment supplier to help with troubleshooting the problem.

  18. yes , may be be O ring broken ,I faced this problem before and fixed it 

    1 Comment

    1. That's what I also feel...so do you recommend me to check that o ring by myself or it would be better to be checked by some experience mechanic? Were you also using same membranes?

  20.  When you have a high concentration of chlorinated hydrocarbons the chlorine becomes less effective. ( may be pesticide spraying time for crops etc. ).   Resolution = Stop using caustic chlorine  to reduce TDS.  Use instead RNA Archaea microbes that have the genetic code to reduce all TDS to their elemental/nutritional form.   When this process is completed there is no reason to dump into rivers etc.  Long term vigorous testing will allow the water to be recycled as potable.  Not economical to refit old stations. But the newer ones can start with the 100% recycling of their water.  No more drought complaints.

  24. What about the Permeat flow? If permeat (produced clean water) flow has been increased, there is a broken probably membrane connector, or even broken membrane. If it is so, you will notify a continous TDS raising during time.

     

  25. Bonjour 

    Bien entendu qu'il s'agit de la membrane qui maintenant est colmatée 

    C'est la problématique majeure de ce genre de dispositif: Dès sa mise en service elle perd de sa performance épuratoire pour finir par colmater ou laisser passer en masse toute la pollution retenue

    Hello, of course, that it is the membrane that now is closed it is the major issue of this sort of device: from its commissioning it loses its purification performance eventually plug or pass all the accepted pollution mass

  26. Dear Dharmendra,

    Since how long you are using these membranes

    Do you follow Cleaning / Flushing CIP of RO Membranes as per DOW recommendations on timely intervals

    Did you check your Inlet TDS, if this is same or changed?

    Do you have a Pre-Filtratioin System before hand also which is functioning well?

    Did you check ORP Meter is funcitioning well if you are using NaOCl as disinfectant in pre-filtration? 

    Does your SMBS Dosing Pump functioning well?

    Does Cartridge Filter cleaned properly or needs replacement?

    The most important, if you recently cleaned/opened the Vessel, then inserting membranes into the vessel is a careful job, each membrane module to be properly "Interlocked" and "Rubber O Ring" must be in place properly, otherwise, this could be the main reason for your issue.

    Increase in Permeate TDS and Decrease in Reject TDS is a clear indication any of your Membranes has worn out/damaged/clogged thus not being able to perform properly the system as a whole. 

    Kindly do the above checks first, then take out membranes. I am sure your problem will be solved.