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Thread: RO Water Sample Infection?

  1. #1
    Join Date
    Nov 2017
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    Italy
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    8

    RO Water Sample Infection?

    Hello Big Brewers!


    I'm searching to find the mystery source of contamination in our brewery. We have taken many tests of unfermented wort, after our heat exchanger and we always find some bacteria ( after incubation) when we view it through the microscope about 20 cells in a 16 square region.


    We backwash our heat exchanger with hot water between and every night (after 2 batches) we cip for 30 minutes with 3% cold chlorinated caustic and then we fill it overnight with 1% peracetic acid and pressure.
    We sanitize the line with 86C/187F for 25 min in every transfer.


    The next day we find the same bacteria. (we always incubate for 7-8 days)


    One thing that came to my mind was, Hey! Let's check the water!


    So I took a sample after our RO filter followed by our UV and viewed it right away.


    I drew circles in every cell that had movement.

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    What are your conclusions?

  2. #2
    Join Date
    Oct 2002
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    Chesterfield, UK
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    Sounds like you've got pinhole leaks in your plates because you clean routinely with hypochlorite. Pressure test the plates by blanking off the water side and pumping up to a couple of bar pressure, leaving the wort side completely open. Assuming there are leaks, you must make sure your wort side pressure is slightly higher than the water pressure so at least wort runs into the water and gets sterilised as a result of heating up.

    I suspect there are sufficient caustic / chlorine residues left after rinsing and when you add acid (PAA) it releases some of the chlorine which then attacks the stainless. Chlorine corrosion of PHEs is well documented.
    dick

  3. #3
    Join Date
    Nov 2017
    Location
    Italy
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    Hello Dick!

    This is a very useful test and maybe I'll try this tomorrow morning.

    (Just to be sure if I got this straight)
    What you mean is to pump water through the water inlet of the PHE and check if there is any water coming out of the wort outlet right?

    I suppose the way to increase the pressure during transferring wort is to have the wort outlet valve slightly closed?

    Some extra info if it helps somehow.

    This heat exchanger is 4 years old and the chlorine routine came up last month because we thought the hot caustic wasn't very effective.

    Ok! Ok! I promise I'll switch to caustic

    I have noticed another thing... sometimes when I backflush with hot water a small "spit" comes inside of the plates when I close and open the outlet valve repeatedly.

    Last one. What do you think about the bacteria?

    If my RO membranes are infected and there are bacteria in the processed water tank, why are they not killed from the UV light?

    We use 1 UV light that recirculates the water 24/7 inside the tank and 1 more placed last in the chain before we use it for brewing.

    Sorry for posting too many questions.

  4. #4
    Join Date
    Oct 2014
    Location
    Kent, WA
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    301
    Quote Originally Posted by Ale_Guy View Post

    [...]
    (Just to be sure if I got this straight)
    What you mean is to pump water through the water inlet of the PHE and check if there is any water coming out of the wort outlet right?
    I'd use gas (CO2, compressed air, whatever) for this test. Pressurize one side, see if pressure rises over time on the other side. Commercially you'd use helium, because it leaks through incredibly tiny holes, but a helium leak detector is a lot more than you need.

    Quote Originally Posted by Ale_Guy View Post

    [...]
    Last one. What do you think about the bacteria?

    If my RO membranes are infected and there are bacteria in the processed water tank, why are they not killed from the UV light?

    We use 1 UV light that recirculates the water 24/7 inside the tank and 1 more placed last in the chain before we use it for brewing.

    Sorry for posting too many questions.
    RO membranes can get slime build up pretty quickly, especially if the water is not pre-treated correctly. And they are subject to pinhole leaks as well, if there is even the slightest amount of chlorine in the feedwater.

    UV sterilization is tricky--too much flow and it's useless. I'm not sure what you have, but there are two UV wavelengths used for this, and they have different applications and end results. One is 185nm, the other is 254nm. 254nm is usually used for it's germicidal capabilities and 185nm will oxidize the organics as well. If you have a 185nm unit, you put a 254nm unit downstream to ensure the ozone is destroyed (if that's needed in the application). But either way, they have a max flow capacity, and if you go over it, they're worthless. So stay well under the rated flow.

    Regards,
    Mike

  5. #5
    Join Date
    Feb 2016
    Location
    Pasadena MD USA
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    33
    Dick already addressed your possible heat exchanger issues, so I'm not going to worry about that. But if I'm reading correctly, you have photos of bacteria in your RO water, taken post-UV filter, correct? If so, that may not be the only cause of your problems, but it certainly would need to be addressed.

    Basically, you're always going to get bacteria growth in an atmospheric RO holding tank, because air is drawn in as the tank empties. Even if your recirculating UV sterilizer kills 100% of bacteria pumped through it, you're merely diluting the live bacteria in the tank. These bacteria are likely being constantly replenished from biofilm in the tank. Your RO holding tank requires periodic sanitation, fortunately your recirculation loop makes it easier. Consult your tank/filter manuals or water technician for chemical recommendations. (QUATS solutions are pretty common but check your local codes and equipment compatibility!)

    As to why your second "tank outlet" UV sterilizer isn't killing everything, that's got to come down to flow rate or light output.

    First, make sure the bulb is less than a year old. They do continue to "light up" even after their effective output is quite degraded.
    Second, pull the bulb sleeve and clean it. A slight film on this blocks a lot of UV.
    Third, check the unit's rated flow rate versus UV saturation and compare that to your actual measured flow rate.

    UV sterilizers don't have one all-purpose flow rate, but sellers often describe them that way. You should be able to dig up manufacturer's info for the UV "dose" (fluence) that will show how different flow rates yield differing levels of sanitation. Naturally the slower the flow, the more UV energy is delivered to each unit of water. Generally this is expressed in mJ/cm2 (millijoule per square centimeter.) You may want to verify that you're above the minimum recommendations - i.e. more like 30-40 mJ/cm2 instead of 16-20 mJ/cm2.

  6. #6
    Join Date
    Oct 2002
    Location
    Chesterfield, UK
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    "I have noticed another thing... sometimes when I backflush with hot water a small "spit" comes inside of the plates when I close and open the outlet valve repeatedly." I'm afraid I am not sure what you mean by this, so don't know how to answer this.

    I agree that gas would pass through pinholes more easily than water, but expect that water should pass through - though the idea of pressurising and leaving to see if the pressure drops is good, you could lose pressure because of leaks to the outside between the PHE plates and the gaskets - but you would probably have already noticed this as a problem if it was happening. Try it this way and see what happens.

    Re RO water hygiene. The big problem of fouling has already been pointed out. The other things to remember about UV treatment is that even if it killed all the bugs, they would still look like bugs!! And UV has absolutely no residual kill effect, so unless your pipework and tanks downstream of the UV system are completely sterile, then anything can grow up. So you need to CIP and sterilise through the UV system on a regular basis, through to point of use. If nothing else, give the system a regular soak in PAA to keep it at least a little more hygienic.

    Re cleaning the PHE and associated mains - you should be back cleaning the PHE at ideally 130 to 150 % of design flow rate - certainly no less than the design cooling flow rate. Secondly, all pipework must be cleaned at turbulent flow rates - so if you have 1 inch pipe, look to be cleaning at 3000 litres / hour, if 1.5 inch, no less than 5500 litres / hr, ideally 7000 litres / hr. All sterilising flow rates should be at the same rates, but probably you will do these in forward flow, which is fine.

    There has been at least one discussion about stripping plate packs apart somewhere on this site fairly recently. Have you had yours apart? Is it full of crud?
    dick

  7. #7
    Join Date
    Jan 2017
    Location
    Aurora, CO, USA
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    2
    Hi, have you tried plating it on any media (HLP, LMDA, etc.) or incubating in something like FastOrange or NBB to confirm the presence of bacteria. Except for the circular guys in the third picture, which resemble yeast, I don't believe anything else you've circled really resembles the normal beer spoilers (Lactobacillus, Pediococcus).

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