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Denitrifying bacteria

  • 1.  Denitrifying bacteria

    Posted 13 days ago
    Does anyone have experience with mitigating denitrifying bacteria in their cooling water system?  ​We are unable to keep the temperature above 140°F, we do have low flow, and we are using a nitrite corrosion inhibitor.  We are considering a system cleanout, but open to hearing what others have done in this situation.  Also curious which biocide treatment was used for denitrifying bacteria.  Thanks!

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    Nina Young
    Chevron Phillips Chemical Company
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  • 2.  RE: Denitrifying bacteria

    Posted 12 days ago
    Nina,
    My experience with problematic closed loop cooling water systems treated with nitrite based inhibitors is that the dentrifying bacteria (once in the system) is almost impossible to erradicate without actually replacing all of the equipment.  We have tried steaming out and biocide treatments, but i believe the bacteria takes safe harbor in subsurface pits or stagnant areas (deadleg) of the system and repopulates after the "sterilization" treatment.

    Alternatively to a cleanout or replacement, I would recommend switching to a molybdenate-based inhibitor with is not utilized as food for the bacteria.  This will halt the poplation growth of the bacteria colony and may even "starve them out." You would still need to perform some chemical cleaning to remove physical tubercules and deposits that could lead to under-deposit corrosion and pitting by simple "oxygen cell corrosion" (AKA under deposit corrosion).

    As a side note, i have found that simple PCR or other bacteria sampling of the water is not sufficient to identify the severity of the contamination, as the planktonic bacteria is not actually causing the corrosion problem.  Sessile bacteria which is actually causing the corrosion, remains on the pipe or in pits and is not able to be sampled in the bulk water.  A more representative indicator of the step change in activity is comparing the nitrate levels, which should increase above baseline and the bacteria consumes nitrite and converts it to nitrate.  If you see an uptick in nitrite makeup and and nitrate levels in the system, then it means the bacteria colony is growing and probably causing more widespread corrosion.

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    Orin Wakefield
    Materials Engineer
    Chevron Corporation; Oronite
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  • 3.  RE: Denitrifying bacteria

    Posted 12 days ago
     Dear Sir / Madam,

    Good Day!

    I would like to suggest the below response against your clarifications. Kindly refer.

    BIOCLENS™ technology uses bacteria encapsulated in lenses as a biocatalyst to enhance and accelerate natural biological processes which break down organic matter. The lenses contain living bacteria which is immobilised in a stable, porous PVA gel matrix. As these are stirred in a reactor, water and dissolved impurities diffuse through the lenses and come in contact with the bacteria, causing targeted reactions to occur.  

    Regards,
    Anandakumar





  • 4.  RE: Denitrifying bacteria

    Posted 12 days ago
    Nina,

    You do not tell us if the cooling system is an open recirculating cooling water system (using a cooling tower) or a closed loop cooling water system (via a heat-exchanger)?
    1. If it is an open cooling water system, then a nitrite-based corrosion inhibitor should never be used, as it simply oxidizes to nitrate and provides a food source for bacteria. Increase the recirculating flow rate with an additional pump, and add bleach to achieve a minimum of 2 mg/L free chlorine. Check for the presence of dead-legs, bio-films,  and other low-flow areas, as it maybe a second system cleanup is needed to remove dead/live slimes; in which case add biodispersant  (say DETA ll , from AMSA (plus probably 2 mg/L silicone antifoam) and 100 mg/L of a non-oxidizing biocide, such as a 1.5% isothiazalinone blend (e.g. Kathon). Recirculate for several hours. Some flushing (or use of side-stream media filtration) is likely needed to remove debris and dead bioslimes from the system.
    2. If it is a closed loop water system (more likely), then you need to first raise the recirculation rate to at least 5 linear feet per second, which may require the use of a supplementary pumps(s). In extremely badly contaminated closed loops, I have had to temporarily further increase the flow rate up to 10 fps before adding a biocide.  You will also need some sort of filter (such as a series of bag filters) to capture dead slime and particulates. Again, add biodispersant  - say DETA ll , from AMSA - (plus probably 2 mg/L silicone antifoam), and 100 mg/L of a non-oxidizing biocide, such as a 1.5% isothiazalinone blend (e.g. Kathon). Recirculate for several hours. Start with 100 micron filter bags, and gradually reduce them down to 50, then 10, then perhaps even 5 micron, to capture dead bioslimes, corrosion debris, and possibly other junk that may be in the systems and permitting microorganisms to proliferate. The larger the particulates of debris in the system ,then the higher the linear flow rate needed, to ensure debris is not lifted up and simply moved to another area and re-deposited. Apart from the use of a filter collection system, you will also need to flush closed loop water to drain at a rate less than the system fill uprate with clean water.
    Regards

    Colin Frayne

    CSci, CChem, CEnv, CWEM, FRSC, FICorr, MCIWEM, FWMSoc (UK), CWT (USA)

    Consultant,

    Aquassurance, Inc.

    156 Red Fox Run,

    Macon,

    GA 31210, USA

    Tel: +1-561-267-4381


    Jun 18, 2020 2:44 PM
    https://www.mti-global.org/network/members/profile?UserKey=72ed3d71-d863-4bb0-bbe3-37bd0faa5469. Click or tap to follow the link." style="margin: 0px; color: rgb(0, 118, 192); text-decoration: underline">Nina Young
    Does anyone have experience with mitigating denitrifying bacteria in their cooling water system?  We are unable to keep the temperature above 140°F, we do have low flow, and we are using a nitrite corrosion inhibitor.  We are considering a system cleanout, but open to hearing what others have done in this situation.  Also curious which biocide treatment was used for denitrifying bacteria.  Thanks!

    ------------------------------
    Nina Young
    Chevron Phillips Chemical Company
    ------------------------------







  • 5.  RE: Denitrifying bacteria

    Posted 10 days ago
    Thank you all for your comments.  It is  a closed-loop system as you thought.  We are wanting to take some immediate action while new exchangers are on order.  We have discussed raising the flow rate and I think that is a longer-term project, although we may need to accelerate that .  ​

    ------------------------------
    Nina Young
    Chevron Phillips Chemical Company
    ------------------------------



  • 6.  RE: Denitrifying bacteria

    Posted 10 days ago
    Nina,

    Thanks for your reply. In my experience of well over 50 years, most closed loop systems are not adequately cleaned and passivated from the time of construction completion and hydrostatic testing. There is often no useful quality standard for the cleanliness and removal of microorganisms, dirt, and construction debris, or adequate method of achieving the desired standard, resulting in permanent microbial infestations and various higher-rate corrosion mechanisms developing. I worked for a long period on a number of very large closed loop systems around the world for a global provider of data centers, search, and other apps, including perhaps the world's largest data center. They experienced detrimental conditions similar to those you mentioned in your enquiry and were keen to avoid the same situation in their latest combined utility building (CUB), and requested me to work with both the building construction team and the water treatment services provider to establish a quality standard, a methodology to achieve this, and to ensure results were delivered in a minimum time frame such as to not impact time/cost overruns.  
     Another respondent -(Orin Wakefield at Chevron)  has advised that "We have tried steaming out and biocide treatments, but i believe the bacteria takes safe harbor in subsurface pits or stagnant areas (deadleg) of the system and repopulates after the "sterilization" treatment." I totally agree with Orin! Thus,  if you w ish to have any hope of eventually operating your new heat exchangers under optimum operating conditions, your company will likely need to do something similar now - to include higher recleaning flow rates.

     Regards

    Colin Frayne

    CSci, CChem, CEnv, CWEM, FRSC, FICorr, MCIWEM, FWMSoc (UK), CWT (USA)

    Consultant,

    Aquassurance, Inc.

    156 Red Fox Run,

    Macon,

    GA 31210, USA

    Tel: +1-561-267-4381