Dear all,
I am carrying out fermentations in bioreactors using the haloarchaea strain Haloferax Mediterranei for the production of PHA with short fatty acids as the carbon substrate in a saline medium. The bacterial growth at the early stage is similar to what I obtained when the experiment was conducted in flasks. After several hours of fermentation (usually around 60h), an excessive foaming takes place, making the culture medium overflowing and disturbing pH and dissolved oxygen control. Nevertheless, the culture should be able to grow further and consume remaining substrate, as it is the case in flasks experiments. To prevent foaming, I used a solution of Antifoam A Concentrate (Sigma Aldrich) diluted in propylene glycol at 1%w. For a 2L bioreactor fermentation, up to 20mL of this antifoam solution was added, and foaming still could not be prevented after some time.
It is expected that exopolysaccharides are concomitantly produced during fermentation, which can increase viscosity of the medium and thus cause foaming.
Is it possible that antifoam is consumed or adsorbed by the microorganisms ?
Should I use a more concentrated antifoam solution, eventhough antifoam A concentrate (Sigma Aldrich) is hard to dissolve properly in propylene glycol (even worse in water as it is a silicon based polymer) ?
Should I reduce the airflow in the bioreactor (currently at 1vvm) to reduce foaming ?
Is it mandatory to add antifoam in a continuous way with an antifoam probe rather than add a consequent volume each day (10mL the first day, 5mL the other days) ?
Thank you,
Lucas Bonnet, PhD student
Hello Lucas!
I had the same problem earlier while working on fungal fermentation. Adding more concentrated antifoam will create mass transfer problems for oxygen. If you use low concentration I suppose it will ineffective as you are observing excessive foaming. let me tell you one thing foaming is autocatalytic process which means you cannot eradicate the problem of foaming once it starts. So don't let the foam to build up. How I am doing this ? simply by putting by antifoam pump (cole palmer) on loop. This system put few drops of antifoam after every set interval of time. In case of excessive foaming I set the timer for 1 hr else I set for 4-5 hrs in case of low foaming. Please let me know if you have any questions.
Please find the attached paper.
Dear Lucas, foaming is a real bother in many fermentations and a lot of solutions are tried and reported and successful depending on the type of fermentation at hand.
First: antifoam agents are generally oil-like stuff. In the very past oils like from sunflowers were used, now silicone type of oils are common, sometimes enriched with small particles to break the foam films.
Oils are in general non-soluble (meaning (almost) non measurable low solubility) but are added in their pure form. By dispersion due to mixing small droplets encounter bubbles and spread over the surface pushing away the surfactants (often proteins,) that are responsible for foaming, from the interface. As a result mass transfer is greatly reduced.
A weird phenomenon is the 'disappearance' of the antifoam in time during the fermentation (in batch). It seems to be related to the biomass concentration (which may change in time), but I never encountered a proven explanation of it. But antifoam agent must be added to compensate.
From using a bucket antifoam to add at intervals to continuous in the feed (both bad ideas) and thereafter to controlled dropwise addition methods were developed.
Other possibilities are mechanical breakage of foam (inside or outside the fermentor) of sucking the foam in by a stirrer close to the surface (search for SAFD).
We encountered once a case of severe foaming and indeed prevented foaming by simply using a lower gasflow resulting from enrichment of the air with oxygen. We even used pure oxygen.
Foaming is a complex phenomenon and maybe nothing will work sufficiently. I am afraid there is no simple solution for your case and maybe you have to try some possibilities in order of simplicity to realize it.
Good luck, may the first try win.
I agree with Mr. Rob van der Lans. I have also encountered defoamer consumption in PHA synthesis. Defoamer should be fed throughout the process. It is very convenient to use an automatic system that includes a foam level sensor and a defoamer supply pump. When the foam level reaches the sensor, then the circuit is closed and the defoamer supply is turned on.
Thanks all of you for your details answers.
For now, I have tried using an external pump so that antifoam is added at regular time intervals, starting after 50h of culture as I know there is no foaming before. I reduced gasflow by 2 and it seems that it worked well.
I will also try another antifoam which is water soluble (Struktol)
I do have an antifoam probe which seems not to work correctly, as it continuously detects foam in the reactor due to condensation, and not foaming itself... Did you have the same problem with such antifoam probe ? The reference is : Antischaumsonde komplett ; 8844461 ; B. Braun Biotech International GmbH
Cheers
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