How do I calculate the aeration rate (VVM) in fermenters/bioreactors in laboratories? VVM stands for vessel volume/minute.
Check http://www.water-chemistry.in/2010/08/how-to-calculate-aeration-tank-air-quantity/
Also check https://www.sciencedirect.com/topics/engineering/aeration-rate
As VVM stands for volume of air sparged (in aerobic cultures) per unit volume of growth medium per minute, it is calculated by dividing measured airflow rate (units: L/m, using a rotameter) with the volume (L) of growth medium (including cultured cells).
Vvm in general is not (used as) a very exact measure. All kind of broth volumes are used, even vessel volume is very common. If you want to be exact, both gas flow rate and broth volume need to be specified. Gas flow rate measured by rotameters must be adapted by temperature and pressure when different from rotameter calibration values. Preferably use a mass flow meter. And which pressure are you going to use? Barometric, bottom, halfway? The latter is most representative. For 'broth volume', you need to specify the actual liquid volume (but how do you measure it in multiphase flow? Maybe use a scale to measure mass). The volume will not be constant in general.
So the most important is to look at how it was defined in the paper from which you want to use the data for comparison. And at small scales corrections are small as well. Just be aware of what you are actually doing.
check https://www.sciencedirect.com/topics/engineering/aeration-rate
There is no need to calculate VVM in laboratories and also in industrial fermentors. Do it with KLa.
VVM is commonly used as a scaling rule (keeping it constant at different scales), and in that case need not be very accurate, since this rule is far from exact. One should consider which scaling rule is best for the process at hand. The big advantage of vvm is that it depends on volume only (as function of scale). Other more specific scaling rules such as constant kLa or P/V require more modelling (kLa versus superficial gas velocity; very scale dependent) or proper measurement {power).
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V. V. Biryukov
Moscow State University of Mechanical Engineering
In shaking flasks it is impossible to determine VVM. That is laboratory, as in Menail Sajid question. There is only volume of liquid, but not volume of air. Where are scaling rules?
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Rob van der Lans
Delft University of Technology
Well, dear V.V., that is an interpretation of Menail's question, I did not make. But since he asked for the aeration rate, I assumed there is aeration. In shake flasks there is only a transfer rate. So, no vvm, agreed.
BTW, in our laboratory, the basic fermenter is a 1 L aerated stirred vessel. So, I also assumed that was the case with Menail.
As far as I know vvm is used only for scaling, and, indeed, quite useless otherwise. If one wishes to scale-down from fermenter to shake flask, it is not possible to use vvm for scaling. But I do not think that was the question.
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Sergey P. Klykov
Alpha-Integrum, Ltd.
I agree with Professor V. V. Biryukov concerning to kLa.
Other parameters, including the VVM, can only play an auxiliary role in the general case. Although, there are also exceptions. If my memory serves me, because I dealt with this a very long time ago, several decades ago, there are microorganisms (some infections) that require increased concentrations of carbon dioxide, CO2 for their growth. The air flow rate per unit volume of the fermenter per minute, VVM, plays an important role for the balance of the processes of sorption and desorption of CO2 in the fermentation liquid.
But, this can be attributed to special cases.
Sincerely,
Sergey P.Klykov
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Rob van der Lans
Delft University of Technology
@Klykov and @Biryukov. Aeration rate is an input variable, so vvm as well. KLa is an output variable, depending, among others, on aeration rate (not in a shake flask of course).
If working with an organism that requires carbon dioxide (or oxygen), one may express this demand absolutely or per volume, and to be consistent absolute aeration rate (or oxygen input rate and so on) and aeration rate per volume should be used. We prefer absolute rates.
And there is still the problem of the volume to be used (for both consumption rate and (oxygen) transfer rate). How is the liquid volume inside the organisms taken into account?
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Sergey P. Klykov
Alpha-Integrum, Ltd.
Dear Dr. Rob van der Lans ,
Thank you for your comment.
However, in light of the question that was asked, it does not matter in this case the ranking of the variables to the input and output variables. Although, of course, this is very important in the general case.
An important point is kLa and the corresponding OTR and OUR (the rate of oxygen uptake by cells).
Intracellular fluid volume is important for the construction of complex compartmental models, which is hardly relevant for our simple discussion, which is aimed at discussing simple laboratory experiments.
By the way, we could consider OTR not as an output parameter, but as an input parameter, if we plan in advance the experiment by measuring the "sulfite number" in the fermenter. Perhaps anyone can easily find these techniques on the Internet. Knowing the "sulfite number", we a priori have an input parameter for the mass transfer of oxygen to the fermentation liquid.
Thus, kLa, OTR and OUR are our key parameters. (At least in my own practice.)
Sincerely,
Sergey Klykov
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Sohel S Shaikh
Pellucid Lifesciences pvt ltd
simply it can be calculated by dividing air in LPM by media volume
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V. V. Biryukov
Moscow State University of Mechanical Engineering
Dear Sohel S Shaikh, you absolutely right. But I cannot believe, that Menail Sajid did not know this rule. May be it is something else?
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Sohel S Shaikh
Pellucid Lifesciences pvt ltd
Menail Sajid can you elaborate your question if anything different that this calculation
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Rob van der Lans
Delft University of Technology
The question 'defines' VVM as Vessel Volume per Minute. Understandable confusion, since the abbreviation is not clear (VVM = (V/V)/min. Relative volume per time). Sometimes written as V/V/min. But that is American style of notation, and incorrect elsewhere.
Remains the question, why stated here, and not find the answer on the web?
But then you may find the wrong answer:
"It is crucial to measure OTR under industry standard conditions with 1 vessel volume per minute (VVM) of air sparging only without oxygen enrichment, as the increase of VVM or oxygen sparging will significantly inflate OTR values" (Eppendorf.com)
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Johnny Lee
American Society of Civil Engineers
I use the average gas flowrate Qa determined from the given gas flow at standard conditions Qs. (The subscript s represents standard). The salient equation to convert Qs to Qa is given by:
Qa = 172.82 Qs Tp [1/Pb + 1/Pp]
where Tp is the gas temperature at the point of flow measurement, K, assumed to be equal to the water temperature. Pp and Pb are the corresponding gas pressure and the barometric pressure respectively. (Units are in Pa). This equation has assumed the standard air temperature to be 20 0C or 293 K, and a standard air pressure of 1.00 atm (101.3 kPa).
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Chandan Mahata
Virginia Tech (Virginia Polytechnic Institute and State University)
Dear Menail Sajid
The question itself has some confusion regarding VVM.
Firstly, VVM (unit of aeration rate) is nothing, but the volume of air per volume of reactor per time (time in terms of the minute). Please note, the volume of air and volume of the reactor should be in the same unit (it may be litter or m3, does not matter).
Now, to find the aeration rate in terms of VVM, VVM = volumetric flow rate of air/reactor volume
It will be more clear if I give an example:
Volumetric flow rate = 10 Litter/minute
Volume of reactor = 5 Litter
(Please note: here both are Litter)
Then aeration rate = 10/5 VVM = 2 VVM
Therefore, we can simply get VVM dividing volumetric flow rate by reactor volume.
All the best
Thanks
Chandan
My website: https://www.chandanw2e.com/
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Johnny Lee
American Society of Civil Engineers
The difficulty is that the volumetric flow rate is a variable in a tank of a physical height. In a gas transfer problem, for example, the transfer coefficient KLa is proportional to this gas flow rate even though the ponderal flow rate is fixed. Therefore, KLa is not a constant and varies spatially and temporarily. In submerged aeration, bubbles are released from the diffuser in a cloud. On collision, they tend to coalesce and form larger bubbles. Thus analysis of bubble aeration depends on average values because calculations of the instantaneous bubble size is not theoretically possible. Gas transfer rate depends on the average surface area of the bubbles and thus on the mean bubble diameter. Therefore, calculation of the vvm is not meaningful, either for a fermentor or an aeration tank. However, it is possible to estimate the average volumetric gas flow rate which can then be correlated to KLa, since the diameter can be related to the air volumetric flow rate.
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Prabakaran Krishnamurthi
Alkaloids Corporation
Dear Menail Sajid: I think the VVM is misunderstood - Volume/Volume/minute is the volume of air related to the volume of the medium used. For example, if the media volume is 10 Liter and if you pass 5 liters of air per minute then it is taken as 0.5 VVM. As VVM stands for volume of air sparged (in aerobic cultures) per unit volume of growth medium per minute, it is calculated by dividing the measured airflow rate (units: L/m, using a rotameter) by the volume (L) of growth medium (including cultured cells).
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V. V. Biryukov
Moscow State University of Mechanical Engineering
Действительно, VVM как входной параметр легко определить из первичных, легко измеряемых параметров. Но для микробной культуры действительно входным параметром является OTR - скорость перехода кислорода в ферментационную жидкость. Этот параметр зависит от KLa - коэффициента массопередачи кислорода, который не эквивалентен VVM и не связан с этим параметром прямым соотношением (линейным или нелинейным). Он зависит от многих других параметров - и параметров ферментёра, и от характеристик ферментационной жидкости. Но это для микробной культуры не выходной, а входной параметр. Поэтому он более часто используется для масштабного перехода.
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Carlos Araújo Queiroz
Universidade NOVA de Lisboa
The KLa mass transfer coefficient tends to determine the dissolved oxygen concentration (DO) of the aerobic fermenter. The air to fermenter's media mass-transfer rate of oxygen (Na) should be dependent on the local oxygen deficit: Na = KLa·(Cs-C). Here, Cs is the DO that would apply for saturation of the fermenter's broth and C is the measured DO. A mean concentration difference can be defined (ΔCm) after accepting some convenient mixing model, so that: KLa = OTR / ΔCm, where OTR stands for oxygen transfer rate. Agitation should contribute for KLa. Such a modelling-based approach implicitly takes into account other variables that may influence KLa; including temperature (T) or pH. Further details on this kind of approach, were given at the following reference (MSc Thesis):
Thesis Controlo do Oxigénio Dissolvido em Fermentadores para Minimi...
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Tagne Tiegam Rufis Fregue
University of Yaounde I
vvm = volume of air/time/volume of medium= 1/t where t= time
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