Hola Alejandro, not sure what the volume of your reactors is, but in lab-scale experimental systems such phenomena is absolutely normal to happen.

On the one hand, I would not add any "anti adherent" agents, since this might influence your experimental observations.

On the other hand, to our experience, such systems require a regular (every day or every other day) cleaning and the removal of biofilm and any residues from reactor walls, pipes and of course, diffusors, among others.

If your objective is to make observations on the suspended culture, fungal biomass adhering to surfaces may well influence your observations in unwanted/unknown ways as (a) they may have different metabolism, OR (b) because it is difficult to account for this biomass in the mass-balance calculations.

The adherence of biomass to the diffusors can influence mass-transfer, of course, but often fungal cultivation involves the formation of filamentous structures that will also influence mass-transfer and mixing in your reactor that should be accounted for.

Finally, it is imporant that the cleaning must take place after the daily sampling, after which there can be, at least, 20-23 hours of undisturbed operation prior to the next sampling.

Hope you find my answer useful.

Hi Alejandro, this problem is common at any scale and have solution. We usually tailor-made troubleshooting solutions depending on the experimental design's objectives. More information is required. If you are still needing to move your research forward this month feel free to drop an email, -Kindly find details in my articles or here

regards,

If you work with filamentous fungi - it is impossible. Think on another production scheme.

Formation of biomass deposition on baffles and impellers does not pose a particular problem. The problem occurs when sparger holes are blocked and aeration and oxygen transfer from the optimal position are removed. This phenomenon can not be completely avoided (especially for viscous media and high cell density in the fed-batch process), but it can be delayed for the duration of its formation. In my opinion, keeping the rate of aeration on the appropriate amount and to close impeller to sparger, the time of formation of the deposit on the sparring can be reduced. Of course, with the proper design of the blades, this problem can be avoided significantly. Also it is necessary sparger (with diluted acid), over and under impellers, sensor surfaces and etc. cleaned more accurately.

No, I wouldn't say that it is impossible to prevent or reduce the biofilm formation. If one knows the anchorage characteristics of the organism inside the fermentor, then one can definitely find ways to reduce it. It is a routine practice in animal cell culture, wherein we study the role of electrical charges both on the cell and on the carrier (if not microcarrier) and then we determine what to do next.

Dear colleagues

Thank you for your quick answers. As Dr. Ghosh said, I think it´s possible to control biofilm formation over spargers. I know it´s a common phenomena in fungal submerged fermentations. I´m working with a lab scale fermentor (3 L total volume, 2.1 L working volume) for my thesis. It has one porous sparger (I coupled 2 fish tank spargers to increase kLa) and I use 3 impellers due to broth viscosity.

My goal is to find the optimal culture conditions through mathematical modeling so I need to be able to calculate the effect of agitation speed and air flow rate. Precisely the problem is that due to the obstruction of the spargers, the dissolved oxygen drops significantly after 2 days max, so I can´t calculate if that happens only because of oxygen consumption or because of the biofilm obstruction.

I thought of using an additive to destabilize the anchorage mechanism, but so far I haven´t identified such mechanism. I´m interested in trying salt, talc, tween 80, olive oil, glycerol, stearic acid or maybe formic acid. Perhaps something as simple as increasing agitation could solve the problem though.

Best regards,

Alejandro

Just some remarks:

- At high viscosity (calculate Reynolds) the area mixed may be seriously limited. Impeller type and size are important. Using large impellers may reduce the effect somewhat. A biofilm on the blades (turbines?) means that the shear at the blades is insufficient, which will occur anyway with increasing viscosity. Indeed, a higher revolution rate will help somewhat.

- At a certain viscosity (from already 20 mPas on) mass transfer will reduce. This reduction is a well known phenomenon: after some time (growth) it reduces to too low levels for growth/production.

- The use of a porous sparger suggest that you do not use the bottom impeller for aeration. Any idea on bubble sizes? When very small (low aeration) the bubbles will follow the flow and may/will be depleted before escaping. When larger, as a result of coalescence at the sparger, bubbles may coalesce further (enhanced by viscosity). Do you see 'blobs' of air at the surface? Again this reduces mass transfer (low residence time, hence low interfacial area).

- Almost any additive will reduce mass transfer anyway (interface characteristics).

Maybe it is possible to use low concentrations, a higher impeller speed and aeration via the impellers.

Success with your thesis.

I have observed similar issues with filamentous fungi fermentation. Wall growth phenomenon prevented reliable biomass concentration measurement via sampling. On the other hand I did not notice (major) differences of the quality of submerged and adhered biomass (lipid content, and fatty acid composition in my case).

What I have found in literature:

- use of glass beads

- addition of carboxypolymethylene

- mutation to pellet morphology

In addition, in the past we changed the sparger design from the standard ring sparger with small holes to a simple open tube and it prevented fouling of the sparger.

Please check also this previous thread ( Prof. V. V. Byriukov suggested some treatment for glass reactors)

https://www.researchgate.net/post/How_to_control_surface_growth_of_filamentous_fungi_in_submerged_fermentation

Best of luck!

Try replacing porous bubblers with perforated stainless tubes. This will not prevent sticking, but will facilitate subsequent cleaning.

First, u need to determine the oxygen consumption rate in ur controlled experiment; then u need to calculate precisely the oxygen supply rate to match the consumption rate. This is more difficult to do, since bubble aeration goes through the process of gas depletion as the bubbles rise to the surface. This gs depletion effect is difficult to model because it changes with the gs flow rate as well as the oxygen consumption rate. But if u can mathematically formulate a proper model, then the system should achieve steady state, and so when u notice a drop in DO concentration, it must be due to biofilm degradation and not the oxygen consumption rate. Whatever remedy u choose to use, the most important is to get the model right first.

Why don't you try changing the surface charges on the spargers etc. Many a time process like anodising helps or particle electrodepositing may also work.

Hello Alejandro:

Reading your question and the answers, two ideas come to my mind:

a) Adding glass beads (as someone suggested) may create an "auto cleaning" effect over the spargers, due to shear. However, this could break the fungal cells for the same reason.

b) If you put the sparger(s) surface vertical instead of horizontal, this could reduce or delay the scale formation, gravity would work in your favor. You could give it a try.

Best regards.