Bioreactor Types Used in Labs: Stirred-Tank, Airlift and Single-Use

Labs run three bioreactor types: stirred-tank, which moves the broth with an impeller; airlift, which moves it with rising gas; and single-use, a disposable bag inside a rigid holder. Stirred-tank runs most lab work because it is the one type you can instrument fully, sterilise in place and carry from 1 L glass to 500 L steel without changing principle.

That last sentence is the whole argument of this article, and we will spend the rest of it showing where it holds and where it breaks. We build fermentation vessels for a living, so the comparison below is not a taxonomy exercise copied from a textbook. It is the type-versus-hardware map we actually use when a lab tells us what they are growing.

Contents

• What actually separates the three bioreactor types?
• How does a stirred-tank bioreactor move the broth?
• Where does an airlift bioreactor win, and where does it quit?
• Is single-use worth it at lab scale?
• Which type maps onto which piece of hardware?
• Where does each type stop being viable?
• Sterilisation is the line most people miss
• Frequently asked questions

What actually separates the three bioreactor types?

One question: what supplies the energy that mixes the liquid and gets oxygen into it?

In a stirred-tank, a motor does it through an impeller. In an airlift, the sparged gas does it. Bubbles rise in one section, liquid gets dragged up with them, sinks in the adjacent section, and the loop circulates. In a single-use system, it depends: most single-use bags are stirred-tanks that happen to be disposable, and a few are wave-rocked. Single-use is a construction category, not a mixing principle, which is why it sits awkwardly in lists like this one. We keep it here because everyone searching for bioreactor types expects it, but it answers a different question than the other two.

Everything else (pH probes, dissolved-oxygen control, foam breaking, feed pumps) bolts onto any of the three. Those are control features, not type definitions. If you are still fuzzy on what the vessel itself is doing before we compare types, we wrote a separate piece on what a bioreactor fermenter does and how working volume behaves inside it.

How does a stirred-tank bioreactor move the broth?

Mechanically, and that is its advantage. An impeller shears bubbles into smaller bubbles, drags them back down against their own buoyancy, and keeps cells suspended even when the medium is viscous or loaded with solids. Because the mixing energy comes from a shaft you control, you can dial it up when oxygen demand spikes mid-fermentation and back off when it does not.

The drive itself splits into two families, and this is a real fork in the road at lab scale. Our laboratory bio fermentation tank uses top mechanical stirring or magnetic-drive mechanical stirring; on the glass fermentation tank we use magnetic-drive stirring with top or bottom pin-free magnetic coupling. A top-entry mechanical shaft goes through a seal, and a seal is a contamination path. A magnetic coupling has no shaft penetration at all, which is why small sterile work drifts toward it.

The cost of stirred-tank mixing is shear. Cells with fragile membranes feel the impeller tip. That is not a reason to avoid stirred-tanks. It is a reason to choose impeller geometry and speed deliberately, and it is why speed sits in the basic control set on every vessel we build rather than being fixed at the factory.

Where does an airlift bioreactor win, and where does it quit?

Airlift wins on three things: no moving parts inside the vessel, no shaft seal to contaminate through, and gentle mixing that shear-sensitive cultures tolerate. Plant cells, some mammalian lines, and filamentous cultures that get shredded by an impeller all do well in one.

It quits on the same physics that makes it elegant. Mixing energy is whatever the gas flow gives you, and gas flow also sets your oxygen transfer, so you cannot tune the two independently. Turn the gas down because your culture is foaming and you have just turned the mixing down too. Airlifts also struggle as the broth thickens: a viscous or high-solids medium damps out the circulation loop, and you get dead zones the bubbles never reach.

The practical consequence, and this is the part prose-only articles skip, is that airlift is a process choice made before you buy anything, not a scale choice. Nobody builds a stirred-tank at 5 L and switches to airlift at 50 L. If the culture needs airlift, it needs airlift at every scale. We build stirred-tank vessels because that is where the demand sits and because the control set transfers, but if your cells cannot take an impeller, no amount of speed tuning fixes that. Say so on your enquiry rather than ordering a stirred vessel and hoping.

Is single-use worth it at lab scale?

Sometimes, and the honest answer depends on how many different things you run in that vessel.

Single-use removes cleaning validation and turnaround. You pull the bag, drop in a new one, go. That trade pays off when you switch products constantly and cross-contamination between campaigns is the thing that would sink you: clinical-scale biologics, multi-product CDMO work.

At bench scale, the calculation flips more often than vendors admit. A 5 L glass vessel that you autoclave between runs has no consumable stream, no vendor lock, and you can see through it. Visibility matters more than people expect: watching foam build, watching cells settle, watching a feed line actually flowing is diagnostic information a bag does not give you. And a lab running the same organism ten times in a row is not paying for what single-use sells.

The place single-use genuinely loses at lab scale is process development itself. You are trying to learn what your organism does under defined conditions so the numbers transfer to a bigger vessel. A rigid, instrumented, in-situ-sterilisable vessel gives you a cleaner dataset than a bag whose geometry changes with fill volume.

Which type maps onto which piece of hardware?

Here is where most bioreactor-type articles stop, having told you three principles and nothing about what you would actually put on a bench. The three vessel families we build are all stirred-tank; they differ in what they are made of, how you sterilise them, and how far up they go.

Read the volume column as the real answer to “which type do I need”. A glass stirred-tank tops out at 10 L total. A steel lab vessel starts at 10 L and runs to 500 L. There is exactly one size where they overlap, and at that size the deciding factor is not volume at all. It is whether you need in-situ steam. The rest of the fermentation tank range sits behind that same volume logic.

Where does each type stop being viable?

Scale bands, stated plainly:

• Glass stirred-tank: viable to 10 L total volume, and that is a hard stop set by the glass, not a preference. Above it, the wall thickness needed to hold pressure and take steam makes glass a bad idea. Below 10 L, glass is usually the right answer.
• Steel lab stirred-tank: 10 L to 500 L in the sizes we build (10, 15, 20, 30, 50, 75, 100, 150, 200, 300, 500). This band is where in-situ steam sterilisation, air-flow control and tank-pressure control become available, and those three are exactly what you need to make a process transfer upward.
• Industrial stainless stirred-tank: from lab and pilot sizes into production-scale configurations, as single tanks or as a multi-stage fermentation system. This is the point where the vessel stops being a piece of equipment and becomes a line.
• Airlift: bounded by broth rheology, not litres. It stops being viable when the medium gets thick enough to kill circulation, whatever the volume.
• Single-use: bounded by bag manufacturing and by economics. Rigid vessels take over once you are running the same process repeatedly and the consumable bill starts compounding.

Notice which two of those five are volume-bounded and which three are not. That asymmetry is why we tell people to specify the process first and the litres second. Our fermentation tank procurement guide walks the same questions in purchase order.

Sterilisation is the line most people miss

Ask a lab which bioreactor type they want and they will talk about mixing. Ask which one they will be happy with in two years and the answer usually turns on sterilisation.

Off-site autoclave sterilisation, which is what the glass vessels use, means the vessel comes apart, goes in the autoclave, comes back, gets reassembled. Fine at 5 L. At 50 L it is not a procedure, it is an event, and it is why the steel vessels use in-situ steam sterilisation instead. Steam goes into the assembled vessel where it stands.

That switch is not free. In-situ steam means the vessel has to hold steam pressure, which means it has to be built to hold pressure, which is where tank pressure appears in the control set on the industrial stainless vessels alongside air flow, agitation speed and feed. The glass vessels control temperature, speed, pH, DO, foam and feeding, but not tank pressure and not air flow, because they are not the kind of vessel that needs to.

So the sterilisation method is a proxy for the whole design generation. It tells you the material, the pressure rating, the control set and roughly the scale band, all from one line on a datasheet.

Frequently asked questions

Is a stirred-tank bioreactor the same as a fermenter?

In practice the words get used interchangeably, and both refer to a vessel that holds a controlled culture. “Fermenter” tends to signal microbial work, “bioreactor” tends to signal cell culture, but the hardware overlaps heavily. Our laboratory bio fermentation tank is specified for microbial and cell-culture process development in the same vessel.

Can I convert a stirred-tank into an airlift?

No. The riser and downcomer geometry that makes an airlift circulate is the vessel, not an accessory. Decide before you order.

Why do glass fermenters stop at 10 L?

Because that is where borosilicate stops being sensible for a vessel you sterilise and pressurise. Our glass range runs 1L, 2L, 3L, 5L, 7L and 10L plus multi-vessel configurations; above that, the same stirred-tank principle continues in 316L / 304 stainless steel.

Does single-use give me the same control set?

The measured parameters are broadly the same: temperature, speed, pH, DO, foam. What changes is what the vessel itself can do around them: in-situ steam and tank-pressure control belong to rigid steel vessels.

Which type should I develop a process in if I plan to scale up?

A rigid stirred-tank, in the smallest size that gives you the controls you will have at production scale. If your production vessel will run in-situ steam and pressure control, developing in a vessel that has neither means you will re-learn the process later.

Choosing your type

Pick in this order. First, can your culture take an impeller? If genuinely not, you need airlift and litres are a secondary question. If yes, and for most microbial and many cell-culture processes the answer is yes, you are in stirred-tank territory, which covers our whole fermentation tank range.

Second, what working volume do you actually need, not what you hope to need? Under 10 L total, take glass: you get visibility, magnetic coupling with no shaft seal, and autoclave sterilisation you can live with. From 10 L to 500 L, take the steel lab vessel and get in-situ steam, air flow and tank pressure with it. Beyond that, you are specifying a production line, single tank or multi-stage.

Third, will you run one process or twenty? Twenty different processes in one vessel is the case where single-use starts to argue for itself. One process, repeatedly, is not.

When you enquire, tell us the organism, the working volume, whether you need in-situ steam, and which sensors you plan to run. Those four answers pin the vessel down almost completely. The selection guide lists the same confirmations we ask for before quoting: working volume, agitation, temperature-control support, sterilisation needs, sensor requirements and downstream equipment.