Different Types of Stirred Tank Bioreactors

ByManish acharya

The most significant bioreactor used in industrial applications is the traditional stirred tank reactor (STR) due to its flexibility and high efficiency, as well as low operating expenses. 

The purchase of bioreactors is often subject to greater scrutiny and discussion than other types of equipment with similar price and complexity. 

The sheer variety of options available to you can be overwhelming. This article provides a brief overview of the four main kinds of STR bioreactors that are used in bioprocess technology or Bioreactor manufacturers in India.

The four major kinds of bioreactors that are stirred according to their application include:

  1. Microbial bioreactors/fermenters (Bacteria, Yeast, Fungi)

  2. Bioreactors for cell culture (Mammalian cells Insect cells)

  3. Bioreactors for single-use or disposable use (SUB’s used to cultivate cells)

  4. Bioreactors with special application (SSF as well as Photobioreactors)

There is no discussion of non-STR systems in this review like membrane bioreactors, air lift as well as fixed bed systems. All of them play crucial roles in their respective applications, however generally, they are associated with industries like wastewater treatment.

1. Bioreactors for microbial life (fermenters)

A Microbial stirred tank reactor should be equipped to provide fast, high-shear mixing as well as efficient oxygen transfer. A high ratio of height/diameter will be utilized to let gas bubbles remain close to the culture the longest time possible. Many flat-bladed Rushton turbines break down gas bubbles by using strong shear forces to increase the surface area available for gas exchange. The rate of gas transfer is usually very high and foaming could cause problems. Microbiological organisms have a long-standing history in the production of food as well as industrial applications, and of pharmaceuticals (white biotechnology).

The typical characteristics of fermenters and bioreactors that contain microbial species.

  • Tall height/diameter aspect ratio

  • Multiple, flat-bladed Rushton turbine impellors

  • High gas transfer rates

  • Antifoam Sensor and antifoam System

2. Bioreactors for cell culture

Cell culture bioreactors will come equipped to reduce the risk for contamination in the long run. This is due to easy mixing, and the use of gas mix to improve oxygen transfer. A large marine impeller and slow-speed mixing shield cells from being damaged by shear, while also ensuring proper mixing. The coupling between the motor drive is typically magnetic. Oxygen transfer to the culture is enhanced by a low flow gas mix with a variable amount of oxygen pure. These organisms produce products usually used in medical research (red biotechnology).

The typical characteristics of bioreactors for cultured cells

  • Gentle, low-speed mixing

  • Broad marine impellor

  • Gas mixture with low flow and exact pO2 control by O2, air and N2.

  • CO 2 instead of acid to control pH

3. Bioreactors with a single use

Single-Use Bioreactors (SUB’s) have the advantage of being ideal to establish a production line quickly in cases where validation is required. Looking at on-going costs, a single-use-bioreactor will save on cleaning and preparation times. But, it’ll require replacement after each cultivation. If the process is validated it is very sensible. However, the benefits may not be as clear in other cases.

Characteristics typical of disposable, single-use bioreactors

  • Pre-sterilized

  • Less customization options

  • Limited sensor options

  • Leachable/extractable considerations

4. Bioreactors designed for specific uses (SSF as well as Photobioreactors)

Bioreactors that are specifically designed are suitable for those organisms that loosely fall into the fourth category. They could be anaerobic bacteria, algae or fungi living on solid substrates. The vessel’s design must be adapted to as well as the geometry and mixing are required in these situations. The organisms are usually involved in biofuels and agricultural applications (green biotechnology). ). The vessel design, geometry and mixing must be adapted. The vessel design, geometry and mixing must be adapted.

Types of bioreactors by size:

The most significant factor in determining the kind of bioreactor required is the amount of culture required per batch. There are three primary options for the standard stirred tank bioreactor:

  • Small-scale, parallel bioreactors (under 1 L)

  • Bench-scale bioreactors (1-10 L)

  • Pilot-scale bioreactors (>10 L)

Scale selection should be determined by the amount of culture needed in a batch. A given bioreactor can be improved by the selection different feeding techniques. Strategies that involve gassing and mixing could boost the density of cells per volume significantly. A bioreactor of 2L could be a potential production unit for a therapeutic protein derived from an individual clone.

Under 1 litre working volume

Screening applications in which multiple multi-bioreactor systems are required is an essential characteristic at this scale. When working with volumes less than 100 ml, a dispersed, high-speed system is beneficial for handling and capacity to optimize. When working with quantities of between 100 and 1000 milliliters, a standard autoclavable glass vessel could be utilized. This permits sufficient sample volumes to be removed, and the loss of evaporation to be controlled within the vessel. Multi-vessel systems can be constructed at this level.

From 1 – 10 litres working volume

This is the most common scale of bioreactors on the bench. They allow for more substance to be produced for testing downstream processing or even the production of a small amount. The vessels used are generally composed of glass and steel. They are sterilized using steam inside an autoclave. One option for bioreactors with microbial life is to use a chemical sterilization in the place (SIP). Single-use vessels are a viable option for cell cultivation at this level. They are sterilized through irradiation prior to the production.

Above 10 litres working volume

The vessels are usually made of stainless steel, and are steam sterilized on site (SIP). Most often, they’re cleaned by a machine in situ (CIP). They’re usually free-standing. One option to use single-use bags to line basic steel vessels is possible between 50 and 1’000 litres. They aren’t commonly used outside of pharmaceutical production.

Bioreactor types based on feeding strategies

How the needs for growth are included and removed from the bioreactor will greatly affect the operation. It permits a small-sized vessel to grow a massive quantity or an extremely extensive culture over the course of. The major types are:

Batch

There is no liquid feed included in the process, and no liquid feed is removed. This is an old-fashioned method and the large size of vessels allow commercial production

Fed-batch

Substrate is added gradually in accordance with the feeding method (linear or step, dose or even exponential). The culture is not removed. This is typical of high-density culture. Certain applications might require several feeds with each using specific genes that switch from a growth phase the production stage.