What are Bioreactors? Definition, Principle, Design, Parts, Types, Applications :
What is a Bioreactor?
- The fermentation process is carried out in a special type of vessel known as Fermenter or Bioreactor.
- A bioreactor is a device used for microbial fermentation, which can improve fermentation efficiency by optimizing the fermentation conditions of microorganisms.
- These bioreactors are commonly cylindrical, ranging in size from a few milliliters to cubic meters, and are usually made of stainless steel.
- According to the aerobic and anaerobic properties of the cultured microorganisms, fermenters can be divided into aerobic and anaerobic types.
- There are different types of bioreactors, The major types are Continuous Stirred Tank Bioreactors, Bubble Column Bioreactor, Fluidized Bed Bioreactors, Packed Bed Bioreactors, etc.
- The size of the biological fermenter is usually different according to the application from small scale to large scale ranges from 50ml to 5000L, which can be independently customized according to the user’s requirements.
- Experimental-scale fermenters with tanks less than 10L are generally made of hard chemical glass for observation.
- Generally, biological fermenters are vertical, with standard jackets, and flat-round turbine stirring devices.
- A typical bioreactor consists of various systems such as a Sterilization system, agitator system, an oxygen delivery system, sampling system, foam control system Cooling system, temperature & pH control system, etc.
- Fermentation tanks are widely used in beverage, chemical, food, dairy, brewing, pharmaceutical, and other industries to play a fermenting role.
Bioreactor Definition :
- A bioreactor is defined as a vessel that carries out a biological reaction and provides a controlled environment such as temperature, pH, substrate, salts, vitamins, oxygen, etc for the growth of microorganisms and product formation.
- A bioreactor is a device used for microbial fermentation, which can improve fermentation efficiency by optimizing the fermentation conditions of microorganisms.
- Fermenters are a device in which the fermentation process is carried out.
- Bioreactor refers to a device system that provides a suitable reaction environment for living cells or enzymes, allowing them to carry out cell proliferation or production.
Principle of Bioreactor:
- The bioreactor is the core heart of the fermentation process, which provides a good environment for the fermentation process.
- The bioreactor provides a suitable growth environment for the growth and reproduction of bacteria and promotes the bacteria to produce the products people need.
- The main principle of the Bioreactor is to make the gas well dispersed in the liquid phase so that the materials can be mixed more evenly, and the uneven other liquid can be evenly suspended or fully emulsified; so that the solid particles can be evenly suspended in the liquid phase.
- Fermentation tanks are constantly being upgraded with the development of the times. From traditional fermentation industry to modern fermentation industry, and then to microbial engineering.
- It has not only become an important pillar of the biotechnology industry but also has become even more powerful when combined with genetic engineering technology.
- In the future, fermenters will be more widely used, and customers should apply them more rationally and scientifically.
- Biological Bioreactors are widely used in dairy products, beverage bioengineering, pharmaceutical, fine-line chemical and other industries, and dairy products and alcoholic beverages.
Characteristics of Ideal Bioreactor:
- The ideal Bioreactor should be simple, easy to use, and provide proper environmental conditions.
- Keep cells evenly distributed throughout the culture volume.
- Keep the temperature constant and homogeneous.
- Minimize nutrient concentration gradients.
- Prevent sedimentation and flocculation.
- Allow the diffusion of nutrient gases at the rate required by the crop.
- Keep the culture pure without contamination.
- Maintain an aseptic environment.
- Maximize performance and production.
- Minimize spending and production costs.
- It should Minimize the time.
- The bioreactor must be designed to prevent the entry of contaminating organisms and to contain the desired organisms.
- Bioreactor must resist corrosion, sterilization pressure and meet the demands of cultivation of different types of microorganisms.
- The volume of culture must remain constant, that is to say, that there are no leaks or evaporation.
- The level of dissolved oxygen must be maintained above the critical levels of aeration and agitation of the culture for aerobic organisms.
- A good Bioreactor must Control temperature, agitation, pH, and dissolved oxygen of the culture medium is necessary to optimize the multiplication of microorganisms.
Structure and Design of Bioreactor:
- Bioreactors is vessel in fermentation process carried out for the production of biomass, antibiotics metabolites, and vitamins.
- Generally Fermentation vessel is made up of Glass and stainless steels.
- The sizes of the bioreactor can vary from small scale to large scale according to application. shake flask (100-1000 ml), laboratory fermenter (1 – 50 L), to plant scale (2 – 500 m3) are some examples of bioreactors.
- An aeration system is one of the very important parts of Bioreactor which includes in sparger and impeller for mixing the gas bubbles and microbial cells through the liquid culture medium for uniform circulation of Nutrients.
- In fermentation vessel four baffles are present inside of an agitation vessel to prevent a vortex and improve aeration efficiency for growth of microorganisms.
- Heating devices uses for temperature control and sterilization. similarly cooling jackets are used for sterilization of media and control the temperature.
- Foam control unit is used to control the level of foam in the fermenter vessel minimize or to avoid contamination.
- Different types of valve are used in Bioreactor such as globe valve, butterfly valve, ball valve, diaphragm valve and safety valve to control the movement of liquid in the vessel.
- A variety of computer monitoring sensors are used to control environmental conditions like temperature, pH, dissolved oxygen concentration, nutrients levels, cell mass and product concentration.
Types of Bioreactor :
There are different types of bioreactors according
- Depending on the input and output flows, the operation of a bioreactor can be in three different ways: continuous (chemostat), semi-continuous (fed-batch), and discontinuous (batch).
- Depending on the biological culture you want to carry out, they can be divided into aerobic, anaerobic, or facultative organisms. In each of the bioreactors, the aeration or insulation system will vary. In the same way, depending on the organism, its growth will be favored by aeration with bubbles, as in the case of lichens, or with agitation, the most normal aeration in bacterial growth.
- According to the types of organisms in bioreactors: microbial reactors, plant cell reactors, animal cell reactors, and enzyme reactors.
The main types of Breactors are :
1) Continuous Stirred Tank Reactors (CSTR).
2) Plug flow Reactor, also known as tubular flow reactor.
3) Tube Reactor.
4) Bubble Column Reactor
5) Airlift Bioreactor.
6) Packed Bed Reactor.
7) Fluidized Bed Reactor.
8) Tower Reactor.
1. Continuous Stirred Tank reactors :
- Continuous Stirred Tank reactors are reaction vessels in which the substrate and other materials are continuously added and the products continuously removed.
- The continuous stirred-tank reactor is also known as a continuous-flow stirred-tank reactor or mixed flow reactor.
- The CSTR reactor is designed with full consideration of the research on the fermentation state of different materials and is equipped with a variety of feeding and discharging methods, which can complete continuous feeding or semi-continuous feeding and fermentation research.
- CSTR is High strength acid and alkali corrosion-resistant stainless steel tank.
- It has an easy modular system, easy to clean and maintain.
- CSTR is suitable for scientific researchers, biogas plants, and for continuous simulation experiments.
- CSTRs are most commonly used in industrial fermentation processing, primarily inhomogeneous liquid-phase flow reactions where constant agitation is required.
- Continuous reactors are used for a wide variety of chemical and pharmaceutical industries and for biological processes, such as cell cultures and fermenters.
- Large-scale production should use continuous reactors as much as possible.
- The advantages of continuous reactors are stable product quality and easy operation and control.
- The disadvantage is that there are different degrees of back mixing in the continuous reactor, which is an unfavorable factor for most reactions and should be suppressed by reasonable selection and structural design of the reactor.
2. Plug Flow Reactor :
- Plug flow reactor (PFR) is a continuous type reactor in which materially added continuously inside the reactor and it flows in a “plug-like” manner.
- The plug flow reactor model (PFR) is also known as a Continuous tubular reactor (CTR).
- The plug flow reactor is suitable for large-scale and continuous chemical production.
- It is composed of an empty tube or a filled tube with a relatively large length and diameter, which can be used to realize gas-phase reaction and liquid-phase reaction.
- Plug flow reactor operates under steady-state conditions.
- The plug flow reactor has a small volume, a large specific surface, and a large heat transfer area per unit volume, which is especially suitable for reactions with large thermal effects.
- Since the reactant has a fast reaction speed and a fast flow rate in the tubular reactor, its production capacity is high.
- The continuous tubular reactor is suitable for both liquid phase reaction and gas-phase reaction.
- It is particularly suitable for pressurized reactions.
3. Tube Reactor:
- The tubular reactor is a continuous operation reactor with a tubular shape and a large aspect ratio, which belongs to the plug flow reactor.
- The tubular reactor has small back mixing and the production capacity per unit volume is high.
- This type of reactor is especially suitable for occasions requiring a high conversion rate or series side reactions.
- Tubular bioreactors are used in gasoline production, oxidation of sulfur dioxide, oil cracking, synthesis of ammonia from its elements.
- Its main disadvantage is that when the reaction rate is very low, the required pipeline is too long, which is not easy to realize in the industry.
4. Bubble Column Reactor:
- A bubble column reactor is basically a cylindrical structure.
- In Bubble Column Reactor the tank is filled with liquid and the gas is introduced from the bottom of the tank.
- Bubble Column Reactor is suitable for gas-liquid reactions and slow and medium speed exothermic reactions.
- Bubble column reactor cannot be used for highly viscous medium.
- Bubble Column Reactor has a simple structure, easy to use, low cost, easy to control and maintain with no difficulty at high-pressure use.
- It has low efficiency due to the liquid phase of the bubble column reactor being over mixed and the bubbles are easily fused.
5. Airlift Bioreactor :
- Airlift bioreactors are a type of bioreactor without mechanical agitation that is widely used.
- The airlift bioreactor is developed based on the bubble column reactor.
- Airlift bioreactors can be further divided into four types: airlift and external circulation fermenters, airlift circulation fermenters, belt lift fermenters, and tower fermenters
- Airlift bioreactor is one of the important reactors used in the field of plant cell culture.
- Its fluidity is more uniform than other bioreactors, and its structure is simple.
- The structure of the airlift bioreactor is relatively simple, easy to clean and maintain, not easy to contaminate bacteria, low energy consumption, high dissolved oxygen efficiency, and low operating cost.
- The disadvantages are relatively few, mainly because the mixing is not uniform enough during high-density culture.
6. Packed bed reactor :
- A packed bed reactor (PBR), is also known as a fixed bed reactor.
- A Packed bed composed of small granular materials (such as fine sand, activated carbon, coke) or immobilized enzymes is stacked in the container.
- The Packed bed reactor tank is filled with an immobilized enzyme to form a stable column bed and then add substrate into the tank.
- This causes enzyme-catalyzed reaction under certain reaction conditions and collects the output conversion liquid at a certain flow rate.
- It is suitable for immobilized enzymes of various shapes and substrate solutions with no solid particles and low viscosity, as well as conversion reactions with product inhibition.
- This type of equipment is widely used in gas-solid phase reactions and liquid-solid phase reaction processes.
- PBR is the most commonly used reactor in industrial production and research.
- Packed bed reactors can be used for stripping, air aeration, sand filtration, activated carbon adsorption, or nitrification.
7. Fluidized Bed Reactor:
- A fluidized bed reactor is a type of reactor device that can be used to carry out a variety of heterogeneous chemical reactions.
- A fluidized bed reactor is a reactor that uses gas or liquid to pass through a granular solid layer to keep solid particles in a suspended motion state and conducts a gas-solid phase reaction process or a liquid-solid phase reaction process.
- When we used it in a gas-solid system, it is also called a fluidized bed reactor.
- It can realize the continuous input and output of solid materials.
- FBR is easy to control and suitable for strong exothermic reactions.
- Fluidized bed reactors have been widely used in chemical, petroleum, metallurgy, nuclear industry, and other sectors.
8. Tower fermenters :
- A tower fermenter is also known as a column fermenter.
- The tower fermentation tank is a hollow cylinder and it has a high tank body and a height-diameter ratio.
- Tower Fermenter was defined by Greenshields et al. in 1971. They described it as an elongated non-mechanically stirred fermenter with an aspect ratio of 6:1 for the tubular section or 10:1 overall.
- It has a simple structure, low energy consumption, is simple to clean and maintain, is not easy to contaminate bacteria, and is suitable for large-scale production.
- Tower fermenters are generally used for the production of single-cell proteins, alcohol production, and the cultivation of plant cells.
- For the production of drugs, the cultivation of cells or microorganisms in bioreactors is often used.
- Bioreactors are generally used for cell culture.
- Bioreactors help speed up cell cultures
- Bioreactors are useful in Tissue Engineering.
- Use in the food industry: production of food additives and fermented products such as beer, fruit wine, vinegar, etc.
- Use in the pharmaceutical industry: By use of a variety of drugs have been developed, such as human growth hormone, recombinant hepatitis B vaccine, certain varieties of monoclonal antibodies, interleukin-2, anti-hemophilia factor, etc.
- They are mainly used in the fermentation of dairy products and alcohol.
- In line with the needs of policies and scientific research on energy conservation, environmental protection, and recycling of waste resources.
- Bioreactors are generally used for the production of glutamic acid, antibiotics, xanthan gum, saccharification enzymes, and citric acid.
- Application in the field of environmental science: municipal and domestic wastewater treatment, industrial wastewater, water purification treatment, and others.
- Bioreactors are also used for gas removal, sludge treatment, and hydrogen production. enhancement of microorganisms in sewage treatment.
- Treatment of polluted air (bio purification): In air pollution, biofeedback is simply the use of microbes to consume pollutants from a polluted air stream.
Disadvantages of Bioreactor:
- The biological fermenter requires a very large air throughput.
- It has Poor interphase mixing and contact.
- The number of substrates, nutrients, and oxygen cannot be kept consistent when the circulating organisms and operating conditions change.
- Mixing and ventilation are coupling problems, and it is difficult to improve the mixing condition without changing ventilation.