• These bioreactors are commonly cylindrical, ranging in size from a few milliliters to cubic meters, and are usually made of stainless steel.

• There are different types of bioreactors, The major types are Continuous Stirred Tank Bioreactors, Bubble Column Bioreactor, Fluidized Bed Bioreactors, Packed Bed Bioreactors, etc.

• 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.

• 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.

• 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.

• 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.

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.

Bioreactor  Applications: 

1. For the production of drugs, the cultivation of cells or microorganisms in bioreactors is often used.
2. Bioreactors are generally used for cell culture.
3. Bioreactors help speed up cell cultures
4. Bioreactors are useful in Tissue Engineering.
5. Use in the food industry:  production of food additives and fermented products such as beer, fruit wine, vinegar, etc.
6. 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.
7. They are mainly used in the fermentation of dairy products and alcohol. 
8. In line with the needs of policies and scientific research on energy conservation, environmental protection, and recycling of waste resources.
9. Bioreactors are generally used for the production of glutamic acid, antibiotics, xanthan gum, saccharification enzymes, and citric acid.
10. Application in the field of environmental science: municipal and domestic wastewater treatment, industrial wastewater, water purification treatment, and others.
11. Bioreactors are also used for gas removal, sludge treatment, and hydrogen production. enhancement of microorganisms in sewage treatment.
12. 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: 

1. The biological fermenter requires a very large air throughput.
2. It has Poor interphase mixing and contact.
3. The number of substrates, nutrients, and oxygen cannot be kept consistent when the circulating organisms and operating conditions change.
4. Mixing and ventilation are coupling problems, and it is difficult to improve the mixing condition without changing ventilation.