bioreactors. These devices perform diverse biochemical processes by employing microbial, fungal, plant cell, and mammalian cell systems to produce various types of bioproducts such as biomass (including single-cell proteins, baker's yeast, animal cells, microalgae, etc.) and metabolites (e.g., organic acids, ethanol, antibiotics, aromatic compounds, biohydrogen, etc.). Bioreactors are widely used in the fields of tissue engineering, pharmaceutical engineering, bioenergy, food engineering and biochemical engineering.

According to the statistics, the global bioreactor market was valued at more than US$ 709.4 Mn in 2018, and is expected to grow between 2019 and 2025 , which is expected to grow at a CAGR of 17.6%. This continuously growing market demand is driving the research and development of efficient, low-cost bioreactors, which involves optimizing design parameters and operational process factors such as inlet flow rate, microbial species concentration, temperature, humidity, pH, and agitation rate (Ugalmugle and Swain, 2019; Kim et al., 2021).

Basic Functions and Requirements

The primary goal of a bioreactor is to provide a suitable and controlled environment to support cell growth and product production. The design and mode of operation needs to meet the requirements of the output targets and process variables to achieve consistent and efficient production of high quality products. The following factors need to be considered when designing a bioreactor: geometry, temperature, pH, light (if required), sterility, aeration and mixing systems (if necessary), low energy consumption, and suitable size and materials (Spier et al. 2011; Stanbury et al. 2013; Panda 2011). Scaling-up criteria primarily relate to reactor geometry, impeller velocity, and aeration rate to ensure appropriate mass transfer rates, taking into account limitations in oxygen supply and carbon dioxide removal, especially at high cell densities.

Thus, bioreactors need to fulfill the following requirements:

- Ability to easily monitor and/or control reaction parameters (e.g., dissolved oxygen concentration, pH, temperature, agitation rate, redox value, etc.) to create the optimal conditions for the growth of biocatalysts such as organisms or cells) to create a controlled and sterile environment for growth.

- The ability to run continuously for days or even weeks to sustain microbial growth, such as Delftella (Zhang et al., 2010; Delavar and Wang, 2021a), ensures that the bioreactor maintains cellular activity over an extended period of time without alteration.

- Maintains sterile conditions for long periods of time while maintaining cellular activity.

- Cost-effectively meets productivity and yield needs.

- Easily maintained and adjusted to the specific response needs of different organisms. The function of the bioreactor should be fully considered during the design process.

Typical bioreactors incorporate complex systems of piping, fittings, sensors, and wiring that can fail but are capable of on-line monitoring and diagnosis of multiple parameters during the process ( Cinar et al. 2003; Spier et al. 2011). Figure 7.1 illustrates a schematic of an industrial fermenter and its components. These devices are widely used to culture microorganisms, proteins, and industrial products (e.g., acetic acid, alcohols, etc.) in controlled environments ranging from laboratory scale to industrial scale (Singhal et al., 2018).