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Fermentation equipment is the heart of the fermentation industry, serving as a bridge between raw materials and products. With the continuous advancement of life sciences and technologies, the fermentation industry has also seen significant improvements. The fermentation tank is one of the most important devices in microbial engineering. An excellent cultivation system should be designed with a robust structure, good liquid mixing capabilities, high mass and heat transfer rates, as well as reliable monitoring and control instruments, in order to achieve maximum production efficiency. I. Main types of fermentation tanks: (1) Aerated mechanical stirred-tank fermenters Aerated mechanical stirred-tank fermenters are the preferred equipment for many fermentation processes, offering high mass and heat transfer capabilities, excellent gas-liquid mixing, a long liquid residence time, and a wide range of operational gas flow rates. However, the disadvantages are also obvious: the shear force is high, which damages many shear-sensitive microorganisms; it requires a lot of energy, and mixing is uneven. Therefore, leveraging the advantages of ventilated stirred tanks and overcoming their disadvantages is one of the key focuses in current research on fermentation tanks. The improvements to the ventilated stirred tank focus on the stirring system, including the optimization of the stirrers and multi-layer stirring systems. New types of stirrers or improved standard stirrers are used, with the aim of reducing the vortices caused by the wake of the impellers in order to save energy, or of altering the flow pattern within the reactor so that shear forces can be distributed evenly, thereby protecting the microorganisms inside the reactor. Multi-layer mixing systems have been in use for a long time, but due to insufficient research into their working principles, simple empirical design methods have been employed over the years, preventing them from realizing their full potential. (2) Air-lift fermenter The air-lift fermenter has significant advantages and has been widely used in the production of SCP, filamentous fungi, and wastewater treatment. A gas-lift fermenter is the most widely used bioreactor equipment. Such reactors have advantages such as simple structure, low susceptibility to contamination, high oxygen dissolution efficiency, and low energy consumption. There are various types, with the common ones including air-lift circulatory type, bubble type, and air-jet type. In the bioindustry, air-lift fermenters that have been widely used include air-lift internal circulatory fermenters, air-liquid dual-jet air-lift circulatory fermenters, and tower-type air-lift fermenters equipped with multiple distribution plates. The bubble column is the most primitive type of aeration fermenter; of course, there is no guide cylinder in a bubble column reactor, so the directional flow of the liquid is not controlled. (3) Self-priming fermentation tank The structure of the tank body in a self-priming fermentation tank is roughly the same as that of a conventional fermentation tank; the main difference lies in the shape and design of the agitator. Self-priming fermenters use agitators with a central air intake. The agitator is driven by a main shaft that extends upward from the bottom of the tank. As the impeller rotates, its blades continuously displace the liquid around them, creating a vacuum behind them. This vacuum draws air from outside the tank in through the suction pipe at the center of the agitator. The air drawn in mixes thoroughly with the fermentation broth and is then discharged at the end of the impeller, where it is immediately dispersed toward the tank walls via guide wheels, and then directed toward the liquid surface by baffle plates to ensure even distribution. The air intake pipe is usually connected to the impeller with a face seal at one end to ensure no air leakage. As air is drawn in by the vacuum created by the high-speed flow of the fermentation broth, gas-liquid contact is excellent and the bubbles remain finely dispersed, thereby increasing the rate at which oxygen dissolves in the fermentation broth. Taking a mechanically stirred fermenter as an example, the following introduces its main structural components and their primary functions. II. Basic requirements for fermentation tanks Mechanical stirring fermentation tanks, also known as standard or general-purpose fermentation tanks, utilize mechanical stirrers to ensure thorough mixing of air with the fermentation broth, as well as its dissolution in the broth, thereby providing the oxygen necessary for the growth and reproduction of microorganisms. To enable the fermentation tank to achieve maximum production efficiency, it must meet several requirements: ① The fermentation tank must be able to withstand a certain pressure. ②The fermentation tank should have an appropriate radius-to-height ratio. ③The stirring and aeration equipment in the fermentation tank enables the mixing of gas and liquid components, facilitating mass and heat transfer and ensuring the dissolved oxygen required during microbial fermentation. ④The fermentation tank should have sufficient cooling area. ⑤Dead zones should be minimized within the fermentation tank to prevent the accumulation of dirt and debris, ensure thorough sterilization, and avoid contamination. ⑥The shaft seal of the mixer must be tight to minimize leaks. III. Structure of the Fermentation Tank The main components of a mechanically stirred and aerated fermentation tank include the tank body, stirrer, baffle plates, cooling system, and air distribution device. Shaft seals, etc. 1. The tank is designed based on the maximum operating pressure. (1) First, the tank must be sealed and able to withstand a certain pressure. (2) It has a cylindrical shape, with its ends welded together using elliptical or disc-shaped end caps; this ensures even stress distribution within the fermentation tank, reduces the presence of dead zones, and facilitates the removal of materials. (3) The material is made of stainless steel or composite stainless steel. (4) The height-to-diameter ratio is 1.7∽4∶1. (5) In addition, there are some auxiliary devices on top of the tank, such as exhaust vents and material inlet ports. The general principle for tank design is that the fewer connection holes on the tank body, the better; any holes that can be combined should be combined. 2. Stirrer Function: To break air into small bubbles. It increases the gas-liquid contact surface, enhances the oxygen mass transfer rate, and ensures thorough mixing of the fermentation broth, while keeping the solid substances in it in a suspended state. Structure: It includes a stirring shaft and stirring blades; a disk is mounted at the center of the stirring shaft, with the stirring blades attached to this disk. Shape of the mixing blades: there are three types – flat blade, curved blade, and arrow-shaped blade. Generally, there are six blades, but this number can range from as few as three to as many as eight.