The difference between solid fermentation and liquid fermentation and the requirement of fermenter

Fermentation technology is one of the core technologies in the field of bioengineering, which is widely used in food, pharmaceutical, agriculture, environmental protection and other industries. According to the state of the medium in the fermentation process, the fermentation technology is mainly divided into solid fermentation and liquid fermentation. These two fermentation methods have significant differences in process characteristics, application scenarios and requirements for equipment. This paper will start with the difference between solid fermentation and liquid fermentation, and discuss their different requirements for fermenters.

The difference between solid and liquid fermentation

1. State of medium

Solid fermentation: The medium is solid or semi-solid, usually composed of natural substrates such as grains, straw, bran, and so on, with a low water content (usually between 30% and 70%). Microorganisms grow on solid surfaces to form mycelia or biofilms.

Liquid fermentation: The medium is liquid, usually composed of water, nutrients, and dissolved oxygen, with a water content close to 100%. The microorganisms are evenly dispersed in the liquid and mixed by stirring or aerating.

2. Microbial growth environment

Solid-state fermentation: Microorganisms grow on solid surfaces to form complex networks of mycelium. Since the transfer of oxygen and nutrients mainly depends on diffusion, there is a certain gradient in the growth environment of microorganisms (such as oxygen concentration, pH value, etc.).

Liquid fermentation: microorganisms are evenly distributed in the liquid, oxygen and nutrients are evenly distributed through agitation and ventilation, and the growth environment is relatively uniform.

3. Process characteristics

Solid state fermentation:

•  The equipment is simple and the investment cost is low.
•  Low energy consumption, suitable for small-scale or resource-limited areas.
•  The product concentration is high and the post-treatment is relatively simple.
•  But the efficiency of mass and heat transfer is low, and the process control is difficult.

Liquid fermentation:

•  The equipment is complex and the investment cost is high.
•  High efficiency of mass and heat transfer, suitable for large-scale industrial production.
•  Precise process control and easy automation.
•  However, the energy consumption is higher, the product concentration is lower, and the post-treatment is complex.

4. Application field

Solid state fermentation:

•  Traditional food: such as soy sauce, vinegar, black beans, fermented bean curd, etc.
•  Agriculture: such as feed fermentation, organic fertilizer production.
•  Biofuels such as the production of cellulosic ethanol.

Liquid fermentation:

•  Pharmaceutical: such as the production of antibiotics, vaccines, enzyme preparations.
•  Food: such as beer, yogurt, amino acid production.
•  Biofuels: such as ethanol, butanol production.

MIKEBIO 300T fermentation system project

Requirements for fermenters for solid and liquid fermentation

Due to the differences between solid fermentation and liquid fermentation in medium state, microbial growth environment and process characteristics, they put forward different requirements for the design and function of fermenters.

1. Requirements for fermenters for solid state fermentation

The solid state fermenter needs to adapt to the characteristics of the solid medium to ensure the uniform growth of microorganisms on the solid surface, while solving the problem of mass and heat transfer.

(1) Structural design

•  Shallow fermenter: Suitable for small-scale production, the medium is spread in thin layers to facilitate oxygen diffusion and heat dissipation.
•  Deep fermenters: Suitable for mass production, usually equipped with stirring units or rotating units to improve mass and heat transfer efficiency.
•  Tray fermenter: The culture medium is placed in a multi-layer tray for oxygen supply and temperature control through air circulation.

(2) Ventilation and humidity control

Solid state fermentation requires an adequate supply of oxygen, so fermenters are often equipped with ventilation systems that deliver oxygen through forced ventilation or natural ventilation.

Due to the low water content of the solid medium, the fermenter needs to have humidity control to prevent the medium from being too dry or too wet.

(3) Temperature control

In the process of solid fermentation, the heat generated by microbial metabolism is difficult to dissipate quickly, and it is easy to cause local temperature to be too high. Therefore, fermenters need to be equipped with effective temperature control systems such as jacket cooling, internal cooling coils or ventilation cooling.

(4) Stir and mix

In order to improve the efficiency of mass transfer, some solid-state fermenters are equipped with stirring devices or rotating devices, so that the medium is evenly exposed to oxygen and microorganisms.

The mixing device should be designed to avoid damaging the structure of microbial mycelia, and is usually stirred at low speed or intermittently.

(5) Sterilization and cleaning

The sterilization of solid fermenter usually uses high-temperature steam or chemical disinfectants, but because of the complexity of solid medium, sterilization is more difficult.

When cleaning, it is necessary to thoroughly remove solid residues to prevent contamination.

2. Liquid fermentation requirements for fermenters

Liquid fermenters need to be adapted to the characteristics of liquid media, ensuring that microorganisms grow in a uniform environment while achieving efficient mass and heat transfer.

(1) Structural design

•  Stirred fermenters: The most common type of liquid fermenter, mixing and mass transfer is achieved by mechanical agitation.
•  Airlift fermenter: Liquid circulation through gas injection, suitable for shear sensitive microorganisms.
•  Membrane bioreactor: combined with membrane separation technology, suitable for high density culture and continuous fermentation.

(2) Ventilation and dissolved oxygen control

Liquid fermentation requires an adequate supply of oxygen, and fermenters are often equipped with ventilation systems, such as bubblers or ejectors, to increase dissolved oxygen levels.

Dissolved oxygen sensors and control systems are the core components of liquid fermenters to monitor and regulate dissolved oxygen concentrations in real time.

(3) Temperature control

Liquid fermenters are usually equipped with a jacket or internal coil to achieve precise temperature control by circulating cooling water or heating media.

Large-scale fermenters also need to consider the uniform distribution of heat to avoid local overheating or overheating.

(4) Stir and mix

The stirring system is a key component of the liquid fermenter, usually using turbine, paddle or spiral agitators to achieve efficient mixing and mass transfer.

The stirring speed should be adjusted according to the characteristics of microorganisms and process requirements, so as to avoid excessive shear force causing damage to microorganisms.

(5) Sterilization and cleaning

Liquid fermenters are usually sterilized with high-temperature steam (such as CIP systems) to ensure that the tank and pipe are sterile.

When cleaning, use high-pressure water or cleaning agent to thoroughly remove liquid residues and biofilms.

(6) Automatic control

Liquid fermenters are usually equipped with advanced automated control systems for real-time monitoring and adjustment of temperature, pH, dissolved oxygen, stirring speed and other parameters.

Data recording and analysis capabilities help optimize fermentation processes and increase production efficiency.

MIKEBIO bioreactor system for  plant nutrition

 

Sum up

There are significant differences between solid fermentation and liquid fermentation in medium state, microbial growth environment, process characteristics and application fields, so different requirements are put forward for the design and function of fermenters. Solid-state fermenters need to solve the problem of low mass and heat transfer efficiency, and are usually equipped with ventilation, temperature control and stirring devices. Liquid fermenters focus on efficient mixing, mass transfer and automated control, and are usually equipped with stirring systems, ventilation systems and advanced monitoring and control systems.

With the continuous development of biotechnology, solid-state fermentation and liquid fermentation technology are moving towards the direction of high efficiency, energy saving and intelligence. In the future, the design of fermenters will pay more attention to process optimization and resource utilization, providing strong support for the sustainable development of the bio-manufacturing industry.

On the other hand, when choosing a bioreactor fermenter, it is necessary to find a regular manufacturer with good reputation and strength, so as to ensure the quality of the product. Jiangsu Mike Biotechnology Co., Ltd. was established in 2008, is a focus on biological fermentation equipment research and development, production and sales of high-tech enterprises. Our company has a pilot fermentation platform, which is integrated with intelligence and automation, and has built a mature fermentation system, which can realize the optimization of pilot fermentation process, commissioning development of all process processes from pilot fermentation production to fermentation product separation and purification, and set up a doctor workstation and a modern laboratory.

Our company has a standardized production plant, with complete sets of equipment and tools required for installation, mainly including a variety of machine tools, automatic argon arc welding machine, automatic polishing machine, automatic cutting machine and flaw detection machine and other more than 60 sets of production and testing equipment, the production process all realize modern standard operation, to provide customers with more professional quality and technical support.