The difference between aerobic fermentation and anaerobic fermentation and the requirement of fermenter

Introduction

Fermentation refers to the process in which microorganisms transform organic matter into other products through enzymatic reaction under suitable conditions. According to the degree of oxygen participation, fermentation can be divided into two types: aerobic fermentation and anaerobic fermentation. There are significant differences in reaction process, product and required environmental conditions between the two, which directly affect the design and use of fermenter. This article will discuss in detail the difference between aerobic fermentation and anaerobic fermentation, and their different requirements for fermenters.

The basic concepts of aerobic fermentation and anaerobic fermentation

Aerobic fermentation

Aerobic fermentation refers to the metabolic process of microorganisms in the environment of sufficient oxygen. Oxygen is involved in the respiratory chain reaction as the final electron acceptor in this process. Common aerobic fermentation microorganisms include yeasts, certain bacteria and fungi. Aerobic fermentation is characterized by high efficiency, can be more complete oxidation of organic matter (such as sugars), release more energy, the product is mostly carbon dioxide and water.

Anaerobic fermentation

Anaerobic fermentation is a metabolic process that takes place in the absence of oxygen or in very low oxygen concentrations. At this point, microorganisms ferment with other chemicals (such as nitrates, carbon dioxide, sulfate, etc.) as final electron acceptors. Anaerobic fermentation usually produces less energy, and the products are mostly organic substances such as acids and alcohols. Anaerobic fermentation is widely used in alcohol fermentation, lactic acid fermentation, methane fermentation and other industrial and food processing processes.

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The difference between aerobic fermentation and anaerobic fermentation

Oxygen requirement

1. Aerobic fermentation: adequate oxygen support is required. Oxygen is an indispensable element in the metabolic process, and it directly participates in the electron transfer of the cell respiratory chain.

2. Anaerobic fermentation: carried out in the absence of oxygen, microorganisms act as terminal electron acceptors through other chemicals.

Energy release efficiency

1. Aerobic fermentation: Due to the completeness of aerobic respiration, the energy release efficiency is high. Microbes are able to completely break down organic matter, releasing more ATP (cellular energy).

2. Anaerobic fermentation: Energy release efficiency is low, because organic matter can not be completely decomposed under hypoxic conditions, and only rely on fermentation to generate a small amount of ATP.

product

1. Aerobic fermentation: the main products are carbon dioxide and water, a small amount of metabolic intermediates. Due to its efficient energy generation, the product is relatively simple.

2. Anaerobic fermentation: The products are more complex, common including ethanol, lactic acid, acetic acid, acetone, methane and so on.

Microbial species

1. Aerobic fermentation: The microorganisms involved include yeast, some bacteria, fungi, etc. Most of them can grow and reproduce in an environment with sufficient oxygen.

2. Anaerobic fermentation: The microorganisms involved include lactic acid bacteria, yeast, methanobacteria, etc., which can grow in anoxic or even anaerobic environments.

Application field

1. Aerobic fermentation: mainly used in the production of fermented food (such as bread, beer, yogurt) and biological products (such as enzymes, antibiotics).

Anaerobic fermentation: mainly used in alcohol fermentation, yogurt fermentation, lactic acid fermentation, biogas fermentation and other processes.

Design and requirement of fermenter

Because aerobic fermentation and anaerobic fermentation have significant differences in metabolic conditions, microbial species and reaction process, they have different requirements for the design and operation of fermenters.

1. Design requirements of aerobic fermenter

Aerobic fermentation requires an adequate supply of oxygen, so there are the following key requirements in the fermenter design:

Oxygen supply system: Aerobic fermenters must be equipped with an effective oxygen supply system. Oxygen is usually provided through an air compressor, oxygen cylinder, or gas generator. The gas supply needs to ensure that the oxygen concentration in the fermenter is maintained in a suitable range to support the metabolic processes of the microorganisms.

Stirring system: In order to maintain an even gas distribution and the uniformity of dissolved oxygen, fermenters are usually equipped with a stirring system. Stirring can not only accelerate the dissolution of oxygen, but also prevent microbial deposition and ensure the uniformity of the fermentation process.

Temperature control: Aerobic fermentation has relatively strict requirements for temperature and usually requires an accurate temperature control system. Different microorganisms have a different range of temperature adaptation, so the fermenter needs to be equipped with a cooling or heating system to ensure a constant temperature.

pH control: During aerobic fermentation, microbial metabolism can affect pH and may result in an environment that is too acidic or too alkaline. In order to ensure the healthy growth of microorganisms, fermenters need to have pH monitoring and automatic regulation systems.

Gas discharge system: Due to the release of oxygen and fermentation products (such as carbon dioxide), the fermenter needs to be equipped with an effective gas discharge system. This can not only avoid excessive gas pressure in the tank, but also ensure the smooth discharge of products.

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2. Design requirements of anaerobic fermenter

Anaerobic fermentation requires a completely or partially anoxic environment, so there are different design priorities:

Tightness: The anaerobic fermenter must have good tightness to prevent air from entering and ensure an anoxic environment inside. In general, the sealing structure of the fermenter needs to keep the air completely isolated.

Gas collection and emission: Since the gases produced by anaerobic fermentation (e.g., methane, carbon dioxide) need to be discharged, specialized gas collection and emission systems are required. At the same time, in order to prevent the entry of outside air, it is also necessary to be equipped with a reverse pressure system.

Agitation and temperature control: Although anaerobic fermentation does not require as intense an oxygen supply as aerobic fermentation, the agitation system is still important to promote reaction uniformity. Temperature control is also crucial, and different anaerobic microorganisms have different temperature requirements, so a high-precision temperature control system is required.

pH control: The anaerobic fermentation process may produce a large amount of organic acids, resulting in a decrease in environmental pH, so it is necessary to maintain an appropriate pH range through an acid-base regulation system to avoid environmental overacid affecting microbial activity.

Conclusion

Although aerobic fermentation and anaerobic fermentation are both microbial metabolic processes, there are significant differences in reaction principle, energy conversion efficiency and product types due to the presence or absence of oxygen. These differences require different adjustments in the design and operation of fermenters. Aerobic fermenters need to ensure adequate oxygen supply and even stirring, while anaerobic fermenters emphasize tightness, gas emission and the reliability of the temperature control system. Only according to the needs of fermentation type, reasonable design of fermenter can achieve efficient and stable fermentation process.

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