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During biogas fermentation, methanogenesis-free organisms and methanogenic bacteria rely on each other, providing one another with the material foundations and suitable environmental conditions necessary to sustain their vital activities； At the same time, they restrict each other to jointly complete the biogas fermentation process. Their interrelationship is mainly manifested in the following aspects: 1. Methanogen-free organisms provide nutrients for methanogens. Complex organic substances in the raw materials, such as carbohydrates, proteins, and fats, cannot be directly absorbed and utilized by methanogens. They must first be broken down into soluble simple compounds through the hydrolysis carried out by non-methanogenic bacteria, and then further decomposed to form a fermentation substrate suitable for methanogens. 2. Methanogen-free organisms create a suitable anaerobic ecological environment for methanogens. During the initiation stage of biogas fermentation, the addition of raw materials and water introduces a large amount of air into the biogas digester, which is clearly harmful to methanogenic bacteria. However, due to the activity of aerobic and facultative anaerobic microorganisms among the non-methanogenic bacterial groups, the redox potential of the fermentation broth continues to decrease (the lower the redox potential, the better the anaerobic conditions), gradually creating an anaerobic environment suitable for the growth of methanogenic bacteria. 3. Methanogen-free organisms remove toxic substances using methanogens. When industrial wastewater or waste is used as a fermentation substrate, it often contains substances such as phenols, benzoic acid, **, long-chain fatty acids, and heavy metals. These substances are toxic to methanogens. Many of the methanogen-free bacteria can degrade and utilize the aforementioned substances, thereby relieving the toxicity to the methanogens. 4. Methanogen-free bacteria and methanogens work together to maintain an appropriate pH level in the environment. In the early stage of biogas fermentation, methanogen-free microorganisms first degrade starch and sugars in the feedstock, producing large amounts of organic acids. At the same time, the carbon dioxide produced also dissolves partially in water, causing the acidity or alkalinity (pH) of the fermentation broth to decrease.