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The process from the start of feeding into a newly built biogas digester until it begins to produce gas in a normal and stable manner is known as the initiation of biogas fermentation. Whether fermentation can start smoothly is crucial for ensuring long-term stable operation of the digester. Therefore, in order to enable a newly built digester to produce gas quickly and efficiently, the initial filling must meet the following requirements: 1. Add an adequate amount of inoculum – Before or after filling the new digester, it is necessary to collect materials such as biogas sludge and liquid from existing digesters, black sediment from septic tanks, pond sludge, sludge from urban sewage channels, and wastewater sludge from slaughterhouses. These materials contain a high concentration of biogas-producing bacteria; the amount of inoculum should be 10–30% of the total amount of raw materials used for fermentation. The inoculum and raw materials should be mixed evenly before being added to the digester. 2. Choose appropriate raw materials for fermentation – The raw materials used in biogas fermentation serve as the basis for gas production. To ensure an adequate and stable supply of raw materials for the start-up and ongoing fermentation process, it is necessary to use organic nutrients such as cow dung, pig dung, and sheep dung as starting materials. These materials have fine particles and contain many low-molecular-weight compounds, with a carbon-to-nitrogen ratio of less than 25:1, which is an ideal ratio for fermentation. This allows for rapid start-up and efficient gas production once the materials are added to the digester. It is not advisable to use only chicken dung or human excrement as starting materials, as in such cases the mixture tends to become acidic due to the low presence of biogas bacteria, preventing proper fermentation. 3. The fermentation concentration during the first filling of the digester should be appropriate – The initial amount of material added to the digester should be 80% of its total volume. If there is a temporary shortage of raw materials and the required amount cannot be added at once (which is unlikely in most household biogas digesters), then water should be added up to 15 centimeters above the inlet and outlet ports, after which the digester should be sealed for fermentation. The initial fermentation concentration should be between 6% and 10%. If it is difficult to determine the correct ratio of raw materials to water in the digester, it is better to use a slightly dilute mixture rather than a too concentrated one, as this can lead to acidification.