Several technologies that should be widely promoted for rural biogas use

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Based on years of practice and experience, the development of rural biogas systems should promote the widespread use of the following key technologies. 　　A biogas digester must be built within the livestock shed. There are six advantages to locating a biogas digester inside the shed: first, it saves land, as each digester can help save around 10 square meters of space ； Second, it facilitates the simultaneous planning and construction of sanitary toilets ； Third, it facilitates the transfer of human and animal waste from the pens and toilets into the biogas digester ； Fourth, it helps to keep the biogas digester warm, thereby increasing the gas production rate ； Fifthly, it facilitates the installation of extraction devices for extracting biogas sludge or biogas liquid, enabling convenient recycling of this liquid for flushing toilets and its comprehensive utilization, thereby improving the overall efficiency of biogas use ； Sixthly, it helps improve the breeding environment for livestock, shorten the fattening period, and reduce breeding costs. 　　The biogas digester must be equipped with a flip-type, sealable movable lid. The presence of such a movable lid facilitates feeding materials into the digester; it is convenient to add materials through this lid, and it also ensures that an adequate amount of raw materials are added in the first instance and are distributed evenly throughout the digester ； The second is to facilitate fuel replacement ； Third, it facilitates shell removal. The movable lid can be opened to stir the liquid mixture and break up the floating scum layer, thereby restoring normal gas production in the biogas digester ； Fourth is maintenance safety. When internal maintenance is required of the biogas digester, the movable cover is opened to connect the inlet and outlet ports with the opening of the movable cover, thereby facilitating ventilation, lighting, and the removal of harmful gases from within the digester, and effectively preventing safety accidents ； Fifth, it must be tightly sealed. The reverse-clamp type sealed movable cover has a smaller opening at the top and a larger one at the bottom; once the cover is sealed, the greater the air pressure, the tighter the seal, making it difficult to force the cover open. 　　Three biogas digesters must be equipped with extraction devices. Rural household biogas digesters must have two such extraction devices installed. First, a flushing device must be installed. There are two main advantages to using such a device: First, it allows the biogas slurry to be used for flushing toilets and animal shelters, thereby enabling human and animal waste to be promptly sent to the biogas digester for fermentation. This reduces the growth of mosquitoes, fly larvae, and pathogens, prevents foul odors from contaminating the environment, and improves the rural environment as well as the quality of life for farmers ； Secondly, using biogas slurry to clean toilets and livestock sheds allows the slurry in the biogas digester to circulate back, ensuring thorough mixing of the fermentation materials, which can **increase the gas production rate**. Second, it is necessary to install a discharge device; installing such a device can improve two aspects: first, it increases the overall utilization rate of biogas. The discharge extraction device can remove the fermentation residues at the bottom of the main tank, ensuring the effective volume of the biogas digester and its gas production efficiency; it also solves the problem of fertilizer needs for farmers in agricultural production. Seal the biogas digester at one time to ensure its normal operation for many years. The discharge extraction device can also be used to extract the biogas slurry from the biogas digester for flushing toilets, thereby enabling the comprehensive utilization of this slurry. Second, effectively increase the gas production rate. The discharge extraction device forces the liquid inside the biogas digester to circulate and return, which not only stirs the liquid but also breaks up the crusts formed on the upper layer of the digester. This allows the liquid containing methanogenic bacteria to mix thoroughly with new material, accelerating the fermentation process and thereby increasing the biogas production rate effectively. 　　The pumping efficiency of the biogas digester material extraction device depends on key components such as advanced extraction pistons and bottom valves. After installing a bottom valve in the extraction tube of the biogas digester, extracting the biogas slurry becomes less labor-intensive; it can be done by people of all ages, and a large amount of slurry can be extracted – one or two extractions are sufficient to fill a bucket. It can extract the liquid material in the biogas digester that is below 2 meters from the ground surface. 　　A main switch and an exhaust (water) switch must be installed on the gas transmission pipeline of the biogas digester. There are two functions to installing a main switch and an exhaust (water) switch on the gas transmission pipeline of the biogas digester. First, it facilitates maintenance. Installing a \"ball valve\" main switch at an appropriate position along the gas pipeline that is close to the gas duct of the biogas digester facilitates the detection of the airtightness of the biogas pipeline and the equipment that uses it, as well as the maintenance of such pipelines and equipment. Second, it facilitates drainage and air release. A main \"ball valve\" is installed on the gas transmission pipeline of the biogas digester, and an exhaust (water) valve is placed at the lowest point of the gas pipeline leading from the biogas pipeline into the indoor area; this valve is used to remove water accumulated in the pipeline as well as gases that enter or exit during the addition and removal of liquid materials from the biogas digester. When biogas production is high or when biogas users are away for an extended period and do not use the biogas, the exhaust valve can be opened outdoors to release gas, ensuring safe management of the biogas.