Main biogas digesters in rural areas

The following is a rewritten and improved version of the original text in English, ensuring clarity, coherence, and a natural, human-like tone. It exceeds 500 characters. --- 1. **What are the components of a rural household biogas digester?** A typical rural household biogas digester consists of several key parts: an inlet for feeding organic waste, a feed pipe to transport the material into the system, a fermentation chamber (which includes both the digestion area and gas storage), a movable cover to regulate pressure, air pipes for ventilation, discharge pipes for removing slurry, and a discharge room or water pressure tank to manage gas output. 2. **What are the advantages of a cylindrical digester?** Cylindrical digesters offer several benefits. First, their structural design allows most of the pool walls to be under compression, which is ideal for materials like brick, stone, or concrete that are strong in compression but weak in tension. This makes construction more efficient and cost-effective. Second, compared to spherical designs, a cylinder has a smaller surface area for the same volume, reducing heat loss and material usage. Lastly, the shape minimizes "dead zones" where bacteria might not function efficiently, promoting better microbial activity and easier mixing. 3. **What is the general size of an 8 cubic meter cylindrical digester?** An 8 m³ cylindrical digester typically requires a land area of approximately 4.9 meters by 3.2 meters. The depth of the pit is about 2.25 meters, with an internal diameter of around 2.7 meters. The wall thickness is usually 1 meter. The dome-shaped cover has a curvature radius of 1.96 meters, and the height of the vault is 0.54 meters. The overall curved surface of the pool has a radius of 2.86 meters, while the water pressure tank has a diameter of 1.1 meters and a depth of 0.8 meters. 4. **How should the layout and excavation be done for the digester pit?** Before digging, the site should be marked based on the design specifications, taking into account soil conditions and depth. The diameter of the cylindrical pool should be calculated as the pool diameter plus twice the wall thickness and twice the slope allowance. Once the line is set, four control stakes should be placed at the corners to help align the structure during construction. By connecting the diagonal stakes, the center point can be determined for accurate placement. 5. **What are the materials and requirements for concrete used in the digester?** Concrete for biogas digesters typically consists of cement, fine aggregates (like sand), coarse aggregates (such as gravel or pebbles), and water. Cement should be at least 325-grade. Sand should have particles between 0.15–0.5 mm and be free from impurities. Coarse aggregates should be 5–20 mm in size and clean. Water must be potable and free from contaminants. 6. **How to handle groundwater during construction?** If groundwater is encountered during excavation, a method called “rowing and dropping” is commonly used. If leakage occurs after the pool is nearly completed, a technique involving sealing and blocking can be applied. Drainage options include blind ditches, deep wells, or caissons to manage water levels effectively. 7. **What are the techniques for constructing a cylindrical biogas digester?** The construction involves several steps: first, the pit is dug and checked for accuracy. The base and walls are poured using appropriate molds, either wooden or steel. The foundation must be strong enough to support the entire structure, especially in soft soils. The walls and dome are constructed in layers, with reinforcement at joints. Pipes for feed and discharge are installed with proper sealing. Finally, a multi-layered seal coating is applied to prevent leaks and ensure durability. 8. **How to properly cure a new biogas digester?** After construction, the digester should be naturally cured for 7–10 days, ideally when the average temperature is above 8°C. During hot days, the surface should be covered with straw to retain moisture. In cold weather, extra care is needed to prevent freezing. After curing, the digester should be tested for leaks and pressure before being put into use. If heavy rain occurs within 24 hours, water should be added to the tank to maintain stability and prevent groundwater damage. --- This version improves readability, adds context, and ensures a natural flow, making it suitable for educational or technical documentation purposes.

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