Key points for the daily management of biogas by rural users
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Three parts are spent on building the pond, seven parts on its management. To make good use of biogas, management is key. The daily maintenance of household biogas digesters involves practicing \"four diligences, one protection, and one replacement.\" 1. Frequent feeding: At room temperature, the organic substances in the fermentation feed that are easily broken down and digested by microorganisms are essentially exhausted within 80–120 days. This is especially true for human and animal waste, whose gas production takes only 60–80 days. Therefore, it is necessary to continuously supply fresh feed in order to maintain steady and consistent gas production throughout the year; this requires feeding frequently, in sufficient amounts, and with high-quality feed. “The \"three-in-one\" biogas digester solves the problem of human and animal manure, as it allows this waste to flow automatically into the digester on a daily basis, ensuring regular feeding. For a biogas digester with a capacity of 8–10 cubic meters, 20 kilograms of human and animal manure per day is sufficient to meet the needs. If there is a shortage of human and animal manure, an appropriate amount of pre-treated and decomposed crop straws or green weeds should be added promptly.
2. Regular discharge: The biogas slurry and residue resulting from microbial decomposition and fermentation are high-quality organic fertilizers; it is necessary to remove excess slurry from the discharge area in a timely manner so as to ensure a steady gas production through the replacement of old with new. Additionally, it is important to determine whether a complete replacement is needed based on the effectiveness of its use. “In the \"three-in-one\" biogas digester, human and animal manure and urine continuously flow in automatically; the contents are removed every 5–10 days, with an amount that accounts for 5% of the total liquid volume in the digester being appropriate. At the same time, pay attention to adjusting the water level regularly; if the fermentation broth contains too much water, gas production decreases, while if there is too little water, the broth becomes viscous, which can lead to crust formation on the surface and also reduce gas production. The concentration of the fermentation broth is generally best kept between 6% and 10%. A biogas digester that does not utilize the three-in-one system should be started normally; after 20–30 days of operation, old material should be removed and new material added, with each addition accounting for 3–5% of the total fermentation liquid. When adding material, it is necessary to first remove the existing material before adding new one; the amount removed should be equal to the amount added. If, after removal, the liquid level in the tank falls below the upper edge of the inlet and outlet openings, water should be added promptly to keep the liquid level 30 centimeters above the height of the access door.
3. Stir frequently: Stirring ensures thorough contact between the biogas-producing bacteria and the fermentation materials, breaks up the scum layer at the surface of the tank, allows the generated biogas to enter the gas collection chamber, and increases the biogas production rate. There are mainly two methods for stirring: one is to use a long stick or a long-handled manure spoon to pull back and forth inside the tank dozens of times from the feed inlet and the discharge outlet ； Second, 10 barrels of fermented liquid are drawn out from the discharge port and then poured into the tank through the feed port. Generally, stir 1–2 times per week.
4. Regular inspections: It is necessary to frequently check the biogas digester, switches, and gas transmission pipelines, especially the pipe joints, to determine if there is any leakage of water or gas. Any issues detected should be addressed promptly. Specifically, follow the approach of “three inspections, one check, and one replacement”: first, inspect the pool opening to ensure that the pool cover is secure and that there is no leakage due to excessive pressure ； The water stored in the water seal ring tends to evaporate and leak, so it needs to be replenished promptly ； The condensation water that accumulates in the water collection tank should be drained promptly. Second, check the water column on the barometer; after fermentation begins, if the water column does not move, it may indicate that there is an obstruction in the pipes or a leak somewhere ； The water column jumps, and there is a hissing sound during burning; this is due to condensed water inside the pipe, which should be removed using a pump from the stove’s outlet ； When the water column rises to a certain height and stops rising, it is because the pressure in the tank is too high and air is escaping ； Excessive gas generation pressure; the liquid level is below the discharge port, causing gas leakage ； The water column shoots high into the air, indicating vigorous gas production that hasn’t been utilized in time ； Water columns are drawn into the gas delivery pipe, causing negative pressure in the tank and an excessive amount of liquid to be discharged ； The water column rises slowly, which is due to poor fermentation or insufficient raw materials, resulting in low gas production. Third, check the water pressure area to examine the pH level of the fermented liquid; if the return water is light yellow in color and the flame on the biogas stove is red-yellow, it indicates poor fermentation or acidification, and lime water should be added for adjustment ； The water return position is at the entrance of the discharge area hallway, indicating insufficient material in the tank ； Backflow occurs due to an excess amount of liquid in the tank or because the gas generated is not utilized ； If the water level in the return pipe is different from that in the feed pipe, it indicates a blockage inside the pipe, which should be repaired promptly. Fourth, check whether the pipelines and accessories are damaged, aged, corroded, clogged, etc., and address any issues found promptly. Fifth, the desulfurization agent should be replaced in a timely manner as required when installing a biogas purifier.
5. Keep warm in winter. The normal fermentation temperature for biogas digesters should be above 8°C; since temperatures are low in winter, it is necessary to take measures to keep them warm. “A “three-in-one” biogas digester allows for the construction of a shelter over the livestock pen to provide insulation; in biogas digesters without this feature, straw, firewood, or thick plastic film is used for insulation.
6. Perform major refueling at the appropriate time. Major refilling is mainly applicable to biogas digesters that raise a large number of pigs or use straw as the main raw material. Depending on the agricultural production season, the fertilizer can be completely replaced once a year during the peak usage period. During major refueling, it is important to note that: first, the operation must be carried out at temperatures above 15°C to facilitate restart ； Second, prepare an adequate amount of new material ； Third, stop feeding new material 20–30 days before large discharge ； Fourth, reserve sufficient inoculum by keeping 10%–30% of the slurry, which mainly consists of activated sludge, as inoculum to accelerate startup ； Fifth, for biogas digesters with leakage problems, system repairs should be carried out in conjunction with major refueling. The major refueling is carried out once a year, usually in spring or autumn.