Analysis of the Comprehensive Utilization Benefits of Biogas Digesters in 2015

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Biogas digesters are not something new; they have been around in our country for a long time. Their promotion in rural areas has seen periods of success and failure. After entering the 21st century, by drawing on the experiences and lessons gained from previous years of biogas project development, applying new technologies, innovating construction methods, and strengthening service networks, we have managed to promote biogas digesters once again across rural areas, achieving significant progress. The vigorous development of the biogas industry has played a crucial role in this, and biogas digesters also offer many advantages of their own. As a worker involved in biogas project implementation, I am well aware of this. Here, I would like to discuss the comprehensive benefits of biogas digesters based on my practical experience. 　　I. Economic Benefits 　　1. Cost savings. 　　　A 10-cubic-meter biogas digester can operate continuously throughout the year, with an effective service life of over 2 years. While maintaining the raising of four to five pigs to ensure a source of raw materials, it generates 8–9 cubic meters of biogas per year, along with 3–35 cubic meters of biogas sludge and around 2 tons of biogas liquid. Biogas, biogas sludge, and biogas liquid can all be made full use of. 1. Biogas is used for daily cooking to prepare meals for the whole family three times a day, saving around 2 tons of coal per year and enabling cost savings of over 12 yuan in fuel expenses ； 2. Using biogas for lighting can save around 2 yuan in electricity costs per year ； 3. Biogas sludge and biogas liquid are used as fertilizers; approximately 5 kilograms of biogas fertilizer are produced per year, which saves around 4 yuan in chemical fertilizers. Since biogas slurry contains no germs or insect eggs, it can reduce the occurrence of plant diseases and pests, as well as help save pesticides. Swamp fertilizer can also improve the soil and increase its organic matter content ； 4. Use biogas slurry instead of pesticides for spraying to prevent plant diseases and pests, which can save over 2 yuan in pesticide costs per year ； 5. Biogas slurry, used as a feed additive for chickens, fish, pigs, cows, etc., can save over 5 yuan in feed costs per year. Feeding pigs with 1% concentration biogas slurry as a organic compound additive resulted in a daily weight gain of 64–66 grams per pig, reduced feed consumption by 48–6 kilograms per pig, and increased profits by about 4 yuan per pig. Feeding cattle, sheep, chickens, and ducks with biogas slurry can increase the pregnancy rate of female animals as well as the egg-laying rate of chickens and ducks. Biogas slurry and digestate generally contain no pathogenic bacteria or parasite eggs; pigs, cows, and sheep fed with these materials are less prone to illness, have shiny coats, grow robustly, and their shelters are free from mosquitoes and flies. According to relevant analyses, when cattle and sheep are fed with biogas slurry and digest, the daily weight gain for cattle is 3–4 grams per animal, while that for sheep is 5–6 grams per animal. 　　Based on the above analysis, over the course of a year, a 1-cubic-meter biogas digester can help farmers save around 3 yuan in expenses. 　　2. Generate benefits. 　　　(1) Advanced processing of biogas slurry: The biogas slurry is rich in nutrients; it serves as an immediately effective water and fertilizer, as well as an excellent feed additive. 　　 Preparing flower fertilizer solution: This solution is used as a liquid fertilizer for flowers as well as an insecticide. The market price for a 5ml glucose bottle is 2 yuan per bottle, while the wholesale price is 1 yuan per bottle. One kilogram of high-quality biogas slurry is collected each day, enough to fill 2 bottles; the selling price of these bottles is 2 yuan each. After deducting the costs associated with packaging, the annual profit amounts to over 7 yuan. 　　Production of feed additives: Biogas slurry, after being processed and filtered, can be used to feed pigs, cows, chickens, and fish. Feeding pigs can shorten the rearing period by about 1 month and reduce costs by around 35% ； Feeding cows daily can increase milk production by over two kilograms ； Feeding chickens can increase egg production ； Feeding fish can promote their better growth. 　　　 Producing plant pesticides: After anaerobic fermentation in biogas digesters, the raw materials for biogas production contain beneficial substances such as hormones that inhibit bacteria and enhance a plant’s stress resistance, as well as antibiotics, which can be used to control plant pests and diseases and improve a plant’s resilience. 1. Control of aphids in crops ； 2. Control of red spider mites on fruit trees ； 3. Use of biogas slurry to control barley yellow leaf disease ； 4. Use biogas slurry to control watermelon wilt ； 5. Biogas slurry for controlling wheat scab. Furthermore, biogas slurry also has a strong inhibitory and killing effect on the pathogens causing cotton wilt and anthracnose, potato wilt, wheat root rot, rice bacterial blight and sheath blight, the pathogens causing southern and northern leaf spot in corn, as well as the pathogens causing root rot in fruit trees. 　　　Preparing a plant seed-soaking solution: Biogas slurry is rich in various water-soluble nutrients, which can be used for soaking seeds of crops and fruit trees, as well as for foliar spraying and root drenching. It offers a high absorption rate and quick results – more than 8% of the applied amount can be absorbed by the leaves within one day. This allows for timely supplementation of the nutrients needed during the plant’s growth period, strengthening the plant’s structure and enhancing its ability to resist pests, diseases, cold weather, and drought. During drought periods, spraying biogas slurry on crops and fruit trees can cause the stomata in the plant leaves to close, thereby providing drought resistance. Reposted from 　　(2) Advanced processing of biogas residue: 　　　Biogas residue is the semi-solid substance that remains at the bottom of the biogas digester after biogas fermentation. It is rich in organic matter, humic acid, crude protein, nitrogen, phosphorus, potassium, and various trace elements, making it an excellent organic fertilizer with slow-release properties as well as a suitable feed for livestock breeding. 　　　Prepare nutrient soil. Nutrient soil is used for seedling cultivation of flowers and special crops. Flower fertilizer in 2-ounce bags is sold at 1 yuan per bag in the market, while the wholesale price is 0.5 yuan per bag. 5 kilograms of fine biogas sludge (dry material) can be collected each day, enough to fill 5 bags; the price of these bags is 25 yuan. After deducting packaging costs, the annual profit is around 8 yuan. 　　For making organic fertilizer: rough biogas residue can be used as a base fertilizer or a top-dressing; it can also be composted with ammonium carbonate or superphosphate to produce organic fertilizer. Based on an income of 5 yuan per day, the annual profit is around 18 yuan. 　　Cultivating edible mushrooms: Sludge can also be used to cultivate mushrooms, oyster mushrooms, and ganoderma, thereby generating greater profits. 　　Rearing with biogas sludge: Biogas sludge can also be used for raising earthworms, loach, eel, and other organisms, thereby generating indirect benefits. 　　　Furthermore, biogas digesters contribute to the development of the livestock industry; by keeping four to five pigs, which can be sold two to three times a year, more than one pig can be sold each time, generating a net income of 1 yuan per pig and thus adding an additional 1 yuan to the income. 　　Based on the above analysis: Throughout the year, if all the processed products derived from the biogas sludge and liquid from an 8-cubic-meter biogas digester are sold, at least 20,000 yuan in revenue can be generated. 　　II. Ecological Benefits The development of biogas can promote agriculture to move in a direction free from pollution and waste, as evidenced in the following aspects: 1. Elimination of environmental pollution: Biogas fermentation helps to eliminate the pollution caused by agricultural and domestic waste such as human and animal excrement on the environment; it also kills some bacteria and parasite eggs present in these wastes, thereby improving living conditions in rural areas. 　　 2. Reducing pesticide use and pollution: The application of biogas slurry as fertilizer or through foliar spraying can prevent pests and diseases in crops to a large extent, thereby reducing the need for pesticides, lowering pesticide residues in agricultural products, and enabling the production of pollution-free green products. 　　 3. The resource utilization of agricultural waste, turning it into valuable resources through comprehensive use, contributes to a healthy cycle in ecosystems and the sustainable development of agriculture. 　　 4. Improve soil quality and increase farmland fertility: The long-term application of biogas slurry to cultivated land can improve the physical and chemical properties of the soil, raise the levels of organic matter and various nutrients in it, which helps to promote crop growth and increase yields. 　　 5. Reducing human-induced ecological damage: The construction of biogas digesters provides farmers with an energy source for their daily needs, which reduces the need to cut down timber, alleviates pressure on farmland and grasslands, increases the availability of feed for livestock, and helps to protect natural vegetation. 　　 III. Social Benefits 　　 1. Improve the mental outlook of farmers and promote the civilized progress of rural society. Biogas-based ecological agriculture technology has broken away from the old production models that hindered the development of productivity, provided employment for a large number of rural surplus laborers, and improved labor productivity. 　　 2. It has trained a large number of biogas technology professionals for society. 　　 3. Promoting the production of pollution-free agricultural products enables a large supply of such products to be available to society. 　　 Through practical analysis, the above three benefits are significant enough to warrant our attention and prompt us to make vigorous efforts to develop them.