“4-in-1”BIOGAS SYSTEM IN NORTHERN CHINA
INTRODUCTION
The “four-in-one” is a new development model that combines renewable energy development and organic agriculture together. It consists of a biogas digester, a pigpen, a toilet, and a greenhouse hence called “four-in-one”. It is established based on principles of environment, economy, and systematic engineering. This model is powered by solar energy and linked by the biogas digester. It has contributed much to the increase of energy supply, the increase of farmers’ income, and the improvement of living environment.
The “four-in-one” is first introduced and developed in Pulandian County in Liaoning Province, China. It is located in the northeast of China. The climate is continental monsoon climate. The average temperature over the year is 5~10℃, with the highest temperature of about +30℃ and the lowest of about -30℃ in the winter. The frost-free period is 124~215 days per year. The annual sunshine duration is 2,300~3,000 hours, and the annual solar radiation is 120~135 Kcak/m2.
Because of the long and cold winter, conventional biogas digesters could only operate for five months per year, growth period of crops and vegetables is also short, and livestock grow slowly. The “four-in-one” is designed to provide all year round constant gas supply for clean cooking fuel, heat and light, and light, and a green house of all seasons harvest with high value organic agriculture products. Through three years’ practice, it has been demonstrated successful if well managed.
STRUCTURE
The four-in-one has four integrated parts – biogas digester, greenhouse, pigpen, and toilet. The biogas digester, pigpen, and toilet are closely connected together with the biogas digester built beneath the pigpen and
the toilet. The feeding ports of the biogas digester are open to the toilet and pigpen on the ground level, and the discharge port is in the greenhouse.
Strawberry grown in the greenhouse
To ensure the quality, the biogas digester must be constructed using brick and cement, or concrete. The greenhouse’s structures can be soil/wood or brick/steel. The soil/wood-structured greenhouse uses soil or mud to build the back wall, and use wood or bamboo to build skeleton to support the greenhouse. The brick/steel-structured greenhouse uses brick and steel instead of soil and wood. The cost of soil/wood greenhouse is much lower than brick/steel greenhouse, but the life is shorter, and resistance to wind and snow is weaker.
WORKING PRINTCIPLE
The feedstock for biogas digester is from toilet and pigpen. Gas is used for cooking and heating, or lighting, which generate CO2, inside the greenhouse and keep the temperature constant during night. The fermentation residue from biogas digester is used as fertilizer for crops, vegetables, fruits, or flowers planted in the greenhouse. Constant gas supply throughout the year.
COST
The cost for construction of a “four-in-one” system varies depends on size and material used. Based on 1999 price indexes, the cost for an 8m3 biogas digester and 15m2 pigpen is about 3,000RMB yuan. The cost for 75x7.5m2 greenhouse supported by wood or bamboo and/or soil is used instead of brick and cement, the cost will be at 8000RMB. Practically, the cost for a model with the same size of the above-mentioned one is about 11,000RMB yuan (including the biogas digester). Two sets of the four-in-one model have been installed in Baima Snow Mountain in Diqing prefecture.
The operation cost primarily includes labor, replacement of plastic sheets and operating/replacing straw curtains, pig forage, and other maintenance. Plastic sheets and straw curtain are generally replaced every two years to ensure the transparency of membrane and insulation. In China, the cost for plastic sheet and straw curtain covering a 75 X 7.5m2 greenhouse is 1,000RMB yuan and 1,300RMB yuan, respectively.
Funds for construction of this system come from either self-investment of farmers or low-interest loan from Chinese Agricultural Bank. Most loans are paid back by farmers in one or two years.
Because the system is primarily designed for Northern China , where the winter is long and cold, some designs are specific for the survival of the model in winter. That is to say, if the local climate is mild, the cost to establish such a model can be less.
BENEFIT
Application of this technology has achieved good economic benefit and environmental benefit.
The productivity of the biogas digester is about 0.15~0.25m3 per one m3 per day, thus, an 8m3 biogas digester produces enough biogas for cooking for a four-member family. If a family owns two or more such models and pipe is installed to connect their house and biogas digesters, the generated biogas can be used for heating besides cooking.
Fermentation residue is used as organic fertilizer for plantation; combustion of biogas and respiration of pigs increase the concentration of CO2 in the green house; all these result in a 30% increase yield compare to field production. Also, the growing rate of pigs bred in the model is higher than natural grazing or in normal-designed pigpen.
The income from the greenhouse production varies with the variety of crops, vegetables, fruits, or flowers planted in the greenhouse. If flower is planted in a
75 x 7.5m2 greenhouse, for example, the annual income is more than 40,000RMB yuan per year. As for peach, the annual income is approximately 15,000RMB yuan, but much less labor is needed, compared with flower plantation. In general the investment for a “four-in-one” module can be recovered in one or two years.
Also, the biogas generated by the biogas digester can be used for cooking and heating. Thus, most of, or even all of, the traditional fuel such as fossil fuel, firewood, and straw that will be otherwise consumed can be saved. If the digester produces 300m3 of biogas a year, then 0.7 ton of coal or 3 ton of fuel wood can be saved.
Environmental benefit includes saving of traditional fuels and therefore decrease of pollutant from these fuels, treatment of human and animal manure, phase out the utilization of pesticides and chemical fertilizer. As a renewable energy source, It provides farmers with clean, much more convenient and climate-benign solutions in rural area.
Conventional fuels, including coal, firewood, straw, are usually used for cooking and heating before biogas is generated. As we have known, these fuels, especially coal, generated much pollutant and smoke into the atmosphere. When “four-in-one” pattern is applied, biogas will replace most of the consumption of these fuels, and thus decrease the pollution of fuel combustion.
Manure, either from human beings or from animals, is a major pollutant source in rural areas. However, after the operation of biogas digester, it is no longer a significant source of pollution. Surveys show that the chance for people living in biogas village to be infected by intestinal contagious disease is 28.7~33.1% less than those living in non-biogas village, for example. Indoor air pollution due to burning of biomass or coal could be eliminated which benefit mostly to Children and woman.
Experiences indicate that 10 pigs in pigpen can provide enough feedstock for an 8m3 biogas digester, and the fermentation residue is enough fertilize plantation over 75 x 7.5m2. That is to say, no more chemical fertilizer is needed, which ensures the quality of crops, vegetables, fruits, and flower while helps keeping the soil quality. Because the plastic membrane separates the plantation, pests are better controlled, the quantity of pesticide that has be used may be very little if not zero. In return, organic agriculture products have better market opportunities with relatively higher values.
