Several key technical links in the construction of rural digesters

The construction of rural biogas digesters is one of the contents of the Ministry of Agriculture’s Ecological Homeland Enrichment Program. Hechuan City in Chongqing has been implementing this project for several years. In the long-term practice, it has concluded a set of effective experience in building pools. Now it is dedicated. Come out and learn from others.

First, the choice of biogas tank type

To build a biogas digester, we must first understand the layout of various types of biogas tanks, because rational layout is an important prerequisite for increasing biogas digesters. Secondly, it is necessary to understand whether the daily management of the pool type is convenient, especially whether slagging and dredging are easy. At the same time, the pool type must have normal metabolic functions, and weeds and straws can be mixed to avoid short circuits. Once a short circuit occurs in the inlet and outlet, there must be a practical method of elimination. On the other hand, the volume should be determined according to the family population and the number and type of poultry, and the pool capacity of the biogas digesters should be budgeted based on the ratio of 1.3-1.5 cubic meters per person, for example: 3 families choose 4 Cubic meters, 5-6 people use 8 cubic meters of pool capacity. Pigs with sufficient raw materials for multi-fermentation can increase the pool capacity appropriately.

Second, the choice of building time

1. Biogas tank fermentation rate, gas production rate and temperature changes are proportional to the relationship. In spring and summer (in the first half of the year), the temperature gradually increased, the anaerobic bacteria in the biogas digesters became active, the fermentation in the biogas digesters was vigorous, and the fermentation in the new tanks started faster and the gas production rate was higher. In autumn and winter (the second half of the year), as the temperature gradually decreased from high to high, the fermentation turned slowly from high to low. Therefore, from the perspective of the rise and fall of seasonal temperatures, it is best to choose the pool with higher temperatures in spring and summer.
2. From the law of rainfall in spring, summer, autumn and winter and the law of groundwater level rise and fall, the former has more rainwater, the groundwater level is higher, and there are certain difficulties in building pools in low-lying areas, but the autumn and winter seasons are the opposite. Therefore, it is better to build a pool in the second half of the year in low-lying areas.
3. From the situation of price fluctuations of building materials, the construction price in the first half of the year is lower than that in the second half of the year. The seasonal price difference per package of cement is generally around 5-6 yuan. If a biogas digester is needed to build 20 packages of cement, then the first half of the year will be built. The pool generally saves about 72 yuan compared with the second half. Therefore, from an economic point of view, it is more cost-effective to build a pool in the first half of the year.
Based on the above analysis, it is more appropriate to choose a pool in the first half of the year. However, in areas with higher groundwater levels and villages, it is advisable to adopt phased construction methods, ie planning in the first half of the year and digging pits in the second half of the year.

Third, the choice of process flow

1. Precast construction. The method has the advantages of cost saving, uniform thickness of each part of the main tank body, good stress, good compressive and tensile resistance performance, and can be constructed in sections, shortening the time of underground construction of the pool, and facilitating the construction of pools in areas with high groundwater level.
2. Cast-in-situ concrete construction. At present, the city mainly adopts this method. However, the technical requirements for cast-in-situ concrete construction are high. If the digging pits and school molds are not accurate, the thickness of the pool wall may vary, and the pool will increase. Cost; In addition, cast-in-place construction requirements at one go, not intermittent, it is inevitable that there are different specifications, the quality is difficult to guarantee the phenomenon. Practice has shown that using this method in areas with higher groundwater levels is much more difficult than prefabrication. Therefore, to build a rural household biogas digester, the precast construction method is better than the concrete cast-in-place construction method.