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Low cost Biodigesters to produce biogas and natural fertilizer from organic waste
What problems can be solved?

Biogas is generated naturally in swamps, where organic matter buried under sludge undergoes anaerobic digestion by bacteria. This gas is known as marsh gas. Biodigesters simulate the same natural process, in which bacteria convert manure into biogas and fertilizer, but in a controlled manner.

The first biodigesters were made in China in the mid-twentieth century. Biodigesters were made of brick and looked like giant cooking pots, buried and sealed. Costs were high, due to the amount of work required to build this type of biodigester, making this technology unaffordable for medium and small producers in rural areas with few resources.

In the 1970’s industrial biodigesters were designed in developed countries, where large amounts of organic material produced massive amounts of biogas, usually used to generate electricity. However, the technology was complex and the high investment costs made biodigesters even less affordable for families with few resources and with few heads of cattle. In the late eighties family biodigestores were promoted as an appropriate technology for development, where investment costs are easily set off by a family in two or three years: this was the beginning of low-cost biodigesters.

The impact of the use of biodigesters

Agricultural activity is being promoted by governments as a strategy for poverty reduction. Uncontrolled agricultural development leads to agricultural land expansion, new human settlements, misuse of chemicals and pollution, poor management of organic waste (potentially contaminating aquifers and ecosystems), and deforestation for fuel, cooking and productive activities (coffee, cheese, yogurt, dried fruit, etc).

Wood consumption in households for cooking leads not only to deforestation but also causes breathing problems, cancer, eye irritation, and other diseases, mainly in women and children. Moreover, it is these two groups who have to bear the burden of finding and collecting firewood. For these reasons, agricultural development must be accompanied by awareness, capacity building, technologies and regulations that promote sustainable development.

If a family possesses two or three cows, or several pigs or a few dozen sheep, producing about 20 kilos of fresh manure per day, and has access to water for most of the year, a low-cost biodigester can bring the following benefits:

Biogas is mainly methane, much like the butane and propane gas sold in cylinders. It can be used for cooking, lighting and heating.

The biol produced is a free natural fertilizer that improves crop yields by up to 30%. It can be poured directly onto the earth to stimulate seed growth or sprayed on leaves. In the case of dairy cows, the use of fertilizer on forage crops like alfalfa, increases production and quality, and this is reflected in higher milk production.

Family Health
Burning biogas for cooking does not produce smoke, thus there is no black soot that enters the lungs of women and children, or that covers kitchen walls. This will prevent respiratory diseases, eye irritation and other diseases.

Animal hygiene
By putting the manure in a biodigester, odours, foci of infection and flies will be eliminated. The decrease in fly population has a direct impact on cows, reducing mastitis.

If each family generates their own fuel for cooking there is no longer any need to cut down trees for firewood, thus reducing pressure on the environment.

Workload and cost

Daily or weekly time spent by families to collect firewood, or the money spent on the purchase of fuel in the rainy season, is replaced by the 20 minutes a day required for loading the biodigester with fresh manure and water.

Sustainable Technology
Since the technology used is simple, it is accessible to anyone, even those with no prior knowledge. It is enough to follow a few simple instructions to set up a biodigester and understand the technology, daily operation, maintenance and repair work. All materials are available locally, without the need to import anything from abroad.

Low investment
The cost of a family biodigester depends on size and climate. In cold climates, the cost in materials is around 250 U.S. dollars, while in tropical climates this drops to $ 150. Investment costs are paid back in two to three years by savings in fuel, time and improved production.

A low-cost digester is a simple and accessible technology that has a positive effect on several aspects of family life, income and production; though not a solution to all problems, it is a resource that brings many significant improvements.