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Low cost Biodigesters to produce biogas and natural fertilizer from organic waste

Organic waste, when left untreated, is a source of infection and is difficult to dispose of. In agriculture and small-scale livestock farming, waste can be treated and transformed into natural fertilizer and, in some cases, fuel.

Biodigesters are natural systems that use organic agricultural waste, primarily manure, to produce biogas (fuel) and biol (natural fertilizer) by means of anaerobic digestion.

Biogas can be used as fuel for cooking, heating or lighting. In large farms, biogas can be used to power an electricity generator. The fertilizer, called biol, was initially considered a byproduct, but now is considered to be of equal or even greater importance than biogas because it provides families with a natural fertilizer that greatly improves crop yields.

There are several types of biodigesters but the focus here is on low-cost biodigesters, namely those that require no active heating systems and/or mobile mixing mechanisms. Thus a low-cost biodigester is an appropriate technology because of its low investment costs, easy management, simple maintenance and accessibility to both small and large-scale producers.

Not only can a family biodigester generate renewable and inexpensive energy but it also provides health benefits for the family, because biogas does not emit smoke when cooking. In cases where families need to collect firewood, a biodigester can greatly reduce the physical work involved, replaced by the loading of manure and water into the biodigester.

In agriculture, it provides a farmer with a natural and organic fertilizer which helps increase crop yields, whether vegetables, fruit, corn, potatoes, coffee, onions, quinoa, etc. Besides increasing productivity, biol gives ecological added value to products because they can be grown free of chemicals. What is more, farmers save money by not having to buy chemical fertilizers for their crops.

One of the most important ecological benefits is the reduction of deforestation due to the collection of firewood for cooking. Pollution is also reduced because a biodigester dispenses with the need for agrochemicals and provides good management of livestock waste, which in cases of high density, can contaminate aquifers. Having self-produced fertilizer increases yields and thus reduces the expansion of agricultural land. Finally, taking into account the greenhouse effect and climate change, emissions of methane gas, which otherwise would go into the atmosphere, are captured in the biodigester. Indeed, the negative impact of methane on climate change is 23 times greater than carbon dioxide.

Low-cost biodigesters have been implemented in developing countries since the 1980's. The first low cost tubular biodigester was the "red mud PVC” model designed in Taiwan by Pound in 1981. The next development was the continuous flow flexible tubular biodigester designed initially by Preston in Ethiopia, Botero in Colombia (1987) and Bui Xuan An in Vietnam (1994) for tropical climates. In 2003 Martí Herrero adapted Botero’s design to the cold weather of the Bolivian highlands. Thus, low-cost biodigesters can currently be implemented in all eco-regions.

The technology is being promoted by different institutions in several countries such as Colombia, Ethiopia, Tanzania, Vietnam, Cambodia, China, Costa Rica, Bolivia, Peru, Ecuador, Argentina, Chile, and Mexico, among others.