Alternative energy is nowadays an umbrella term used for any source of energy which replaces fuel sources without the undesired consequences of the replaced fuels. Some time ago fossil fuel was also an alternative energy source for whale oil.
Renewable alternative energy sources such as biomass are sometimes regarded as an alternative to ecologically harmful fossil fuels. One technology expanding in this direction is biogas.
Biogas typically refers to a gas (a mix of mainly methane and carbon dioxide) produced anaerobically by the biological breakdown (fermentation) of organic matter. The gases can be combusted or oxidized with oxygen releasing energy, which can be used by mankind.
Silage is a very interesting substrate for biogas production. Under normal conditions, ensiling allows feeding the fermenters with a material having a low variation in composition. A relatively constant composition is a prerequisite for stable fermentation and biogas production. However, to keep the composition and diminish losses is not a phenomenon which occurs per se.
The biogas production is a very complex poly factorial fermentative microbiological process. The end product is a gas called biogas which is the name for a mixture of methane and carbon dioxide, so-called because of the microorganisms involved in its production. In Graphic 1 the processes for biogas production are shown. the breakdown of substances proceeds with a further acido genesis and aceto genesis caused by bacteria, with production of acetic acid/ acetates, hydrogen and carbon monoxide. these substances are the fundamental elements for methane production.
A key factor in optimal function of the biogas plants is to guarantee an optimised and stable substrate during the fermentation. That is why a substrate rich in acetic acid/acetates provides an essential substance for the methanogenesis, but also exists as an important constituent for the stability of the substrate in contact with the air. Doubtless silages are a very promising alternative for guaranteeing a substrate for winter with relatively low variation in composition if good ensiling practices are implemented. With regard to the selection of corn for biogas production, there is always a compromise between corn quantity and quality.
A controversial topic, not only for biogas producers but also for farmers, is the particle length. In the second case (farmers), the particle length is a compromise between silage quality and effective fiber for normal functioning of the rumen. Shorter particle length means better compacting and therefore better silage quality, however it could have a negative effect on the gastrointestinal tract of the ruminants. Since in the biogas production the end consumer is not a ruminant, a shorter particle length could always be used. It also simplifies the mixing process in the fermenter.
Other aspects such as covering, advance in the silo in the feed out phase, clean cut of the external layer of the silage, mitigation of aerobic instability and the concomitant huge losses must be always first priority for biogas producers. In spite of the variations in the silage quality during the feed out phase, the variations are very small compared with substrates used fresh, very often agricultural residues from kitchens, forests, cafileries, etc, as well as the irregular supplies in several cases. The microorganisms responsible for aerobic instability are mainly yeast and bacteria.January 2012