Development of On-Farm Anaerobic Digestion

Although humankind has always relied on generating energy from biomass in some form (e.g. firewood), it has only recently been re-conceptualised as ‘bioenergy’. This is possibly because it was seen as an anachronism in the developed world for most of the last century (Plieninger et al., 2006). About 80% of the world‘s energy supply is currently derived from fossil fuels, but of the renewable energy sources, biomass is still by far the most important with between 10 to 15% of demand (or about 40-50 EJ per year). ‘Biomass’ is biological material derived from living, or recently living organisms such as forest residues (e.g. dead trees, branches and tree stumps), green wastes and wood chips. A broader definition of biomass also includes biodegradable wastes and residues from industrial, municipal and agricultural production. It excludes organic material which has been transformed by geological processes into substances such as coal or petroleum. In industrialised countries biomass contributes some 3–13% of total energy supply, but in developing countries this proportion is much higher (up to 50% or higher in some cases). The recent scientific interest in bioenergy can be traced through three main stages (Leible & Kalber, 2005, cited in Plieninger et al., 2006): the first stage of discussion started with the 1973 oil crisis and the publication of the Club of Rome’s report on ‘The Limits to Growth’. Along with Rachel Carlson’s ‘Silent Spring’, the Limits to Growth report was an iconic marker of the environmental movement’s emergence and a precursor to the concept of sustainable development. The second stage of interest in bioenergy began in the 1980s in Europe as a result of agricultural overproduction and the need to diversify farm income. Triggered by increasing concern over climate change, a third stage started at the end of the 1980s, and continues to this day. In the early years of expansion in renewable energy technologies, bioenergy was considered technologically underdeveloped compared with wind energy and photovoltaics. Now biomass has proved to be equivalent and in some aspects even superior to other renewable energy carriers. Technological progress facilitates the use of almost all kinds of biomass today – far more than the original firewood use (Plieninger et al., 2006). Biomass has the largest unexploited energy potential among all renewable energy carriers and can be used for the complete spectrum of energy demand – from heat to process energy and liquid fuel, to electricity. Direct combustion is responsible for over 90% of current secondary energy production from biomass. Biomass combustion is one of the fastest ways to replace large amounts of fossil fuel based electricity with renewable energy sources. Biomass fuels like wood pellets and