Small scale, distributed anaerobic digestion plants could offer an environmentally and economically stable solution for locally produced biogas.
In Germany government incentives have led to the development of over 6000 anaerobic digestion (AD) facilities, generating twice as much power as all of the country's waste to energy facilities combined.
However many of these are large scale, 1 MW plus facilities, and the proliferation of such plants has affected both tipping fees for food waste - which have fallen from between Eur 60 to 80 per tonne down to Eur 10 to 20 per tonne - and biocrop prices to such an extent as to put many at risk of becoming economically unviable.
According to Craig Benton of Composting and Recycling Consultants, mini-biogas facilities could offer the ideal solution for farm waste.
Speaking at the Energy from Biomass and Waste Conference in London today, Benton claimed that most vendors of anaerobic digestion and biogas equipment offer systems starting at around 250 kW. In most farm applications, such systems lead to a dependence on importing feedstocks from the surrounding area which can be economically risky.
However, Benton claimed that a new system from Austrian firm, Bio4gas could offer the ideal solution. Available in two sizes - 20/25 kW and 50 kW - the system enables farmers to use animal slurry from their own farm to generate heat, power and digestate.
At the heart of the product is the patented 'Thermal Gas Lift' - a passive mixing system that Benton said offers reduced energy consumption through the use of gas pressure to force the slurry mixture through holes in the bottom.
The smaller of the two systems features a 220 cubic metre tank that is dug into the ground and holds 180 cubic metres of material. In addition a double chamber digester produces more biogas than a single tank.
According to Benton the advantages offered by a more distributed approach to biogas are significant, with potential returns on investment ranging between 12.5% and 16.4% based on conservative figures.
Benton added that small scale biogas production could free the operator from the "whims of the market", insulating them from rising biocrop prices and the prospect of falling tipping fees.
Additionally, as all of the feedstock is sourced from the host farm itself, the digestate can be used to fertilise the farmer's own land with no solid waste permit or license is required.