Biofuels in Perspective

172 Biofuels
heat production, but it can also be applied as an automotive fuel or for the production of
hydrogen, which can be used in fuel cells. Biogas production in the agricultural sector is
a very fast growing market, especially in many European countries. This chapter presents
some aspects of the current situation in Germany and Brazil. The first has the highest
number of agricultural biogas plants in Europe. The second has a large potential of biogas
production from the residues of the bioalcohol programme that is being applied in that
country.
10.2 Introduction
Anaerobic digestion of organic wastes and by-products from agriculture and the food
industry is a process known for many years and is widely used for waste stabilization,
pollution control, improvement of manure quality and biogas production. Anaerobic digestion
is a process that exhibits many advantages: It can convert a disposal problem into
a profit centre, it allows agricultural crops to be converted into a valuable fuel and it can
reduce mineral fertilization demand by nutrient recovery. Therefore, anaerobic digestion
has become a key method for both waste treatment and the production of renewable fuels.
During recent years, governments of many European countries as well as in other regions
have increased their interest in anaerobic digestion based biogas production because it is
an environmentally friendly energy source with large potential for reducing green house
gas emissions. Therefore, several acts on granting priority to renewable energy sources
have come into force and different governmental programs have given incentives in order
to promote the development of anaerobic digestion biogas plants.
In the following, applications of biomass digestion for biogas production in the agricultural
sector will be shown and discussed for the conditions in Germany and Brazil. In
Europe, Germany is the leading country in this field with the highest number of installed
biogas plants. In Germany, biogas is produced mainly from manure, organic waste from
household, the food- and agro-industry and especially cultivated energy crops. Considerable
attention will be given to Brazil. Indeed, this country has already long-term and
large scale experience with the use of renewable fuel (bio-ethanol). The case of a close
integration of biogas and bio-ethanol production is therefore of particular significance.
Figure 10.1 shows that the biogas yield of different substrates is strongly dependent
on the type of the biomass. The fermentation of manure alone results in relatively low
biogas yields. Co-digestion of manure with other wastes has a positive effect on process
stability due to its high buffering capacity and its high content of trace elements. In order
to increase the gas yield most of the biogas plants are operated today by co-fermentation
of manure together with non-agricultural organic wastes, harvesting residues and energy
crops (Figure 10.2).
Nevertheless, the treatment of organic wastes in agricultural co-fermentation plants is
declining, because the regulations concerning hygiene and nutrient recycling are more
stringent and the legal conditions are much more complicated as well (Weiland, 2004).
Considerably higher investment and operating costs are the result, which decrease the
economic benefits. The latter are coming from the entrance fee and the gas yield. On
the other hand, a higher compensation is paid for the produced electricity according
to the Renewable Energy Act (EEG) if only substrates from agriculture are used for