Biogas from biomass and sewage sludge
In principle, a distinction needs to be made between two different basic substances for the production of biogas. On the one hand, there is biomass that arises through vegetation detritus, animal waste or manure and the utilization of carcasses or through the targeted cultivation of so-called energy plants, e.g. corn. On the other hand there is sewage sludge, which must be treated by fermentation in order to produce biogas for generating energy in the form of electricity and heat. These biogases are cleaned to produce a quality of natural gas, compressed and used as fuel for vehicles or fed into the natural gas network.
What is special about methane
After carbon dioxide, methane is the most important greenhouse gas emitted by man. Being an odourless and colourless hydrocarbon, it is the main constituent of natural gas and e.g. also of biogas. It is emitted continuously into the Earth’s atmosphere in all kinds of ways. During its relatively brief stay in the atmosphere, its effect as a greenhouse gas is over twenty times more powerful than the most important greenhouse gas released by man, carbon dioxide. Methane could at present well constitute one fifth of the effect of all greenhouse gases emitted by man.
Various types of biomass
Biomass is a term used to describe all organic matter generated directly or indirectly through photosynthesis that has not undergone change as a result of geological processes (unlike fossil biomass – mineral oil, coal, and natural gas). With energy utilization of biomass, only so much CO2 can be released as was previously bound in the biomass with the help of solar energy by means of photosynthesis. The following distinctions are made:
1. Ligneous dry biomass:
- e.g. forest timber, woodland timber, hedges, fruit planting, dead wood, scrap timber, solid waste from industrial processes, trade and households.
- Suitable processes for energy utilization: combustion and gassing.
2. Low ligneous, wet biomass:
- For example, farmyard dung (liquid and solid manure), harvest residue, biogenetic waste from the food industry, catering and households, etc.
- Suitable processes for energy utilization: fermentation.
In Switzerland, energy-producing vegetation does not play a significant role – i.e. plants that are cultivated with the specific aim of obtaining energy, such as special cultivation of corn in Germany. It is possible to obtain power and heat or fuel from biomass.