Currently biogas plays a smaller, but steadily growing role. Energy recovery from biogas by anaerobic digestion (AD) has been a welcome by-product of sewage sludge treatment for a number of decades. However, biogas has become a well established energy resource, especially through the use of biomass residues and crops. Keep on reading to know more about biogas and about how Arudo donax can contribute to a sustainable future!
Development of crop digestion – all you need to know about biogas
The concept of crops for methane production (anaerobic digestion, biogas, methanisation or biomethanation) is not new. Early investigations on the biomethanation of different crops and plant materials were carried out in the 1930’s, and since the 1950’s biogas production from crops has continued to develop as an important new farm enterprise in European countries such as Austria, Denmark and Germany.
In the 1990’s steadily increasing oil prices and improved legal framework conditions, stimulated crop research and development. In Germany, for example, the number of digesters using crops was 100 in 1990. At the end of 2010 about 6000 biogas plants were in operation in Germany. 90-95% of them use crops and several of them employ mono-digestion.
The steady increase in crop digesters in Germany can be directly attributed to the favourable supportive national legal framework coupled with the tariffs paid for renewable energy. Feed-in tariffs are also exist in other countries, for instance in Switzerland, the Netherlands and France.
Sweden, Finland and France do not have any dedicated crop digesters but co-digestion does take place at a few facilities. Denmark focuses very much on animal slurries and waste while the United Kingdom focuses on waste. The crop digestion industry is dominated by Germany (ca. 5700 digesters) and Austria (290 digesters).
Having established an overview of history and facilities, the question is: what is so challenging about biogas production?
Agricultural sustainability
Crop digestion leads to increased activity in the agricultural sector by increasing demand for locally grown biomass. Furthermore, the cultivation of crops promotes investment in the rural economy and the production of disperse sustainable rural employment. Currently, most crops are grown as intensive monocultures. Annual monocultures are often associated with high rates of soil erosion. Some crops, like maize, deplete soil nutrients more rapidly than others, and might require significant levels of agrochemicals (fertilizer, pesticides). Other, non-edible crops, however, offer a solution to this issue. Arundo donax has no pests or diseases typical of this species, therefore it requires no aggressive chemical treatment.
High yield crops in Continental Europe may also depend on irrigation and risks of water depletion may occur. Luckily, it was proven that Arundo donax requires no fresh water for its irrigation, and being irrigated with wastewater does not lessen its yields.
Comprehensive investigations for the selection of optimised plantation systems for different habitats have been started in countries such as Germany, The Netherlands and Austria. Results so far indicate the influence of soil quality, climate, water availability, crop rotation and last, but not least, the time of harvesting on biomass yield, methane production potential and consequently the overall economic viability. You can read about biogas and time of harvesting of giant reed here!
Land availability for crop production
Land available for crop production is limited. The surface of the earth is mostly covered by oceans (361.106 km2). Of the remaining area of 149.106 km2, 55.7 % are covered by forests, 16.1 % (or 24.106 km2) is deemed pastureland and only about 9.4 % (or 14.106 km2) is arable land. The world’s growing population requires growing quantities of food. This puts pressure on finite agricultural land resources which are required to produce feed for humans and animals, for biomass for industrial use, for alcoholic beverage production, and increasingly for energy production. Advantageously, biogas systems are very flexible. Biogas can also be produced from plants which are not used directly for human consumption; examples include giant reed.
Also, soils which are marginal and unsuitable for food production can be used for the cultivation of crops for biogas production. Several studies agree on the existence of about 1.350 000 hectares of land only in Europe deemed less favourable for conventional agriculture. These sites provide an opportunity for new and sustainable investments into Arundo donax plantations, and thus, into biogas feedstock production.
Read more about biogas production and giant reed on our website!
Sources:
J., Murphy, R., Braun, P., Weiland, A., Wellinger. Biogas from Crop Digestion. IEA Bioenergy.
