There are biogas plants worldwide with different degree of technical development. The overall world market was approximately two billion euro in 2006 and is expected to increase to more than 25 billion by 2020 total (http://www. hkc22. com/biogas. html, updated in July 2008). Measures are taken worldwide to promote biogas and its market development (Sakulin, 2009). Among the initiatives taken, the feed-in tariff is a motivation to promote the adoption of renewable energy policy through legislation. According to this, the regional or national

electricity utilities are obliged to buy electricity generated from renewable sources (solar power, wind power, hydropower, geothermal as well as biomass). Table 12.4 lists the feed-in tariff for several European countries.

Europe has high-tech biogas plants in operation, with Germany being the leader. In 2006, 900 plants were built, reaching 3600 in total (Helmut Kaiser) in Germany. A market size of 7.5 billion euro, 30% export and 85 000 jobs are expected by 2020 in Germany. As in Germany, Denmark also has a variety of biogas plants of different capacity. The digestion of manure and organic waste is a well-established practice in Denmark with 20 centralised plants and over 35 on-farm plants (Raven and Gregersen, 2007), although there is a decline in the construction of new plants. In Austria and Switzerland, there are mostly small farm scale plants due to the national agricultural structure. In Sweden, there are also quite a few large scale plants (Fischer and Krieg, 2001). Table 12.4 reports the status of biogas plants and capacity in Europe.

Unlike Europe, experience with anaerobic digestion in North America is quite limited. Farm-based anaerobic digestion in North America only began out of necessity for odour control due to urban encroachment (Lusk, 1998). In the USA, which rejected the Kyoto protocol, most of the methane from wastes is allowed to escape into the atmosphere where it contributes to global warming. However, there is a strong movement towards the use of renewable energy from biogas. The development of anaerobic digesters for livestock manure stabilisation and energy production has accelerated at a very fast pace over the past few years. According to the EPA, about 111 digesters operate at livestock facilities in USA up to 2007 (U. S. EPA, 2007). The energy production was 215 million KWh (electrical energy: 170 million KWh). It was estimated that besides electricity generation, the biogas was used in boilers and fed in the natural gas gridding (after upgrade) or flared for odour control. In Canada, approximately 16 farm-scale anaerobic digesters operate or are being built (Wohlgemut, 2006). In 2006, the Ontario government implemented a Renewable Energy Standard Offer Program, which guaranteed farmers a higher rate for biogas-produced electricity, along with a financial assistance programme designed to reduce the capital costs of digester construction (Hilborn et al., 2007). On the other hand, in the Manitoba province, anaerobic digestion is less promoted due to the well-established and cost-effective hydroelectricity industry (Wohlgemut, 2006).

In Australia, the installed capacity for biogas was 458 MW in 2001. Electricity generation from biogas has increased considerably from 23 GWh in 1995 to 729 GWh in 2001, an average growth rate of 78% per year. Wastes from food processing plants, livestock manure and human sewage are the primary feedstocks for biogas production. Most of the installed capacity is at sewage treatment plants, which are considered highly cost effective.

In developing or less developed areas of the world, anaerobic digestion is spreading fast. In Asia (mostly China and India, but also Vietnam, Thailand, etc.) there are millions of low-tech, hand-made, plants consisting of underground, non­insulated digesters in operation for decades (Fischer and Krieg, 2001). Manure and food residues are the main feedstocks used and the biogas energy generated is used for cooking and lighting. According to the ministry of agriculture in China, 15 million households in China were using biogas in 2004, with the aim to increasing this number to 27 million by 2010, which will account for over 10% of all rural households. By the end of 2005 there were 2492 medium and large-scale biogas digesters in livestock and poultry farms, while 137 000 biogas bioreactors had been constructed for the household wastewater treatment (van Nes, 2006). In order to support the development of renewable energy sources, China enforces suitable legislation and takes steps to promote industrialisation of the construction of biogas plants. In India, 3.67 million biogas units were installed in 2004. The ministry of non-conventional energy resources implements a programme (national biogas and manure management programme) for providing financial, training and technical support for the construction and maintenance of biogas plants. Similar initiatives have been taken in Nepal and Vietnam (van Nes, 2006). European companies and organisations, mainly from Germany, Denmark and Austria, have already entered the Japanese and Korean market and transferred high-tech anaerobic technology, while they promote anaerobic digestion to the developing countries such as China, India, etc.

In Africa, there are attempts by international organisations and foreign aid agencies to promote biogas technology. Some digesters have been installed in some sub-Saharan countries, making use of feedstocks such as slaughterhouse wastes, municipal wastes, industrial waste, animal dung and human excreta. Small-scale biogas plants have been established all over the continent (Table 12.5) but only few of them are operational (Parawira, 2009). Insufficient know-how concerning anaerobic technology is claimed to be the main reason for

inadequate operational potential of the installed plants. In some cases, the installation of the plant is of poor quality and the appropriate maintenance lacks.

In Latin America, many biogas plants operate in the agricultural, industrial and municipal sectors. Biogas is mainly used for cooking, lighting, as town gas or as vehicle fuel. The quantity of biogas produced in Latin America was estimated at 217 million m3 per year in 1993 (Ni et al., 1993).

The future of biogas as a competitive biofuel relies on the economic feasibility of the anaerobic technology. The income sources of a biogas plant are the energy and fertiliser sales as well as the tipping fees for receiving off-farm waste. Remuneration or subsidies from the government is an extra income. If the cost of energy production is too high, the biogas can be flared to eliminate odours and greenhouse gas emissions, but this is not a viable option. The costs of biogas production are distinguished into the capital (or investment) and operational costs for the installation of the plant and its maintenance, respectively. Capital costs are determined mainly by the size of the plant and the technology selected. The price of components (feeders, stirrers, CHP, etc.) and construction materials (concrete, steel) also affect the investment cost. The operational costs include maintenance of the biogas plant, labour costs, insurance and other utilities. Laaber et al. (2007) estimated that the capital costs vary between 3000 and 5000 €/kWelectricity for the anaerobic digestion of energy crops, while the operational costs range between 2

and 4.5 ct/kWh