Overview of biogas extension

Abstract

An overview of biogas extension work considers the background to the development and use of the technology in less developed countries. The technology is placed in the wider global context of a concern for the environment since the early 1970s. It offers a long list of benefits to the users of the technology. A brief history looks at its origin in India and China, as well as applications for sewage processing in Europe and the USA. The benefits of biogas technology for small farmers led to programmes in China and India, which inspired the programme in Nepal. This book is the latest publication following a series of reports and a previous book about the biogas programme in Nepal. People in Europe and the USA have only lately realised that a technology for processing sewage is also a good source of renewable energy.

Keywords: biogas, anaerobic digestion, overview

The global context of the development of biogas extension programmes

Biogas has been seen as the classic example of a renewable energy technology or 'Appropriate Technology' since concerns were expressed at the rate of development in the world in the early 1970s. Several books at the time suggested that the world needed sources of energy other than oil. The key books were Limits to Growth (by Donella H. Meadows, Dennis L. Meadows, Jorgen Randers, and William W. Behrens III) (Meadows et al., 1972) from the Club of Rome in 1972; 'Small is Beautiful: A Study of Economics as if People Mattered ' by E.F. Schumacher in 1973 (Schumacher, 1973); and 'Our Common Future', the report of the Brundtland Commission (set up in 1983, but published in 1987) (Brundtland, 1987). The two oil price-hikes of 1973–74 and 1979–80, caused first by OPEC restricting their supplies and then by the first Gulf war, confirmed this concern, especially for leaders in developing countries that were badly affected by the price hikes.

In India and China, various groups had been experimenting since the 1930s with using animal dung to generate biogas. The idea had been fairly well known before that time. There are reports of a sewage gas plant built in Bombay in 1859 and the idea was brought to the UK in 1895, when the gas produced was used to light street lamps. The 1970s oil price-hike encouraged both the Chinese and Indian governments to invest in programmes to spread the technology into rural areas. The second hike encouraged greater emphasis on biogas in India and China; it also encouraged governments to start programmes in many other countries across the world, particularly in the USA, the UK and in mainland Europe.

The rapid drop in oil prices in the mid-1980s meant that many biogas programmes faltered. Those in the USA, Europe and many other places were abandoned. In China and India, biogas technology was seen as a way of offering development to rural farmers, encouraging them to stay on the land rather than moving to the cities. These programmes therefore grew slowly but steadily from their initial foundations, which allowed a large amount of expertise and experience to be built up. The Chinese government, in particular, has been keen to share its expertise with other countries, including African nations. Various groups in Germany, especially Bremen Overseas Research and Development Association (BORDA) and German Appropriate Technology Exchange or Deutsches Zentrum fur Entwicklungstechnologien (GATE) worked to spread information about these technologies in other parts of the world (Kossmann et al., 1999; Sasse et al., 1991).

The growing concern about the effects of climate change, combined with concerns about 'peak oil', since the early 1990s has triggered a new interest in biogas technology. The launch of the United Nations Framework Convention on Climate Change in 1994 (UN, 1992) and the subsequent Kyoto Protocol (UN, 2008) put pressure on many countries to develop alternatives to fossil fuels. Biogas is seen as an effective way to generate energy from agricultural and food residues that are often consigned as wastes for disposal.

The developed country that has taken most interest in biogas is Germany, based on its experience working in developing countries and also encouraged by the influential Green movement. Other European countries following close behind are Sweden, Denmark, Belgium and Austria. The USA has also developed a small, but steady, programme in biogas technology.

The countries that have built millions of biogas units, such as India and China, have a wealth of expertise that needs to be shared with the rest of the world.

Benefits of biogas technology

Biogas comes from anaerobic digestion, a process that uses naturally occurring microbes to break down food materials into methane and carbon dioxide in the absence of oxygen. The methane is very similar to natural gas, so is an easy-to-use high-grade fuel that can be used for cooking, heating or to run engines to generate shaft power or electricity. The presence of the carbon dioxide does reduce the heating value of the gas, but this does not seriously affect the value of biogas for these applications. However, the presence of carbon dioxide does make it more difficult to store biogas under pressure.

The microbes that break down food materials are similar to those used to compost the same materials. Aerobic composting generates water and carbon dioxide as well as heat. Using an anaerobic (without oxygen) process means the break down proceeds via a different pathway, so that energy is retained in the gas, rather than released as heat. The residue left after the digestion process is good compost, which can be used to enhance soil fertility and structure. The residue also has the huge benefit of having greatly reduced odour. Volatile fatty acids and other breakdown products are the source of the smells from rotting food and dung. Anaerobic microorganisms consume volatile fatty acids, which are the products of the breakdown of food materials by other microorganisms. Since methanogenic microorganisms use these volatile fatty acids to make biogas, they reduce the smell that the other microbes generate.

The microbes (which include both bacteria and archaea) that perform anaerobic digestion exist in the gut of cattle, as they help them digest grass and other plant foods. Most of the early programmes identified animal dung as the main feedstock material for the generation of biogas, because it already contains the right microbes. However, food material that has not been through the gut of an animal can also be used and produces much more biogas per kilogram, because the animal has not extracted a proportion of the food value for its own use.

In traditional farming systems, organic wastes are recycled back to the land, enabling soil fertility and structure to be conserved. The rapid growth in the use of inorganic fertilizer has increased crop yields, but at the cost of weakening soil structure. The centralization of food supply and waste disposal led to valuable organic matter being buried in landfill. This food waste rots in the anaerobic conditions in the landfill and releases methane, which is a potent greenhouse gas. While this gas can be collected and used to provide heat or generate electricity, the organic matter is permanently buried and lost to the topsoil. Biogas technology can be seen as a way of recycling both the energy and the organic matter available in food residues. The most effective systems are on-farm systems, as the compost made from the biogas plant effluent can be used directly on the fields nearby. This is one of the reasons that small-scale on-farm biogas systems have been so successful in China, India and Nepal.

For small-scale on-farm systems, the main use of the gas is for cooking food. In China, India and Nepal, a family can do all its cooking on the gas produced from dung produced by about four cattle or eight pigs (Ashden, 2005a). Biogas systems built for institutions, such as schools and hostels, in Kerala, India, have replaced 50 per cent of the LPG used for cooking with biogas produced from the sewage and food wastes that the institution produces (Ashden, 2007a). Prisons in Rwanda have replaced 50 per cent of the wood needed for cooking by using biogas from the sewage produced by the inmates (Ashden, 2005b). Stoves that burn biogas are fairly easy to design and make. Stoves for LPG or natural gas can be used with biogas, but only if they are properly adapted.

Biogas is a high-grade fuel that can be used in internal combustion engines. In the USA and Europe, the main use of biogas is to run engines to generate electricity. In Germany, Sweden and other countries in Europe, biogas is being cleaned of carbon dioxide, then pressurised and injected into the gas grid. Biogas has also been used to run vehicles and even a small train in Sweden. Since the source of the biogas is plant material that absorbs carbon dioxide from the atmosphere as it grows, the process is seen as carbon neutral. Biogas technology can therefore attract carbon credits and other subsidies that have been designed to encourage the replacement of fossil fuels with renewable sources of energy.

A brief history of biogas technology

The idea that a flammable gas can be generated from the break down of organic materials has been known for several centuries. Various sources (Harris, 2008) quote anecdotal evidence that suggest biogas from rotting wastes was used to heat bath water in Assyria in the 10th century BC. Other sources suggest that marsh gas was conveyed by bamboo pipes in China to provide energy in 400 BC (Hopkins, 2007). Also in China, there has been a history of covered cesspits, where the collection of night soil for compost has a very long tradition.

Various researchers in the past have investigated the flammable gas from rotting vegetation in marshes, although it was Alessandro Volta (Wolfe, 2004) in 1778, who identified this flammable gas as methane using marsh gas from Lake Maggiore. Humphrey Davey, found methane in 'fire-damp' in coal mines in 1815 (Hartley, 1960).

Anaerobic digestion has a strong, but fairly specialist, development history as the most effective way to process sewage. Cesspits, as a way of storing sewage, have been known since Roman times, but these are only useful if they are emptied regularly. As cities grew rapidly, especially in the 1800s, large concentrations of people made for large amounts of sewage, and in 1849 Dr John Snow (Frerichs, 2001) recognised that many diseases, such as typhoid and cholera, were spread through sewage. Attempts were made to install drains to direct the sewage away (Burian et al., 2000) or to collect it in cesspits (Alleman, 1982). Initially, these attempts meant that rivers flowing through urban areas became heavily polluted, but at least the sewage was washed away to the sea. Where there was a concern about the possibility of transfer of infection, cesspits were used to collect and isolate sewage from possible sources of disease.

Various sources (Harris, 2008) suggest that the first anaerobic digester was built at a leper colony in Bombay in 1859. It was probably built as a contained cesspit to prevent the spread of leprosy, but it was discovered that it generated a flammable gas. Research on biogas digestion was started in China in 1880s (Chen et al., 2010). Gas from an anaerobic digester was used to provide gas lights in 1897 at the Ackworth Leper Home Matunga in Bombay (Kansal et al., 1998). In 1907, the gas from this digester was used to run an internal combustion engine (Kurian, 2004). A Frenchman, John Louis Mouras (Cooper, 2001), patented the septic tank, in which the solid material is decomposed by anaerobic digestion. Dr Donald Cameron in Exeter, England built a version of the septic tank in 1895. Biogas was recovered from his 'Monster Septic Tank' and used to fuel street lamps (Enongene, 2003).

As engineers built sewage drainage systems in cities they discovered that the sewage generated biogas in the pipes, which rose to the highest points and blocked the pipes. The system in Sheffield in the UK had this problem, but vents at the highest places generated bad odours. In 1895, Joseph Edmund Webb, a builder from Birmingham, patented a 'sewer gas destructor', which was a gas street light that stayed on continuously to burn the sewage gas (Caldwell, 2008).

A sewage sludge digester was patented by Imhoff in Germany in 1906 (Gikas et al., 2004; Parkin, 1986) and it separated the solid matter as sludge from the liquid wastes and then allowed the solid sludge to anaerobically digest. This was replaced with a two-stage system that used one chamber to separate the sludge from where it was transferred to a second chamber for digestion. In the 1920s, the two-stage sewage-sludge digester was further developed. In 1922, the gas from one such plant in Birmingham was used to power a gas engine that ran the pumps required in the operation of the plant (Hobson and Bousfield, 1981). In the 1920s and 1930s, active research by the Illinois State Water Survey Division in the USA provided a strong basis for the understanding of the different ways of treating sewage including the use of anaerobic digestion (Buswell, 1936, 1930). This work was continued at the University of Illinois.

Cylindrical sludge-digester tanks have been used very widely in Europe and in the USA since then and they generate biogas as the sludge is broken down. In many of these systems, the biogas has routinely been collected and used to heat the digester plant to speed the digestion process. During and after the Second World War, when petroleum was in short supply, electric generators were fitted to some sewage digesters, so that power could be generated using the gas. Some plant engineers ran their vehicles on pressurised gas as well, especially in the UK.

Many of these sewage-gas systems were seen as of peripheral interest until the early 1990s, when renewable energy became politically important. For example, many of the early projects funded by the Non-Fossil Fuel Obligation (NFFO ) scheme in the UK were new sewage-gas-fuelled generators, replacing old systems that had become out of date. The approach to biogas technology in the USA and Europe has been based on large-scale centralized systems, using the experience gained with these sewage systems. In many places, particularly in parts of Europe, aerobic sewage-processing systems have been used in preference to anaerobic systems. However, aerobic systems require energy to run, whereas anaerobic systems generate energy in the form of biogas as they process the sewage.

The history of biogas technology in developing countries has been very different, as the technology has been small scale and geared to the needs of small farmers. The motive has been to replace firewood for cooking with an alternative clean energy source that also produced good compost. The main uptake has been in China, India and Nepal, where the programmes have been very successful and millions of biogas plants have been built.

There is a new interest across the world in the processing of food wastes using anaerobic digestion. As people move into cities from rural areas, food wastes cannot be composted and easily returned to the land. As cities become more developed, the gardens in which animals used to be kept have been built on, so the animals have stopped being available to eat food waste. People tend to add these food wastes to their waste bins, so they become part of the general solid wastes that must be removed and processed by municipal services. The same approach has been adopted by food processing industries, many of which have contracts with municipal services to dispose of their wastes. The general practice has been to put these wastes into landfill. Concern about both gaseous and liquid pollution from landfills has inspired regulators in many countries to impose requirements for the collection and burning off of the methane generated, either in flares, or in engines where energy can be recovered. The regulations are becoming even stricter in many countries prompting many groups to look at anaerobic digestion as a means to process food wastes.