India's low-tech energy success.
Cow dung may not be the first thing that comes to mind when you think of state-of-the-art energy technology. Yet in the tiny village of Pura in south India, this humble waste material is providing people with basic amenities formerly in short supply: electric light, pumped water, and clean cooking fuel. An ingeniously simple process that converts dung into a flammable gas, called biogas, has greatly improved daily life for Pura's 485 inhabitants - and for over 10 million other rural Indians.
Biogas, as its name suggests, is produced by extracting chemical energy from organic materials. This process takes place in a sealed container known as a biogas digester. The digester is usually a squat, cement cylinder two to four meters in diameter, with a duct in the side that allows the dung or other organic wastes to be fed in, along with water. In ambient temperatures of 25 to 35 degrees centigrade, the material soon begins to ferment. This produces a mixture of gases, primarily methane and carbon dioxide, and a nutrient-rich slurry. The gas is drawn out through a valve at the top of the digester, and the slurry is drained off into settling troughs at its base. [ILLUSTRATION OMITTED].
Methane is the combustible component of biogas. It is piped into homes to be used as a cooking fuel, or used to fire a diesel engine to generate electricity, as in the case of Pura. The slurry is such an excellent fertilizer that it's often more highly valued than the gas - biogas plants are often called "biofertilizer plants."
Biogas dates as far back as the 16th century, when it was used for heating bath-water in Persia, and it has been used in India for almost a hundred years. In 1981, however, the Indian government launched biogas production on a large scale, by embarking on a "National Project on Biogas Development." Close to 2 million digesters have been constructed in India since then, and although the program has had its share of problems, it has made substantial progress. Most plants are located in rural, agrarian parts of the country and are designed to serve the cooking needs of a single household of four to seven people. Over 1,150 large "community" plants - like the one in Pura - have also been installed. These are operated by an entire village, and the cooking fuel or electricity is shared by the community.
Ostensibly 84 percent of Indian villages are connected to the electrical grid, but only 27 percent of their inhabitants actually had access to power in 1991, according to R.K. Pachauri of the Tata Energy Research Institute in New Delhi. That means 435 million people, more than half of India's population, lack electricity. And 80 percent of rural India faces difficulties in obtaining sufficient cooking fuel. Biogas bypasses these shortages and transmission problems by providing a decentralized and locally-controlled fuel supply from a readily available material.
Generating biogas also makes sense in the Indian cultural context. All products of the cow, including dung (or "gobar" in Hindi) are considered purifying agents by Hindus, according to O.P. Joshi, a sociologist at the H.C. Mathur Institute of Public Administration in Rajasthan. In the classical Indian epic, the Mahabharata, says Joshi, "gobar is described as the living place of Lakshmi, the goddess of wealth." Traditionally in India, dung is collected and fashioned into dung-cakes, to be burned directly as fuel or composted for fertilizer. Dung accounts for over 21 percent of total rural energy use in India, and as much as 40 percent in certain states.
Usually, dung used for one purpose is lost to the other, but biogas provides a means to both ends. It exploits the caloric content of the waste, while retaining the nutrients as fertilizer - and on both counts, it is more efficient than traditional methods. Direct burning only captures about 11 percent of the dung's energy value, but biogas generation has a 45 to 60 percent efficiency. In other words, biogas captures approximately 5 times as much energy as does direct burning. And the by-product slurry has twice the nitrogen content of composted dung because open-air composting allows much of the nitrogen to escape in the form of volatile compounds. The slurry also releases its nutrients more readily than composted dung. And unlike decomposing dung, it is odorless and does not attract flies or mosquitoes. Farmers in Pura say it actually repels termites, and inhibits weed growth.
In addition to the slurry's nutrient recycling function, the gas itself has important environmental benefits. It offers an ecologically sustainable alternative to fuel wood, which currently provides over half of India's rural household energy. Biogas can help check deforestation; in the 1980s, for instance, when biogas technology was introduced into villages near the Gir Lion Sanctuary in Gujarat, woodcutting within the Sanctuary dropped substantially. And since the conversion process in the digester is anaerobic (it occurs in the absence of oxygen), it destroys most of the pathogens present in dung and waste, thereby reducing the potential for infections like dysentery and enteritis.
The burning of traditional fuels like dung cakes or wood releases high levels of carbon monoxide, suspended particulates, hydrocarbons, and often, contaminants like sulfur oxides. (Dung contains traces of hydrogen sulfide, which is converted to sulfur oxides on combustion.) Exposure to these fumes in unvented cooking spaces increases the risk of respiratory disease. According to a study sponsored by the World Health Organization, Indian women cooking over firewood were inhaling as much of the carcinogen benzopyrene - a combustion by-product of wood - as they would by smoking 20 packs of cigarettes a day. Because it is a gas, biogas burns much more efficiently than these solid fuels. It leaves very few contaminants, although it is true that biogas releases small quantities of sulfur oxides. Biogas offers perhaps the most environmentally benign method for tapping the solar energy stored in bio-mass. It's a renewable and decentralized alternative to the other methane-based fuel, natural gas, which is commonly used in cities.
THE ECONOMICS OF SELF-SUFFICIENCY
But biogas is more than just a renewable energy technology. As a comprehensive rural development tool, it allows villages to meet fundamental needs using local resources. It is a labor-intensive technology, and therefore a significant source of employment, especially for village women who collect the dung and sell the slurry, and for the rural laborers who construct and maintain the plants. Some family biogas digesters even support small-scale enterprises, by providing electricity for agricultural and cottage industries. Community digesters encourage collective responsibility and local participation in decision-making. The role that women play in the operation enhances their social standing. Biogas also helps ease the traditional burdens of women and girls, by reducing the amount of time they have to spend collecting fuel-wood. And with the advent of biogas-powered pumps, it also reduces the time spent fetching water.
A biogas digester with a 2 cubic meter capacity - enough to meet the cooking needs of a family of five - costs approximately $350. The costs of inputs are minimal assuming the household has a water supply and at least five cows - the minimum necessary to supply the digester. Yet despite government subsidies that run as high as 85 percent of total costs, start-up expenses can seem formidable to farmers, whose participation in the cash economy is often limited.
FINDING A STRATEGY THAT WORKS
India's biogas plants are generally sound investments, particularly the community digesters, which can achieve greater economies of scale. Yet the biogas program has not yet taken off as some experts expected it to. According to the Tata Institute's Pachauri, only two-thirds of the installed plants are actually functioning (although official figures have placed this figure at 89 percent), and the project is now faced with major funding cuts. Given the technical simplicity and the many advantages of biogas production, what went wrong?
Biogas production is limited by environmental conditions such as the need for warm temperatures and availability of water and dung. In cooler or drought-prone regions, or in villages with insufficient cattle, projects have failed. These and other problems relating to construction and maintenance have been compounded by institutional factors that obstruct most renewable energy projects. As an essentially decentralized energy strategy, biogas has suffered from a far too centralized and top-down planning approach. Across-the-board implementation policies have led to the construction of plants in areas unsuited to biogas production; plants that suffered from technical difficulties were abandoned when project technicians failed to follow up. And although the government introduced many financial incentives such as subsidies and tax benefits to encourage biogas use, conventional fuels like diesel, kerosene and LPG are also highly subsidized in rural areas, so there is little incentive to make the switch.
TAPPING INTO THE POTENTIAL
Restructuring rural energy subsidies, and bringing the planning down to the local level, would unlock an enormous energy potential. India has more cattle than any other country - 262 million head. (It is possible that this immense herd may eventually prove unsustainable, but for the present at least, rural India needs its cows. They do much of the plowing and transporting that is done by tractors and trucks in other parts of the world.) Given the amount of dung available, it has been estimated that biogas could provide cooking fuel to 52 percent of the Indian population during the part of the year when conditions are optimum, and for 25 percent of the population during the lean season, when dung production, water supply, and temperatures are low. According to Amulya Reddy of the International Energy Initiative in Bangalore, harnessing this total potential would conserve some 130 million tons of wood. In theory, that amount of wood could yield enough liquid or gaseous fuel to power every truck, bus, and irrigation pump in the country.
Many other developing nations, primarily in Asia but also in Africa and Latin America, have implemented biogas programs. The Chinese program is the largest. In 1991, it had 5 million digesters; these use human waste as well as animal dung. The United States and several western European countries are interested in the biogas potential of other sources of organic waste, mainly municipal solid waste. It's too early to say how much power this approach will eventually yield, but over the next few years, a number of large U.S. and European biogas plants are scheduled to go online.
The goal of India's biogas program is to construct digesters for the 12 million rural Indian households that have enough cattle to maintain a regular supply of dung. Depending on family size, this would mean a regular supply of fuel for 60 to 85 million people. In a largely agrarian nation where rural electrification is limited and commercial fuels make up only 11 percent of rural energy use, biogas could go a long way toward improving the energy and environmental future. And given the broad availability of dung, crop residues, and other organic wastes, biogas could do the same elsewhere. Along with other renewable technologies like photovoltaics, biogas could help form the foundations of a decentralized energy strategy in many developing countries.
Payal Sampat was a research intern at the Worldwatch Institute and is currently studying international environmental policy at Tufts University.
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|Date:||Nov 1, 1995|
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