Ibadan, the second largest city in Nigeria, is the center of a large agricultural
region in Oyo State. Since the nineteenth century, fierce intertribal rivalries and
other political unrest have pushed large influxes of refugee and military populations
into the city. This chaotic growth has discouraged the kind of municipal infrastructure
that is taken for granted in the developed world. Soon, however, Ibadan’s power needs,
at least, will get a boost from a relatively simple but extremely effective source
of energy that is increasingly finding favor across Africa: biogas.
Biogas technology, which converts biological waste into energy, is considered by many
experts to be an excellent tool for improving life, livelihoods, and health in the
developing world. Worldwide, about 16 million households use small-scale biogas digesters,
according to Renewables 2005: Global Status Report, a study by the Worldwatch Institute.
The Ibadan plant will be one of the larger biogas installations in Africa, providing
gas to 5,400 families a month at around a quarter the cost of liquefied natural gas.
The Ibadan digester will take advantage of the city’s Bodija Municipal Abattoir, where
nearly two-thirds of the animals in Oyo State are slaughtered, according to a study
in the January 2002 African Journal of Environmental Assessment and Management. The
wastes from the slaughtering process are rinsed into open drains that connect to surface
water; they also percolate into groundwater. About 60% of Ibadanians get water from
hand-dug wells vulnerable to contamination from surface sources, and about 15% have
private wells tapping a deep aquifer, according to Tijani Moshood, a geologist at
the University of Ibadan.
Abattoir waste carries high levels of microorganisms that cause disease in humans
and animals, such as Salmonella and Escherichia coli bacteria, Rift Valley fever virus,
and parasites that cause toxoplasmosis and trichinellosis. Pesticides, antibiotics,
metals, industrial chemicals, and the agents responsible for bovine spongi-form encephalopathy
(BSE) may also enter the human food chain at an abattoir if they are present in the
animals. Furthermore, decomposing organic material releases methane and carbon dioxide
(CO2). CO2 is a primary culprit in climate change, but methane is even worse—23 times
more potent than CO2, according to the Intergovernmental Panel on Climate Change report
Climate Change 2001: The Scientific Basis.
Fortunately for the people of Ibadan, the new plant should mitigate many of these
hazards. The project, dubbed Cows-to-Kilowatts, is a joint venture among the Nigerian
branch of the Global Network for Environment and Economic Development Research, a
nongovernmental organization (NGO); the Biogas Technology Research Centre of King
Mongkut’s University of Technology in Thonburi, Thailand; the Centre for Youth, Family
and the Law, a Nigerian NGO; and the Sustainable Ibadan Project, which is part of
UN-HABITAT. Cows-to-Kilowatts was a 2005 winner of the Supporting Entrepreneurs for
Environment & Development (SEED) Awards, which honor outstanding new entrepreneurial
ideas for sustainable development worldwide.
Joseph Adelegan, a civil engineer and project director for Cows-to-Kilowatts, estimates
the project will cost around US$300,000. Startup funds have been procured, and construction
of the new plant is expected to begin by July 2006. The Ibadan system will employ
a sophisticated design known as an anaerobic fixed-film digester, in which the active
microorganisms are attached to an inert medium. The fixed-film technique shortens
the time it takes for complete digestion, which enables the digester to be more compact.
Nuts and Bolts
Biogas is one of many biomass energy sources, which include anything that was once
alive and that can generate energy (except for fossil fuels, which are not renewable).
In addition to direct use of wood and charcoal, biomass energy sources include ethanol
and biodiesel. But these forms require considerably more investment, advanced technology,
and/or resources than basic biodigesters provide. Ethanol, for example, requires advanced
technology, whereas biodiesel, although relatively easy to produce, requires the availability
of plant oil. Biogas technology simply formalizes the natural decomposition process.
A biogas digester consists of one or more airtight reservoirs into which a suitable
feedstock—cow dung, human waste, abattoir waste—is placed, either in batches or by
continuous feed. Small-scale digesters for household use are commonly made of concrete,
bricks, metal, fiberglass, or plastic. Larger commercial biogas digesters are made
mainly of bricks, mortar, and steel.
Digestion is accomplished in two general stages. First, acidogenic bacteria turn biomass
into volatile fatty acids and acetic acid. Then methanogenic bacteria metabolize these
compounds into a combination of methane-rich gas and an odorless phosphorus- and nitrogen-laden
slurry, which makes excellent fertilizer. Depending on temperature and moisture content,
it takes about 6–25 days to fully process a batch, according to a fact sheet from
WASTE, a development NGO based in the Netherlands. Simpler digesters may take longer.
The end product is about 60–70% methane and 20–30% CO2, with small amounts of hydrogen
sulfide and other impurities. The gas can be connected to a household stove for cooking,
to a light fixture with a gauze mantle for lighting, or to other appliances with simple
natural gas plumbing; it burns like liquefied petroleum gas. Depending on the design
and size, prices for small-scale biodigesters run from US$100 to US$1,700.
It takes 1–2 cows, 5–8 pigs, or 4 adult humans to supply adequate daily feedstock
for a single-household biodigester, according to a UNDP–Global Environment Facility
fact sheet. The daily input of dung and urine from a single cow produces 1–2 kilowatt-hours
of electricity or 8–9 kilowatt-hours of heat. Over a year, this is just about enough
to run a refrigerator. In most African applications, a household biogas installation
provides sufficient energy for cooking and some lighting.
The Environmental Health Payoff
Properly designed and used, a biogas digester mitigates a wide spectrum of environmental
undesirables: it improves sanitation; it reduces greenhouse gas emissions; it reduces
demand for wood and charcoal for cooking, and therefore helps preserve forested areas
and natural vegetation; and it provides a high-quality organic fertilizer. A well-maintained
digester can last over 20 years and will pay for itself in one-fifth that time. But
for the developing world, biogas’s greatest benefit may be that it can help alleviate
a very serious health problem: poor indoor air quality.
Some 2 billion people around the world, including 89% of the sub-Saharan African population,
use biomass for cooking and heating, according to Energy for Development: The Potential
Role of Renewable Energy in Meeting the Millennium Development Goals, a report stemming
from a 2004 conference of the same name organized by the Dutch government. Where combustible
biomass is the chief energy source, life often revolves around an indoor cookstove
or open fire that likely has no vent to the outdoors. Just gathering the fuel takes
several hours a day—work that, in sub-Saharan Africa, is done almost entirely by women
and children, according to Energy for Development. Since women also do most of the
housework, including cooking, they and their children are exposed to cookstove smoke
far more than men.
Their respiratory health suffers accordingly. In 2000, burning solid fuels caused
1–2 million deaths, comprising 3–4% of total global mortality, according to Renewables
2005. Indoor air pollution such as that stemming from biomass burning may increase
the risk of acute lower respiratory infections in children, chronic obstructive pulmonary
disease in adults, tuberculosis, low birth weight, asthma, ear infections, and even
cataracts, according to the 2002 WHO report Addressing the Links between Indoor Air
Pollution, Household Energy and Human Health. The Global Health Council, an international
group of health care professionals and organizations based in Washington, DC, states
that of all infectious diseases worldwide, those in the lower respiratory tract are
the leading cause of death.
Clearly, biogas—being free of smoke—offers dramatic improvement of this particular
health problem. Even so, concerns among potential users about other health risks of
biogas generation have impeded more widespread adoption of the technology.
The Question of Sanitation
A biogas digester can function well on human and animal waste. A quantity of liquid
also is necessary; usually water is used, but urine works, too. Different kinds of
waste can be mixed, although the cellulose and lignins in plant waste resist decomposition
and may cause problems in the digester.
Some potential users are thus reluctant to try the digesters out of concern about
sanitation, according to Dhananjay Kunte, a researcher in the Department of Internal
Medicine at Evanston Northwestern Healthcare in Illinois, who has conducted several
biogas pathogen reduction experiments funded by the government of India. In the developing
world, this is no small worry. According to the Global Health Council, almost 40%
of deaths in Africa are due to diarrheal diseases; the figure is even higher in Southeast
Asia.
There is no question that human and animal waste is loaded with pathogens—Salmonella,
E. coli O157:H7, Campylobacter jejuni, Yersinia enterocolitica, Giardia lamblia, and
several types of Cryptosporidium, among others. Most of these pathogens are transmitted
via the oral–fecal route and can cause diarrhea, abdominal cramps, dehydration, fever,
vomiting, and—in vulnerable populations such as infants, children, the elderly, and
immunocompromised persons—death. Even though the biodigestion process naturally reduces
the pathogen load, handling biogas feedstock and using biogas slurry as fertilizer
does carry some risk of infection.
It is not entirely clear whether digester slurry can still harbor enough pathogens
to infect humans who handle it or eat crops fertilized with it. In several experiments
using human waste as a feedstock, Kunte studied Salmonella, Shigella, and Vibrio cholerae,
pathogens common in India that produce symptoms similar to those cited above. Kunte
found that separating the overall digestion process into discrete acidifying and methanogenic
stages—thereby isolating the acidogenic bacteria in their own tank—resulted in complete
eradication of live pathogens. (Biodigesters probably can not break down the prions
that cause BSE, although this is not known to have been tested. However, the risk
of BSE is probably low in Africa because most cattle there are free-ranging and not
fed cattle parts.)
Greg Austin, director of AGAMA Energy, a Cape Town, South Africa–based alternative
energy company, says that once people see a digester in action and are trained in
proper hygiene, such as washing their hands while working with it, they realize that
health risks associated with operating a biodigester are relatively minor. Austin
himself has installed a number of biogas systems in rural areas.
Attitudes and Applications
Beyond concerns about sanitation, successful adoption of biogas in the developing
world is highly dependent on political, economic, logistical, and social factors.
Again, a key to successful adoption of biogas technology appears to be direct observation
and experience. “The problem for anaerobic digester technology is that it is seen
as complicated, but it really can be very simple,” says Paul Harris, an agricultural
engineer at the University of Adelaide in Australia. “And because it is seen as complicated,
it is regarded as hard and expensive, but many thousands of rural units worldwide
show that this is not true.”
In 1982 Tanzania started distributing concrete-and-steel digesters that cost about
US$1,400; by 1991 there were only 200 functioning biogas units in the country, according
to an article by Innocent Rutamu in the July 1999 issue of Livestock Research for
Rural Development. Rutamu, a development officer with the Tanga Dairy Development
Programme in Tanzania, was testing a plastic unit that cost only US$50. He surveyed
72 farmers in the Tanga region and found that about half had heard of producing biogas
from cow dung, but none were already using a digester. Three-quarters thought digesters
would be expensive, but most of them could easily pay half the estimated construction
cost of $50. Nearly all looked forward to not having to gather wood in the rainy season
and no longer risking injury from snakes and thorns during firewood collection. Rutamu’s
team distributed and installed 46 of the plastic digesters in several villages. After
the digesters had been running for five months, respondents said they were doing an
average of five fewer hours of housework per day.
Somewhat larger-scale biogas plants also operate successfully in a number of African
locations. Biodigesters in five of Rwanda’s largest jails provide more than half of
the prison kitchens’ energy, according to a 30 June 2005 BBC report. And a 30 November
2005 article in the Rwandan newspaper The New Times states that the Institute for
Scientific Research and Technology in Kigali plans to install some 1,500 biogas digesters
by 2009 in the imidugudu settlements, villages where rural Rwandans were relocated
after the genocidal wars of the mid-1990s.
Other regions, too, have seen a reasonable amount of adoption, says Harris. Nepal
celebrated the construction of its ten-thousandth unit a few years ago, and there
are thousands of polyethylene digesters operating in Vietnam, as well as a huge number
of Chinese and Indian gobar gas units.
In regions where there is already a mature electrical grid, there is limited incentive
to use simple biogas digesters because they are not easily scaled up to produce energy
comparable to hydropower and coal. Likewise, large farms and dairy operations need
appropriately scaled treatments for the mountains of dung and waste their animals
and crops generate. In developed markets, energy companies are seeking to convert
100% of biomass to energy, says Mark Kendall, an energy specialist in the renewable
resource division of the Oregon Department of Energy. Using biogas alone has an energy
conversion efficiency (the proportion of energy produced to that consumed) of about
10% or less, according to Solid Waste Conversion: A Review and Database of Current
and Emerging Technologies, a 2003 report by the University of California, Davis, Department
of Biological and Agricultural Engineering. By comparison, nonrenewable natural gas
has an energy conversion efficiency of 55%. Austin counters, however, that this figure
depends on conversion technology and energy type (for example, thermal or electrical).
When used in a combined heat and power configuration, he says biodigester efficiency
can approach 88%.
Still, with its sulfur compounds and other impurities, biogas is too dirty to feed
directly into natural gas systems driving motors or to be used as transport fuel in
place of gasoline. And in many African countries, bottled liquefied petroleum gas
is used rather than natural gas due to lack of both infrastructure and large markets
to justify investment in piped gas supply systems. Biogas is not easily bottled and
thus must be used near its sources.
The Bright Side
Basic biogas technology is therefore probably limited to places like sub-Saharan Africa—but
in those places, it can make a big difference. In those environments, says Austin,
the cost per unit of energy over a digester’s 15- to 20-year life cycle is lower than
both solar electrification and the cost of extending a conventional electrical grid.
There is plenty of scope for biogas technology to expand in Africa. An AGAMA Energy
fact sheet estimates that in South Africa there are 400,000 households with two or
more cows and no electricity that could make use of biogas digesters. The fact sheet
further notes that 45% of schools in South Africa have no electricity, 66% have poor
sanitation facilities, 27% have no clean water, and 12% have no sanitation at all.
Biogas installations could help mitigate all of these problems.
According to Renewables 2005, global energy demand nearly doubled between 1971 and
2002. Whether developed or developing, nations are caught between a rising population
generating massive amounts of waste and the impending arrival of hard limits to nonrenewable
energy sources. The need for clean, renewable energy is especially acute in the developing
world, where few efficiencies have been introduced. In this context, biogas technology
is a very good solution to local energy needs, and provides significant benefits to
human and ecosystem health. Further expansion of biogas solutions via relatively inexpensive
policy initiatives and the development of new technology combinations offers one very
bright spot in the diminishing constellation of energy choices, wherever in the world
they must be made.