Biogas: A Bright Idea for Africa 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 spongiform 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.
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From abattoir to energy. A
biodigester converts slaughterhouse
waste into energy and solves two environmental
problems--unhealthy waste and
a need for power--at once.
images (top to bottom): Sam Roberts/iStockphoto; SEED Initiative |
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.
Valerie J. Brown
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