In this Project Report, an analysis of biogas technology as a very viable replacement for fossil fuel used in a farm is presented. Biogas (70% CH4 and 30% CO2) which is a clean, economical, environmentally compatible and renewable form of energy could very well substitute (especially in the agricultural applications) for conventional sources of energy (fossil fuels, oil, etc) which cost farms huge sums of money per month, causing ecological–environmental problems and at the same time being depleted at a high rate. Despite its numerous known advantages, the potential of biogas technology has not been fully harnessed or tapped, as certain constraints are also associated with it. Most common among these is low gas production in cold weather. The study was undertaken by using a triangulation method consisting of literature review, background research/case studies and direct interviews. This paper reviews the techniques that could be used to enhance the gas production rate from solid substrates. Mathematical computations have been made to optimize different analysis, namely; organic waste generating capacity, suitable volume of digester, energy requirements/needs of the farm, available energy sources to the farm and its biogas generating potentials. The design criteria for thermal heating of an active, fixed-dome type biogas plant, with emphasis on thermal efficiency, are presented. The economic analysis takes into account, capital and maintenance costs, life of the plant, as well as priced and unpriced benefits of owning a biogas plant. The benefit – cost ratio, internal rate of returns and net present values of the investment are also computed to establish the viability of the proposed biogas project.
TABLE OF CONTENTS
Title Page – – – – – – – – – – i
Certification – – – – – – – – – – ii
Dedication – – – – – – – – – – iii
Acknowledgement – – – – – – – – – iv
Table of Contents – – – – – – – – v
List of Tables – – – – – – – – – viii
List of Figures – – – – – – – – – x
Abstract – – – – – – – – – – xiv
CHAPTER ONE: INTRODUCTION – – – – – 1
1.1 Non-renewable energy sources – – – – – 1
- Primary and secondary energy sources – – – – 2
- Available non-renewable energy sources – – – – 2
- Non-renewable energy and their advantages – – – 4
- Non-renewable energy and their liabilities – – – – 4
1.2 Renewable energy resources – – – – – – 5
1.2.1 Solar energy – – – – – – – – 6
1.2.2 Wind energy – – – – – – – – 9
1.2.3 Geothermal energy – – – – – – – 10
1.2.4 Hydropower – – – – – – – – – 10
1.2.5 Ocean energy – – – – – – – – 11
1.2.6 Wave energy – – – – – – – – 11
184.108.40.206 Tidal energy – – – – – – – – 11
220.127.116.11 Ocean thermal energy conversion – – – – – 12
1.2.7 Hydrogen energy – – – – – – – – 12
1.2.8 Biomass energy – – – – – – – – 13
1.2.9 Bio-fuels – – – – – – – – – 19
18.104.22.168 Current Bio-fuels used as energy sources – – – – 20
1.3 Biogas – – – – – – – – – – 23
1.3.1 Mechanisms of biogas production – – – – – 25
- Environmental requirements for anaerobic digestion – – – 28
1.4 Biogas plants in integrated farms – – – – – 29
1.4.1 Biogas Application in integrated farms – – – – – 29
1.5 Solar heating biogas plant – – – – – – 35
1.6 Environmental impact – – – – – – – 36
1.7 Methodology – – – – – – – – – 37
1.8 Update of Biogas technology in some countries – – – – 38
CHAPTER TWO: DESCRIPTION OF THE CASE STUDY FARM – – 40
2.1 Description of the case study farms – – – – – 40
2.1.1 Accommodation/Offices – – – – – – – 40
2.1.2 Growth level of farms – – – – – – – 40
2.1.3 Farm implements and facilities – – – – – – 41
2.1.4 Farm power – – – – – – – – – 41
CHAPTER THREE: ANALYSIS OF A BIOGAS PLANT FOR
THE CASE STUDY FARM – – – – – 43
3.1 Technical Analysis of the Biogas plant – – – – – 43
3.1.1 Analysis of the energy requirement of the Farm – – – 43
3.1.2 Analysis of organic waste generation of the farm – – – 45
- Design of the proposed biogas plant – – – – – 47
3.1.4 Volume calculation of the digester and hydraulic Chamber – 56
3.1.5 Thermal analysis – – – – – – – 59
- Analysis of biogas generation prospects of the
Farm with its energy requirements – – – – – 62
3.2 Economic Feasibility – – – – – – – – 63
3.2.1 Introduction – – – – – – – – – 63
3.2.2 Financial analysis – – – – – – – – 63
3.2.3 Project life – – – – – – – – – 64
3.2.4 Benefits and cost – – – – – – – – 65
3.2.5 Cash flow Analysis – – – – – – – 69
3.2.6 Time Value of Money and Discount Rate – – – – 70
3.2.7 Net present value (N P V) – – – – – – 70
3.2.8 Internal Rate of Returns (I R R) – – – – – 71
3.2.9 Benefit-Cost ratio – – – – – – – – 72
3.3 Economic Analysis – – – – – – – 75
3.3.1 Economic valuation of firewood – – – – – 76
3.3.2 Economic valuation of Kerosene, PMS, and Diesel – – 76
3.3.3 Economic valuation of labor – – – – – – 76
3.3.4 Valuation of slurry – – – – – – – 77
3.3.5 Investment cost – – – – – – – – 77
CHAPTER FOUR: RESULTS AND DISCUSSION – – – – 78
- Parameters and Values used in the Analysis – – – 78
- Energy Audit of the Farm – – – – – – – 80
- Volume calculation of digester and hydraulic chambers – – 81
- Volume of digester – – – – – – – 81
- Hydraulic chamber – – – – – – – 81
- Area and Dimension of digester – – – – – 81
- Variation of volume of biogas with percentage total solid
Concentration – – – – – – – – 83
- Variation of digester volume with substrate at HRT of
40 days – – – – – – – – – 85
- Variation of digester volume with HRT at substrate value of
13,625kg – – – – – – – – – 86
- Comparison of biogas generation prospects of the Farm with its
Energy requirements – – – – – – – 88
- Thermal Analysis – – – – – – – – 89
- Financial Analysis – – – – – – – – 89
- Cost distribution of 681.3 m3 biogas plant – – – – 91
CHAPTER FIVE: CONCLUSION – – – – – – 93
REFERENCES – – – – – – – – – 96
The energy crisis in the early 70’s caused economic problems for many countries that depend on imported oil and gas. The exploitation of new energy sources and the adoption of new energy conversion technologies became necessary towards reduction of enormous organic waste generated especially in the integrated farms and providing an alternative, environment friendly and cheap source of renewable energy for such farms. Huge quantities of organic waste running into several hundreds of tons are generated in integrated farms each year. At the same time, these farms spent huge sums of money on electricity bills, operating private power generating plants, fuel wood, kerosene, etc. to meet their energy needs.
Biogas (also called “Marsh gas”), a by-product of anaerobic decomposition of organic waste has been considered as an alternative source of energy. Williams (2005) noted that the common raw materials for biogas generation are often defined as “waste materials”, e.g. animal manure, sewage sludge and vegetable crop residues, all of which are rich in nutrients suitable for the growth of anaerobic bacteria.
In order to fully appreciate biogas production from organic waste as an alternative source of energy, it is necessary to understand the sources of energy in general
1.1 NON-RENEWABLE ENERGY SOURCES
A non-renewable energy source is one that is depleted once it is used. It is finite in quantity and runs out over time; examples include, fossil fuels – oil, coal and natural gas.
Because of the energy crisis that rocked some countries, attention has been gradually shifted from fossil fuels. The developments of new techniques that will tap into renewable energy sources to produce biofuels are in progress.
Non-renewable energy sources as earlier mentioned, refers to those energy resources of which only fixed amount is available on earth. As these resources are used, the total quantity available diminishes, and a time may come when the resources are either exhausted or cannot be economically exploited further. Typical examples are fossil fuels and nuclear fuels.
- Fossil fuels are those fuels which were formed by the fossilization of the remains of plants and animal materials, through the application of heat and pressure over long periods, the materials were transformed into solid, liquid or gaseous materials containing large proportions of combustible matter. Examples of solid fossil fuels are coal, lignite and anthracite, while an example of liquid fossil fuels is crude oil. Fossil fuel in form of gas is usually called natural gas.
- Nuclear fuels are such natural or artificial materials that may undergo sustainable nuclear reactions with the release of energy. The most important nuclear fuels are Uranium and Thorium, which can undergo fission reactions.
- PRIMARY AND SECONDARY ENERGY SOURCES
Energy sources may also be classified into primary and secondary forms. The primary forms include all the non-renewable and renewable resources, and they are considered primary in that they are available naturally. Secondary resources are derived from the primary forms by applying suitable conversion technologies. Typical examples are electricity and heat.
1.1.2 AVAILABLE NON-RENEWABLE ENERGY SOURCES
Nigeria has a land area of over 0.9million square kilometers and the robust multi-ethnic population of about 140million. She is endowed with extensive and varied reserves of primary energy resource, including petroleum, natural gas, coal, lignite, tar-sands, shale oil and uranium.This is shown in table 1.1
Table1.1 SUMMARY OF ESTIMATED NON-RENEWABLE ENERGY RESERVES IN NIGERIA
|Energy Reserves||Units||Estimated Reserves|
|Natural gas||109 tonnes||4670|
|Tar-sand||106 tonnes of oil equivalent.||4270|
Sources: Enibe (1998).
The world has a land area of over 100 million square kilometers and a population of about 6 billion people Gustavsson (2000). The world is endowed with varied reserves of non-renewable energy sources, including crude oil, natural gas, coal and lignite, tar-sands, uranium and thorium.
Table 1.2 shows the availability of non-renewable energy sources in the world.
Table1.2: SUMMARY OF ESTIMATED NON-RENEWABLE ENERGY RESERVES IN THE WORLD
|Energy Resources||Nigeria (2003)||World|
|Crude oil||33 billion bbl||1, 067.2 billion bbl (2002)|
|Natural gas||159 Trillion scf||6, 280 trillion scf (2002)|
|Coal and lignite||2.7 billion tones||1,106 billion tonnes+|
|Tar-sands||31 billion bbl oil equivalent||100-300 billion bbl oil equivalent (1970)|
|Uranium||NA||20 million tons|
|Thorium||NA||1 million ton.|
bbl = barrel source: Iloeje, (2004)
scf = Standard cubic feet
+ = Recoverable
NA = Not recoverable
Forty years from now, oil reserves will be totally utilized in Nigeria with the present reserve. But more research is going on for more oil reserves over the country.
1.1.3 NON-RENEWABLE ENERGY AND THEIR ADVANTAGES
Fossil fuel accounts for 91% of electricity generation in Australia. In the UK, EC, and US, percentage of fossil fuel used in electricity generation is 74.96%, 71.61%, and 55.88% respectively, Eastop and McKonkey (1999)
In the world, electricity generation from fossil fuel is 63%. What a highly dependable source of energy! Other advantages include:
- They possess concentrated energy.
- They are relatively light for the amount of energy contained in them.
- They can be transported easily.
- They are storable.
- Fossil fuels retain their properties even after long storage periods.
- They possess high energy content per unit mass
- NON-RENEWABLE ENERGY AND THEIR LIABILITIES
Presently, most (about 80%) of the world energy demand is met by the fossil fuels The energy story (2007). However, according to reliable estimates, production of fossil fuel is soon to start decreasing. According to Hubbert (1985), the world petroleum production will peak sometime between the years 1990 and 2000, and will then start to decline – as cited in Furlan, Rodriquez and Violini (1982). It can be seen that the world fuel production will reach its peak around the year 2010, and then will start decreasing; Furlan, Rodriquez and Violini (1982).
- Fossil fuels are depleting fast without replenishment.
- An important type of pollution, air pollution is caused mainly by fossil fuels used to obtain energy for transportation, electricity generation, heat, etc. – hence respiratory diseases are increasing and life-span decreasing, The energy story (2007).
- Acid rains are also produced by burning of fossil fuels – killing aquatic lives, etc.
- Huge volumes of CO2 and other related gases are produced – leading to global warming and green house effects, The energy story (2007).
- Fossil fuels are not distributed evenly among the countries or regions of the world – causing International problems/conflicts between suppliers and consuming nations.
- Fossil fuels are not renewable
- They are environmentally degrading – unfriendly.
- Fossil fuels also contain radioactive materials, mainly Uranium and Thorium that are released into the atmosphere. In 2000, about 12, 000 metric tons of thorium and 5000 metric tons of uranium were released worldwide from burning coal The energy story (2007). In 1982, US coal burning released 155 times as much radioactivity into the atmosphere as the Three Mile Island Coal burning generates fly ash and bottom ash The energy story (2007).
Tapping, processing, and distributing fossil fuels can create environmental problems. Coal mining and oil drilling methods e.g. mountain top removed and strip mining, and offshore oil drilling create hazard for terrestrial and aquatic organisms respectively.
In the US, more than 90% of greenhouse gas emissions come from burning fossil fuels The energy story (2007).
- RENEWABLE ENERGY RESOURCES
A renewable energy resource is one that is replaced in a reasonable period of time by natural processes; examples include solar, wind, geothermal, hydro, ocean, wave, tidal and biomass etc.
RENEWABLE ENERGY SOURCES AND THEIR SHORTCOMINGS
Presently, about 21% of the world’s electrical energy demand is met by renewable energy sources and 20% of the world’s energy demand is supplied by renewable energy (Iloeje, 2004) . However, some of its shortcomings are as follows:
- Some renewable energy resources are intermittently available – e.g. solar radiation (day times only). Intensity also varies with time of the day and seasons.
- Some renewable energy resources too far away from the consumption centers, e.g. ocean energy site are only at the equatorial regions of the oceans.
- Wind energy generators cause electromagnetic interference.
- Wind power plants generate noise – hence causing noise pollution.
- Geothermal fluids contain chemicals, which endanger our biological environment.
- Higher geothermal fluid temperatures could be harmful to animal and plant life in the environment – the discharge areas.
- Hydrogen sulphide, carbon dioxide, methane gases, etc. escaping from the geothermal fluid may represent a risk factor.
- The indoor combustion of biomass based fuels (fuel wood) causes chronic diseases such as respiratory infections, ailment of the lungs, bronchitis, asthma, lung cancer, and coronary artery disease.
RENEWABLE ENERGY SOURCES AND THEIR ADVANTAGES
- They are continuously available source of energy.
- They are unlimited in amount.
- They are environmentally compatible.
- They are distributed more evenly around the world than fossil fuels.
Let us briefly examine renewable energy below;
- SOLAR ENERGY
The earth receives energy directly from the sun. Indirectly, the sun or other stars are responsible for all our energy. Solar energy is silent, inexhaustible, and non-polluting. The means of collecting and distributing solar energy is the “collector”, though twice as costly as convectional electricity generation, solar energy is tapped by means of solar collectors – which track the sun’s diurnal motion to ensure a continuous maximum reception of sun rays. Nigeria lies within a high sunshine belt and, within the country solar radiation is fairly well distributed. The annual average of total solar radiation varies from about 12.6 MJ/m2-day (3.5 KWh/ m2-day) in the coastal latitudes to about 25.2 MJ/ m2-day (7.0 KWh/ m2-day) in the far north. This gives an average annual solar energy intensity of1934.5 KWh/m2-yr; thus, over a whole year, an average of 6,372,613 PJ/year (≈1, 770 TWh/year) of solar energy falls on the entire land area of Nigeria. This is about 120 thousand times the total annual average electrical energy generated by the NEPA (Energy Commission of Nigeria – Renewable Energy Master Plan, 2005).
Let us look at ways in which we can use the sun’s energy.
- Solar Water heating: – In the 1890s, solar water heaters were being used all over the US, and in 1897, 30% of homes in Pasadena were equipped with solar water heaters, In 1911, solar water heaters were installed in homes in Pomona valley, California. By 1920, tens of thousands of solar water heaters had been sold, The energy story (2007).
Eastop and McConkey (1999) pointed out that about 50% of the water heating of buildings in the UK is powered by solar water heaters. The solar water heaters along with solar collectors (panels) are usually installed on the roof of buildings. They also heat swimming pools.
- Solar Air Heating: – According to Tiwari (2006), it may be said that the state of the art of solar air heaters has been a technical achievement awaiting commercial exploitation. Solar air heaters are used in space heating and for drying purposes – in buildings.
iii. Solar Crop Drying: – Solar crop dryers have found applications in food processing industries, agricultural farms and food storage. Solar crop drying is a process that uses solar energy to dry the moisture contents in crops for better storage, processing, use, etc.
- Solar Distillation: – Solar distillation of brackish water or saline water is a good method to obtain fresh water. The distillation system uses the direct solar energy to distill brackish waters into fresh drinkable one.
- Solar Thermal Electricity: – Solar energy can also be used to make electricity. Three experimental solar power stations have been erected in Almeria, Spain, one of 1000KW and two of 500KW rating Eastop and McConkey (1999).
In California, solar thermal power plants use solar energy to make electricity for more than 350, 000 homes. Also in California, a central tower power plant called “solar II” make enough electricity to power about 10, 000 homes, Eastop and McConkey (1999).
- Solar Cells or Photovoltaic Energy: – Solar cells change the sunlight directly into electricity. Solar cells electricity can be used directly in homes for lights and appliances. Some experimental cars also use PV cells, which convert sunlight directly into energy to power electric motors on the car.
Other applications of solar energy include:
- Collection – cum – storage water heater
- Non-convective solar pond
- Solar water heating system.
- Heating of swimming pool by solar energy.
- Controlled environment Greenhouse
- Heating of Biogas plant by solar energy.
- Solar cooker
- Solar cooling.
- WIND ENERGY
Wind technology dates back many centuries. The kinetic energy of wind can be changed into other forms of energy, either mechanical energy or electrical energy.
Windmills have been used for many years to drive mill mechanisms. Wind energy is clean, safe and a renewable form of energy. The search for alternative power sources has led to the re-discovery of wind power and many wind-driven power stations, large and small, have been built and are generating power. Wind speeds in Nigeria range from a low 1.4 to 3.0m/s in the southern areas and 4.0 to 5.12m/s in the extreme North. Initial study has shown that total actual exploitable wind energy reserve at 10m height, may vary from 8 MWh/yr in Yola to 51 MWh/yr in the mountain areas of Jos Plateau and it is as high as 97 MWh/yr in Sokoto, (Renewable Energy Master Plan, 2005). Hence, Nigeria falls into the poor/moderate wind regime.
According to The energy story (2007), the first wind-powered electricity plant was built in Ohio in 1888. It had a rated power of 12Kw (dc). In the 1930s, the first large scale AC wind turbine was constructed in the US. Eastop and McConkey (1999) revealed that in Germany, a Growian, near Marne, built in 1982 on the North Sea coast has 3MW output. In Denmark, two 630KW wind power plants were built – near Nibe and were commissioned in 1979 and 1980. In UK, a 20M diameter wind turbine generator (250KW) on Orkney at Burgar Hill, and a 3MW unit with a 60 Inch diameter blade. Still in UK, other companies built machines of 20KW and 60Kw. In 1992, there were 49 projects under way on wind-power generation with a total of 82MW. California alone has wind farms running with a capacity of 1400MW.
As of 1999, there were 11, 368 wind turbines in California. For mechanical power, farmers use wind energy to pump water from wells using windmills. With these, about 11% of the entire world’s wind-generated electricity output is found in California.
In Holland, windmills have been used for centuries to pump water from low-lying areas. Wind energy is also used to turn large grinding stones to grind wheat or corn.
- GEOTHERMAL ENERGY
Geothermal energy has been around for as long as the earth has existed. “Geo” means the earth and “thermal” means heat.
At about 10,000ft below the surface, water sometimes make its way close to the hot rocks and turns into boiling hot water – or steam. The hot water can reach temperatures of more than 300 Fahrenheit (148 degrees Celsius). This is more than boiling water (212 degrees F/100 degrees C). It does not turn into steam because it is not in contact with the air. When this water comes up through a crack in the earth, we call it a hot spring.
For every 100 meters into the ground, temperature increases by 3 oC .
The transformation of the heat content of natural steam to electricity is the best-known form of exploitation of geothermal energy. The most spectacular examples are in Italy, (Larderello) since 1904, the USA (The Geysers), New Zealand (Wairakei), Mexico (Cerro Prieto), Japan and the Philippines. A geothermal plant of 10MW capacity was built in Hawaii in 2004. Geothermal heat buildings uses ground source heat pump.
Geothermal fluids (less than 100oC) are used in plant cultivation and animal husbandry, soil heating in the Soviet Union, Hungary and Iceland. As at 1982, 45,000 apartments in France were heated by natural hot waters.
- HYDRO POWER
Hydroelectric power uses the kinetic energy of moving water to make electricity. Dams can be built across rivers. The river is simply sent through a hydroelectric power plant or powerhouse. Water flow through is made to push against turbine blades, causing them to turn. The turning turbine spins a generator to produce electricity.
In 1998, hydropower accounted for 8.9% of India’s electricity (EIA 1998), as in Jo Lawbuary (2007). Hydropower is one of the largest producers of electricity in the United States. Waterpower supplies about 10% of the entire electricity used in California, about 15% of all electricity comes from hydroelectric. The State of Washington leads US in hydro electricity. About 87% of the electricity made in Washington State is produced by hydroelectric facilities. A 20.4mw H.E power plant was built in Hawaii in 2004.
- OCEAN ENERGY
The world’s ocean provides her population with energy to power farms, homes, and businesses. Currently, there are very few ocean power plants and most are fairly small. There are three basic ways to tap the ocean for its energy – namely; ocean’s waves, high and low tides, and temperature difference in water depth.
- WAVE ENERGY
Kinetic energy (movement) exists in the moving waves of the ocean. That energy is used to power turbine. The wave rises into a chamber. The rising wave forces the air out of the chamber. The moving air spins a turbine, which can turn a generator. When the wave goes down, air flows through the turbine and back into the chamber through doors that are normally closed.
Others actually, use the up and down motion of the wave to power a piston that moves up and down inside a cylinder. That piston turns a generator. Most wave energy plants are small scale.
- TIDAL ENERGY
The use of tidal energy has a long history of at least 900 years the energy story (2007) in the UK – as early as 1806. When tidal waves come into the shore, they can be trapped in reservoirs behind dams. Then when the tides drops, the water behind the dam can be let out just like in a regular hydroelectric power plant.
Tidal energy has been used since about 11th century. Presently, modern tidal power plant exists. There are two; one in Rance estuary in France (544 x 106KWh/annum from twenty four 10MW units) and at Kislaya near Murmansk, Russia (400KW) The energy story (2007). The potential power is very high but so is the capital investment.
- OCEAN THERMAL ENERGY CONVERSION (OTEC)
Using the temperature of water to make energy actually dates back to 1881 – with a French engineer Jacques D’Arsonval, who pioneered this technology.
In ocean, water is warmer on the surface and colder in the deep. Power plants are built that use this temperature difference to produce electricity. A difference of at least 23 oC is needed between the warmer surface and the colder deep ocean water. Using this type of energy source is called “Ocean Thermal Energy Conversion ” or OTEC. It is being demonstrated in Hawaii.
- HYDROGEN ENERGY
Hydrogen is a colorless, odorless gas that accounts for 75% of the entire mass of the universe Eastop and McConkey (1999). It is found on earth only in combination with other elements such as oxygen, carbon and nitrogen. To use hydrogen, it must be separated from these other elements. Hydrogen is used in NASA’s space programme as fuel for the space shuttles, and in fuel cells that provide heat, electricity and drinking water for astronauts The energy story (2007). Fuels cells are devices that directly convert hydrogen into electricity.
In the future, hydrogen could be used to fuel vehicles and aircrafts, and provide power for our homes and offices. Hydrogen as a fuel is high in energy, yet a machine that burns pure hydrogen produces almost zero pollution. NASA has used liquid hydrogen since the 1970s to propel rocket and now, the space shuttle into orbit. Hydrogen fuel cells power the shuttle’s electrical systems, producing a clean by product – pure water, which the crew drinks.
Fuel cells are a promising technology for use as a source of heat and electricity, in buildings, and as an electrical power source for vehicles. Auto companies are working on building cars and trucks that uses fuel cells. In a fuel cell vehicle, an electrochemical device converts hydrogen (stored on board) and oxygen from air into electricity to drive an electric motor and power the vehicle.
In the future, hydrogen could also join electricity as an important energy carrier. An energy carrier stores, moves and delivers energy in a usable form to consumers.
- BIOMASS ENERGY
Biomass is usually thought of as garbage, some of it just lying around dead trees, tree branches, yard clippings, left-over crops, wood chips, and bark and saw dust from lumber mills. It also includes livestock and poultry manures, trash, paper products and other household waste. All these contain some biomass that can be used.
Recycling biomass for fuel and other uses cut down on the need for “land fills” to hold garbage. This waste can be used to produce electricity, heat, compost materials or fuels. California produces more than 60million bone dry tons of biomass each year. Lagos state – Nigeria generates over 8000 tons of waste a year according to the Solar Energy Society of Nigeria (2003). Also Rivers State generates over 5,500 tons of waste per year from food processing, plastics, rubbers, etc. Kano generates at least 1,700 tons of waste mainly from farming industries while Kaduna produces over 3,400 tons of waste from the industries annually.
If all these waste are used, the 60,800,600 tons of biomass in California and Nigeria can produce about 2,500MW of electricity. That’s enough energy to make electricity for about two million houses. How biomass works is simple. The waste – wood, tree braches, etc. is dumped in huge hoppers. It is then burnt in a furnace, the heat is used to boil water in boilers and the energy in the steam is used to turn turbines and generators.
Fig1.1: Nigeria’s Livestock Population
Source: Source: ECN and UNDP, (2005), Renewable Energy Resources, Technologies and Markets, REMP, Final Report 2005, P78
Biomass can also be tapped right at the landfills with burning waste products. When garbage decomposes, it gives off methane gas. The methane gas can be collected. It is used in power plants to make electricity. This type of biomass is called ‘land fill gas’. A similar thing can be done at animal feed lots. In farms where lots of animals are raised, the animals – like cattle, pig, goat, and even poultry – chickens produce manure. Considering cattle for instance, reported values of daily manure production range from 10kg to 60kg per animal (Renewable Energy Master Plan-ECN 2005).
Fig.1.2 Nigeria’s Production of Major Crops (in million tones)
Source: Source: ECN and UNDP, (2005), Renewable Energy Resources, Technologies and Markets, REMP, Final Report 2005, P78
This indicates that Nigeria’s 2001 cattle population of 21 Million should be expected to produce from 210 million Kg to 1,260 million Kg (i.e. 0.21 to 1.26 million tones) of manure daily. These values result in an annual manure production from cattle alone ranging from 76.7 to 450 million tones for Nigeria. From the foregoing it is seen that Nigeria’s livestock manure aggregated production of 285.1 million tones shown in figure 1.1 is potentially able to produce far more than 3 billion cubic meters of biogas yearly, and this is more than 1.25 million tones of fuel oil per annum. From Fig. 1.2, it can be seen that in 1996 Nigeria recorded an aggregate crop production of about 93.3 million tones for the major crops. This quantity refers to the harvested useful parts of the plants. The discarded parts consisting of roots, leaves, stalks, straws, chaff and other parts of plant shoot (otherwise called crop biomass) would be far in excess of the figures shown in Fig. 1.2. From all the above, it is seen that Nigeria’s annual production of agricultural biomass is enormous. When these manures are fermented in digesters, it gives off methane gas. This can be burned right at the farm to make energy to run the farm. This technology is in use in India, China, Nepal, Brazil, etc. The Chinese programme was launched on a very large scale, with reports of 7,000,000 on-farm family sized biogas digesters built in the early 1980s. The Indian government launched a programme in the 1960s, with the Khadi and Village Industries Commission (KVIC) developing biogas plants Jo Lawbuary (2007).
Currently, it is estimated that about 2.5 million household and community biogas plants are installed around India – according to Jo Lawbuary, HES (2007). Biogas alone currently meets 57% of natural energy demand in India, (Tata, 1998) as cited in Jo Lawbuary (2007). In India, the enormous potential of biogas, is estimated at 17,000MW. This capacity is derived principally from estimated agricultural residues and dung from India’s 300million cattle.
A clean and particulate – free source of energy also reduces the likelihood of chronic diseases that are associated with the indoor combustion of biomass-based fuels (fuel wood), such as respiratory infections, ailments of the lungs, bronchitis, asthma, lung cancer and coronary artery diseases (Banerjee, 1996). The use of biogas systems generated from waste in an agrarian community can increase agricultural productivity. Biomass energy is a good source of energy that is friendly to the environment.
The production of methane from biomass e.g. human excreta, animal manure, sewage sludge, and vegetable crop residues can be used in families, farms and industrial units for cooking, heating, and lighting, and in larger institutions for power generation.
Fig.1.3: Nigeria’s Estimated Wood Requirements
Source: ECN and UNDP, (2005), Renewable Energy Resources, Technologies and Markets, REMP, Final Report 2005, P78
AVAILABLE RENEWABLE ENERGY SOURCES
Table1.3 Availability of primary energy resources in the world and Nigeria.
|Energy Resources||Nigeria (2003)||World|
|Hydropower (large scale)||10,000MW||14.4 trillion KWh/yr++ (1999)|
|Hydro power (small scale)||734MW||N.A|
|Fuel Wood||13.1million ha forest wood land||N.A|
|Solar Radiation||3.5 – 7.0KWh/m2 – day||0.6-8.7KWh/m2-day|
|Wind||2-4m/s annual average||As high as 10-15m/s|
|Animal Waste||61*million tons/yr||N. A|
|Crop Residue||83* million tons/yr||N.A|
|Tidal Energy||N.A||45 billion – 15trillion KWh/yr.|
Keys: ++ = technically exploitable capacity of
NA = Not available * = Estimated production.
Source: Iloeje (2004).
From table1.3, the availability of animal waste and crop residue in Nigeria are estimated to be 61 million tons/year and 83 million tons/year respectively. These huge organic wastes (raw materials) can be tapped into for the generation of biogas in farmstead and homes in order to cope with agricultural and domestic1 energy demands/consumptions especially in the rural areas. In table 1.4, Nigeria has no biogas-powered plant among the installed electricity generation plants in the country. Hence there is the need for Nigeria to integrate biogas technology and generate biogas on large scale so as to connect or tie into the national electricity grid and boost overall power output in the country
|POWER PLANT||TYPE [ENERGY SOURCE]||YR 1ST COMMISSIONED||INSTALLED CAPACITY||AVAILABLLE CAP MWAVLL GENERATION
|Afam||Gas turbine (N.G)||1965||709.6||205||200|
|Delta||Gas turbine (NG)||1966||912||500||492|
|Sapele||Gas & steam turbine (NG)||1978||1020||85||74|
|Ijora||Gas turbine (diesel)||1978||60||15||0|
|Oji||Steam Turbine (coal)||1956||30||0||0|
|IPP||Gas turbine (NG)||2002||270||237||228.4|
IPP = Independent Power Plant Source: O.C. Iloeje (2004).
Biomass derived fuels are derived from agricultural sources, as distinct from petrochemical sources, is referred to as biofuels.
A Biofuel is any renewable source of combustible material whose energy content can be beneficially utilized. The emphasis here is on Renewable. This means all biofuels stem from agricultural sources and the carbon (iv) oxide produced during their combustion can be recycled as renewed biofuel. Fossil fuel such as coal, oil and natural gas are not renewable. They are finite sources and once consumed, they are lost forever.
Thus, for both environmental reasons and the need to consider future energy requirements, the transition to biofuel-based society is practically inevitable.
- CURRENT BIOFUELS USED AS ENERGY SOURCES
(i). BIO ETHANOL
Bio-ethanol is most commonly produced by the fermentation of sugars [molasses]. The conversion of starch, called “Saccharification”, significantly expands the choice of feedstock to include corn, barley, sorghum, triticale, etc. Beer brewing, Saki and Vodka manufacture are typical examples, but most importantly, these less expensive starch sources open the way for commercial manufacture of bio-ethanol for transport fuel production. The third alternative route to bio-ethanol involves the enzymatic conversion of cellulose and semi cellulose. The chemical reactions involved in bio-ethanol production can be simplified;
+ enzyme + yeast
Thus, in terms of molecular weight conversion, 180kg of glucose can theoretically produce 92kg of ethanol and 88kg of carbon (iv) oxide.
Conversion of starch into bio-ethanol involves several more process steps. It starts by making a “beer” from the milled grain, then distilled of alcohol, followed by the recovery of the residual solids and recycle of water
Fig.1.4: STARCH – BIO-ETHANOL CONVERSION PROCESS
Care must be taken with each step of the process to ensure efficient conversion, particularly as it is a biological process where stray reactions can occur causing loss in yield and different grains have different process requirements. The following are some important issues in the sequence of process:
– Slurry preparation – Distillation
– Hydrolysis – Dehydration
– Saccharification – Centrifuge
– Fermentation – Evaporation
– Drying – CO2 Recovery
Bio-ethanol is a clear colorless liquid, which boils at a temperature of 80oC, well within the distillation range of gasoline. It has a similar density and fully miscible with gasoline. It is used mostly as transportation fuel.
(ii) BIO DIESEL
Bio diesel is a mixture of methyl esters of long chain fatty acids like lauric, palmitic, stearic, oleic, and so on. It is produced by the transesterification of animal fats and vegetable oils – all of which belong to a group of organic esters called “triglycerides”. Typical examples are rape/canola oil, Soya bean oil, sunflower oil, palm oil and its derivatives, etc. from vegetable sources, beef and sheep fallow and poultry oil from animal sources and also from used coking oil. The chemistry is basically the same irrespective of the feedstock.
The production of bio-diesel involves intensively mixing methanol with the oil or fat in the presence of a suitable catalyst and then allowing the lighter methyl ester phase to separate by gravity from the heavier glycerol phase. However, as with most organic reactions the degree of conversion depends on the equilibrium reached as well as the influence of other reactions.
1 oil or fat + 3 methanol 3 methyl esters + 1 Glycerin
1 Triglyceride + 3 Alcohol
R1, R2 and R3 are symbolic representations of the fatty chains, which can vary in molecular chain length from typically C8 to C22, and also their degree of unsaturation.
Bio-diesel is used as transport fuel, and heating fuel. Its price is not very sensitive to capital cost making it more economic fuel source.
Biogas (70% CH4 and 30% CO2) is generated from slurry (50% dung and 50% water) at an average temperature of 35-40oC. Biogas (also called “marsh gas”), a by-product of anaerobic decomposition of organic matters has been considered an alternative source of energy. It can be used for cooking, heating, and lighting, and in larger institutions for heating or power generation.
The common raw materials used for biogas generation are often defined as “waste materials”, e.g. animal waste, sewage sludge and vegetable crop residues, all of which are rich in nutrients suitable for the growth of anaerobic bacteria. Although some of these materials can be used directly as fuels and fertilizers, they could be used for biogas production – to gain some additional heat value (from the biogas) while the other benefits are still retained.
Depending on factors such as the composition of the raw materials, organic loading applied to the digesters, and the time and temperature of anaerobic decomposition, some variations in the composition of biogas can be noticed, but it approximately conforms to the following:
– Methane (CH4) 55-70 percent
– Carbon (IV) Oxide (CO2) 30-45 percent
– Nitrogen (N2) 0-3 percent
– Hydrogen (H2) 0-1 percent
– Hydrogen Sulphide (H2S) 0-1 percent.(Gustavvson2000)
Of the different gases produced, CH4 is the most desirable gas, because it has a high calorific value of 20MJ/ m3. The approximate heat value of biogas is 20MJ/ m3 – 26MJ/ m3 depending on the content of the gases besides CH4.
Biogas is produced by decomposition of biomass and animal wastes, human excreta, sewage sludge and vegetable residues and poultry wastes by decomposer organisms like bacteria under anaerobic (airless) condition. This process is favored by warm, wet and dark conditions. This involves chemical and biological processes known as “anaerobic fermentation”, but “digestion” is often used in anaerobic conditions, that lead to methane production.
Biogas consists of 70% methane [CH4] and 29% carbon dioxide [CO2], and 1% of hydrogen sulphide [H2S], nitrogen [N2], and some hydrogen [H2]. It is highly combustible and economic fuel. The optimum temperature for maximum production of biogas from slurry is about 37oC. The quantity of gas production depends on the nature of dung used. The optimum temperature of maximum production is achieved after a number of days, referred to as retention period, after feeding the slurry into the digester of the system. The production of gas starts only after the retention period. Supplying thermal energy to the system by external means, i.e. by heating slurry using either passive or active method, can reduce the length of the retention period.
- MECHANISM OF BIOGAS PRODUCTION
The anaerobic digestion of organic material is biochemically a very complicated process, involving hundreds of possible intermediate compounds and reactions, each of which is catalyzed by specific enzymes or catalysts. However, the overall chemical reaction is often simplified to:
Organic matter anaerobic CH4 + CO2 + H2 + NH3 +H2S…………1.1
In general, anaerobic digestion is considered to occur in the following stages:
- The hydrolysis phase – liquefaction or polymer breakdown.
- Acid formation phase
- Methane formation.
In a biogas plant, all the three phases occur simultaneously and if only one phase dominates, production of methane is seriously affected. The three main stages of bio-chemical mechanism in biogas production are shown in figure 1.5.
A). GROUPS OF BIOGAS MICROPES, Source: Bio-gas project, LGED (2007)
1st stage: Fermentative bacteria
In stage 1 as seen above, the hydrolysis reactions convert protein into amino acids, carbohydrates into simple sugars, and fat into long chain fatty acids. Volatile acids, H2 and CO2 are liberated as end product in stage 1.
Rxn: Substrate(S) CO2(g) + H2(g) + CH3COOH(aq)
Substrate Propionate + butyrate + ethanol.
In stage 2, acid producing bacteria convert the simplified compounds into acetic acid [CH3COOH], hydrogen [H2], and carbon dioxide [CO2]. In the process of acidification, the facultative anaerobic bacteria utilize oxygen and carbon, thereby creating the anaerobic condition necessary for methanogenesis.
Fig.1.5: STAGES OF BIO-CHEMICAL MECHANISM IN BIOGAS PRODUCTION
In stage 3, the final stage, the obligatory anaerobes that are involved in methane formation decompose compounds with a low molecular weight, [CH4] and [CO2].
Rxn: CH3 COO– + H2O CH4 + HCO–3 + energy
4H2 + HCO3– +H+ CH4 + 2H2O + energy.
The resulting biogas sometimes referred to as “gober” gas or “marsh gas ” consist of methane and carbon dioxide, and some trace of other gases, e.g. H2S.
- ENVIRONMENTAL REQUIREMENTS FOR ANAEROBIC DIGESTION
Anaerobic digestion is a multi-parameter controlled process, each individual parameter having control over the process either through its own effect on the system or through interaction with other parameters. These parameters are summarized below:
a). Temperature (inside digester) 25-40oC(optimum 37 oC, mesophilic)
b). PH 6.6-7.6 (optimum 7.0-7.2)
c). Alkalinity (mg CaCo3 /L) 2,500-5,000
d). Loading rate
In (kgVS/m3-day) 1-4 (dispersed growth digesters)
1-15(attached growth digesters)
In (Kg COD/m3-day) 1-6 (d.g.d)
Feed solid content (%) 5-10
e). Hydraulic Retention Time (days) 10-60 (d.g.d)
0.5-6 (up-flow sludge blanked digester)
f). C/N ratio 25 – 30
Mixing of slurry is important to provide better contact between the anaerobic bacteria and the incoming organic wastes, so that biogas production is enhanced.
h). Presence of toxic compounds:
The presence of some elements and compounds e.g. K, Ca, Na, Cu, Cr, Ni, Fe, S, NH4, volatile acids in inhibiting concentration must be checked regularly. Diluting the content of digester could do this.
(i). Bio degradability of organic substrate: – This is one of the most important parameters affecting the performance of reactors. Usually, the biodegradable materials constitute 30-50% of the total waste. Biodegradability may be increased by physical, chemical and biological pretreatment means. Because of the associated high costs, only the physical and biological techniques are used. The physical methods involve cutting, grinding or shredding to increase the surface area per unit volume, and thereby increasing the area open to attack by hydrolytic enzymes. The biological method of pretreatment consists of pre-composting agricultural residues before digestion.
- BIOGAS PLANTS IN INTEGRATED FARMS
A biogas plant consists of the digester and the gas storage space. A biogas digester is a plant used for the conversion of fermentable or digestible organic matter into combustible gas [methane] and fully matured organic matter [slurry].
- BIOGAS APPLICATION IN INTEGRATED FARMS
Biogas has many applications in integrated farms some of which are:
a). Biogas serves as a cooking fuel for farmers.
b). Biogas is used for lighting purposes on the farm.
c). Biogas lamps are use to warm birds and animals.
d). It is also possible to power an internal combustion (IC) engine that may be found on the farms setting.
By-products – slurry
e). Biogas slurry has proved to be a high quality organic manure compared to farm yard manure, digested slurry have more nutrients.
f). Digested slurry [in form of dried sludge] serves as feed to animals in the farms.
g). Biogas slurry has proved to be a better feed input for fishpond than raw cow dung.
h). Slurry when used as fertilizer, has strong effects on plant tolerance to diseases such as potato wilt (pseudomonas salana cearum), late blight, cauliflower mosaic, etc. and thus can be used as bio-chemical pesticide.
i). Cold-resistance property of early season rice seedlings is effectively enhanced by soaking seeds with digested slurry.
j). Digested slurry increases crop resistance to many diseases and improves the quality of yield.
Application of biogas in integrated farms is widely spreading in Nepal, India, China, Tanzania and Kenya.
k). Biogas can be used in refrigerators on the farm.
l). Incubators are operated using biogas in poultry farms.
m). It also finds application in boiling of water.
There are different designs of biogas plants and they may be classified under two headings:
a). The continuous plant in which the feeding is done everyday and digested slurry equivalent to the amount of feed overflows from the plant.
b). The batch plant in which feeding is done between intervals; and the plant is emptied once the process of digestion is completed.
Furthermore, digesters are divided into:
Dispersed – growth digesters
- Fixed dome digesters (Chinese)
- Floating gas holder digester (Indian)
- Plug-flow digesters (Horizontal displacement digesters)
- Separate gas holder digesters
- Conventional digesters.
Attached – growth digesters
- Anaerobic filter (Young and McCarty, 1969)
- Up-flow anaerobic sludge blanket [UASB] reactor.
Normally, biogas plant in integrated farms is a continuous plant with automatic discharge at the overflow. The digester content or the substrate flowing out of the plant is called ‘slurry’.
The slurry consists of:
- A light solid fraction, mainly straw or fibrous particles, which float to the top forming the scum [total solid 15 – 50%];
- A very liquid watery fraction remaining in the middle layer of the digester [total solid is 1-2%];
- A viscous fraction below which is the real slurry or sludge [total solid is 6 -7%];
- The heavy solids [soil sand particles], which rest at the bottom.
There are three main types of biogas plants suitable for integrated farms – the fixed dome plant, the floating drum plant and the plastic covered ditch
Fig. 1.6: FIXED – DOME DIGESTER
Source: Tiwari (2006)
The fixed – dome plants are more durable and cheaper than the floating drum plants.
FLOATING (GAS HOLDER)
Source: Tiwari (2006)
Fig. 1.7: FLOATING DRUM [GAS HOLDER] DIGESTER
The floating drum digester is more expensive and requires relatively less excavation. In farms located in regions where temperature is below 25oC, biogas plants can be heated to 37oC using passive or active methods.
The passive methods include:
- Greenhouse integrated biogas plants.
- Use of water heater/solar stills over dome.
- Constructing the digester with insulating materials to reduce the bottom and side losses.
More than 90% of the populations in rural areas are engaged in agriculture. Therefore, any technology that can influence agriculture or gets influenced by the agricultural practices becomes a subject of concern not only to the biogas users but also to the farms as a whole.
By-products of agriculture, mainly animal wastes and crop residues are the primary inputs for biogas plants. The biogas (Methane) is used in farms for lightings, cooking and warming. The digested slurry as one of the outputs of a biogas plant can be returned to the agricultural system. Proper application of the slurry as organic fertilizer increases agricultural production because of its high content of soil nutrients, growth hormones and enzymes. Dried slurry can also safely replace a part of animal and fish feed concentrates. Furthermore, slurry treatment also increases the feed value of fodder with low protein content when the digested slurry is placed into the food chain of crops and animals; it leads to a sustainable increase in farm income.
This close relationship between biogas and agriculture can be taken as an indicator of “environmental friendly” nature of the technology as shown in figure1.8
Fig. 1.8 Relationship between Biogas Plant and Agriculture in a Farming Family
Source: (FAO/TCP/NEP/4415-T, 1996)
Biogas plants in integrated farms are commonly found in countries such as India. Others are China with more than 7 million installed units, Tanzania and Egypt. Vietnam, Thailand and Indonesia also install biogas plants in farms. Nepal has since the early 1970s, put effort to diffuse the technology.
- SOLAR HEATING OF BIOGAS PLANTS
Fig. 1.9 CROSS SECTIONAL VIEW OF AN ACTIVE FIXED-DOME BIOGAS PLANT
Source: Tiwari (2006)
During winter period or in cold regions [below 25oC], heating of biogas digesters in farms may be necessary, so as to achieve the desired temperature, i.e. 37oC, for greater fermentation, while keeping the retention period short. The active heating method may be used in the heating process.
The biogas plant is integrated with a panel of solar collectors through a heat exchanger placed inside the digester as shown in figure1.9. When the heated water from the collector passes through the heat exchanger, heat is transferred to the slurry by conduction and convection, thus raising its temperature, although an excessive rise in the temperature may lead to the death of anaerobic bacteria. Hence the slurry should be heated slowly so that anaerobic bacteria may exist for microbiological process.
In an active biogas plant, more methane gas is produced as a result of greater fermentation that occurs inside the plant. Also the optimum temperature for maximum production of biogas is achieved after a very short retention period.
1.6 ENVIRONMENTAL IMPACT
The use of biogas can be environmentally friendly because the wastes [organic wastes] are reduced, recycled and then re-used. Nitrogen, phosphorus, and potassium are conserved in the process of biogas production and can be recycled in agriculture; Agunwamba (2001). The slurry, if used as organic fertilizer helps to conserve the soil. The slurry that is returned after methanogenesis is superior or higher in terms of its nutrients contents; the process of methane production serves to narrow the carbon-nitrogen [C: N], while a fraction of the organic nutrients is mineralized to ammonium [NH4+], and nitrate [NO3–], the form, which is immediately available to plants. A clean and particulate-free source of energy also reduces the likelihood of chronic diseases that are associated with indoor combustion of biomass-based fuels such as respiratory infection, ailments of the lungs, bronchitis, asthma, lung cancer, and increased severity of coronary artery disease (BanerJee, 1996) as cited in (Jo Lawbuary, 2007).
The use of biogas enhances a significant reduction in emissions associated with the combustion of biofuels, such as sulphur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), total suspended particles (TSPs) and poly-aromatic hydrocarbons (PAHs) and carbon (iv) oxide (CO2) which help reduce global warming, acid rain (The energy story, 2007) etc.
It reduces the concentration of pathogens (typhoid, paratyphoid, cholera, and dysentery bacteria) considerably, thereby breaking the cycle of re-infection and leading to improved public health (Gustavsson, 2000)
The national benefit of savings to the environment (against deforestation) is an added advantage. Biogas application reduces dependence on fuel wood, which induces deforestation. Biogas does not pollute the air or environment as it is in the case of fossil fuels.
This project was conducted by using a triangulation method consisting of: literature review, background research/case studies and direct interviews. The literature review and background research provided an initial overview of biogas. These sources described what biogas is, how it is produced, and how it could be used. The literature review transcribed what studies have been done in reference to biogas and current projects using biogas technology.
Background research and case studies were reviewed and will serve as a comparison to the potential Concordia farms project and provide information as to the size, capacity, and type of biogas plant that would best suit Concordia farms limited. Interviews were conducted to several local farm workers about organic wastes including farmers, farm manager, and farm equipment operators/maintenance workers, and marketers. The verbal interview questions were reviewed and passed by Concordia farms Office of Research Ethics. Approval from the Research Ethics Office was needed to interview the manager and farmers. Interview participants were selected from criteria, which were based on the proximity of the participants to the farm, and the volume of wastes that could be generated. Maximum waste could be collected from such farm as compared to slaughters’ wastes. Participants were contacted directly.
Series of questions were asked regarding where the waste goes currently, farms sources of energy, farm’s cost on energy, energy needs of the farm and whether they would be willing to donate their organic waste if a biogas plant is built on the farm for biogas generation, and the sludge used as manure in agriculture. The collected data was taken and assessed to determine extra amounts of organic waste needed for the biogas plant. The economic feasibility of the biogas plant was conducted with all data collected. This was then followed by a discussion, recommendations and alternatives for the feasibility of this project. This method of triangulation attempts to use the most recent and innovative technologies to minimize potential operational and start-up problems. This method also emphasizes the benefits a biogas operation would have on the local community and Concordia farms limited.
Update of Biogas technology in some Countries
In China, India, Germany and Nepal etc, biogas has been widely used as a source of energy and waste management, and as liquid fertilizer for soil enhancement, since the 1950’s. By 2005, there were over 25 million small-scale operational biogas systems worldwide – with over a million now being installed each year – as well as over 100,000 large centralized biogas plants capturing biogas for conversion into useful energy , Agama Energy (2007). For example, there are over 300,000 rural South Africa household that are technically viable beneficiaries of on-site energy production through biogas technology to meet all their cooking needs, Agama Energy (2007).
In this section we aim to provide an insight and update of the state of biogas technology and research in some countries in the world and sub-Saharan Africa. It will also highlight some countries’ strengths and weaknesses in biogas development capacity. Table1.5 gives summarized list of countries with biogas production units as at 2007. It also shows the sizes of the largest plants so far built in some countries of the world. Though there are large-scale anaerobic digestion technology in Europe and Asia, The development of large-scale anaerobic digesters in Africa is still embryonic, although the potentials is there.
Table 1.5. Countries with biogas producing units
Source: (Anthony1 & Wilson2 2009; GTZ & ISAT 2007)
|Country||Number of small/medium (100 m3)||Number of large digesters (>100 m3)|
Several (>500 m3)
>90 (>100 m3)
>150 (500 m3 – 1,200 m3)
Several (>600 m3)
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