A final year research project -part 3 (Literature Review,Results& Conclusion)

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CHAPTER ONE
1.0 INTRODUCTION
In today’s energy demanding life style, need for exploring and exploiting new
sources of energy which are renewable as well as eco-friendly is a must. In rural
areas of developing countries various cellulosic biomass (cattle dung, agricultural
residues, etc.) are available in plenty which have a very good potential to cater to
the energy demand, especially in the domestic sector. In India alone, there are an
estimated over 250 million cattle and if one third of the dung produced annually
from these is available for production of biogas, more than 12 million biogas
plants can be installed (Kashyap et al., 2003).
Biogas technology offers a very attractive route to utilize certain categories of
biomass for meeting partial energy needs. In fact proper functioning of biogas
system can provide multiple benefits to the users and the community resulting in
resource conservation and environmental protection. (www.need.org)
The high demand for fuelwood which is a big business in places like Nigeria, has
monumentally grown with the rise in the population of the world, leading to the
loss of trees and forests, through a process called deforestation. However, people
seem to forget that the wood emanates from the trees in the forest, and despite
certain regulations concerning the use of woods, the activities of illegal loggers
cannot be entirely supervised or curtailed. The deforestation level is higher than
the forestation efforts, and this has resulted in environmental degradation. The
greatest hindrance to the observance of these regulations is the absence of

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alternative source of fuel such as the kerosene and other petroleum domestic fuels
(www.biogas-renewablenergy.info/biogas_resources.html)
Biogas is a gaseous fuel containing 60% methane, 40% carbon dioxide and small
amount of hydrogen sulphide, nitrogen and hydrogen. It is obtained from
biomass-plant and animal materials, by the process of anaerobic (absence of
oxygen) digestion or fermentation, of which the in-feed to the biogas plant
includes: urban waste (garbage), urban refuse, agricultural waste, cow dung-case
study. Biogas is used as biofuels which originates from biogenic material, can be
used for cooking, heating, generating electricity and running a vehicle.
(http://ezinearticles.com/?Biogas-Technology)
1.1 PROBLEM STATEMENT
Because of the population explosion, and related energy demands of deforestation
level due to the over use of fuelwood by the felling of trees and reduction of
forest, are higher than forestation efforts, they have resulted to environmental
degradation.
Another major cause of the environmental degradation, which has become the
greatest threat to the health of the environment and the economy of the
underdeveloped worlds, and most especially the developing and the developed
worlds, is the use of fossil fuels. These fossil fuels are non-renewable, although
the major source of the energy and income of the economy of many countries
such as Nigeria. But with the discovery and utilisation of biogas, which is a
gaseous fuel obtained from biomass by the process of anaerobic digestion, most
problems (e.g. air, land, water pollution) and associated with the fossil fuels, are
being resolved.

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1.2 AIM AND OBJECTIVES
The aim of this research project is to design; fabricate and test run a bench scale
bioreactor for the production of biogas and the objectives for the research are:
i. Design and fabricate a bioreactor using available and non-expensive material.
ii. Test run a bioreactor using cow dung, to obtain biogas as a biofuel to be
recommended as a substitute for the non-renewable and expensive domestic fuels
Kerosene.
iii. To calculate and record the cumulative volumes of biogas being produced after
the anaerobic digestion.
1.3 JUSTIFICATIONS
The justifications of this research project are as follows:
i. Anaerobic production of biogas does not produce any offensive smell, causing
reduction of pollution, hence making it environmentally friendly.
ii. It is cost efficient.
iii. The raw materials are cheap and readily available.
iv. It reduces greenhouse effect.
v. Greatly increases the fertilizer value of the manure and protects water source.
vi. Biogas is a renewable energy resulting from biomass which replaces fossil
energy.
vii. Electricity resulting from biogas can be sold to the electricity distributors.
viii. For agronomic advantages, transformation of liquid manure into fertilizer, more
easily assimilated by the plants, with reduction in the odours and disease causing
agents.

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1.4 SCOPES
The scopes for this research are as follows:
i. Design the bioreactor
ii. Fabricate the bioreactor
iii. Test run with cow dung.

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CHAPTER TWO
2.0 LITERATURE REVIEW
Biogas simply refers to a gas produced by the biological
breakdown/disintegration of organic matter in the absence of oxygen. Organic
waste such as dead plant and animal material, animal dung, and kitchen waste can
be converted into a gaseous fuel known as the ‘Biogas’. Biogas originates from
biogenic material (i.e resulting from biological activities) and is a type of biofuel,
which is generally used to describe secondary renewable fuels which are obtained
by thermo chemical processing or the bioconversion of biomass especially
carbonaceous waste materials.
Biogas is a gaseous fuel obtained from biomass by the process of anaerobic
digestion or fermentation, when bacteria degrade biological material in the
absence of oxygen. The in-feed or raw material to the biogas plant or bioreactor
for the production of biogas includes:
i. Manure (for example cow dung)
ii. Urban waste(garbage)
iii. Green waste
iv. Sewage
v. Agricultural waste.
Biogas comprises primarily methane (CH4), and carbon dioxide CO2 and may
have small amount of hydrogen sulphide (H2S), moisture and siloxanes. The
gases methane, hydrogen and carbon monoxide (CO) can be combusted or

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oxidized with oxygen. This energy release allows s biogas to be used as a fuel.
Biogas can be used as fuel in any country for any heating purpose, such as
cooking. It can also be used in anaerobic digesters where it is typically used in a
gas engine to convert the energy in the gas into electricity and heat. Just like the
natural gas, the biogas can also be compressed and used to power motor vehicles.
In the UK, for example, biogas is estimated to have the potential of replacing
around 17% of vehicle fuel. Biogas is a renewable fuel, so it qualifies for
renewable energy subsidies in some parts of the world. Biogas can also be
cleaned and upgraded to natural gas standards when it becomes bio-methane.
Figure 2.1 shows the cycle of how biogas is produced, its sources and how it is
being utilized.
Figure 2.1: The Biogas cycle

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2.1 ORGANIC WASTE
In order to haven an in-depth of biogas, it is very vital to have a good
understanding of organic waste; what they are, their examples, and their
environmental impacts.
An organic waste therefore, is anything that comes from plants or animals that is
biodegradable, which are substances that will decay relatively quickly as a result
of the action of bacteria and break down into elements such as carbon that are
recycled naturally.(Encarta Dictionaries, 2009).
2.1.1 Types of waste
Several types of organic waste can be used:
i. Agri-food industries waste: They are very charged organic effluents and are
potentially strong in methane. This includes the Fruit and vegetable by-products,
and canteen waste,
ii. Green waste: Waste of the communities - shearing of grass, sheets etc and have
seasonal character.
iii. Wastewater treatment plants sludge : They are divided into the Primary and
secondary sludge.
iv. Grease: They could be obtained from restaurant vats of degreasing and are
potentially strong in methane.
Other examples of wastes are: Eggshells, rice, beans, cheese, bones, frozen
refrigerated food, paper towels etc
2.1.2 Impacts of Organic Waste
Organic waste has both negative and positive impacts to the environment and its
entire component (biotic and abiotic). The following are some specific areas of
the impact of organic waste.

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a. Contamination
Much of the land used for waste disposal cannot be reused in the future because
of contamination. This occurs when rubbish in landfills is compressed and the air
is squeezed out. The rubbish breaks down anaerobically (without oxygen), which
means that acids are produced. The acids affect other rubbish items, such as
plastic, to create a toxic mix known as leachate. Leachate collects at the bottom of
landfills where it then seeps into the ground water and from there into the
waterways.
b. Landfill space
In many areas the land allocated to waste disposal is rapidly filling up.
Approximately half of all household waste is organic. Most of this waste can be
recycled through composting – turning waste materials into a rich soil supplement
for use in your garden. By composting, not only can you help to reduce the
amount of waste that goes into landfill but you can also help to reduce
contamination and greenhouse gasses.
c. Greenhouse gases
As organic waste decomposes in landfill it produces the greenhouse gases,
methane and carbon dioxide.
These greenhouse gases contribute worldwide climate change. Most landfill gas
is made up of 54% methane and 40% carbon dioxide. Methane is twenty four
times more damaging as a greenhouse gas than carbon dioxide. Scientists predict
that climate change will impact on all our lives, especially in the areas of
agriculture and human health.

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2.1.3 Benefits of Compositing
i. Compost improves drainage in clay soils and helps sandy soils retain water.
ii. Compost assists plant growth and disease resistance.
iii. Compost also helps to absorb and filter runoff, protecting streams from erosion
and pollution.
iv. Composting reduces unwanted insects, limiting the need for commercial
herbicides or pesticides, therefore preventing runoff pollution.
v. You won't have to bag and drag garden waste to the kerb for collection or pay to
have it trucked to the tip.
2.1.4 Composition of Cow Dung
The composition of Cow dung slurry is given in the table 2.1.
Table 2.1: Table showing the composition of Cow dung
Component Percentage
Nitrogen (N2) 1.8-2.4%
Phosphorus (P2O5) 1.0-1.2%
Potassium (K2O) 0.6-0.8%
Organic humus 50-75%
About one cubic foot of gas may be generated from one pound of cow manure at
around 28°C.
2.2 BIOMASS
Biomass is any organic matter—wood, crops, seaweed, animal wastes— that can
be used as an energy source. Biomass is probably our oldest source of energy
after the sun. For thousands of years, people have burned wood to heat their
homes and cook their food.

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Biomass gets its energy from the sun. All organic matter contains stored energy
from the sun. During a process called photosynthesis, sunlight gives plants the
energy they need to convert water and carbon dioxide into oxygen and sugars.
These sugars called carbohydrates, supply plants and the animals that eat plants
with energy. Foods rich in carbohydrates are a good source of energy for the
human body.
Biomass is a renewable energy source because its supplies are not limited. We
can always grow trees and crops, and waste will always exist.
2.2.1 Types of Biomass
We use four types of biomass today—wood and agricultural products, solid
waste, landfill gas and biogas, and alcohol fuels.
i. Wood and Agricultural Products
Most biomass used today is home grown energy. Wood—logs, chips, bark, and
sawdust—accounts for about 49 percent of biomass energy. But any organic
matter can produce biomass energy. Other biomass sources include agricultural
waste products like fruit pits and corncobs.
Wood and wood waste, along with agricultural waste, are used to generate
electricity. Much of the electricity is used by the industries making the waste; it is
not distributed by utilities, it is cogenerated. Paper mills and saw mills use much
of their waste products to generate steam and electricity for their use. However,
since they use so much energy, they need to buy additional electricity from
utilities.
Increasingly, timber companies and companies involved with wood products are
seeing the benefits of using their lumber scrap and sawdust for power generation.
This saves disposal costs and, in some areas, may reduce the companies’ utility

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bills. In fact, the pulp and paper industries rely on biomass to meet half of their
energy needs. Other industries that use biomass include lumber producers,
furniture manufacturers, agricultural businesses like nut and rice growers, and
liquor producers.
ii. Solid Waste
Burning trash turns waste into a usable form of energy. One ton (2,000 pounds) of
garbage contains about as much heat energy as 500 pounds of coal. Garbage is
not all biomass; perhaps half of its energy content comes from plastics, which are
made from petroleum and natural gas.
Power plants that burn garbage for energy are called waste-to-energy plants.
These plants generate electricity much as coal-fired plants do, except that
combustible garbage—not coal—is the fuel used to fire their boilers. The
electricity from garbage, costs more than that from coal and other energy sources.
The main advantage of burning solid waste is that it reduces the amount of
garbage dumped in landfills by 60 to 90 per cent, which in turn reduces the cost
of landfill disposal. It also makes use of the energy in the garbage, rather than
burying it in a landfill, where it remains unused.
iii. Landfill Gas
Landfill gas is a complex combination of different gases created by the action of
microorganisms within a landfill, which is a carefully engineered depression in
the ground (or built on top of the ground, resembling a football stadium) into
which wastes are put. The aim of having this landfill is to avoid any hydraulic (or
water-related) connection between the wastes and the environment, most
especially the groundwater (www.ejnet.org/landfill). Bacteria and fungi are not
picky eaters. They eat dead plants and animals, causing them to rot or decay. A

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fungus on a rotting log is converting cellulose to sugars to feed itself. Although
this process is slowed in a landfill, a substance called methane gas is still
produced as the waste decays.
New regulations require landfills to collect methane gas for safety and
environmental reasons. Methane gas is colourless and odourless, but it is not
harmless. The gas can cause fires or explosions if it seeps into nearby homes and
is ignited. Landfills can collect the methane gas, purify it, and use it as fuel.
Methane, the main ingredient in natural gas, is a good energy source. Most gas
furnaces and stoves use methane supplied by utility companies. In 2003, East
Kentucky Power Cooperative began recovering methane from three landfills. The
utility now uses the gas at five landfills to generate 16 megawatts of electricity—
enough to power 7,500 to 8,000 homes.
Today, a small portion of landfill gas is used to provide energy. Most is burned
off at the landfill. With today’s low natural gas prices, this higher-priced biogas is
rarely economical to collect. Methane, however, is a more powerful greenhouse
gas than carbon dioxide. It is better to burn landfill methane and change it into
carbon dioxide than release it into the atmosphere.
Methane can also be produced using energy from agricultural and human wastes.
Biogas digesters are airtight containers or pits lined with steel or bricks. Waste
put into the containers is fermented without oxygen to produce a methane-rich
gas. This gas can be used to produce electricity, or for cooking and lighting. It is a
safe and clean-burning gas, producing little carbon monoxide and no smoke.
Biogas digesters are inexpensive to build and maintain. They can be built as
family-sized or community-sized units. They need moderate temperatures and
moisture for the fermentation process to occur. For developing countries, biogas

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digesters may be one of the best answers to many of their energy needs. They can
help reverse the rampant deforestation caused by wood-burning, and can reduce
air pollution, fertilize over-used fields, and produce clean, safe energy for rural
communities. Examples of biomass used as the raw materials for the production
of biogas are shown in Figure 2.2.
Figure 2.2: Types of Biomass.
Almost half of the biomass used today comes from burning wood and wood
scraps such as saw dust. More than one-third is from biofuels, principally ethanol,
that are used as a gasoline additive. The rest comes from crops, garbage, and
landfill gas.
Industry is the biggest user of biomass. Over 51 percent of biomass is used by
industry. Electric utilities use 11 percent of biomass for power generation.
Biomass produces 0.7 percent of the electricity we use.
Transportation is the next biggest user of biomass; almost 24 percent of biomass
is used by the transportation sector to produce ethanol and biodiesel.

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The residential sector uses 11 percent of the biomass supply. About one-tenth of
American homes burn wood for heating, but few use wood as the only source of
heat.
2.2.2 Using Biomass Energy
Usually we burn wood and use its energy for heating. Burning, however, is not
the only way to convert biomass energy into a usable energy source. There are
four ways:
i. Fermentation: There are several types of processes that can produce an
alcohol (ethanol) from various plants, especially corn. The two most
commonly used processes involve using yeast to ferment the starch in the
plant to produce ethanol. One of the newest processes involves using
enzymes to break down the cellulose in the plant fibres, allowing more
ethanol to be made from each plant, because all of the plant tissue is
utilized, not just the starch.
ii. Burning: We can burn biomass in waste-to-energy plants to produce
steam for making electricity, or we can burn it to provide heat for
industries and homes.
iii. Bacterial Decay: Bacteria feed on dead plants and animals, producing
methane. Methane is produced whenever organic material decays.
Methane is the main ingredient in natural gas, the gas sold by natural gas
utilities. Many landfills are recovering and using the methane gas
produced by the garbage.
iv. Conversion: Biomass can be converted into gas or liquid fuels by using
chemicals or heat. In India, cow manure is converted to methane gas to

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produce electricity. Methane gas can also be converted to methanol, a
liquid form of methane.
2.2.3 Biomass and the Environment
Environmentally, biomass has some advantages over fossil fuels such as coal and
petroleum. Biomass contains little sulphur and nitrogen, so it does not produce
the pollutants that can cause acid rain. Growing plants for use as biomass fuels
may also help keep carbon dioxide levels balanced. Plants remove carbon
dioxide—one of the greenhouse gases—from the atmosphere when they grow.
2.3 RENEWABLE RESOURSES
Renewable energy is energy which comes from natural resources such as
sunlight, wind, rain, tides, and geothermal heat, which are renewable (naturally
replenished) and the renewable power capacities with respect to years are
represented on Figure 2.3. About 16% of global final energy consumption comes
from renewables, with 10% coming from traditional biomass, which is mainly
used for heating, and 3.4% from hydroelectricity. New renewables (small hydro,
modern biomass, wind, solar, geothermal, and biofuels) accounted for another 3%
and are growing very rapidly.(Renewables 2011: Global Status Report) The share
of renewables in electricity generation is around 19%, with 16% of global
electricity coming from hydroelectricity and 3% from new renewables.
(Renewables 2011: Global Status Report).
Wind power is growing at the rate of 30% annually, with a worldwide installed
capacity of 238 gigawatts at the end of 2011, and is widely used in Europe, Asia,
and the United States. (Alex M., 2011). At the end of 2011 the photovoltaic (PV)
capacity worldwide was 67 GW, and PV power stations are popular in Germany

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and Italy. Solar thermal power stations operate in the USA and Spain, and the
largest of these is the 354 megawatt (MW) SEGS power plant in the Mojave
Desert. The world's largest geothermal power installation is the Geysers in
California, with a rated capacity of 750 MW. Brazil has one of the largest
renewable energy programs in the world, involving production of ethanol fuel
from sugarcane, and ethanol now provides 18% of the country's automotive fuel.
Ethanol fuel is also widely available in the USA. (World Energy Assessment
(2001), Renewable energy technologies). While many renewable energy projects
are large-scale, renewable technologies are also suited to rural and remote areas,
where energy is often crucial in human development. As of 2011, small solar PV
systems provide electricity to a few million households, and micro-hydro
configured into mini-grids serves many more. Over 44 million households use
biogas made in household-scale digesters for lighting and/or cooking and more
than 166 million households rely on a new generation of more-efficient biomass
cook stoves. United Nations' Secretary-General Ban Ki-moon has said that
renewable energy has the ability to lift the poorest nations to new levels of
prosperity. (Renewables 2011)
Climate change concerns, coupled with high oil prices, peak oil, and increasing
government support, are driving increasing renewable energy legislation,
incentives and commercialization. New government spending, regulation and
policies helped the industry weather the global financial crisis better than many
other sectors. According to a 2011 projection by the International Energy
Agency, solar power generators may produce most of the world’s electricity
within 50 years, dramatically reducing the emissions of greenhouse gases that
harm the environment (Ben S., 2011).

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Figure 2.3: Global renewable power capacity excluding hydro
(www.wikipedia.org)
Renewable energy flows involve natural phenomena such as sunlight, wind, tides,
plant growth, and geothermal heat, as the International Energy Agency explains
that the renewable energy is derived from natural processes that are replenished
constantly. In its various forms, it derives directly from the sun, or from heat
generated deep within the earth. Included in the definition is electricity and heat
generated from solar, wind, ocean, hydropower, biomass, geothermal resources,
and biofuels and hydrogen derived from renewable resources.
(Renewables, 2010)
Renewable energy provides 19% of electricity generation worldwide. Renewable
power generators are spread across many countries, and wind power alone
already provides a significant share of electricity in some areas: for example, 14%
in the U.S. state of Iowa, 40% in the northern German state of Schleswig-

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Holstein, and 20% in Denmark. Some countries get most of their power from
renewables, including Iceland and Paraguay (100%), Norway (98%), Brazil
(86%), Austria (62%), New Zealand (65%), and Sweden (54%).
(Renewables, 2010)
Solar hot water makes an important contribution to renewable heat in many
countries, most notably in China, which now has 70% of the global total (180
GWth). Most of these systems are installed on multi-family apartment buildings
and meet a portion of the hot water needs of an estimated 50–60 million
households in China. Worldwide, total installed solar water heating systems meet
a portion of the water heating needs of over 70 million households. The use of
biomass for heating continues to grow as well. In Sweden, national use of
biomass energy has surpassed that of oil. Direct geothermal for heating is also
growing rapidly. Transport fuels. Renewable biofuels have contributed to a
significant decline in oil consumption in the United States since 2006. The 93
billion liters of biofuels produced worldwide in 2009 displaced the equivalent of
an estimated 68 billion liters of gasoline, equal to about 5% of world gasoline
production. (www.wikipedia.org)
2.3.1 Mainstream forms of Renewable Energy
The following energies are examples of renewable energy.
i. Wind power.
ii. Hydro Power.
iii. Solar Energy
iv. Biomass
v. Biofuels
vi. Geothermal energy.

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2.4 NON-RENEWABLE SOURCES
A non-renewable resource is a natural resource which cannot be produced,
grown, generated, or used on a scale which can sustain its consumption rate, once
depleted there is no more available for future needs. Also considered non-
renewable are resources that are consumed much faster than nature can create
them. Fossil fuels (such as coal, petroleum, and natural gas), nuclear power
(uranium) and certain aquifers are examples shown and on figure 2.4. In contrast,
resources such as timber (when harvested sustainably) or metals (which can be
recycled) are considered renewable resources.
Natural resources such as coal, petroleum (crude oil) and natural gas take
thousands of years to form naturally and cannot be replaced as fast as they are
being consumed. Eventually natural resources will become too costly to harvest
and humanity will need to find other sources of energy. Natural resources such as
coal, petroleum (crude oil) and natural gas take thousands of years to form
naturally and cannot be replaced as fast as they are being consumed. Eventually
natural resources will become too costly to harvest and humanity will need to find
other sources of energy. (McClain et al, 2007)
Figure 2.7: Examples of Energy sources. (www.wikipedia.org)

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2.5 BIOGAS
Biogas is a gas that has a composition of about 50-70% Methane (CH4), 30-50%
Carbondioxide (CO2) with the remaining gases being: H2, O2, H2S, N2 and water
vapor, generated from the anaerobic digestion of organic waste. To ensure
optimal Bio-gas production, the three groups of micro-organisms must work
together. In case of too much organic waste, the first and second groups of micro-
organisms will produce a lot of organic acid which will decrease the pH of the
reactor, making it unsuitable for the third group of micro-organisms. This will
result in little or no gas production. On the other hand, if too little organic waste
is present, the rate of digestion by micro-organisms will be minimal and
production of Bio-gas will decrease significantly. Mixing could aid digestion in
the reactor but, too much mixing should be avoided as this would reduce bio-gas
generation. Table 2.2 below shows the amount of biogas generated from animal
waste and agriculture residue. (www.biogasworks.org)
Table 2.2: Amount of bio-gas generated from animal waste and agriculture
residue animal. (www.apo-tokyo.org/BiogasGP3.pdf)
Animal Gas produced L/kg-solid
Pig 340-550
Cow 90-310
Chicken 310-620
Horse 200-300
Sheep 90-310
Straw 105
Grasses 280-550
Peanut shell 365
Water Hyacinth 375

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2.6 THE ANAEROBIC DIGESTION PROCESS.
Anaerobic biodegradation of organic material proceeds in the absence of
oxygenand the presence of anaerobic microorganisms. AD is the consequence of
a series ofmetabolic interactions among various groups of microorganisms. It
occurs in threestages, hydrolysis/liquefaction, acidogenesis and methanogenesis.
The first group of microorganism secretes enzymes, which hydrolyses polymeric
materials tomonomers such as glucose and amino acids. These are subsequently
converted bysecond group i.e. acetogenic bacteria to higher volatile fatty acids,
H2 and aceticacid. Finally, the third group of bacteria, methanogenic, convert H2,
CO2, andacetate, to CH4. These stages are described in detail below. The AD is
carried out in large digesters as shown in Figure 2.8 that are maintained at
temperatures ranging from 30° C -65° C.
Figure 2.8: The digesters at Tilburg Plant in The Netherlands
(http://www.steinmuller-valorga.fr/en)
The following are the various stage by stage anaerobic digestion processes, which
is also illustrated in the figure 2.9 below.

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2.6.1 Hydrolysis/liquefaction
In the first stage of hydrolysis (figure 2.9), or liquefaction, fermentative bacteria
convert the insoluble complex organic matter, such as cellulose, into soluble
molecules such as sugars, amino acids and fatty acids. The complex polymeric
matter is hydrolyzed to monomer, e.g., cellulose to sugars or alcohols and
proteins to peptides or aminoacids, by hydrolytic enzymes, (lipases, proteases,
cellulases, amylases, etc.) secreted by microbes. The hydrolytic activity is of
significant importance in high organic waste and may become rate limiting. Some
industrial operations overcome this limitation by the use of chemical reagents to
enhance hydrolysis. The application of chemicals to enhance the first step has
been found to result in a shorter digestiontime and provide a higher methane yield
(RISE-AT, 1998).
Below are examples of Hydrolysis/Liquefaction reactions:
Lipids → Fatty Acids
Polysaccharides → Monosaccharides
Protein → Amino Acids
Nucleic Acids → Purines & Pyrimidines
2.6.2 Acetogenesis
This is the second stage (from figure 2.9), where an acetogenic bacteria, also
known as acid formers, convert the products of the first phase to simple organic
acids, carbon dioxide and hydrogen. The principal acids produced are acetic acid
(CH3COOH), propanoic acid (CH3CH2COOH), butanoic acid
(CH3CH2CH2COOH), and ethanol (C2H5OH). The products formed during
acetogenesis are due to a number of different microbes, e.g., syntrophobacter
wolinii, a propionate decomposer and sytrophomonos wolfei, abutyrate

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decomposer. Other acid formers are clostridium spp.,
peptococcusanerobus,lactobacillus, and actinomyces (www.biogasworks.com-
Microbes in AD)
An acetogenesis reaction is shown below:
C6H12O6→ 2C2H5OH + 2CO2
2.6.3 Methanogenesis
As seen in figure 2.9 also, the final and also the third stage, methane is produced
by bacteria called methane formers(also known as methanogens) in two ways:
either by means of cleavage of acetic acid molecules to generate carbon dioxide
and methane, or by reduction of carbondioxide with hydrogen. Methane
production is higher from reduction of carbondioxide but limited hydrogen
concentration in digesters results in that the acetatereaction is the primary
producer of methane (Omstead et al, 1980). The methanogenic bacteria include
methanobacterium, methanobacillus, methanococcus and methanosarcina.
Methanogens can also be divided into two groups: acetate and H2/CO2consumers.
Methanosarcina spp. and methanothrix spp. (also, methanosaeta)are considered to
be important in AD both as acetate and H2/CO2 consumers. Themethanogenesis
reactions can be expressed as follows:
CH3COOH → CH4 + CO2
(acetic acid) (methane) (carbon dioxide)
2C2H5OH + CO2→ CH4 + 2CH3COOH
(ethanol)
CO2 + 4H2 → CH4 + 2H2O
(hydrogen) (water)

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(www.need.org)
Figure 2.9: Anaerobic Digestion Diagram. (Naskeo Environnement, 2009)
2.6.4 General Process Description
Generally the overall anaerobic digestion process can be divided into four stages:
Pretreatment, waste digestion, gas recovery and residue treatment. Most digestion
systems requirepre-treatment of waste to obtain homogeneous feedstock. The
preprocessinginvolves separation of non-digestible materials and shredding. The
waste received byanaerobic digester is usually source separated or mechanically
sorted. The separationensures removal of undesirable or recyclable materials such
as glass, metals, stonesetc. In source separation, recyclables are removed from the
organic wastes at the source. Mechanical separation can be employed if source

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separation is not available.However, the resultant fraction is then more
contaminated leading to lower compostquality (RISE-AT, 1998).
The waste is shredded before it is fed into the digester. Inside the digester, the
feed is diluted to achieve desired solids content and remainsin the digester for a
designated retention time. For dilution, a varying range of watersources can be
used such as clean water, sewage sludge, or re-circulated liquid fromthe digester
effluent. A heat exchanger is usually required to maintain temperature inthe
digesting vessel (Figure 2.10). The biogas obtained in AD is scrubbed to
obtainpipeline quality gas. In case of residue treatment, the effluent from the
digester is dewatered,and the liquid recycled for use in the dilution of incoming
feed. Thebiosolids are aerobically cured to obtain a compost product.
(www.need.org)
Figure 2.10: The flow diagram of low solids Anaerobic digestion.
(http://www.soton.ac.uk/~sunrise/anaerobicdig.htm#ADsolidwaste)

26
2.6.5 Benefit of Bio-Gas Technology
The following benefits will be obtained from bio-gas technology:
(i) Energy
Bio-gas could be used as a fuel alternative to wood, oil, LPG and electricity.
(ii) Agriculture
The use of sludge from the bio-gas reactor could be used as compost. Organic
nitrogen from waste will be transformed into ammonia nitrogen, a form of
nitrogen which plants can uptake easily.
(iii)Protect environment
Using bio-gas technology on animal waste treatment will reduce risk of infection
from parasite and pathogenic bacteria inherent in the waste. Odor and flies will be
significantly reduced in the area, and water pollution created by the dumping of
waste can also be prevented.
2.7 REVIEW OF BIOGAS REACTOR.
The anaerobic digestion of organic waste materials, such as farm manure, litter,
garbage, and night-soil, accompanied by the recovery of methane for fuel, has
been an important development in rural sanitation during the last few decades.
This development is basically an extension of the anaerobic process for sludge
digestion used in municipal sewage treatment to small digestion-tank installations
on farms. These farm plants comprise of one or more small digesters and a gas-
holder. Manure and other wastes are placed in a tank which is sealed from
atmospheric oxygen, and are permitted to digest anaerobically. The methane gas,
which is produced during the anaerobic decomposition of the carbonaceous
materials, is collected in the gas-holder for use as fuel for cooking, lighting,

27
refrigeration, and heating, and for other domestic or agricultural purposes, such as
providing power for small engines. This method provides for the sanitary
treatment of organic wastes, satisfactory control of fly breeding, efficient and
economical recovery of some of the waste carbon as methane for fuel, and
retention of the humus matter and nutrients for use as fertilizer. Most of the farm
installations have, so far, utilized only animal manure and organic litter; however,
night-soil can be satisfactorily treated together with the other wastes in these
digesters if adequate digestion time is allowed to permit the destruction of the
pathogenic organisms and parasites. Such a practice has many advantages on
farms and in villages where water-carried sewage disposal is not available. The
use of the digestion tank can eliminate the dangerous insanitary practice of
allowing night-soil to be deposited on fields, and in the immediate environment
of homes, without proper treatment. Straw, weed trimmings, or any other type of
cellulose materials may be digested together with the manure and night-soil for
the production of methane.
Digester tanks with gas collection are particularly advantageous in areas which
are short of fuel and where animal dung is burned for cooking. The burning of
dung destroys, with digestion, the valuable nitrogen and other nutrients which
could be used as fertilizer. The nitrogen, phosphorus, potash, and other nutrients
are retained in the tank as humus and liquid while much of the carbon and
hydrogen are evolved as methane, for collection and use as fuel.
The quality of the humus is similar to that obtained from aerobic composting, and
when the liquid is utilized together with the solids as fertilizer; practically all of
the fertilizer nutrients are reclaimed. The evolved gas, which consists
approximately of two-thirds methane and one-third carbon dioxide, will contain

28
4500 to 6000 calories per cubic meter, thus providing a convenient source of heat
at low cost. One cubic meter of the gas at 6000 calories is equivalent to the
following quantities of other fuels: 1,000 liters of alcohol; 0.800 liters of petrol;
0.600 liters of crude oil; 1.500 m3 of commonly manufactured city gas; 1.400 kg
of charcoal; and 2.2 kilowatt-hours of electrical energy.
The gas can be stored in the gas-holder and piped into the house to provide clean
fuel for cooking and lighting. It has a slight barn-yard odor by which any leaks
can be readily detected, and a very low toxicity since it contains very little carbon
monoxide—the toxic constituent of most city gas. It burns with a violet flame
without smoke. Since a considerable amount of CO2 is mixed with the methane,
the risk of fire or explosion is somewhat less than in the case of city gas.
However, every precaution should be taken to avoid obtaining a mixture of
methane and air, except when the methane is burned as an open flame. Mixtures
of 5% - 14% methane in air are explosive when large quantities are ignited.
There are several basic factors to be considered when constructing or purchasing
a digester installation. These are: (1) climate; (2) single or multiple family
installations; (3) amount of wastes available; (4) gas production; (5) location of
digesters; (6) gas requirements and storage. (www.biogasworks.com)
2.8 VARIOUS ANAEROBIC DIGESTION SYSTEMS.
Anaerobic digestion processes can be classified according to the total solids (TS)
content of the slurryin the digester reactor. Low solids systems (LS) contain less
than 10 % TS, medium solids (MS) contain about 15%-20%, and high solids (HS)
processes range from22% to 40% (Tchobanoglous, 1993). Aanerobic digestion
processes can be categorized further on thebasis of number of reactors used, into

29
single-stage and multi-stage. In single stageprocesses, the three stages of
anaerobic process occur in one reactor and areseparated in time (i.e., one stage
after the other) while multi-stage processes make use of two or more reactors that
separate the acetogenesis and methanogenesis stagesin space. Batch reactors are
used where the reactor is loaded with feedstock at thebeginning of the reaction
and products are discharged at the end of a cycle. The othertype of reactor used,
mostly for low solids slurries, is continuous flow where thefeedstock is
continuously charged and discharged.As noted earlier, the anaerobic digetion
systems treat various types of waste-streams and in someplants MSW is mixed
with sewage sludge or other type of waste. These types ofprocesses will be
discussed in more detail later. (www.biogasworks.com)
2.9 IMPORTANT OPERATING FACTORS IN ANAEROBIC DIGESTION
PROCESS
The rate at which the microorganisms grow is of paramount importance in the
anaerobic digestionprocess. The operating parameters of the digester must be
controlled so as toenhance the microbial activity and thus increase the anaerobic
degradation efficiencyof the system. Some of these parameters are discussed in
the following section.
i. Digestion period.
The digestion period is also called the Retention time. The required retention time
for completion of the AD reactions varies with differing technologies, process
temperature, and waste composition. The retention time for wastes treated in
mesophilic digester range from 10 to 40 days. Lower retention times are required

30
in digesters operated in the thermophilc range. A high solids reactor operating in
the thermophilic range has a retention time of 14 days.
(Personal Communication with M. Lakos, May 2001).
Digestion period =
𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑅𝑒𝑎𝑐𝑡𝑜𝑟
𝐷𝑎𝑖𝑙𝑦 𝑖𝑛𝑝𝑢𝑡 𝑜𝑓 𝑤𝑎𝑠𝑡𝑒
……………………………….. (2.1)
ii. Waste composition/Volatile Solids (VS)
The wastes treated by Anaerobic Digestion may comprise a biodegradable
organic fraction, a combustible and an inert fraction. The biodegradable organic
fraction includes kitchen scraps, food residue, and grass and tree cuttings. The
combustible fraction includes slowly degrading lignocellulosic organic matter
containing coarser woodpaper, and cardboard. As these lignocellulosic organic
materials do not readily degrade under anaerobic conditions, they are better suited
for waste-to-energy plants.
Finally, the inert fraction contains stones, glass, sand, metal, etc. This fraction
ideally should be removed, recycled or used as land fill. The removal of inert
fraction prior to digestion is important as otherwise it increases digester volume
and wear of equipment. In waste streams high in sewage and manure, the
microbes thrive and hydrolyse the substrate rapidly whereas for the more resistant
waste materials such as wood, digestion is limited.
The volatile solids (VS) in organic wastes are measured as total solids minus the
ashcontent, as obtained by complete combustion of the feed wastes. The volatile
solidscomprise the biodegradable volatile solids (BVS) fraction and the refractory
volatilesolids (RVS). Kayhanian (1995) showed that knowledge of the BVS
fraction of MSW helps in better estimation of the biodegradability of waste, of

31
biogasgeneration, organic loading rate and C/N ratio. Lignin is a complex organic
materialthat is not easily degraded by anaerobic bacteria and constitutes the
refractoryvolatile solids (RVS) in organic MSW. Waste characterized by high VS
and low non-biodegradable matter, or RVS, is best suited to anaerobic digestion
treatment. The compositionof wastes affects both the yield and biogas quality as
well as the compost quality.
iii. pH Level
Anaerobic bacteria, specially the methanogens, are sensitive to the
acidconcentration within the digester and their growth can be inhibited by
acidicconditions. The acid concentration in aqueous systems is expressed by the
pH value,i.e. the concentration of hydrogen ions. At neutral conditions, water
contains a concentration of 10-7 hydrogen ions and has a pH of 7. Acid solutions
have a pH less than 7 while alkaline solutions are at a pH higher than 7. It has
been determined(RISE-AT, 1998) that an optimum pH value for AD lies between
5.5 and 8.5. During digestion, the two processes of acidification and
methanogenesis require different pH levels for optimal process control. The
retention time of digestate affects the pH value and in a batch reactor
acetogenesis occurs at a rapid pace. Acetogenesis can lead to accumulation of
large amounts of organic acids resulting in pH below. Excessive generation of
acid can inhibit methanogens, due to their sensitivity to acid conditions.
Reduction in pH can be controlled by the addition of lime or recycled filtrate
obtained during residue treatment. In fact, the use of recycled filtrate can even
eliminate the lime requirement. As digestion reaches the methanogenesis stage,
the concentration of ammonia increases and the pH value can increase to above 8.
Once methane production is estabilized, the pH level stays between 7.2 and 8.2.

32
iv. Temperature
There are mainly two temperature ranges that provide optimum digestion
conditions
for the production of methane – the mesophilic and thermophilic ranges. The
mesophilic range is between 20°C - 40°C and the optimum temperature is
considered to be 30o-35oC. The thermophilic temperature range is between 50°C-
65°C (RISEAT, 1998). It has been observed that higher temperatures in the
thermophilic range reduce the required retention time. (National Renewable
Energy Laboratory, 1992).
v. Carbon to Nitrogen Ratio (C/N)
The relationship between the amount of carbon and nitrogen present in organic
materials is represented by the C/N ratio. Optimum C/N ratios in anaerobic
digesters are between 20 – 30. A high C/N ratio is an indication of rapid
consumption of nitrogen by methanogens and results in lower gas production. On
the other hand, a lower C/N ratio causes ammonia accumulation and pH values
exceeding 8.5, which is toxic to methanogenic bacteria. Optimum C/N ratios of
the digester materials can be achieved by mixing materials of high and low C/N
ratios, such as organic solid waste mixed with sewage or animal manure.
vi. Total solids content (TS)/OrganicLoading Rate (OLR)
As discussed earlier, Low solids (LS) AD systems contain less than 10 % TS,
medium solids (MS) about 15-20% and high solids (HS) processes range from
22% to 40% (Tchobanoglous, 1993). An increase in TS in the reactor results in
acorresponding decrease in reactor volume.
Organic loading rate (OLR) is a measure of the biological conversion capacity of
the AD system. Feeding the system above its sustainable OLR results in low

33
biogas yield due to accumulation of inhibiting substances such as fatty acids in
the digester slurry (Vandevivere, 1999). In such a case, the feeding rate to the
system must be reduced. OLR is a particularly important control parameter in
continuous systems. Many plants have reported system failures due to
overloading (RISE-AT, 1998).
vii. Mixing
The purpose of mixing in a digester is to blend the fresh material with digestate
containing microbes. Furthermore, mixing prevents scum formation and avoids
temperature gradients within the digester. However excessive mixing can disrupt
the microbes so slow mixing is preferred. The kind of mixing equipment and
amount ofmixing varies with the type of reactor and the solids content in the
digester.
viii. Basic Design
The central part of an anaerobic plant is an enclosed tank known as the digester.
This is an airtight tank filled with the organic waste, and which can be emptied of
digested slurry with some means of catching the produced gas. Design differences
mainly depend on the type of organic waste to be used as raw material, the
temperatures to be used in digestion and the materials available for construction.
Systems intended for the digestion of liquid or suspended solid waste (cow
manure is atypical example of this variety) are mostly filled or emptied using
pumps and pipe work. A simpler version is simply to gravity feed the tank and
allows the digested slurry to overflow the tank. This has the advantage of being
able to consume more solid matter as well, such as chopped vegetable waste,
which would block a pump very quickly. This provides extra carbon to the system

34
and raises the efficiency. Cow manure is very nitrogen rich and is improved by
the addition of vegetable matter.
ix. Compost
When the digestion is complete, the residue slurry, also known as digestate, is
removed, the water content is filtered out and re-circulated to the digester, and
thefilter cake is cured aerobically, usually in compost piles, to form compost. The
compost product is screened for any undesirable materials, (such as glass
shards,plastic pieces etc) and sold as soil amendment. The quality of compost is
dependent on the waste composition. Some countries have prescribed standards
for compost quality. The U.S. Department of Agriculture has set standards for
heavy metals in the compost . These standards are for compost treated by the
aerobic process but may also be applied to AD compost product.
2.10 GAS REQUIREMENT AND STORAGE
The gas may be used for domestic purposes, such as cooking, heating water, food
refrigeration, and lighting. The following are some approximate quantities of gas
for these different uses : domestic cooking, 2.0 m3 per day for a family of five or
six people; water heating, 3m3 per day for 100-litre tank or 0.600 m3 for a tub
bath and 0.35 m3 for a shower bath; domestic food refrigeration, 2.5-3.0 m3 per
day for a family of five or six people; lighting, 0.100-150 m3 per hour per light.
Since the gas is produced continuously, day and night, but is used largely during
the daytime, it is necessary to provide storage facilities so that the gas will not be
wasted and will be available when needed. The storage capacity should be

35
estimated to meet peak demands. For small installations, storage capacity of
about one day’s requirement of gas should be provided. The volume of the gas-
holder should not be less than about 2.0 m3, even for very small installations. The
gas-holder may be circular or square and should be provided with a water seal to
prevent the escape of gas or admission of air. The weight of the floating cover of
the gas-holder provides the gas pressure.
2.11 TYPES OF ANAEROBIC DIGESTION SYSTEMS.
As discussed previously in the methods used to treat MSW anaerobically can be
classified into following categories:
 Single Stage
 Multi Stage
 Batch
These categories can be classified further, based on the total solids (TS) content
of the slurry in the digester reactor. As noted earlier, low solids (LS) contain less
than 10% TS, Medium solids (MS) contain about 15-20% High solids (HS)
processes range from about 22% to 40%. The single stage and the multi stage
systems can befurther categorized as single stage low solids (SSLS), single stage
high solid (SSHS), multi stage low solids (MSLS) and multi stage high solids
(MSHS). The drawback of LS is the large amount of water used, resulting in high
reactor volume and expensive post-treatment technology. The expensive post
treatment is due to de-watering required at the end of the digestion process. HS
systems require a smaller reactor volume per unit of production but this is
counter-balanced by the moreexpensive equipment (pumps, etc.) required.
Technically, HS reactors are morerobust and have high organic loading rates.

36
Most anaerobic digestion plants built in the 80's werepredominantly low solids
but during the last decade the number of high solidsprocesses has increased
appreciably. There is substantial indication from theobtained data that high solids
plants are emerging as winners.
2.11.1 Single Stage Process
Single stage reactors make use of one reactor for both acidogenic phase as well
asmethanogenic phase. These could be LS or HS depending on the total solids
contentin a reactor.
2.11.2 Single Stage Low Solids (SSLS) Process
Single stage low solids processes are attractive because of their simplicity. Also
theyhave been in operation for several decades, for the treatment of sludge from
thetreatment of wastewater. The predominant reactor used is the continuously
stirredtank reactor (CSTR). The CSTR reactor ensures that the digestate
iscontinuously stirred and completely mixed. Feed is introduced in the reactor at
arate proportional to the rate of effluent removed. Generally the retention time is
14-28 days depending on the kind of feed and operating temperature.Some of the
SSLS commercial AD plants are the Wassa process in Finland, theEcoTec in
Germany, and the SOLCON process at the Disney Resort Complex,Florida
(www.soton.ac.uk). The plant examined in more detail is the Wassa processplant
(10%-15 % TS) that was started in 1989 in Waasa, Finland (Figure 2).
Currently there are three Wassa plants ranging from 3000-85000 tons per
annum,some operating at mesophilic and others at thermophilic temperatures.
The retentiontime in the mesophilic process is 20 days as compared to 10 days in
thethermophilic. The feed used in this process is mechanically pre-sorted MSW
mixedwith sewage sludge. The organic loading rate (OLR) differs with the type

37
of waste.The OLR was 9.7 kg/(m3 day) with mechanically sorted organic MSW
and 6 kg/(m3day) with source separated waste. The gas production was in the
range of 170 Nm3 CH4/ton of VS fed and 320 Nm3 CH4/ton of VS fed and 40-
75% reduction of thefeed VS was achieved (Vandevivere, 1999).The advantages
offered by SSLS are operational simplicity and technology that hasbeen
developed for a much longer time than high solids systems. Also, SSLS makesuse
of less expensive equipment for handling slurries. The pre-treatment
involvesremoving of coarse particles and heavy contaminants. These pre-
treatment stepscause a loss of 15 - 25 % VS, with corresponding decrease in
biogas yield. The othertechnical problem is formation of a layer of heavier
fractions at the bottom of thereactor and floating scum at the top, which indicate
non-homogeneity in the reactingmass. The bottom layer can damage the
propellers while the top layer hinderseffective mixing. This requires periodic
removal of the floating scum and of the heavy fractions, thus incurring lower
biogas yield. Another flaw is the shortcircuiting, i.e a fraction of the feed passes
through the reactor at a shorter retentiontime than the average retention time of
the total feed. This lowers the biogas yieldand impairs hygienization of the
wastes.For the solids content to be maintained below 15%, large volumes of
water areadded, resulting in large reactor volumes higher investment costs, and
amount ofenergy needed to heat the reactor. Also, more energy and equipment are
required forde-watering the effluent stream. The high investment costs associated
with dilutionand reactor volume plus the complex pre-treatment step offset the
gains from the lowcost equipment to handle slurry.

38
2.11.3 Single- Stage High Solids (SSHS) Process
The advances of the HS technology were the result of research undertaken in the
80's that established higher biogas yield in undiluted waste. Some of the examples
of SSHS are the DRANCO, Kompogas, and Valorga processes. The DRANCO
and Valorga processes ar described in more detail later in this thesis. All three
processes consist of a single stage thermophilic reactor (mesophilic in some
Valorga plants)with retention time of 14-20 days.In the DRANCO reactor (Figure
2.12 below), the feed is introduced from the top anddigested matter is extracted
from the bottom. There is no mixing apart from thatoccurring due to downward
plug flow of the waste. Part of the extracted matter isreintroduced with the new
feed while the rest is de-watered to produce the compostproduct.The Kompogas
process (Figure 3b) works similarly, except the movement takesplace in plug flow
in a horizontally disposed cylindrical reactor. Mixing isaccomplished by the use
of an agitator. The process maintains the solidsconcentration at about 23% TS. At
solids content lower than 23%, the heavyfraction such as sand and glass can sink
and accumulate at the bottom; higher TSconcentrations impede the flow of
materials.(Vandevivere, 1999).
Figure 2.12: The DRANCO reactor (A) and Kompogas Reactor (B)
(Vandevivere, P. et al, 1999).

39
The design of the Valorga process is unique. The reactor is a vertical
cylindricalreactor divided by a partial vertical wall in the center (Figure 2.13).
The feed entersthrough an inlet near the bottom of the reactor and slowly moves
around the verticalplate until it is discharged through an outlet that is located
diametrically opposite tothe inlet. Re-circulated biogas is injected through a
network of injectors at thebottom of the reactor and the rising bubble result in
pneumatic mixing of the slurry.The injectors require regular maintenance, as they
are prone to clogging.
Figure 2.13:The Valorga Digester
(The Anaerobic Digestion and the Valorga Process, Jan 1999.)
The high solids content in HS systems requires different handling, mixing and
pretreatment than those used in the LS processes. The equipment needed to
handle andtransport high solids slurries is more robust and expensive than that of
the LS,comprising of conveyor belts, screws, and powerful pumps. On the other
hand, thepre-treatment is less cumbersome than for LS systems. The HS systems

40
can handleimpurities such as stones, glass or wood that need not be removed as in
SSLS.Contrary to the complete mixing prevailing in SSLS, the SSHS are plug-
flowreactors hence require no mechanical device within the reactor (De Baere,
1999).
The economic differences between the SSLS and SSHS are small.SSHS
processes exhibit higher OLRs, as compared to SSLS; for example, OLRvalues of
15 kg VS/m3 per day are reported for the DRANCO plant in Brecht,Belgium,
where, whereas in the Waasa Process the OLR is 6 kg VS/m3 per day. Thebiogas
yield is usually high in SSHS as heavy fractions or the scum layer is notremoved
during the digestion.There are pronounced differences between SSHS and SSLS
reactors, in terms ofenvironmental impacts. The LS process consumes one m3 of
fresh water per tonMSW treated whereas the water use in HS is one tenth of that
(Nolan- ITU, May1999). Consequently, the volume of wastewater to be
discharged is several-fold lessfor HS reactors.
2.11.4 Multi-Stage Process
The introduction of multi-stage AD processes was intended to improve digestion
byhaving separate reactors for the different stages of AD, thus providing
flexibility tooptimize each of these reactions. Typically, two reactors are used, the
first forhydrolysis/liquefaction-acetogenesis and the second for methanogenesis.
In the firstreactor, the reaction rate is limited by the rate of hydrolysis of
cellulose; in the second bythe rate of microbial growth. The two-reactor process
allows to increase the rate ofhydrolysis by using microaerophilic conditions (i.e.,
where a small amount of oxygen issupplied in an anaerobic zone) or other means.
For methanogenesis, the optimum growthrate of microbes is achieved by

41
designing the reactor to provide a longer biomassretention time with high cell
densities or attached growth (also known as “fixed filmreaction”, where the
microbes responsible for conversion of the organic matter areattached to an inert
medium such as rock, or plastic materials in the reactor). Animportant
requirement to be met in such reactors is removal of the suspended particlesafter
the hydrolysis stage. Multi-stage processes are also classified as multi-stage
lowsolids(MMLS) and multi-stage high-solids (MMHS). There is a lot of
similarity, in terms of solids content, pre-treatment steps, handling of waste,
requirement of water etc., between SSLS and MMLS as well as SSHS and
MMHS processes.
2.11.5 Multi-Stage Low Solids Process
Some of the MSLS facilities are the Pacques process (Netherlands), the BTA
process (Germany, Canada) and the Biocomp (Germany) process as shown on
figure 2.14. The Pacques process uses two reactors at mesophilic temperature.
Initially, The feed consisted of fruit and vegetable waste but recently source-
separated MSW is also being processed. The first reactor where hydrolysis occurs
has solids content 10 %. Mixing is achieved by means of gas injection. The
digestate from the first reactor is de-watered, and the liquid is fed to an Upflow
Anaerobic Sludge Blanket reactor where methanogenesis occurs. The fraction of
the digestate from the hydrolysis reactor is re-circulated with the incoming feed to
the first reactor for inoculation. The remaining fraction is sent for compost
production. In the BTA process (Figure 2.14 ) the solid content is maintained at
10% and the reactors are operated at mesophilic temperatures. This process is
described in detail in the case study section. It is very similar to the Pacques

42
process except that the methanogenic reactor is designed with attached growth
(“fixed film reaction”) to ensure biomass retention. The effluent from the
hydrolysis reactor is de-watered and the liquor is fed to the methanogenic reactor.
This reactor receives only the liquid fraction from hydrolysis reactor to avoid
clogging of the attached growth. At times, in order to maintain the pH within the
hydrolysis reactor in the range of 6-7, the process water from the methanogenic
reactor is pumped to the hydrolysis reactor. The multi-stage low solids processes
are plagued with similar problems to those of the SSLS reactors, such as short-
circuiting, foaming, formation of layers of different densities, expensive pre-
treatment. In addition, the MSLS processes are technically more complex and
thus require a higher capital investment. (www.soton.ac.uk)
Figure 2.14: The flow diagram of BTA Process
(www.canadacomposting.com).

43
2.11.6 Multi -Stage High-Solids Process
The Biopercolat process is a multi-stage high-solids process but is somewhat
similar to th Pacques process (MSLS) in that it consists of a
liquefaction/hydrolysis reactor followed by a methanogenic Upflow Anaerobic
Blanket Sludge reactor (UASB) with attached growth. However hydrolysis is
carried out under high solids and microaerophilic conditions (where limited
amount of oxygen is supplied in anaerobic zone). The aeration in the first stage
and the attached growth reaction in the second provide for complete digestion at
retention time of only seven days.
The advocates of multi-stage processes cite the advantages of high OLR for all
types of multi-stage systems, such as 10kg VS/(m3.d) and 15kg VS/(m3.d) for the
BTA(MSLS) and Biopercolat processes (MSHS), respectively. This is due to
higher biomass retention with attached biofilm, which increases the resistance of
methanogens to high ammonium concentrations (Vandevivere, 1999). The
biological stability thus achieved offers potential for increased OLR. However,
high OLR does not result in high biogas yield. The lower biogas yield observed in
practice is due to removal of solids that contain some biodegradable matter, after
the short hydrolysis period before feeding the methanogenic reactor. In recent
years, the single-stage systems have also achieved high OLRS thus canceling this
advantage of multi-stage systems. According to De Baere 1999, commercial
applications of multi-stage systems amount to only 10 % of the current treatment
capacity, as will be discussed later, under current trends of AD systems.

44
2.12 BATCH REACTORS
Batch reactors are loaded with feedstock, subjected to reaction, and then are
discharged an loaded with a new batch. The batch systems may appear as in-
vessel landfills but in fact achieve much higher reaction rates and 50- to 100%
higher biogas yields than landfills for two reasons. First, the continuous re-
circulation of the leachate and second, they are operated at higher temperatures
than landfills. There are three types of batch systems - single stage batchsystem
sequential batch system and an Upflow Anaerobic Sludge Blanket reactor.
(Vandevivere, 1999)
Figure 2.15:Types of Batch Reactors (Vandevivere, et al (1999)
The single-stage batch system involves re-circulating the leachate to the top of the
same reactor An example of such a system is the Biocel process in Lelystad, The
Netherlands that was started in 1997 and treats 35,000 tons/y of source-sorted
biowaste. The system operates at mesophilic temperatures and consists of
fourteen concrete reactors each of 480m3 capacity. The waste fed to these
unstirred reactors is pre-mixed with inoculums. The leachates are collected in
chambers under the reactors and recycled to the top of each reactor. The waste is

45
kept within the reactor for over40 days, until biogas production stops. The Biogas
plant produces on the average 70kg biogas/ton of source-sorted biowaste which is
40 % less than from a single stage low-solids digester treating similar wastes
(Vandevivere, 1999).
The sequential batch process comprises two or more reactors. The leachate from
the first reactor, containing a high level of organic acids, is re-circulated to the
second reactor where methanogenesis occurs. The leachate of the methanogenic
reactor, containing little or no acid, is combined with pH buffering agents and re-
circulated to the first reactor. This guarantees inoculation between the two
reactors.
The third type of batch process is the hybrid batch-UASB process, which is very
similar to the multi-stage process with two reactors. The first reactor is simple
batch reactor but the second methanogenic reactor is an up flow anaerobic sludge
blanket (UASB) reactor. Batch processes offer the advantages of being
technically simple, inexpensive and robust. However, they require a large land
footprint as compared to single-stage HS reactors since they are much shorter and
their OLR two-fold less (Vandevivere, 1999). Other disadvantages are settling of
material to the bottom thus inhibiting digestion and the risk of explosion while
unloading the reactor.
2.13 ECONOMICS OF BIOGAS
Biogas technology is a complete system in itself with its set objectives (cost
effective production of energy and soil nutrients), factors such as microbes, plant
design, construction materials climate, chemical and microbial characteristics of

46
inputs, and the inter-relationships among these factors. Brief discussions on each
of these factors or subsystems are presented in this section.
2.13.1 Economic.
An ideal plant should be as low-cost as possible (in terms of the production cost
per unit volume of biogas) both to the user as well as to the society. At present,
with subsidy, the cost of a plant to the society is higher than to an individual user.
2.13.2 Simple design
The design should be simple not only for construction but also for operation and
maintenance. This is an important consideration especially in areas where the rate
of literacy is low and the availability of skilled human resource is scarce.
2.13.3 Utilization of local materials.
Use of easily available local materials should be emphasized in the construction
of a biogas plant. This is an important consideration, particularly in areas where
transportation system is not yet adequately developed.
2.13.4 Durability.
Construction of a biogas plant requires certain degree of specialized skill which
may not be easily available. A plant of short life could also be cost effective but
such a plant may not be reconstructed once its useful life ends. Especially in
situation where people are yet to be motivated for the adoption of this technology
and the necessary skill and materials are not readily available, it is necessary to
construct plants that are more durable although this may require a higher initial
investment.

47
2.13.5 Suitable for the type of inputs.
The design should be compatible with the type of inputs that would be used. If
plant materials such as rice straw, maize straw or similar agricultural wastes are
to be used, then the batch feeding design or discontinuous system should reused -
instead of a design for continuous or semi-continuous feeding.
2.13.6 Frequency of Using Inputs and Outputs.
Selection of a particular design and size of its various components also depend
on how frequently the user can feed the system and utilize the gas.
Inputs and their Characteristics and any biodegradable organic material can be
used as inputs for processing inside the bio-digester. However, for economic and
technical reasons, some materials are more preferred as inputs than others. If the
inputs are costly or have to be purchased, then the economic benefits of outputs
such as gas and slurry will become low. Also, if easily available biodegradable
wastes are used as inputs, then the benefits could be of two folds: (a) economic
value of biogas and its slurry; and (b) environmental cost avoided in dealing with
the biodegradable waste in some other ways such as disposal in landfill.
2.14 SAFETY CONSIDERATION
Like water, electricity, automobiles and most of life biogas is not completely
safe. Some of it effects include:
i. Asphyxiation
Biogas consists mainly of CH4 and CO2, with low levels of H2S and other gases.
Each of these components has its own problems, as well as displacing oxygen.
CH4 – Lighter than air and will collect in roof spaces, explodes when in mixed
with air.

48
CO2 – Heavier than air and will collect in sumps; slightly elevated levels affect
respiration rate, higher levels displace O2 as well.
H2S – Has a rotten egg smell, destroys olfactory tissues and lungs, and become
odourless as the level increase to dangerous and fatal. The preventive measures
include; adequate ventilation, suitable precautions and adequate protective
equipment will minimize the dangers associated with biogas.
ii. Diseases
Anaerobic digestion relays in a mixed population of bacteria of largely unknown
origin, but often including animal wastes, to carry out waste treatment process,
car should be taken to avoid contact with the digester content and to wash
thoroughly after working around the digester. This also helps to minimize the
spread of odours which may accompany the digestion process.
iii. Fire/Explosion
Methane forms explosive mixtures with air, the lower limit being 5% methane
and the upper limit being 15% methane. Biogas mixtures containing more than
50% methane are combustible while lower percentages may support, or fuel,
combustion. Therefore, no naked flames should be used in the vicinity of a
digester and electrical equipment must be of suitable quality, normally explosion
proof. If conducting a flame test, take a small sample well away from the main
digester or incorporate a flame trap in the supply line.
As biogas displaces O2 level restricting respiration, so any digester are needs to
be well ventilated to minimize the risks of fire/explosion and asphyxiation
(www.adelaide.edu.au/biogas/safety/).

49
CHAPTER THREE
3.0 MATERIALS AND EQUIPMENT
3.1 MATERIALS
The following are the materials were used during the cause of this
research work;
3.1.1 Waste and Water
Waste and water are the materials needed for the experimental process. Also,
water is also used to wash any other equipment that is needed to be washed
before use.
3.1.2 Cattle dung
This is the feed material to the floating drum bio-digester that is mixed with water
and some other needful materials, which undergoes fermentation to produce the
biogas needed.
3.1.3 Single Super Phosphate
This served as source of acid which was added to the slurry during mixing,
decreasing the pH of the slurry, and thereby increases the acidity of the slurry.
3.1.4 Ash
Ash consists majorly of the element known as potassium. In solution in easily
reacts with water to form a basic or alkaline solution (KOH). It serves as the
source of base to the slurry during mixture.
3.2 EQUIPMENT
3.2.1 Weigh Balance; Model PIC 45284
This equipment was used to measure the weigh the waste, water and any other
material that needs to be weighed for the purpose of the laboratory work.

50
3.2.2 Aluminium Sheet
The aluminium sheet was the material used for the fabrication of the bio-
digester.
3.2.3 Thermometer
This equipment/instrument was used to measure the temperature of the
surrounding (ambient) and that of the water in the bio-digester.
3.2.4 Hose
This is a slender rubber tube (about 5-10mm i.e. internal to external diameter)
which was used as a channel of collecting the gas from the digester.
3.2.5 Mortar and Pestle
This was used in reducing the size of the waste in order to increase its surface
area for better digestion of the slurry by the bacteria.
3.2.6 pH Meter JENWAY model 3150
This was used to determine the PH of the waste both before and after digestion.
Figure 3.1 a bio-digester Figure 3.2 Burner

51
Figure 3.3: a pH meter Figure 3.4: a Weighing balance
Figure 3.5: Slurry before digestion Figure 3.6: Slurry after digestion

52
CHAPTER FOUR
4.0 METHODOLOGY
4.1 MATERIAL SELECTION
The material selection for this research work was done considering the feed
material, type of gas to be produced, convenience and availability. Aluminium
was used as the material of fabrication.
4.2 SELECTED BIO-DIGESTER
From all the types of digesters described in the literature survey, with respect to
the scope of this research work, the digester selected for the production of biogas
using Cow-Dung is the ‘Floating drum digester’.
4.2.1 Criterion for selecting Floating drums digester
The following factors are considered for selecting the Floating drums digester in
the production of biogas using cow dung:
i. The design is simple to understand, operate and maintain.
ii. They provide gas at a constant pressure, and the stored gas-volume is
immediately recognizable by the position of the drum.
iii. In terms of production cost per unit volume of biogas, both to user and to
society, the designing and fabricating of the Floating drum digesters is
cost effective.
iv. It is durable, depending on the type of material used in fabrication and
how it is done.

53
4.3 DESIGN, FABRICATION AND ASSEMBLY OF THE BIODIGESTER
The bio-digester was designed and then fabrication was done by a well
experienced fabricator in Samaru. These joints where sealed using a special gum
and then checked again using water and allowed to dry. After the sealing, the
digester was coupled in this manner; the Reactor (layer 2) was put into the water
seal (layer 1) and Gas collector (layer 3) served as the cover of which a tube was
connected to it, leading to the burner. For this fabrication, the Gas collector was
calibrated to observe the changes of volume of gas produced.
4.4 PREPARATION OF SAMPLES
The cow dung being the raw material for the preparation of the sample for the
production of biogas was obtained from the Abattoir at Zango here in Zaria. It
was initially wet, but after transporting it to the school, it was dried by spreading
it in an open air and at ambient temperature. It took about four days for the
substrate (Cow dung) to get dried. After drying the substrate, it was taken to the
department of chemistry to be pounded, in order words, reducing the dried
substrate to smaller size, therefore increasing the surface area of the dried
substrate for better solubility between it and the solvent (water) and also better
digestion by the bacteria. Before mixing the substrate with water and loading it
into the digester, nylons and other foreign materials were carefully picked. The
concentration of substrate from literature (between the ranges of 5-10) was
assumed to be 7.5%.
 Volume of reactor is 34380cm3/1000 = 34.38L
 7.5% of VR = 0.075×34380= 2578.5 =equivalent value of the weight of substrate.
 Therefore, the calculated weight of dry cow dung = 2578.5g.

54
In order to have a favourable pH range for the anaerobic digestion of the slurry,
Single super phosphate (SSP) which is acting as the acid, is added in the ratio of
10:1 = 257.85g. Also, ash which is acting as the base/alkali is also added in the
ratio of 2:1, with respect to the weight of SSP. Therefore, the weight of ash
=
257.85
2
= 128.925g.
The ratio of the cow dung to water mixture is 1:10. Therefore, the weight of tap
water mixed with the cow dung is = 2578.5×10 = 25785g.
The mixed slurry was then poured into the digester tank and sealed properly to
ensure air-tightness. The experiment was subjected to a retention period of 14-
40days.
The temperature of the slurry in digester was observed daily through the
thermometer. The ambient temperature, that is, the temperature of the
surrounding was also measured daily. The pH of the fresh Cow dung as well as
the slurry was determined using the pH Meter JENWAY model 3150 at the
Department of Biochemistry A.B.U, Zaria.
The percentage composition of the Cow dung (Carbon and Nitrogen) was
carried out at I.A.R (Institute for Agricultural Research) A.B.U, Zaria using
Walkley Black method and Kjedhal method.
4.5 COST EVALUATION FOR THE DESIGN AND FABRICATION OF
THE BIO-DIGESTER
The cost of every material, equipment and all other expenses made during the
research work was recorded and the total cost per unit volume of the bio-digester
was also calculated.

55
4.6 TEST RUN OF THE COW DUNG
The cow dung was test ran for a period of 95 days, to observe the retention time
(Digestion period) and also the days of gas production. The gas obtained was
also burned to test its combustibility.

56
CHAPTER FIVE
5.0 RESULTS AND DISCUSSION OF RESULTS
5.1 RESULTS FROM THE MATERIAL SELECTION
The material selection was done considering the feed material, type of gas to be
produced, convenience and availability. Aluminium was used as the material of
fabrication. The reason why Aluminum was selected as the material is because of
its ability to resist corrosion, which is caused by gases such as H2S, which when
mixed with water can cause acid corrosion. Using other materials such as steel
will combine with water and cause the metal to rust, therefore, reducing the
efficiency of the outcome of the research work and also becomes a liability, as it
causes more spending in trying to control it. And so this makes Aluminum the
choicest material for the fabrication of the bio-digester.
5.1.1 Cost Evaluation for the Design and Fabrication of the Bio-Digester
The cost evaluation for the design and fabrication of the bio-digesters is shown on
table 5.2, including the total cost per unit volume of digester.
Table5.2: Cost Evaluation for the Design and Fabrication of Bio-Digester
S/N Description Of Items Quantity Unit
Price(N)
Amount(N)
1 Fabrication of Bio-
digester(aluminium sheets,
fabrication and small size hose)
1 - 6,500
2 Burner 1 500 500
3 Thermometer 1 300 300
4 About 400g of Inoculums
(Rumen content)
2 40 80

57
5 Bags of Cow dung 3 60 180
6 Polyethene Bag 6 30 180
7 Detergent 1 20 20
8 Superglue 4 50 200
9 Potti 1 50 50
10 Transportation ------ ------ 500
11 Pair of mortar and pestle 1 800 800
12 miscellaneous ------ ------ 2,500
TOTAL 11,810
VOLUME ……….. ……….. 31,863.57cm3
𝑻𝑶𝑻𝑨𝑳 𝑪𝑶𝑺𝑻 𝑼𝑵𝑰𝑻 𝑽𝑶𝑳𝑼𝑴𝑬⁄ ……….. ……… 3.70643×10-1
N/cm3
(Note: N= Naira, Nigerian currency)
5.2 RESULTS FOR THE DESIGN OF THE BIO-DIGESTER
The whole idea behind the bio- digester is the production of biogas with waste
using anaerobic digestion process. Some factors were considered in the design of
the bio-digester including the material selection, and its availability, pressure of
the gas and the volume. The digester is a series of cylinders which include the
water seal and the Gas collector that are coupled together.
The volume of the digester was estimated and calculated. The shape of the
digester is cylindrical. Therefore, the volume was used to determine the size of
the digester. The estimated volume is; V = 31863.57cm3
From the formula of a cylinder given as: V =𝜋𝑅2
𝐻, Where; R =
𝐷
2
= 13cm;
(Where D=Diameter, R=Radius of the Cylinder)
H = 60cm = Height of the Cylinder. The design of the floating drum bio-
digester was done with the aid of AUTOCAD, having all layers placed

58
accordingly, that is; layer 2 (Reactor), placed in the layer 1(Water seal), and then
layer 3 (Gas collector) placed on layer 2. This is illustrated in figure 5.1.
LEBEL
First layer
Cylinder 1
Second layer
Cylinder 2
Third Layer
Cylinder 3
NOTE: All dimensions are in centimetres (cm)
Figure 5.1: AUTOCAD design of the Bio-digester with all layers coupled
together

59
5.3 RESULTS OF FABRICATION OF THE BIO-DIGESTER
In order to account accurately for the volumes of gas produced and any other
calculations needed in this research work, it is vital that the sketched dimensions
of all the layers of the bio-digester was done. The Table 5.1 shows the dimensions
of all the components of the Bio-digester used for various calculations and also
given to the fabricator for fabrication.
Table 5.1: shows the design specification and sketches that was used for the
calculation and fabrication.
Specification Sketches Calculation
HR =60cm
DR =26cm
Layer 2
(Reactor)
60
26
Volume of
digester is given
as; V=𝜋𝑅2
𝐻
Where; R =13cm,
H = 60cm.
V=𝜋 ∗ (13)2
∗ 60
V=31863.57cm3
Hw =68cm
D w =28cm
Layer 1
(Water seal)
68
28
H c =63cm
Dc =27cm
Layer 3
(Gas collector)
63
27
The following figures are the pictorial fabricated layers of the Bio-Digesters.

60
Figure 5.2a: Layer 1 (Water Seal) Figure 5.2b: Layer 2 (Reactor)
Figure 5.2c: Layer 3 (Gas Collector) Figure 5.2d: Bio-Digester (Layer1,
Layer2 and Layer 3 all together)

61
5.4 RESULTS FROM THE TEST RUN OF COW DUNG IN THE
DIGESTER
The cumulative volumes of biogas produced from day 1 of mixing the cow dung
slurry, to through the digestion period and the biogas production period, are all
illustrated on figure 5.3
Figure 5.3: a bar chart, representing the cumulative volumes of biogas produced
from day 1 to day 95.
During the course of the project work, three regimes of the biogas production
were observed from the results obtained. This is as a result of notable changes of
the rate of biogas production. They are:
i. the Digestion period (Retention time), from day 1 to day 37,
0
20000
40000
60000
80000
100000
120000
1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89 93
CummulativevolumeofBiogas
Days
Barchart representation of the Cummulative volume of Biogas and
Days (from Day 1 to Day 95)
Series2
Series1

62
This is the period of anaerobic digestion (fermentation) of the cow dung slurry,
consisting of the three distinct stages of reaction, which are the:
 hydrolysis
 Acetogenesis, and
 Methanogenesis
Although this is the most vital regime of biogas production of which the success
of the biogas production, no biogas was produced. On the 35th day, more
ruminant content (Inoculums) was added to the cow dung slurry to increase the
anaerobic bacteria, to hasten the digestion of the cow dung slurry, thereby
releasing the production of the biogas. This is illustrated by Figure 5.4
Figure 5.4: shows that there was no biogas produced during the digestion
period/Retention time.
ii. Rate of Biogas production from day 38 to day 55, and
On the 38th day, there was a notable change in height from the gas collector of
7cm, equivalent to the calculated volume of 4011cm3 of biogas. The cumulative
volume of the biogas from that day was daily taken and recorded. The range of
0
0.2
0.4
0.6
0.8
1
0 10 20 30 40
CummulativeVolumesofBiogas
Days (Retention Time)
Rate of Biogas productionduring the Retention
time/DigestionPeriodfromDay 1 to Day 37
Series1

63
height during this period was between 5 and 7cm. Also, the average rate of biogas
production obtained illustrated by Figure 5.5, was 2863.8cm3/day =
119.325cm3/hour = 1.98875cm3/min.
Figure 5.5: shows the rate of biogas production from the 38th day to the 55th day,
with respect to the cumulative volumes of Biogas produced and the days.
iii. Rate of biogas production from day 56 to day 95.
From day 56, there was a change (decrease) in the rate of biogas production from
2863.8cm3/day to 1273.1cm3/day. The range of height observed from the gas
collector during this period was between 2 and 3cm. This is shown by figure 5.6.
y = 2863.8x - 104231
R² = 0.9997
0
10000
20000
30000
40000
50000
60000
0 20 40 60
CumulativeVolumesofBiogas
Days
Rate of Biogas production from
the 38thDay to the 55thday.
Series1
Linear
(Series1)

64
Figure 5.6: shows the rate of biogas production from the 56th day to the 95th day.
5.4.1 Burning Test
After the 38th day, a burning test was carried out several times to ascertain the
combustibility of the gas that has been produced. It was observed that, the gas
produced from the digester and stored in the gas collector was combustible and it
burnt with a blue flame. This is illustrated by the following figures 5.6
Figure 5.7 a: Blue flame from Biogas Figure 5.7 b: match, burner and flame
y = 1273.1x - 13243
R² = 0.9955
0
20000
40000
60000
80000
100000
120000
0 20 40 60 80 100
CumulativevolumesofBiogas
Days
Rate of Biogas productionfromthe 56thday to the
95thday.
Series1
Linear (Series1)

65
Figure 5.7c: Flames illustrating burning Figure 5.7d: Research student in the
Test, from the Biogas produced. Laboratory with the Bio-digester

66
CHAPTER SIX
6.0 CONCLUSION
From this research project, the following are the conclusions:
i. A floating drum bio-digester was designed and fabricated.
ii. The fabricated bio-digester was test ran using the cow dung as the feed
material.
iii. The digestion of the slurry was done anaerobically (in the absence of air),
for a period of 95 days.
iv. Biogas was produced in the floating Drum Digester with a cumulative
volume of 106432cm3, and was tested to be combustible, using a burner,
with a theoretical calculated equivalent heating value is about
1974.084
BTU
𝑚3
.

67
CHAPTER SEVEN
7.0 RECOMMENDATIONS
During the course of this research project, from challenges encountered and
observations noted, the following are my recommendations:
i. The continuous method of the floating drum instead of the batch method should
be applied in subsequent biogas production research project.
ii. Also, other types of digesters such as the bay digesters, fixed drum et al could
also be good platforms of biogas research work.
iii. More research should be carried out on the methane productivity of other waste
types such as chicken droppings, grasses, pig dung et al, so that their operating
conditions can also be optimized.
iv. The biogas project work could also be done not just in a small scale as it has
always been carried out, but in group since its expenses will definitely be high.

68
LIST OF REFERENCES
1. Adelekan B.A., Assessing Nigeria’s Agricultural Biomass Potential as a
Supplementary Energy Resource through Adoption of Biogas Technology.
Nigeria Journal of Renewable Energy. Sokoto Energy Research Center, Vol.10,
Nos. 1&2, Pp. 145-150, 2002.
2. Chynoweth, D.P., C.E. Turick, J.M. Owens, D.E. Jerger and M.W. Peck (1993).
Biochemical methane potential of biomass and waste feedstocks. Biomass and
Bioenergy, 5:95-111.
3. Cornejo, C. and Wilkie, A.C., “Greenhouse gas emissions and biogas potential
from livestock in Ecuador”. Energy for Sustainable Development, 2010.
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2011.
5. Ezekoye, V.A and Okeke C.E “Design, construction, and performance evaluation
of plastic bio-digester and the storage of biogas.” Pacific journal of science and
Technology. pg 176-184, 2006.
6. Florian N., .Electricity from wood through the combination of gasification and
solid oxide fuel cell. A PhD Thesis, Swiss Federal Institute of Technology
Zurich, 2008.

69
7. Lagrange B. “Bio-methane 2: Principles - Techniques Utilisation.” EDISUD, La
Calade France, 1979.
8. Lincoln, E.P., Wilkie, A.C. and French, B.T. “Cyano-bacterial process for
renovating dairy wastewater. Biomass and Bio-energy”, 1996.
9. Lettinga, G. and van Haandel, A.C. Anaerobic digestion for energy production
and environmental protection. In: Renewable Energy Sources for Fuels and
Electricity. T.B. Johansson et al. (Eds.), Island Press, Washington DC. p.817-839,
1993.
10. Marchaim U., “Biogas Processes for Sustainable Development”, FOA
Agricultural Services Bulletin 95, 1992.
11. Song Y.C, Kwon J.H., “Mesophilic and Thermophilic Temperature Co-Phase
Anaerobic Digestion Compared with Single Stage Mesophilic and Thermophilic
Digestion of Sewage Sludge”. p. 1653-1662. 2004.
12. Smith, W.H., Wilkie, A.C. and Smith, P.H. “Methane from biomass and waste - a
program review”. TIDE (Teri Information Digest on Energy), 2(1):1-20 (1992)
13. State Energy Conservation Office (Texas) “Biomass Energy: Manure for
Fuel.”State Energy Conservation Office (Texas).State of Texas, 2009.

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14. Tower P., Lombard, “New Landfill Gas Treatment Technology Dramatically
Lowers Energy Production Costs” Applied Filter Technology. (Retrieved, March
2012)
15. Wilkie, A.C., Anaerobic digestion of flushed dairy manure. In: Proceedings -
Anaerobic Digester Technology Applications in Animal Agriculture - A National
Summit. p. 350-354. Water Environment Federation, Alexandria, Virginia, 2003.
16. Wilkie, A.C., Smith, P.H. and Bordeaux, F.M. An economical bio-reactor for
evaluating biogas potential of particulate biomass. Bio-resource Technology,
92(1):103-109, 2004.
www.claverton-energy.com (Accessed march, 2012)
www.afdc.energy.gov (Accessed march, 2012)
www.ashdenawards.org (Accessed march, 2012)
www.clarke-energy.co.uk (Accessed march, 2012)
www.sgc.se/dokument/Evaluation/pdf (Accessed march, 2012)
www.ecotippingpoints .org (Accessed march, 2012)
www.alfagy.com (Accessed march, 2012)
www.nnfcc.co.uk/publications/nnfcc-renewable-fuels-and-energyfactsheet-
anaerobic-digestion (Accessed march, 2012)
www.wikipedia.org (Accessed march, 2012)
www.biomassenergycenter.org.uk (Accessed march, 2012)
www.wiki.answers.com. (Accessed March, 2012)
www.library.thinkquest.org (Accessed march, 2012)

71
www.fao.org/sd/Egdirect/Egre0022.html (Accessed February, 2012)
www.habmigern2003.Info/biogas/biofuels.html (Accessed March, 2012)
www.environment.nationalgeographic.com (Accessed March, 2012)
www.alternative-energy-news.info (Accessed march, 2012)
www.biofuelguide.net (Accessed March, 2012)
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(www.fastonline.org/CD3WD40/BIOGSHTM/EN/APPLDEV/DESIGN/DIGEST
YPES.HTML). (Accessed June, 2012)

72
APPENDIX
DETERMINATION OF TOTAL NITROGEN
(Regular Macro-kjedahl Method)
Apparatus:
 Macro-kjedahl digestion-distillation apparatus/Aluminum block digester.
 Macro-kjedahl Flask, 500ml or Tubes.
 Volumetric Flasks, 100ml.
Reagents:
 Concentrated sulphuric acid.
 Catalyst- 500gm sodium sulphate (𝑁𝑎2 𝑆𝑂4) or Potassium Sulphate (𝐾2 𝑆𝑂4).
50gm of anhydrous Copper Sulphate. 0.5gm of Selenium powder (mix this
different reagents and ground to powder).
 Boric Acid (2%) - Dissolve 20gm of Boric Acid in 1000𝑐𝑚3
volumetric flask.
 40% NaOH- Weigh out 400gm of NaOH and dissolve in 800𝑐𝑚3
distilled water
.Leave to cool before making to mark in 1 liter volumetric flask.
 0.01M HCL- Measure 0.86ml of concentrated HCL and make it up in a 1000𝑐𝑚3
volumetric flask.
 Mix Indicators: Weigh out 0.2gm of methyl blue into a 100𝑐𝑚3
volumetric flask
and also add 0.4gm of methyl red into another 100𝑐𝑚3
volumetric flask. Dissolve
both indicators with ethanol. Mix content of both flask in a 200𝑐𝑚3
volumetric
flask and mix thoroughly.
OR
Methylred-Bromocresol green mixed indicator: Dissolve 0.5gm of bromocresol
green and 0.1gm of methylred in 100𝑐𝑚3
of 95% ethanol and adjust PH to 4.50
with 0.1M of NaOH or HCL.

73
Procedure:
 Weigh out 2gm dried cow dung into kjedahl flask or digestion tube.
 Add 20ml of distilled water swirl the flask for some minutes and allow it to stand
for 30minutes.
 Add about 30gm of catalyst and 20ml of 𝐻2 𝑆𝑂4.
 Heat continuously on a low heat. When the water has been removed and frothing
has ceased, increase the heat until the digest clears. Then boil the mixture for 5
hours. Regulate the heating during this boiling so that the 𝐻2 𝑆𝑂4 condenses about
half way up the neck of the flask or tube.
 Allow the flask to cool and slowly with shaking, add some distilled water.
 Carefully transfer the digest into another clean flask. Retain all particles in the
original digestion flask because, the particle can cause severe bumping during
distillation. Wash the residue with 50ml of distilled water for about four times
and transfer each portion into the same flask. Make to mark with distilled water.
 Add 10ml of 𝐻3 𝐵𝑂3 into a 500ml Erlenmeyer flask which is then placed under
the condenser of the distillation apparatus. The end of the condenser should be at
about 4cm above the surface of the 𝐻3 𝐵𝑂3 solution.
 Keep condenser cool (below 30℃) by allowing sufficient water to flow through
and regulate heat to minimize frothing and prevent suck back.
 Collect about 50ml distillate and then stop distillation.
 Titrate𝑁𝐻3 liberated with standard HCL or𝐻2 𝑆𝑂4. Add 2- 3 drops of indicator.
The colour change at the end point is from green to pink.
 Calculate the %N Content in the cow dung thus
 Run a blank similar but without cow dung sample.

74
% N = (0.014*VD*N*100*TV)
(Weight of Cow dung*AD)
Where VD= Volume of digest
N= Normality of acid
TV= Titer value
AD= Aliquot of digest.
ORGANIC CARBON DETERMINATION
(Walkley- Black Method)
Apparatus:
 Burette; 50ml 0r 25ml
 Conical flask;250ml or 500ml
 Measuring Cylinders
 Pipette
Reagents:
 Potassium dichromate (𝐾2 𝐶𝑟2 𝑂7); 1N- dissolve 49.04gm of 𝐾2 𝐶𝑟2 𝑂7 in distilled
water and dilute to 1 liter.
 Concentrated Sulphuric acid (𝐻2 𝑆𝑂4) if chloride is present in the sample, add
(𝐴𝑔2 𝑆𝑂4 ) to the acid at the rate of 15gm per liter.
 O- Phosphoric acid (𝐻3 𝑃𝑂4), concentrated.
 O- Phenanthroline – ferrous complex 0.025M (ferrous). When the indicator is not
available it can be prepared by dissolving 14.85gm of O- Phenanthroline
monohydrate and 6.95gm of Fe 𝑆𝑂4. 7𝐻2O in water and dilute to 1 liter.
 Barium diphenylamine sulphate (0.16%). This can be used in place of

75
O- Phenanthroline- ferrous complexes (0.25M). Dissolve 7.425gm of O-
Phenanthroline and 3.475gm of ferrous sulphate in distilled water and dilute to
500ml.
 Ferrous sulphate (0.5N)- dissolve 140gm of Fe 𝑆𝑂4. 7𝐻2O in water ;add 15ml
concentrated 𝐻2 𝑆𝑂4 , cool and dilute to 1 liter. Standardize this reagent daily or
each time before determining organic carbon by titrating against 10ml 1N
𝐾2 𝐶𝑟2 𝑂7.
Procedure
 Take a representative sample and grind to pass through a 0.5mm sieve.
 Weigh out 1.00gm cow dung and place in the 250ml flask. Use 2.00gm cow dung
if organic carbon is suspected to less than 1%.
 Pipette 10ml 1N 𝐾2 𝐶𝑟2 𝑂7 accurately into each flask and swirl gently to disperse
the cow dung.
 Rapidly add 20ml concentrated 𝐻2 𝑆𝑂4 from a measuring cylinder. Immediately
swirl flask gently until cow dung and reagent are mixed, then swirl more
vigorously for one minute. Rotate flask again and allow to stand on a sheet of
asbestos for about 30minutes. End point is easier to observe when suspension is
cool.
 Add 100ml of distilled water after standing for 30minutes and let cool again.
Filter suspension if cloudy.
 Add 5ml of O- Phosphoric acid (𝐻3 𝑃𝑂4) to sharpen the end point (optional).
 Add 3- 4 drops indicator and titrate with 0.5N ferrous sulphate solution on a
white background. Note; As the end point is approached, the solution takes on a
greenish cast and then changes to dark green. At this point add the ferrous

76
sulphate solution until the color changes sharply from blue to red (maroon color)
in reflected light against a white background.
 Make the blank determination in the same way but without cow dung sample to
standardize the dichromate.
 Calculate the result according to the following formula:
% organic carbon in cow dung = (meq𝐾2 𝐶𝑟2 𝑂7 – meq Fe𝑆𝑂4)*0.003*100*f
(Air-dry basis) Weight of air- dry cow dung
(Where f=Correction factor = 1.33)
Meq=Normality of solution*ml of solution used
OR
% organic carbon in cow dung = (Blank titer – actual titer) * 0.3* m * f
(Air-dry basis) Weight of air- dry cow dung
Where f= Correction factor= 1.33
m=Concentration of Fe 𝑆𝑂4.
% organic matter (OM) may be calculated thus:
% OM= %OC*1.729
 % organic carbon can also be expressed on oven dry basis after correction for
moisture content in air- dry cow dung.
RATES OF BIOGAS PRODUCTION
 The cumulative gas as at the 83rd Day was 92,680cm3 (92,680,000mm3=
92.680L= 0.09268m3). Also, the rate of gas production was observed and
calculated to have changed (decreased) from 2863.8
cm3
𝑑𝑎𝑦

77
= 119.325
cm3
ℎ𝑜𝑢𝑟
×
1ℎ𝑜𝑢𝑟
60𝑚𝑖𝑛𝑠
= 1.98875
cm3
𝑚𝑖𝑛
(between day 38 and55), to
1273.1
cm3
𝑑𝑎𝑦
×
1𝑑𝑎𝑦
24ℎ𝑜𝑢𝑟𝑠
= 53.046
cm3
ℎ𝑜𝑢𝑟
(between the 56th Day and the 95th day).

A final year research project -part 3 (Literature Review,Results& Conclusion)

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A final year research project -part 3 (Literature Review,Results& Conclusion)