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2017-2018

Biogas in Ghana

Authors: Floyd van Schaik (NT)

Tom Koolhaas (NT/NG)

Subjects: Physics

Chemistry

Mentors: Mrs Van Elk

Mr De Groot

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Table of contents

Summary p. 6

Introduction

Motivation p. 7

Subject choice process p. 7

Method p. 7

Defining the problem p. 8

Dealing with the problems p. 8

Requirements p. 9

Answering the sub-questions

1: What are the basic principles of biogas production? p. 10

2: What are the possible processes for making biogas? p. 12

3: What are the possible biogas installations in situ? p. 14

4: What are the advantages and disadvantages? p. 16

5: What is the impact on climate change? p. 18

6: Are there any safety or health risks and how could one deal with those? p. 18

7: What materials can be used for the biogas installation? p. 16

8: Can the biogas be used directly or does it have to be converted into methane? p. 16

9: How does one calculate and maximise yield? p. 17

10: How does one calculate the demand for biogas? p. 18

Conclusion p. 19

Reference list p. 20

Appendix 1: Log p. 22

Appendix 2: Reflection p. 26

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Summary

This school research paper explores the ideal design for a biogas installation that can be used to cook

with for about fifty people at the Vocational Training Centre for street girls in Kumasi, Ghana, that

runs on green waste and chicken excrements produced locally by the farm. Literature study has been

done to come to the following conclusions:

1. The basic principles of biogas production: the basic principle of biogas production relies on

methanogens, bacteria that produce methane. The production of biogas is only possible if

there are anaerobic conditions. Otherwise, other bacteria will turn this methane into carbon

dioxide and water.

2. The process: a wet stirrer-less mesophilic process is the best alternative for making biogas in

the given situation. Other processes for making biogas are either too expensive or too

labour-intensive.

3. The installation: The plastic tank is the best choice out of all the possible installation designs;

it really suits all the needs of the Centre. This design is nor too expensive nor too labour

intensive nor too flimsy.

4. (Dis)advantages: the usage of biogas has a lot of advantages over using wood or charcoal as a

fuel. By using biogas, the foundation severely cuts the number of pollutants produced. This

also means they will be energy self-sufficient. Besides these benefits, the foundation will

have a new source of free organic fertilizer, which ensures they will have more and better

crops. The installation also provides an easy way to dispose of manure and other forms of

organic waste. There are some disadvantages, though, namely the investment costs; these

can be quite high. The people of the centre also need training on how to use the installation.

5. Climate change: the use of biogas is a proven measure for cutting back emissions of

greenhouse gasses. Burning gas will also alleviate the need for charcoal and wood, which are

enormous polluters when burned.

6. Safety or health risks: when dealing with manure, it is wise to wear gloves and avoid skin

contact as much as possible; this rule also applies to the sludge. Biogas is a fuel and can burn

or explode, always make sure the biogas installation is anaerobic and sealed to prevent the

possibility of fire.

7. Construction: all sorts of materials can be used and have been used, although brick,

concrete, and plastic are the most popular. The use of plastic is recommended for the given

situation because the alternatives are more labour-intensive.

8. Usage: the biogas is directly flammable if burned in a regular gas stove or a dedicated biogas

stove.

9. Yield: the given circumstances can provide about 1050 litres of biogas a day if a wet

mesophilic plastic tank digester with a volume of 1600 L is implemented and maintained

correctly.

10. Demand: it is estimated that the Centre needs 660L of biogas each day.

The ideal design for a biogas installation at the Vocational Training Centre would be a wet,

mesophilic and stirrer-less digester. It would have to be a plastic tank digester system with a volume

of 1600 L.

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Introduction

Motivation

When we were tasked with constituting a subject for our school research paper, we had trouble

coming up with ideas. We roamed through the library and on the internet for hours, but it was hard

to find something that was not too difficult, nor too simple, and something we thought we could find

enough information about, etc. Eventually, we remembered the introduction speech of Mr Kom

wherein he mentioned World School, an organization that offers local, national and international

research programmes designed for teaching students to perform research and develop social

commitment. One could choose a programme, which corresponded with one’s educational profile,

out of a diverse list of possibilities. We were really drawn to the idea of doing our research while

actually participating in something real, something linked to a contemporary topic. World School

solved our problem of not being able to choose a subject all by ourselves.

Subject choice process

We came across several projects suitable for us and finally decided to pick one: Biogas in Ghana. For

this project, we had to design a biogas installation for domestic use for about fifty people at the

Vocational Training Centre for street girls in Kumasi, Ghana. We had to do so in cooperation with

Adamfo Ghana. Adamfo Ghana is a Dutch foundation that aims to create a better future for street

children and vulnerable youngsters in Ghana. Adamfo Ghana wants to contribute to a world in which

all children can grow up in a safe environment and go to school to develop their talents and skills to

the best of their ability. There were a couple of requirements, the biogas had to be produced from

chicken excrements and green waste of the community living in and around the Centre for example.

After a while, however, we discovered that the exact requirements of World School’s programme on

the one hand and those of our school on the other hand did not quite correspond to each other, so

we decided to distance ourselves from World School and focus mainly on the terms to acquire a good

grade. We made this decision partly because we did not receive much support from Adamfo (they

did not answer our emails or took very long to do so).

Method

A lot of research has been conducted on our topic. These scientific findings have been very helpful to

understand all aspects of biogas installations and production. There are many different conditions

and there are many varieties of digester and purpose. Biogas installations have been used in

developing projects for decades. The effects of biogas installations have been very well studied too.

These studies show how a biogas installation can if used correctly, have a sustainable long-term

effect on the welfare of the community. We chose to do theoretical research into the concept of

biogas, especially its production in the circumstances at the Vocational Training Centre for street girls

in Kumasi, Ghana. We chose this path because most general theoretical research about biogas had

already been conducted and an experiment could not recreate the exact conditions in Ghana. The

internet has been used for finding our information. We also visited the library but were only able to

find little useful information there.

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Defining the problem

The inhabitants of the vocational centre are currently cooking with charcoal and wood. This is a

problem because of three reasons:

- The use of charcoal and wood as a fuel poses real risks to the health of the community. The burning

of wood, for example, produces many toxic fumes (22)1. These fumes are also found in cigarette

smoke and are known to cause cancers. Exposure to big amounts of pollutants in the air is also a

cause of respiratory diseases.

- The use of charcoal and wood as a fuel is bad for the environment because the chemicals which are

listed in source 22 also contribute to the forming of smog and to the enhanced greenhouse effect.

Smog poses serious health hazards because it is known to increase the risks of getting diseases such

as asthma or lung cancer dramatically. The emission of carbon dioxide is not such a big problem

because this greenhouse gas was previously chemically stored by the trees themselves. That is why

burning wood is considered carbon neutral; one is essentially burning the energy which the organism

has captured during its life. The problem with burning wood, however, is that it is never a complete

combustion of the fuel, so other greenhouse gasses, such as methane, which contributes to global

warming significantly more than carbon dioxide, are also released. Even though the burning of wood

and charcoal is carbon neutral, it does worsen the problem of global warming. Besides, the wood

needed for cooking comes mostly from unsustainable sources, which worsens existing problems, like

deforestation.

- The Use of charcoal and wood as a fuel is expensive, the purchase of wood and charcoal costs a

considerable amount of time and money. These resources could otherwise be used for the

Foundation.

Dealing with the problems

A good way of dealing with these problems is switching to biogas. Biogas is a cleaner alternative; the

burning of the gas is usually a complete combustion because there is a sufficient amount of oxygen.

Therefore, the burning is more efficient. Because of the complete combustion, harmful gasses such

as carbon monoxide are not produced. This also lifts the problem of environmental pollution

because, aside from carbon dioxide, no pollutants are produced. This carbon dioxide has first been

absorbed by the plants for photosynthesis, so, in effect, no extra greenhouse or polluting gasses are

produced by burning biogas. Considering long-term use, biogas is also cheaper than wood or

charcoal. The investment in the necessary equipment might be a considerable amount, but because

there are no further investments needed in the daily use of biogas, the operation is free. Besides the

savings that the use of biogas for cooking leads to, the fertilizer, which is a by-product of the

production of biogas, might increase yield for the farm and save money by reducing the need to buy

other fertilizer.

1 In this paper, all references will be given at the end. In the text, the yellow-marked numbers in parentheses will refer to the corresponding sources in the reference list.

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Requirements

Our proposed biogas installation will have to meet these requirements:

- The installation must produce enough gas to cook for all of the centre’s guests and inhabitants. This

amounts to fifty people a day.

- The installation must be safe for the people in the centre and for the environment.

- The installation must be made of low tech parts and be easy to construct and repair.

Main question:

What would be the ideal design for a biogas installation that can be used to cook with for about 50

people at the Vocational Training Centre for street girls in Kumasi, Ghana and that runs on green

waste and chicken excrements produced by the farm?

Sub-questions:

1. What are the basic principles of biogas production?

2. What are the possible processes for making biogas?

3. What are the possible biogas installations in situ?

4. What are the advantages and disadvantages (social, economic, environmental, health)?

5. What is the impact on climate change?

6. Are there any safety or health risks and how could one deal with those?

7. What materials can be used for the construction of biogas installation?

8. Can the biogas be used directly or does it have to be converted into methane?

9. How does one calculate and maximise yield?

10. How does one calculate the demand for biogas?

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Answering the sub-questions

1: What are the basic principles of biogas production? (6) (18) (19) (20) (24)

The production of biogas is based on the process of anaerobic digestion of organic matter by

different types of bacteria, of which methanogens are the most important. For these bacteria to

flourish, there has to be an anaerobic environment, in which oxygen is not available for redox

reactions. Methanogens are bacteria that produce methane gas (methanogenesis = birth of

methane), the most important and valuable component of biogas (45 to 65 molar % (15; p. 6)).

Methanogens can be found in the digestive systems of herbivores, wetlands, or lake bottoms and

most of them require warm conditions to work best. Along with these, a lot of other bacteria take

part in the process. For the production of methane, organic materials such as cattle excrements,

sewage and vegetable peels, which contain these bacteria, are mixed with the right amount of water

and placed in a digester tank.

With anaerobic digestion, the digester’s input undergoes four chemical steps to become biogas. This

process basically breaks large molecules in the waste material down to smaller components and

ultimately turns it into biogas.

Hydrolysis

Biomass is usually comprised of large polymers, namely proteins, fats, and carbohydrates. Such

polymers are first depolymerised by hydrolysis, often in the presence of an acidic catalyst. Hydrolysis

is a chemical reaction in which chemical bonds are cleaved by the addition of water. Through

hydrolysis, the large molecules like proteins are broken down by bacteria into smaller molecules such

as amino acids, fatty acids, and simple sugars. This step is necessary for the water-insoluble organics

to be converted into smaller, soluble components so that they can be used by the bacterial cells.

Whereas some of the formed molecules, like hydrogen and acetate, can be directly used by the

methanogens, the majority of the molecules, being still relatively large, must first be catabolised into

smaller compounds for them be used to create methane.

Image 1: Anaerobic Pathway (6)

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Acidogenesis

Acidogenic bacteria are fermentative bacteria that produce an acidic environment in the digestive

tank. This results in the further breakdown of the remaining components. Here, ammonia, hydrogen,

carbon dioxide, hydrogen sulphide, volatile fatty acids, carbonic acids, alcohols, and trace amounts of

other by-products are created. Most of the organic matter is now still too large and thus has to be

further broken down.

Acetogenesis

Acetogenesis is the creation of acetate by acetogens, another kind of bacteria. These organisms

break down many of the products created in the former step, producing acetate, carbon dioxide, and

hydrogen. At this point, methanogens can utilise the three last mentioned chemicals to create

biogas.

Methanogenesis

In the last step, methanogens convert carbon dioxide, hydrogen, and acetate into biogas and water.

There are two main reactions for methanogenesis:

CO2+ 4H2 → CH4 + 2H2O

CH3COOH → CH4 + CO2

The main mechanism to create methane is the second pathway, involving acetate. This path creates

methane and carbon dioxide, the two main components of biogas and the main products of

anaerobic digestion.

Apart from the biogas that is produced, sludge, the remaining organic material which has been

broken down into small molecules, remains as a residue, which can be used as a fertilizer. This

fertilizer mainly contains molecules the bacteria cannot use for digestion, such as phosphates,

nitrates, and other trace elements.

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2: What are the possible processes for making biogas? (23)

For biogas production, various process types are applied which can be subdivided into wet and dry

fermentation systems. Most often applied in developing countries are wet digester systems using

diffusion rather than stirrers to save cost (5). Dry digesters need mechanical stirrers, which makes it

expensive and labour intensive. We think that the wet digester is the best alternative because a dry

digester would demand a lot more manpower and time, which is not attractive to the centre.

Image 2: an example of an industrial scale thermophilic, wet, and stirred digester (11)

Another classification can be made by the separation of thermophilic and mesophilic anaerobic

digesters. The words mesophilic and thermophilic are simply terms used to classify broad groups of

bacteria and just describe the temperature of their liveable environment. Ideally, one should know

the exact microorganism used and know the range that is most suitable for that specific species.

Thermophilic digesters need to have a constant temperature of above 50 degrees centigrade, which

means that the digester has to be heated at all times, which makes it expensive and dangerous,

whereas mesophilic bacteria require temperatures roughly between 20 and 42 degrees centigrade.

The thermophilic digesters are more efficient and faster than their mesophilic counterparts because

thermophilic temperatures provide more rapid reactions, especially for hydrolysis and

methanogenesis.

We think that the mesophilic digester is the best alternative, though, because this is the safest and

because it does not take as much energy, in the form of heat, to keep it running. In fact, the climate

in Ghana is nearly perfect for this kind of digester because the temperature is almost constantly

fluctuating inside the ideal range of temperatures for mesophilic digestion (21).

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Image 3: Example of a mesophilic, wet, and stirrer-less digester (10)

From this point on, we are only going to focus on the wet, mesophilic anaerobic digester for our

project.

All biogas installations need a ‘starter’ for it to work properly. This usually is just a mixture of a

manure that is a couple days old mixed with water. For the process to start, you need to wait a

couple of days until the maximum amount of biogas is produced. During this time the bacteria colony

will grow to sufficient size.

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3: What are the possible biogas installations in situ? (15; pp. 9-11)

The possibilities are nearly endless. A good reactor which is sustainable and can be bought cheaply or

created using cheap resources is a plus. The capture system also does not need any very specific

parts; cheap materials such as a garden hose could do.

This diagram shows the most common types of digesters and their positive traits as well as their

negative traits.

Technology Positive Traits Negative Traits

Plastic tube digester

- Inexpensive technology - Very fragile - Short lifespan: 4 years max - Difficult to operate

Plastic tank digester (This is an above ground variation of the fixed dome digester)

- Easy installation - Quick production start-up - Smaller tank volume - Easy to operate

- Expensive - If not underground, potentially damageable - Smaller tank volume - Requires dismantling and recycling

Fixed dome digester - Long lifespan - Not damageable (underground)

- Expensive technology - Potentially long startup

Floating-drum digester - Provides constant gas pressure - Visual indication of gas stored

- Very expensive (compared to the fixed dome) - If the drum is made of steel, it will be subject to corrosion - Lower lifespan than the fixed dome

Table 1: Pros and cons for four digester varieties

These pictures give a clear idea of what these types of digesters would look like:

Image 3: Plastic tube digester (9)

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Image 4: Fixed dome digester (7)

The plastic tank digester is a variation of the fixed dome digester. It works on the exact same

principles as the fixed dome digester and also has no moving parts. The plastic tank digester is above

ground, whereas the fixed dome digester would be underground, usually constructed with bricks and

cement.

Image 5: Floating dome digester (8)

We think the plastic tank digester is a very good alternative since it requires very little investment

and upkeep. This plastic tank cannot be placed in direct sunlight in order to prevent overheating.

Eventually, the residents can choose to install a fixed dome digester, if that is possible considering it

takes more time, money, and manpower to install.

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4: What are the advantages and disadvantages? (15; pp. 7-8)

Advantages

Stopping the pollution!

The current situation is unhealthy for the people who cook with charcoal and wood. During the

combustion of wood or charcoal, certain toxic substances are released, such as soot, carbon

monoxide, formaldehyde, dioxin, benzene, lead, and other harmful gasses which are produced by the

incomplete burning of organic matter (12) (22). Carbon monoxide, formaldehyde, benzene, and lead,

for instance, are also found in cigarette smoke, along with 24 other chemicals. The burning of these

fuels also creates smog, which is known to cause respiratory diseases, such as asthma. Switching to

biogas will lower the risks of these diseases for the inhabitants of the compound. The indoor air

quality improves strongly by using biogas since a gas stove emits less smoke and harmful particles. Of

course, this would not solve all the health risks: in the surrounding area there probably still are

enough polluters to pose a serious health hazard. Big (governmental) support programs can make a

difference by encouraging everyone to invest in a biogas installation. If used correctly, such initiatives

are known to be really successful. Nepal, for example, has installed an average of 1040 biogas plants

per month for 20 years straight. Nowadays the country has approximately 250.000 biogas

installations. Most of these are of the fixed dome design. The construction of these plants creates

quite a few jobs.

Being energy self-sufficient

If prices of fuels were to rise drastically in the coming years, because of sustained growth of demand

and a lacking growth of supply in Ghana, for example, the continued usage of wood as a fuel would

do financial damage to the foundation. The implementation of a biogas installation would make the

foundation self-sufficient concerning fuel for cooking, this could be a major benefit for the financial

situation of the foundation. It would also cut out the middleman, who currently profits by buying the

fuel and selling it for a higher price.

It is estimated that 68% of Afrika’s the population lives without clean cooking fuels (13). Having

access to renewable and sustainable energy resources is an excellent way to mitigate poverty. These

seemingly small savings can be reinvested in education. That way the multiplier effect of such

investments is usually quite big and can really help to get neighbourhoods out of poverty.

Organic fertilizer produces more and better crops

The residue of the biogas installation can be used as fertilizer. This fertilizer richly contains

phosphates, nitrates, potassium, and magnesium. If used correctly, the organic fertilizer greatly

improves crop yields, compared to non-fertilized crops. In Ethiopia, for example, wheat yields have

increased by 64% to 72% after applying bio-slurry (2). The application of this organic fertilizing slurry

makes the crops organic, which greatly improves their value if sold. The additional crop yield

consequently creates bigger sales for the farmer, these extra sales will help to alleviate poverty.

Low operation and maintenance costs

All the former benefits can be achieved with little to no operation and maintenance costs. The only

extra work that has to happen is the dilution of the biological waste that goes into the biogas reactor.

The reactor, which can be built of considerably cheap materials, will last significantly longer if

maintained and operated correctly. If the reactor is built underground, which costs more money and

work as a minus, it will not take up additional space on the compound. The reactor should not

produce any odours; the reactor is supposed to be airtight, so no gasses can escape the container. In

the unlikely event of a broken seal, the biogas will leak out as well, which poses a fire risk.

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Easy disposal of manure and other forms of organic waste

Using the biogas installation to dispose of chicken manure is a healthier and cleaner way of getting

rid of excrements than for example burning it. The lack of oxygen in the reactor ensures no worms,

flies, or other plague animals are able to feed on the manure. This reduction in flies, worms, and

other insects will greatly improve living quality and health. If the toilet is connected to the biogas

installation, the treatment of human excrements will become a lot easier. This use of a biogas

installation is especially useful in situations where there is no access to public sewage systems.

Cooking remains can easily be disposed of too and by collecting this waste, additional fuel can be

created.

Reduction in workload and tastier food

Using a biogas system can significantly reduce the daily workload since firewood collection and fire

tending is no longer necessary. Because these house tasks are usually done by women, using a biogas

installation will help reduce gender disparities. The women have more free time and can spend it on

more education or other activities. Moreover, cooking with wood gives the food a specific taste, an

aroma we all recognize from barbecuing. This taste is not always desirable and therefore cooking

with biogas is a good alternative, as it does not give the food a distinct taste.

Disadvantages

Building the biogas installation

Experts are needed to design the reactor. However, there are a lot of designs available for free on

the internet. Besides, the construction of a good system requires skilled labour. This is hard to come

by, but there are countless initiatives to learn the necessary skills to people for a small fee or

sometimes even for free. A lot of prefabricated alternatives are available for purchase.

The substrates have to contain high amounts of organic matter

Substrates need to contain high amounts of organic matter for biogas production, this means that

elements such as dirt, sand and other inorganic matter should be avoided as much as possible.

Below temperatures of 15°C, biogas production is economically not interesting.

Luckily, this is no issue in Kumasi, Ghana, as the average temperatures during the coldest times of

year are never below 19°C.

Requires a start-up time

Before biogas can be collected, a couple of days need to pass. During this time, the anaerobic

bacteria population grows to an ample size.

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5: What is the impact on climate change?

Using biogas has a positive impact on climate change. The energy, initially captured by plants, would

otherwise be lost due to rotting. During the rotting, the same amount of carbon dioxide is produced.

Using biogas is carbon-neutral; all the carbon dioxide that is emitted has been adsorbed by

photosynthesis and is now reintroduced to the atmosphere. Nowadays, because of global warming, a

lot of peat, which used to be frozen in the permafrost, is melting. Anaerobic bacteria are producing

methane in this newly melted peatland. About half of all the methane is directly released into the

atmosphere, the rest is converted into energy, water, and carbon dioxide by other organisms. This

melting of the permafrost peatlands is really extending the consequence the enhanced greenhouse

effect will have on the climate.

Besides, biogas substitutes enormous pollutants, namely wood and charcoal (12) (22), with

something much cleaner. The use of biogas instead of wood and charcoal will also save forests and

prevent illegal forestry and deforestation. The use of the organic fertilizer decreases the demand for

inorganic fertilizer, which is a very energy-intensive production process (25). Inorganic fertilizer often

uses fossil fuels as a resource. Therefore, it contributes heavily to the enhanced greenhouse effect

(3). Fertilizer also enables some bacteria to emit nitrous oxide, a greenhouse gas 300 times stronger

than carbon dioxide (4). This way, about 5% of fertilizer is converted to nitrous oxide. This is an

enormous source of unnatural greenhouse gasses.

6: Are there any safety or health risks and how could one deal with those?

The biogas is really safe; there is no risk of illness when inhaled. However, do make sure not to go

into the digester, as there is no oxygen. Because it is a fuel, there is, of course, a risk of fire; be

responsible when dealing with fire. It is advisable not to light any fires in the vicinity of the reactor.

The sludge can contain pathogens that can cause illnesses. The sludge is less contaminated than the

manure, however, because most of the organic elements are digested by the anaerobic bacteria. To

prevent decease, it is essential not to eat or make contact with the sludge with any part of one’s

body that contains membranes, such as the eyes, nose, etc. We strongly recommend using things like

buckets and gloves to minimize the amount of sludge that makes contact with one’s body. Washing

one’s hands afterwards is also recommended.

7: What materials can be used for the biogas installation?

There are specific materials used for different reactor designs. The fixed dome reactor, for instance,

is usually built with bricks, stones, or concrete, whereas the floating drum reactor is usually built with

plastic and sometimes with metal. Reactor designs can be made of the least expensive materials

there are, though. All airtight materials can be used, although some last longer than others. Plastic,

for example, lasts way longer than metals do. Plastics are also cheaper. Therefore, plastic is the best

choice. Some metal parts will still be needed, though; for the stove, for example.

8: Can the biogas be used directly or does it have to be converted into methane?

Biogas can be used directly for cooking because it contains over 50% methane per volume. This is

enough to be burned with sufficient oxygen, which is available in the open air (15; p. 6).

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9: How does one calculate and maximise yield? (15; p. 12)

We will use some of the data given by the foundation and some scientific data to calculate the

amount of organic matter produced.

It is important to know how big the bio-digester needs to be. Its sizing can be determined by the

parameters in the following table.

Table 2: Main design parameters for biogas plants (15; p. 12)

The digester volume is determined on the basis of the organic waste quantity and the retention time:

Where represents the relative amount of volume that is occupied by

the gas within the digester. For dome or plastic tube digesters, a typical value is x = 0,25, as the gas

volume in the dome or the tube usually represents around 25% of the total digester volume. When

the gas is stored in a separate tank, as is the case with floating drum or plastic tank technologies, for

example, x ≈ 0 is applied because there is almost no gas within the digester. Therefore, x can be

eliminated from the equation for our project, as we are planning on using a plastic tank digester.

The centre has a chicken farm with around two hundred chickens. Chickens produce an average of

120g of manure per day (17) and the density of chicken manure is 1,1 kg/L (65 lb/ft3) (14), so the

chicken farm produces 24 kg of manure (120g*200) a day, which is 21 L (24/1,1). Of course, a lot of

the manure gets lost on the farm, on the ground and such, and cannot be recovered. We think it is a

good estimate to state that half of the chicken manure, 11 L, can be used.

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The centre also has a vegetable garden/farmland of about 860 m2, where crops such as corn, tomatoes, peanuts, plantains, and yams are grown. We have sent Adamfo an email, but we have not gotten a response from them, so we will have to make an estimate on how much plant-based organic material is available for the biogas production. As it is important that most of the organic waste is withdrawn into the ground for the ground to stay fertile, a modest estimation is required. Two litres a day might be a reasonable estimate.

The third thing that the centre could use as input is their own faeces. We will make our calculation for fifty people because that is the number of people we also want to be able to provide enough biogas for. Medical daily claims that "the average individual poops about once a day, releasing around one ounce of excrement per 12 pounds of body weight" (1). As it is hard to find a number on the internet, we will assume the average weight of a person at the centre is about 65 kilograms. A pound is equal to 454 grams, so 12 pounds will be 12*454 = 5,4*103 gram = 5,4 kilograms. An ounce is 48,35 grams. This results in the fact that an average person in Ghana excretes (65/5,4)*48,35 = 5,8*102 gram = 0,58 kilogram of faeces a day. With fifty people, this makes 29 kilograms of droppings. As it is, again, hard to find a number on the internet, we will assume the average density of human faecal matter is about one kilogram per litre. This comes down to 29 litres of droppings a day at the centre. Of course, the people will not throw all their dung into the digester. However, it is good to throw in some human excrements, about four litres a day, so that the biodiversity is as high as possible, which provides a greater diversity of organisms that can grow (16).

Concludingly, the total estimated daily volume of available organic waste comes down to 27 litres, which is mostly comprised of chicken manure.

Water or urine has to be added to all of this before it goes into the digester, as the waste must be diluted in case of a wet digester. For the fixed dome or plastic tank digester, the typical water to waste ratio is 1:1. This means that the organic material has to be diluted with the same volume of water or urine as the volume of the waste itself, namely 27 litres, resulting in a total of 54 litres.

The retention time is estimated around 30 days. Vdigester = 30*54 = 1,6*103 L = 1,6 kL. This is about eight times the size of an average oil drum (approx. 210 L); the measurements can be 1 m * 1,6 m * 1 m (= 1,6 m3 = 1,6 kL), for example. Note that this is an estimated average that can differ significantly depending on the retention time.

Our installation uses 24 kg chicken manure, 2 kg plant-based organic material (on the basis of a

density of 1 kg/L) and 4 kg human faeces, together amounting to 30 kg organic waste a day. Whereas

35 litres of biogas is produced with each kilogram of dung (15; p. 13), a biogas installation which uses

30 kg of waste a day produces 30*35 = 1050 litres biogas a day. Note that this is an estimated

average of the yield if all organic waste is put into the digester.

The residents can use pH test strips to determine the pH in the digester. The pH should be around 7.

10: How does one calculate the demand for biogas? (15; p. 13)

220 L biogas is needed to cook for an hour on one stove. If we assume the foundation needs three

hours of cooking daily on one stove, it needs 660 L of biogas daily. This is our estimated amount

needed for one day of usage. Concludingly, 1050 - 660 = 390 L is left over and can be used for

lighting, or can be sold, for example. The digester could also be scaled down by a factor of 0,7. Then

it would produce just as much as the centre would need (735 L a day).

21

Conclusion

We have searched for the ideal design for a biogas installation that provides enough biogas to cook

for about fifty people at the Vocational Training Centre for street girls in Kumasi, Ghana, that runs on

green waste and chicken excrements produced locally. It is estimated that the Centre needs a total of

660 L of biogas each day. With the proposed digester of 1600 L, it is possible to produce 1050 L of

biogas, of which 390 L remains for other purposes.

The usage of biogas has a lot of advantages over using wood or charcoal as a fuel. Usage of biogas is

a proven measure for cutting back emissions of greenhouse gasses. Burning gas will also alleviate the

need for charcoal and wood, which are enormous polluters when burned. By using biogas, the

foundation severely cuts the number of pollutants produced. This also means they will be energy

self-sufficient. Besides these benefits, the foundation will have a new source of free organic fertilizer,

which ensures they will have more and better crops. The installation also provides an easy way to

dispose of manure and other forms of organic waste. It is important to monitor acidity throughout

the process; the pH has to be around 7.

There are some disadvantages, though, namely the investment costs (both time and money); these

can be quite high. Moreover, the people of the centre need training on how to use a biogas

installation.

The basic principle of biogas production relies on methanogens, bacteria that produce methane. This

has to happen in an oxygen-free, that is anaerobic, environment, because otherwise other bacteria

would burn this methane.

After this process, the biogas is directly flammable if burned in a regular gas stove or a stove

dedicated specially for biogas.

There is a multitude of possible processes for making biogas. There are wet and dry, and

thermophilic and mesophilic installations. The one most useful for this particular situation is a wet

one because this variety does not need a stirrer and a mesophilic one because Ghana’s climate is

perfect for this type of installation.

Moreover, there are also many varieties of installation designs. The four most prominent are the

plastic tube, the plastic tank, the fixed dome, and the floating drum digester. The plastic tank is the

best choice out of all the possible installations; it really suits all the centre’s needs. This design is nor

too expensive nor too labour-intensive nor too flimsy.

All sorts of materials can be used and have been used for the construction of the wet mesophilic

plastic tank digester, although brick, concrete, and plastic are the most popular. The use of plastic is

recommended for the given situation because the alternatives are very labour-intensive.

When dealing with manure it is wise to wear gloves and avoid skin contact as much as possible. This

rule also applies to the sludge. Biogas is a fuel and can burn or explode, always make sure the biogas

installation is anaerobic and sealed to prevent the possibility of fire.

The ideal installation would concludingly be a wet, mesophilic plastic tank digester with a volume of

1600 L, which uses chicken manure, organic waste of the farmland, and some human excrements to

produce biogas for the centre. This could also be scaled down if not all organic waste is to be used for

biogas production.

22

Reference list

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Current-state-and-perspectives.pdf [Accessed 27 Nov. 2017].

Books

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Mar. 2018].

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zUZCUHMWx5Q/Tz3upoCSO-I/AAAAAAAABQc/1NBtSMOjai8/s1600/float_dome.jpg [Accessed 4

Mar. 2018].

9. Egergypedia, (2016). Low-Cost Polyethylene Tube Digester Scheme. [image] Available at:

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[Accessed 4 Mar. 2018].

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projects-in-developing-countries.pdf [Accessed 4 Mar. 2018].

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http://www.cornerstoneeg.com/2013/06/05/organics-anaerobic-digester-septic-tank/

[Accessed 4 Mar. 2018].

23

PDFs

12. Burning Issues, (2017). Wood Smoke Tobacco Smoke Burning Issues. 1st ed. [pdf] Available at:

http://burningissues.org/pdfs/WoodSmokeTobaccoSmtablemira.pdf [Accessed 18 Oct. 2017].

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15 Dec. 2017].

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Iowa State University, p. 13. Available at:

http://msue.anr.msu.edu/uploads/files/ManureCharacteristicsMWPS-18_1.pdf [Accessed 3 Dec.

2017].

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ed. [pdf] Paris: ENEA Consulting, pp. 6-11. Available at: http://www.enea-consulting.com/wp-

content/uploads/2015/05/Open-Ideas-Domestic-biogas-projects-in-developing-countries.pdf

[Accessed 21 Oct. 2017].

16. Schnürer, A. and Jarvis, Å. (2010). Microbiological Handbook for Biogas Plants. 1st ed. [pdf]

Uppsala: Swedish Waste Management, p. 6. Available at: http://www.eac-

quality.net/fileadmin/eac_quality/user_documents/3_pdf/Microbiological_handbook_for_bioga

s_plants.pdf [Accessed 4 Mar. 2018].

17. Williams, C. (n.d.). Poultry waste management in developing countries: Poultry manure

characteristics. 1st ed. [pdf] Raleigh NC: North Carolina State University, pp. 1-2. Available at:

http://www.fao.org/docrep/013/al715e/al715e00.pdf [Accessed 3 Dec. 2017].

PowerPoints

18. Billet, P. (2016). Methanogens and Biogas. [PowerPoint] Available at:

http://www.gc11.ac.in/wp-content/uploads/2017/02/METHANOGENS-AND-BIOGAS.ppt

[Accessed 10 Oct. 2017].

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19. Biarnes, M. (2017). Biomass to Biogas—Anaerobic Digestion. [online] E Instruments. Available

at: http://www.e-inst.com/biomass-to-biogas/ [Accessed 20 Nov. 2017].

20. Biogas Renewable Energy, (2009). Biogas composition. [online] Available at: http://www.biogas-

renewable-energy.info/biogas_composition.html [Accessed 20 Nov. 2017].

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data.org/location/764142/ [Accessed 27 Nov. 2017].

22. Houtrook.nl, (2017). Houtrook bevat vele gevaarlijke stoffen. [online] Available at:

http://houtrook.nl/houtrook-bestaat-uit-giftige-stoffen-rivm/ [Accessed 18 Oct. 2017].

23. The Eco Ambassador, (2017). Anaerobic Digestion - Mesophilic Vs. Thermophilic. [online]

Available at: https://www.theecoambassador.com/Anaerobic-Digestion-Temperature.html

[Accessed 27 Nov. 2017].

24. Wikipedia, (2017). Anaerobic digestion. [online] Available at:

https://en.wikipedia.org/wiki/Anaerobic_digestion [Accessed 20 Nov. 2017].

25. Wikipedia, (2017). Fertilizer. [online] Available at:

https://en.wikipedia.org/wiki/Fertilizer#Environmental_effects [Accessed 20 Oct. 2017].

24

Appendix 1: Log

Datum Omschrijving Naam Gespendeerde tijd

27-02-2018 | 15:00 Werken aan vraag 3 Tom 2 uur

Reflectie: Goede schematische tekeningen vinden is erg lastig, opgezocht hoe het vermeld moet worden

25-02-2018 | 10:00 Werken aan punten Tom 3 uur

Reflectie: Ging op zich wel goed, soms zie ik sommige fouten pas na enkele keren lezen

10-02-2018 | 12:30 Aan deelvraag 1 gewerkt Floyd 4 uur

Reflectie: Goh wat is dit ingewikkeld. En wat moet je veel opzoeken!

05-03-2018 | 07:30 Printen Floyd 2 uur

Reflectie: Ging goed. Alles op tijd geregeld.

05-03-2018 | 00:00 De laatste loodjes Floyd 5 uur en 30 min

Reflectie: Toch nog wel tot laat moeten doorwerken. Had helaas ik de vakantie geen tijd vanwege ziekte.

04-03-2018 | 15:15 Ik heb net mijn logboek items ingevuld, maar ik heb een fout gemaakt bij de entries van 27-03-2018 en die van 25-03-2018, dit zou natuurlijk allemaal in februari moeten zijn, maar ik heb me vergist in het invoermenuutje. De overige ingevulde items kloppen allemaal wel

Tom 10 min

Reflectie: Jammer :(

04-03-2018 | 14:30 Werken aan laatste loodjes Tom 2 uur en 30 min

Reflectie: Komt wel goed voor de bakker, wel minder productief dan vanochtend

04-03-2018 | 13:30 Opmaak en bronvermelding regelen Floyd 10 uur en 29 min

Reflectie: Bronvermelding kost aanvankelijk veel tijd maar als je het doorkrijgt gaat het steeds sneller!

04-03-2018 | 10:00 Werken aan laatste puntjes Tom 2 uur en 30 min

Reflectie: Best productief

24-02-2018 | 10:30 Werken aan punten zoals overeengekomen

Tom 2 uur

18-02-2018 | 14:00 Werken aan PWS, werken aan de punten zoals overlegd met Floyd op laatste moment dat we er samen aan werkten.

Tom 2 uur

Reflectie: Het is erg saai en vervelend om elke zin langs te lopen en alles inhoudelijk ook te controleren

13-02-2018 | 19:30 Werken aan overeengekomen punten Tom 1 uur en 30 min

09-02-2018 | 09:30 Werken aan PWS a.d.h.v. opmerkingen mevr. van Elk

Floyd 6 uur

Reflectie: Niet heel goede focus vandaag, maar toch wel wat kunnen doen.

25

09-02-2018 | 09:30 Werken aan PWS, veel aandacht voor punten aangehaald in laatste gesprek. Document staat nu in Word Online, was best wat gedoe om het erin te krijgen.

Tom 6 uur en 15 min

21-12-2017 | 00:00 Zie vorig item Floyd 2 uur en 30 min

Reflectie: Zie vorig item. Ik kan niet in 1x een sessie van 9 uur 's avonds tot half 3 's nachts invoeren helaas

20-12-2017 | 21:15 Gewerkt aan eigen vragen, deel Floyds vragen, omdat ik handige bronnen vond

Tom 1 uur en 45 min

Reflectie: Goed gewerkt

20-12-2017 | 21:00 Veel geschreven en aan het beantwoorden van de vragen gewerkt.

Floyd 2 uur en 59 min

Reflectie: PWS is voor een groot deel al af, maar er moeten nog een aantal zaken gebeuren. Morgen leveren we de conceptversie in.

20-12-2017 | 19:30 Werken aan mijn deel vragen, bronnen gezocht, en opgezocht hoe je bronnen moet verwerken

Tom 1 uur en 30 min

Reflectie: Niet meer zo efficiënt als begin middag, wel een goeie bron gevonden

20-12-2017 | 17:50 Gewerkt aan - What is the impact on climate change? en - Are there any safety or health risks and how could you deal with those?

Tom 40 min

Reflectie: Moet nog langer denk ik, ik kan er dieper op in gaan

20-12-2017 | 14:30 Aan deelvraag 9 gewerkt Floyd 5 uur

Reflectie: Er valt een hoop op te zoeken en te berekenen

20-12-2017 | 13:00 De Defining the problem en Dealing with the problems herschreven en gewerkt aan - What are the advantages and disadvantages (social, economic, environmental, health)?

Tom 3 uur en 30 min

Reflectie: Meer dan 2 kantjes goed Engels geschreven, goed gewerkt over het algemeen

15-12-2017 | 14:00 Aanpassingen deelvraag 4 Floyd 3 uur

Reflectie: Wel weer even goed gewerkt :)

15-12-2017 | 12:00 Werken aan mijn individuele vragen Tom 2 uur en 30 min

Reflectie: Wel goed gewerkt op zich, wel lastig om in je eentje gefocust te blijven.

14-12-2017 | 20:30 Voorblad gemaakt + PWS-boekje gelezen Floyd 1 uur en 30 min

Reflectie: Ik heb wat vragen over hoe belangrijk het is de afspraken met de begeleider in AXM te zetten en er een verslag bij te maken. Hierover zal ik de eerstvolgende les vragen stellen aan mevr. van Elk.

06-12-2017 | 16:00 De vragen verdelen Tom 30 min

Reflectie: Snel en effectief

26

03-12-2017 | 13:30 Deelvraag 9 aangepast Floyd 2 uur

Reflectie: Even 2 uurtjes geknald. De deadline komt dichtbij! schouders eronder.

02-12-2017 | 12:15 Werken aan vragen in document Tom 2 uur

Reflectie: Wel efficiënt gewerkt, maar wel alleen, dus is het wel lastiger de focus erin te houden.

27-11-2017 | 16:00 Aan deelvraag 2 gewerkt Floyd 7 uur en 59 min

Reflectie: Er valt erg veel te leren over het proces. Mijn valkuil is denk ik mezelf er te diep in kwijt te raken. Ik wil dit in de kleinste details weten hoe het zit en dat is soms te veel.

20-11-2017 | 16:30 Begonnen aan deelvraag 10 Floyd 2 uur

Reflectie: Vandaag had ik niet zo'n goede concentratie

21-10-2017 | 13:00 Gewerkt aan deelvragen en van elk gemaild+ verdere oriëntatie op energieproductie

Tom 3 uur en 30 min

Reflectie: Na drie-en-een-half uur toch wel de concentratie kwijt

21-10-2017 | 13:00 Gewerkt aan deelvragen en van elk teruggemaild. + verdere oriëntatie op anaerobe digestie.

Floyd 3 uur en 30 min

Reflectie: Na drie-en-een-half uur toch wel de concentratie kwijt.

20-10-2017 | 14:00 Gewerkt aan deelvraag 3 Floyd 2 uur

Reflectie: Geen problemen hebben zich voorgedaan

20-10-2017 | 10:00 Mailen naar World School, werken aan deelvragen

Tom 2 uur en 30 min

Reflectie: Lastig om je te blijven focussen op de onderwerpen die belangrijk zijn.

18-10-2017 | 15:00 Aangepast deelvraag 5 Floyd 2 uur

Reflectie: Geen problemen voorgedaan

18-10-2017 | 09:30 Mevrouw van Elk mailen, opdrachtgever mailen, probleem definiëren, hoofd en deelvragen goed formuleren en voor een deel al uitwerken.

Floyd 7 uur

Reflectie: We hebben erg hard gewerkt, goede start gemaakt.

18-10-2017 | 09:30 Goed gewerkt aan o.a. Mevrouw van elk mailen opdrachtgever mailen probleem definiëren hoofdendeelvragen goed formuleren en voor een deel al uitwerken.

Tom 7 uur

Reflectie: We hebben erg hard gewerkt, een goede start.

13-10-2017 | 12:00 Delft "werken met World School" Erik Vos van World School

Tom 3 uur en 30 min

Reflectie: Was wel zinnig, presentatie en organisatie van World School wel slordig

10-10-2017 | 12:20 Informatie opzoeken, meer te weten komen over productie van biogas.

Floyd 1 uur en 55 min

27

Reflectie: Samenwerking verloopt prima. Hard op weg naar meer kennis. We zijn er wel achter dat er nog vrij veel gelezen en opgezocht moet worden voor we echt aan de slag kunnen.

10-10-2017 | 12:20 Informatie opzoeken, meer te weten komen over productie van biogas

Tom 1 uur en 55 min

Reflectie: Samenwerking verloopt prima hard op weg naar meer kennis. We zijn veel te weten gekomen over de vergassing van organisch materiaal. We zijn er wel achter gekomen dat er heel veel moet worden opgezocht voordat we echt aan de slag kunnen

27-08-2017 | 16:00 Lezen World School opdrachten plastic en biogas

Floyd 1 uur

Reflectie: Oriënterend

26-08-2017 | 17:00 Lezen en doornemen World School opdracht

Tom 1 uur

Reflectie: Oriënterend

23-08-2017 | 12:35 AXM en World School verkennen Floyd 2 uur en 45 min

Reflectie: Nuttig + inspirerend voor een onderwerp

23-08-2017 | 12:35 AXM oefenen en World School verkennen Tom 2 uur en 45 min

Reflectie: Goed werk geleverd en nu een onderwerp

22-08-2017 | 12:30 Zoeken naar bronnen, oriëntatie Floyd 3 uur

Reflectie: We hebben nog geen goed onderwerp dus zijn we qua bronnen ook niet echt ver gekomen.

22-08-2017 | 12:30 Oriëntatie onderwerp en maken bronnen opdracht

Tom 3 uur

Reflectie: We hadden nog niet direct een goed onderwerp maar wel een aantal goede bronnen voor de bronnen opdracht

22-08-2017 | 11:00 Verhaal Meneer Kom, eerste kennismaking PWS

Tom 1 uur

Reflectie: Nuttig

22-08-2017 | 11:00 Eerste kennismaking PWS, verhaal meneer Kom en Cornelisse

Floyd 1 uur

Reflectie: Nuttig

28

Appendix 2: Reflection

This has been a very long project and we have had quite a number of ups and downs. In the

beginning, we did not know what subject to choose. There were so many subjects to choose from,

but most were either too simple or too difficult. Especially the subject Floyd wanted, quantum

physics, was quite hard to work on for a school research paper. This is mainly because this topic is so

diverse and so in depth that you need years of work to simply ‘understand' the underlying principles.

Luckily, we found World School where we could choose from ready-made school research paper

questions and topics including a main question and a complete list of details and contact

information. We chose biogas as our topic because we thought it would be the perfect mix between

Physics, Chemistry, and Biology.

We also learned quite some English, as we chose to write our paper in English. This will come in

handy in the continuance of our school careers, especially as we learned a lot academic and technical

words.

From the beginning, the communication with World school was quite slow to respond to our

questions. Adamfo Ghana never responded to our emails.

The first ‘real’ contact with World School was an introductory day organized by World School at the

Technical University of Delft. The day was very hectic and badly organized, no one from our ‘client’

Adamfo was there that day although they were supposed to be there so that we could ask questions.

It also did not help that Floyd was sick that day, so he could not come.

Then we started on answering our sub-questions and decided that this would be a theoretical study

into biogas for the specific situation in Kumasi, not a design cycle that corresponds perfectly with the

job we were given by World School, we decided to distance ourselves from the specific project and

focus on the requirements of our school for the paper. As we took that road, we noticed that we felt

a lot better and we made more progress. Then we started on answering our sub-questions and

decided that this would be a theoretical study into biogas for the foundation. We also distanced

ourselves from World School because of the reasons listed above.

The communication improved a lot too. Before we started this project, we did not know each other

very well and had not talked to each other so much before, so at first, we had a little trouble

communicating flawlessly. As time advanced, however, we started to get to know each other and to

work together better. That was a nice thing to remark about this project.

29

30