JANUARY, 2013

THE FABRICATION OF BIOGAS DIGESTER AND

PRODUCTION OF BIOGAS FROM COW DUNG AND RUMEN

FLUID

BY

ODETUNDE, Ibrahim Omoniyi (070264),

OLAWUYI, Iretioluwa (062135),

JEGEDE, Olanrewaju John (072157),

AGBOOLA, Olanike Elizabeth (072702).

BEING A PROJECT WORK SUBMITTED TO THE

DEPARTMENT OF MECHANICAL ENGINEERING

FACULTY OF ENGINEERING AND TECHNOLOGY

LADOKE AKINTOLA UNIVERSITY OF TECHNOLOGY (LAUTECH)

OGBOMOSO,

OYO STATE, NIGERIA.

IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF

BACHELOR OF TECHNOLOGY (B.TECH) DEGREE

IN

MECHANICAL ENGINEERING.

ii

CERTIFICATION

This is to certify that this project work was duly carried out by ODETUNDE,

Ibrahim Omoniyi (070264), OLAWUYI, Iretioluwa (062135), JEGEDE,

Olanrewaju John (072157) and AGBOOLA, Olanike Elizabeth (072702) of the

department of Mechanical Engineering, Faculty of Engineering and Technology,

Ladoke Akintola University of Technology, Ogbomoso.

_______________________ ____________________

Dr. Oladeji, J.T. Date

Supervisor

________________________ ____________________

Dr. Durowoju, M.O. Date

Head of Department

iii

DEDICATION

This project work is dedicated to Almighty God for making this project work realistic

and sparing our lives till this moment.

iv

ACKNOWLEDGEMENTS

We will like to make use of this medium to thank The Almighty God for enabling us

to carry out this project work successfully. We will also like to express our

appreciation to our lovely parents, who know and cherish the value of education in a

man‟s upbringing.

We really appreciate the effort of our supervisor in person of Dr. Oladeji. J.T. for his

fatherly love and supervision in making this project work a huge success. We also like

to appreciate the effort of Dr. Adebayo A., of Agricultural Engineering Department,

for his support, and contributions to the success of this project work.

Grateful acknowledgement is also made to our colleagues in the department for their

assistance and encouragement. God bless you all greatly.

v

ABSTRACT

The utilization of energy is of paramount importance and cannot be over

emphasized ranging from domestic purposes, industrial use and transportation

purposes which are dependent on fuel. It unarguably is the cornerstone of economic

and social development. However, there is energy shortage worldwide including

Nigeria and this necessitates producing energy from other sources, especially from

biomass. Therefore, this project work is focused on fabrication of a bio-digester and

generation of biogas using cow dung and rumen fluid as substrate.

A biogas digester with a capacity of 105litres was designed and fabricated.

The substrate (cow dung and rumen fluid) was mixed in the ratio 3:2 and water to

substrate ratio of 2:1 was used. The digester was stirred thrice daily to avoid scum

formation in the digester and to allow for easy escape of the gas produced. The

retention time used for this experiment was 42 days during which the daily internal

temperature reading was taken in order to determine temperature variation and also to

determine the effect of sunlight on the production rate. A rubber hose was connected

to the digester gas outlet located at the top of the digester and the other end of the

rubber hose was connected to a tyre tube provided for storing the gas generated,

which was further taken to the laboratory for analysis.

The biogas yielded consists of 57.99% of methane (CH4), 39.99% of carbon

dioxide (CO2), 2.00% of oxygen (O2), 0.01% of hydrogen sulphide (H2S) and 0.01%

of water vapour. The methane has the highest percentage which represents the main

source of energy and oxygen having 2.00% which shows that the process was purely

carried out under anaerobic condition.

Result of this study showed that methane has the highest percentage and

generally cow dung with rumen fluid easily subjected them to anaerobic digestion.

vi

TABLE OF CONTENTS

CERTIFICATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

TABLE OF CONTENTS vi

LIST OF FIGURES x

LIST OF PLATE xi

LIST OF TABLES xii

CHAPTER ONE 1

1.0 INTRODUCTION 1

1.1 Background to the Study 1

1.2 Problem Statement 2

1.3 Aim and Objectives 3

1.4 Justification for the Research 3

1.5 Scope of the Study 4

CHAPTER TWO 5

2.0 LITERATURE REVIEW 5

2.1 What is Biogas? 5

2.2 History of Biogas 5

2.3 The Renewable Source for Obtaining Biogas 8

vii

2.3.1 Solid Bio-energy Sources 9

2.3.2 Liquid Bio-energy Sources 10

2.4 Biogas Plant 10

2.5 Biogas Plants in Developing Countries. 11

2.5.1 Fixed Dome Digester 12

2.5.1a Characteristics & Functions Fixed Dome Digester 13

2.5.1b Advantages of Fixed Dome Digester 13

2.5.1c Disadvantages of Fixed Dome Digester 14

2.5.2 Floating Dome Digester 14

2.5.2a Characteristics 15

2.5.2b Advantages of Floating Dome Digester 15

2.5.2c Disadvantages of Floating Drum Digester 16

2.5.3 Bag Digester/ Balloon plants 16

2.5.3a Advantages of Bag Digester/ Balloon plants 17

2.5.3b Disadvantages of Bag Digester/ Balloon plants 17

2.5.4 Maintenance of Biogas Plants 17

2.6 Biogas Production with Substrate 18

2.7 Composition of Biogas 18

2.8 Uses of Product of Biogas 18

2.8.1 Methane 19

2.8.2 Carbon-dioxide 20

viii

2.8.3 Liquid 21

2.9 The Benefits of Biogas Technology 22

2.10 Conversion Processes in Anaerobic System 22

2.10.1 Hydrolysis 23

2.10.2 Acidification 23

2.10.3 Methane Formation 23

2.11 Factors Affecting Biogas Production 24

2.11.1 Temperature range of anaerobic fermentation 25

2.11.1a Minimal Average Temperature 25

2.11.1b Changes in Temperature 25

2.11.2 Available Nutrient 26

2.11.3 pH Value 26

2.11.4 Retention Time 27

2.12 Review of Previous Work 27

CHAPTER THREE 37

3.0 MATERIALS AND METHODS 37

3.1 Choice of Feedstock 37

3.2 Material Procurement 37

3.3 Material Preparation 37

3.4 Materials and their Uses 38

3.5 The following are the component parts of the digester 39

ix

3.6 Design of Biogas Digester 39

3.7 Fabrication Process of the Digester 43

3.8 The Experimental Procedures 43

3.9 Characterization of the wastes 44

3.10 Biogas Purification 45

3.11 Cost Analysis 45

CHAPTER FOUR 47

4.0 RESULTS AND DISCUSSIONS 47

4.2: Discussion of Results 50

CHAPTER FIVE 52

5.0 CONCLUSION AND RECOMMENDATION 52

5.1 Conclusions 52

5.2 Recommendations 52

REFERENCES 54

x

LIST OF FIGURES

Fig.2.1: Fixed Dome Plant 12

Fig.2.2: Cross- section of a floating dome digester 14

Fig. 2.3: Bag digester in Bolivia 16

Fig. 2.4: The Conversion Processes in Anaerobic System 24

Fig. 2.5: Schematic diagram for methanogenic activity test and reactor setup 33

Fig 3.1: Cross-section of a digester 42

Fig.4.1 Graph showing temperature (oC) against HRT (weeks) 49

xi

LIST OF PLATE

Plate 3.1 A cylindrical drum digester 41

xii

LIST OF TABLES

Tables 2.1: General Characteristics for the Biomass Batches 28

Table 2.2: Major Elements for the Biomass Batches 28

Table2.3: Physical Characteristics of 5-L and 20-L Working Volume Digesters 35

Table 3.1: Materials and Uses 38

Table 3.2: Cost Analysis of Materials Used for Construction 46

Table 4.1: Chemical composition of the substrate 47

Table 4.2: Average Weekly Temperature Readings for Biogas Production 48

Table 4.3: Percentage Composition of Biogas 49

1

CHAPTER ONE

1.0 INTRODUCTION

1.1 Background to the Study

Energy is one of the most important factors to global prosperity in which its

importance cannot be over emphasized ranging from domestic purposes (heat energy

for cooking food and heating water), for industrial use (for heating furnaces and

running electric motors) and for transport purposes which run on fuel. It is also

important because it is the cornerstone of economic and social development (El-

saeidy, 2004).

There is energy shortage worldwide including Nigeria, which is as a result of

less potential energy to harness, making hydropower a less desirable energy

source(Okoye, 2007). The projected refining capacity only supports 445,000 barrels a

day, and the actual output of these refineries is far below capacity (Rilwanua, 2003).

Additionally, the refineries do not capture the gas that is given off in the refining

process and it is instead burned as flares. There is a trend of deforestation in Nigeria

at 300,000 hectares per year (Girod and Jacques, 1998).

Fossil fuel is one of the principal sources of energy. 86% of all the energy

consumed comes from fossil fuels (Kaliyan and Morey, 2009). There are many

problems associated with fossil fuels, which include high costs and fluctuation of

prices, increase in demand, disruption in supply, and environmental pollution which is

a major problem of fossil fuels. This is because they give off carbon dioxide when

burned thereby causing a greenhouse effect. This is also the main contributory factor

to the global warming experienced by the earth today.

2

Agricultural residues and Animal wastes are increasingly being diverted for

use as domestic fuel to displace fossils fuel and reduce environmental pollution and

reduce emission of greenhouse gases. Cassava solid wastes, amongst other plant

wastes have been widely used (Kozo et al., 1996). Agricultural residues in their

natural forms will not bring a desired result because they are mostly loose and of low

density materials in addition to the fact that their combustion cannot be effectively

controlled (Oladeji, 2009). Agricultural residues and even animal wastes are used in

production of biogas.

Biogas is a mixture of methane and carbon dioxide, produced by the

breakdown of organic waste by bacteria without oxygen (anaerobic digestion). It

contains methane and carbon (IV) oxide with traces of hydrogen sulphide and water

vapour. It burns with pale blue flame and has a calorific value of between 25.9-30J/m3

depending on the percentage of methane in the gas. Biogas production is a profitable

means of reducing or even eliminating the menace and nuisance of urban wastes in

many cities in Nigeria (Akinbami et al., 2001).

Consequently, biogas can be utilized in all energy consuming applications designed

for natural gas.

1.2 Problem Statement

There is energy scarcity all over the world and fluctuation in prices of energy.

Fortunately, Nigeria is an agricultural country that can use these agricultural residues

and animal wastes in biogas production. There is need to generate energy from other

sources, especially from agricultural residues, which are generated in large quantities

from farming activities. The large quantities of agricultural residues produced in

3

Nigeria can play a significant role in meeting her energy demand. Cassava and yam

are ones of the most important agricultural products in Nigeria, especially in southern

and western parts of the country. Residues in form of peels are generated from

processing of these crops. Initial digestion studies carried out on cassava peels

showed that the peels are poor producers of biogas probably as a result of their

content of toxic cyanogenic glycosides (Okafor, 1998). This work is therefore on one

of the techniques involved in production of biogas from cow dung and rumen fluid.

1.3 Aim and Objectives

The broad aim of this project was to produce biogas from cow dung and rumen

fluid. To achieve this, the project had the following specific objectives:

i. To prepare sample of cow dung and rumen fluid.

ii. To design and fabricate a digester that will facilitate conversion of cow dung

and rumen fluid into biogas.

iii. To produce biogas from cow dung and rumen fluid.

1.4 Justification for the Research

Biogas is a form of energy produced when organic materials such as animal

excrement or products that are left over from agriculture are fermented easily and at

low cost. The advantage of biogas is that it replaces other energy sources for example

charcoal, firewood, electricity, liquid petroleum gas and oil. After animal excrement

had been fermented in the gas plant it becomes a good quality and odourless substrate,

which is better than fresh manure in improving the soil for the agriculture. As an

4

energy source, it prevents deforestation and animal excrement from causing pollution,

smell, flies and water pollution in the community.

Also the problem of agricultural waste disposal is posing challenge to the

farmers and to the general public as this waste constitutes a nuisance to the

environment as well as an eyesore to the public. Therefore if these wastes could be

used to generate energy, it would be a welcomed solution to the problem of waste

pollution, disposal and control (Enweremadu et al., 2004a).

Nowadays the use of bio-gas has spread from small farms to big animal farms.

It is expected that biogas will be a significant source of energy in the future to

preserve the environment, solve the pollution problem and to promote better health to

agriculture and community.

1.5 Scope of the Study

The study covered the production of biogas from cow dung and rumen fluid.

5

CHAPTER TWO

2.0 LITERATURE REVIEW

2.1 What is Biogas?

Biogas is a renewable fuel provided by anaerobic digestion of organic material

as substrate for biomethanation. The gas is flammable, which is obtained through the

action of methanogenic bacteria, which work in the absence of oxygen through a

process of anaerobic digestion (Quaak et al., 2001).

It contains 50-75% methane, carbon dioxide, hydrogen sulphide and hydrogen.

It can be used as fuel in boilers and dual fuel engines. It is made by fermenting

organic wastes in biogas digesters.

The wastes are fed into the digesters via the inlet pipe and undergo digestion

in the digestion chamber.

The temperature of the process is quite important because methane producing

bacteria do their work best at temperatures between 30-40 o

C and 50-60oC. It takes 2-

8 weeks to digest a load of wastes.

2.2 History of Biogas

Ancient Persians observed that rotting vegetables produce flammable gas. In

1859 Indians built the first sewage plant in Bombay. Marco Polo has mentioned the

use of covered sewage tanks in China. This is believed to go back to 2,000–3,000

years ago in ancient China.

6

This idea for the manufacturing of gas was brought to the UK in 1895 by

producing wood gas from wood and later coal. The resulting biogas was used for gas

lighting in street lamps and homes (Ioana and Cioabla, 2010).

Biogas typically refers to a gas produced by the biological breakdown of

organic matter in the absence of oxygen. Biogas originates from biogenic material and

is a type of bio-fuel. One type of biogas is produced by anaerobic digestion or

fermentation of biodegradable materials such as biomass, manure, sewage, municipal

waste, green waste, plant material and energy crops. This type of biogas comprises

primarily methane and carbon dioxide. The other principal type of biogas is wood gas

which is created by gasification of wood or other biomass. This type of biogas is

comprised primarily of nitrogen, hydrogen, and carbon monoxide, with trace amounts

of methane.

The gases methane, hydrogen and carbon monoxide can be combusted or

oxidized with oxygen. Air contains 21% oxygen. This energy release allows biogas to

be used as a fuel. Biogas can be used as a low-cost fuel in any country for any heating

purpose, such as cooking, etc. It can also be used in modern waste management

facilities where it can be used to run any type of heat engine, to generate either

mechanical or electrical power. Biogas can be compressed, much like natural gas, and

used to power different energy chains. It is a renewable fuel, so it qualifies for

renewable energy subsidies in some parts of the world.

Biogas typically refers to a gas produced by the biological breakdown of

organic matter, in absence of oxygen. Biogas originates from biogenic material and is

a type of bio-fuel (Cioablă, 2009). Biogas arises from decomposition of organic

substance, by means of bacteria, in anaerobic or aerobic fermentation processes

(Bejan and Rusu, 2007). Organic matter consists mainly of water, albumin, fat,

7

carbohydrates and minerals and together with bacteria; they decompose the original

components, carbon dioxide, minerals and water. Thus a mixture of gas, called

biogas, arises as a metabolic product. Flammable methane (CH4) is the main

component of biogas, with a percentage of 50-85 % by volume, and thus represents

the main source of energy.

This natural process of decomposition occurs only in anaerobic environment, i.e. only

when oxygen is absent. The decomposition process is called decay in this case and is

naturally occurring in swamps, lakes, etc. In case of oxygen presence, decomposition

is carried out by other bacteria; the term for this process is rotting or composting.

Microorganisms that generate methane production are called methanogen

microorganisms, of liquid and acidogene origin. The energy released in the anaerobic

decomposition process is transferred as energy heat in the form of composting, and it

is used by bacteria to form methanogen flammable methane molecules. Collected and

stored in the biogas, the energy is of renewable nature, being derived from organic

matter of the green plants. More and more, the fossil energy will be less used and

replaced, alternatives are becoming necessary and the use of biogas is becoming

increasingly important.

The use of waste water and so-called renewable resources for energy supply is

not a novelty, with evidence of such practices even before Christ‟s birth. Even around

3000 BC, Sumerians practiced anaerobic waste cleaning (Deublein and Steinhauser,

2008). Old Roman scholar Plinius described around 50 years BC lights that glittered

phenomena, in the ponds area.

By 1776, Alessandro Volta personally collected gas from the atmosphere over

the Lake Como, in order to analyse it. His research showed that the formation of gas

depends on a fermentation process and can even form an explosive mixture with air.

8

English physicist Faraday made experiments with swamp gas and identified a type of

hydrocarbon in its composition. Later, around 1800, Dalton, Henry Davy described

the first chemical structure of methane. The final chemical formula was elucidated by

Avogadro in 1821.

In the second half of 19th

century, in France, a systematic and scientific

research for a better understanding of the process of anaerobic fermentation started.

The objective was to remove bad odour emanating from waste water. During

investigations, the researchers have detected typical microorganisms that are retested

nowadays as essential for the fermentation process. Bechamp identified by 1868 that a

mixed population of microorganisms is necessary to convert ethanol to methane, since

more final products were formed by the fermentation process; the whole process

depends on the substrate used.

By 1876, Herter reported the presence of acetate in the waste water, forming

methane and carbon dioxide in stoichiometric amounts. Louis Pasteur tried by 1884 to

produce biogas from horse droppings, collected from the streets of Paris. Together

with his students he managed to produce 100 m3 of methane from a fermentation

process, developed at 35 °C. Pasteur explained that the rate of production is sufficient

to cover energy needs for street lightening in Paris. Practically, this is considered the

starting point of larger application of renewable energy.

2.3 The Renewable Source for Obtaining Biogas

Biomass is the only renewable energy source that can be transformed into gas,

liquid or solid fuel by special conversion technologies. This universal renewable

energy carrier can be used in a wide range of applications, in the energy sector, for

9

small scale but also larger applications. Presently it is possible to provide this

renewable resource for the whole range of applications that require energy input,

starting from heating stations until providing electricity to mobile applications for

transport. On average, the industrialized countries contribute to the total biomass

energy sources used in a proportion of 9- 13 %, while in developing countries it

contributes in a percentage ranging from 5 % to 30 % ( Faaij, 2006). Typically, after

the biomass was treated, it is transformed into one of the major energy forms: (i)

Electricity or (ii) Heat. Range of application and disposal of biomass form the two,

very important advantages of biomass. Another major argument for using the energy

resources originated in bio – resources is the possibility of protecting the environment

and climate. When stored in biomass energy use, greenhouse gases like carbon

dioxide are emitted, but this amount is not a supplementary generated product, as it is

result from a natural decay processes. Thus bio-energy carriers can be considered

neutral in terms of climate damage, particular CO2 emission.

2.3.1 Solid Bio-energy Sources

The largest group of solid bio-energy sources includes products made from

wood. They are derived from industrial processing of wood waste. In many areas of

agricultural by-products such as straw, are also used to generate energy from biomass.

On one hectare of straw cereals is approximately equivalent to 200 litres of oil (Ioana

and Cioabla, 2010). However, straw and other products in this category have different

combustion characteristics from those of woody fuels. Point transformation in ash and

emission behaviour of biomass type straw means that different technical approaches

are needed.

10

Another important category of waste, which is not necessarily part of the old

wood sector, represents the wood residues from environmental management. These

occurred during maintenance work on roads and canals, parks and care. Wood

residues from environmental management are usually a mixture of wood, leaves and

straw type products. Only very rarely it is possible to consider these mixtures for a

new final product, thus utilization of its energy content is a very good strategy.

2.3.2 Liquid Bio-energy Sources

Mobility is essential in industrialized society. With few exceptions, passenger

transport and freight are based on liquid fuel. Today, there are few alternative bio-

fuels for these tasks. Ethanol, the alcoholic fermentation and methanol produced from

cellulose can be considered as having a biomass origin.

2.4 Biogas Plant

In many countries worldwide, biogas plants are in operation, producing biogas

from the digestion of manure or other biomass (GTZ, 2007). In addition, with success

small scale biogas plants are utilized to displace woody fuels and dung in many

developing countries. For example, the Dutch Development Organization, SNV,

implemented with success in Nepal and Vietnam over 220,000 household on site

biogas plants (FMO, 2007). Moreover, in China and India, millions of plants are in

operation. In conclusion, biogas plants have proven to be an effective and attractive

technology for many households in developing countries.

Under the right conditions a biogas plant will yield several benefits for the end-

users, the main benefits are (GTZ, 2007):

11

i. Production of energy for lighting, heat, electricity

ii. Improved sanitation (reduction of pathogens, worm eggs and flies)

iii. Reduction of workload (less firewood collecting) and biogas stoves has a

better cooking performance

iv. Environmental benefits (fertilizers substitution, less greenhouse gas emission)

v. Improved indoor air quality (less smoke and harmful particle emission of a

biogas stove compared to wood or dung fuels).

vi. Economic benefits (substitution of spending on expensive fuels and fertilizer)

The problems experienced by the biogas production include the following:

(a) Design faults

(b) Construction faults

(c) Difficulty of financing

(d) Operational problems due to incorrect feeding or poor maintenance and

(e) Organizational problems arising from the differences of approaches and lack of

coordination.

All these aspects need to be taken into account. In addition, back up services are

important, i.e. monitoring of the performance by experts.

2.5 Biogas Plants in Developing Countries.

In developing countries, there are several digesters in operation; the most

familiar is the fixed dome digester. In addition, the floating dome digester and bag

digester are found in many developing countries. These types of digesters are

respectively explained below:

12

2.5.1 Fixed Dome Digester

The fixed dome digester is the most popular digester; its archetype was

developed in China. This is CSTR type digester. The digester comes in various types,

notably the Chinese fixed dome, Janata model and Janata II model.

Fig 2.1: Fixed dome plant

(Source: http://www.gtz.de/de/dokumente/en-biogas-volume2.pdf)

Legend:-

1. Mixing tank with inlet pipe and sand trap.

2. Digester.

3. Compensation and removal tank.

4. Gasholder.

5. Gas pipe.

6. Entry hatch, with gastight seal.

7. Accumulation of thick sludge.

8. Outlet pipe.

9. Reference level.

13

10. Supernatant scum, broken up by varying level.

2.5.1a Characteristics & Functions Fixed Dome Digester

A fixed dome digester is a closed dome shaped digester. The waste (manure,

dung, human excrement) is fed to the digester. After that the methanogen bacteria

„digest‟ the waste and produce biogas and slurry (digested waste). The gas is captured

in the gasholder and the slurry is displaced in the compensating tank. The more gas is

produced, the higher the level at the slurry outlet will be. The level of slurry in the

digester depends on the loading rate, gas production and consumption. During gas

production slurry is pushed back sideways, displaced to the compensation tank. When

gas is consumed slurry enters back into the digester from the compensation tank. As a

result of these movements, a certain degree of mixing is obtained of slurry of different

ages; therefore this design approaches a mixed digester reactor (Stalin, 2007).

The fixed dome digester is relatively inexpensive. It is simple, has no moving

parts and has therefore a long lifespan, up to 20 years (GTZ, 1999). The plant is

suitable for cold climates, because most part is beneath the ground level. Therefore

the plant is protected against low temperatures occurring during night and in cold

seasons. The temperature within the digester is lower during day time and higher

during night-time (GTZ, 1999). This fluctuation is beneficial for the methanogenic

bacteria and subsequently for the biogas production. The main advantages and

disadvantages are:

2.5.1b Advantages of Fixed Dome Digester

1. Relatively cheap and durable

2. No moving parts

3. Well insulated

14

2.5.1c Disadvantages of Fixed Dome Digester

1. High technical skills are required for a gas tight construction

2. Special sealant is required for the gasholder

3. Gas leaks occur when not designed well

4. Difficult to construct in bedrock

5. Amount of gas available for cooking is hard to detect

6. Enormous structural strength required for construction (Sharma and Giuseppe,

1991)

Experiences for the China biogas program teaches us that special attention is required

when constructing a fixed-dome digester (Daxiong, 1990). GTZ only advices to

construct such a plant under the supervision of experienced biogas technicians (GTZ

2007). This should not be taken lightly. Cleary, the design has many favourable

aspects, but its success is dependent on the input of high technical manufacturing.

2.5.2 Floating Dome Digester

Floating drum digesters are mainly found in India and this is semi CSTR type

reactor. A floating drum digester is shown below:

Figure 2.2: Cross- section of a floating dome digester, based on the original design developed by KVIC in

India.

(Source: www.ganesha.co.uk/Articles/Biogas%20Technology%20in%20India.htm)

15

The ideal situations for a community based biogas digester recommend a

central collection area for the plant substrate, be it animal manure, excrete or

food/vegetable waste. Here lies the first area of logistical headache which calls for

organizational skills from the responsible community. Studies by SRE (Sustainable

Rural Energy) for a Community based biogas plant in Haor (Wetland) involved

providing all the families in the community an improved sanitary latrine which was

connected to a central digester. According to SRE (2002) “a beneficiary committee

has been formed and this community is entrusted with the responsibility of proper

operation and maintenance of the system”.

2.5.2a Characteristics

The operation of a floating dome digester is not that different from a fixed

dome digester. The produced gas is collected in a movable steel drum, the gasholder.

The steel drum is guided by a guide frame. When gas is consumed the drum sinks.

Slurry is pushed out of the digester after the digestion (GTZ).

In contrast to the fixed dome digester, a floating drum digester is not a mixed

reactor like fixed dome, but here also some mixing take place due to gas production

and removal of gas.

2.5.2b Advantages of Floating Dome Digester

1. The operation of the plant is easy to understand and operate

2. Gas drum is air tight provided the drum is de-rusted and painted regularly

3. Constant gas pressure as a result of the weight of the drum

16

2.5.2c Disadvantages of Floating Drum Digester

1. Steel drum is relatively expensive and needs regularly maintenance (priming,

painting,

Coating)

2. Steel drum can get stuck

2.5.3 Bag Digester/ Balloon plants

A balloon plant or also referred to as a bag digester is a plastic or rubber bag

combining the gas holder and digester. This is a plug-flow type reactor. Gas is

collected in the upper part and manure in the lower part; the inlet and outlet are

attached to the skin of the bag. The pressure of the gas is adjustable by laying stones

on the bag. The next picture shows a bag digester as used in Bolivia on the Altiplano.

Figure 2.3: Bag digester in Bolivia.

(Source: www.tecnologiadesarrollo.tk)

According to GTZ (unknown date) these bags have a limited life span of 3-5

years. In China red mud bags, a by-product from the production of aluminium is used

since 1983 with success. However, the effective life span was also limited to 3-5 years

(Daxiong, 1990).

17

2.5.3a Advantages of Bag Digester/ Balloon plants

1. Low costs

2. Simple technology

3. Uncomplicated cleaning

2.5.3b Disadvantages of Bag Digester/ Balloon plants

1. Short life-span

2. Susceptible to physical damage

3. Hard to repair

4. Need for high quality plastic/PVC

5. Difficult to insulate

2.5.4 Maintenance of Biogas Plants

The manual of GTZ asserts that a dome digester needs to be cleaned every 5

years, which is probably also true for a floating dome digester. During the operation

of a digester some materials settle, such as sand or other heavy non digestible

materials, and therefore cleaning is necessary (GTZ, 1999). Cleaning consists of

emptying the complete digester and a cleaning rate of once every five year is

consistent.

A steady decrease in gas production rate over the years, probably due to the

settling of materials leading to a reduction of the effective digester volume (Kalia and

Kanswar, 1998). After cleaning, the biogas production increased to the highest levels

of the first years of operation. (Kalia and Kanswar, 1998) therefore suggested

cleaning the digester every 5 years. A bag digester has such a limited life span that

cleaning does not have to be considered. To avoid a long period with no gas

production, we suggest recycling most of the content of the emptied digester apart

from the settled materials.

18

The steel drum of the floating dome needs a new coating once in every three

years by applying corrosion resistant paint (Nazil, 1991). Higher quality materials

could be more leak resistant and more resistant to damage.

2.6 Biogas Production with Substrate

Many substrates are generally used as feedstock in biogas plants and the

potential for biogas production varies with feedstock. Generally animal waste, human

waste, kitchen waste and some crop residues are used in small scale biogas plants.

Gas production rate varies with the type of substrate used in the biogas plant.

Normally 1 m3 of biogas is enough to cook three meals for a family of 5-6 members

(Practical Action Org, 2006).

2.7 Composition of Biogas

Biogas is a mixture of gases that is composed chiefly of:

· Methane (CH4): 40-70 vol. %

· Carbon dioxide (CO2): 30-60 vol. %

· Other gases: 1-5 vol. % including

· Hydrogen (H2): 0-1 vol. %

· Hydrogen Sulphide (H2S): 0-3 vol. %

2.8 Uses of Product of Biogas

Biogas (methane and carbon dioxide) is the primary output product of the

bioconversion process. Biogas and/or its components may be utilized in a variety of

applications.

19

2.8.1 Methane

Methane (CH4) is the main component of biogas, representing the energy

produced from the bioconversion of wastes. This energy is recovered by using the gas

in one or more of the following ways:

i. Electricity

Biogas may be consumed in an engine generator set to produce electricity.

Typically, this is the lowest value option. The revenue from such use is dependent

upon prevailing local rates and how the produced electricity is distributed. Generally,

the electricity is sold at a wholesale rate to the local utility through an independent

meter. Such arrangements/rates are governed by an area‟s utility commission. “Net

metering” (exporting electricity through an existing meter for the “retail” rate) is a

reality in many states, but the size of most bioconversion systems exceeds applicable

limits. “Wheeling” (power purchase agreements between geographically separate

generators/consumers with access to a common power grid) is one method of

achieving higher value for generated power which has begun to be put into practice.

Another method is to provide the power “in-house”, thereby reducing the amount of

electricity which would otherwise need to be purchased.

ii. Thermal Energy

With equipment modification, biogas may replace the thermal energy in propane

or natural gas for cooking, heating, refrigeration and/or lighting. This provides

increased value when replacing propane, but once converted, the selected equipment

won‟t be able to use its original fuel unless it is “converted back”. However,

20

equipment can be converted or purchased to use two types of fuel (bi-fuel), which

would preserve the equipment‟s function if one fuel source was interrupted.

iii. Transportation Fuel

With further processing, the methane in biogas can replace standard transportation

fuels. This use presents one of the greatest values, both economically and

environmentally. Energy is never produced or consumed; it is only converted from

one form to another. Our fossil-fuel-based economy is rapidly depleting solar energy

stored long ago in the form of plant and animal tissue (coal and oil, respectively).

Also, for every conversion step there are associated losses (efficiencies).

Pollution is inversely proportional to energy efficiency. One of the least

efficient (most polluting) uses of energy is as gasoline for vehicle fuel. Replacing the

least efficient use of non-renewable energy with a form of renewable energy, biogas.

This option provides the greatest environmental benefit at the same time it (usually)

provides the greatest economic return.

Vehicles can be purchased or converted to use compressed gas as fuel, instead

of gasoline or diesel. As with appliances, functionality can be preserved by converting

to or purchasing vehicles which are capable of bi-fuel operation.

2.8.2 Carbon-dioxide

Carbon dioxide (CO2), the other major component of Biogas, has several uses

when separated from the total gas stream. This option is exercised when there is a

market for the products and an economic return is indicated relative to the capital

equipment required to produce them. The standard uses of CO2 are for carbonation of

21

beverages and for dry ice production. Dry ice is used in transportation of frozen

perishables. Chipped dry ice replaces grit and sand used in sandblasting operations

without polluting the immediate environment.

Additional uses include freeze tunnel applications for meat, fish, vegetable,

and fruit processing. As a supercritical fluid, CO2 is used as an extraction solvent in

the food and pharmaceutical industries for products such as coffee, tea, tobacco, hops,

corn oil, flavours, and colours. Its use is also recommended in industrial processes and

for in-situ remediation of halogenated hydrocarbons and other solvents.

2.8.3 Liquid

Liquid co-products are also available from the bioconversion process:

i. Bio Green

The process of bioconversion results in a naturally-balanced liquid product

containing ammonium (fast-acting) and amino-protein (slow-release) nitrogen, in

addition to phosphorous, potassium, calcium, iron, sulphur, and magnesium. This

liquid is screened and pasteurized to create Bio green.

ii. Bio Activator

By further processing the screened effluent with a filter, a concentrated, slow-

release plant food is produced. Bio Activator feeds the soil micro environment

because 70% of its nitrogen is available as amino acids, protein, and polysaccharides

chelated to phosphorous, potassium, calcium, iron, sulphur, and magnesium.

iii. Bio Tonic

22

The other product from filtering is a fast-acting foliar, which improves bud and

flower production while increasing root development. 70% of bio tonic nitrogen is in

the readily-available ammonium form, along with soluble phosphorous and

potassium.

2.9 The Benefits of Biogas Technology

Well-functioning biogas systems can yield a whole range of benefits for their

users, the society and the environment in general, some of these benefits are:

i. Production of energy (heat, light, electricity)

ii. Transformation of organic waste into high quality fertilizer

iii. Improvement of hygienic conditions through reduction of pathogens, worm eggs

and flies

iv. Reduction of workload, mainly for women, in firewood collection and cooking.

v. Environmental advantages through protection of soil, water, air and woody

vegetation

vi. Micro-economic benefits through energy and fertilizer substitution, additional

income sources and increasing yields of animal husbandry and agriculture

vii. Macro-economic benefits through decentralized energy generation, import

substitution and environmental protection.

2.10 Conversion Processes in Anaerobic System

Biogas microbes consist of a large group of complex and differently acting

microbe species, notable the methane-producing bacteria. The whole biogas-process

can be divided into three steps: hydrolysis, acidification and methane formation.

23

2.10.1 Hydrolysis

In the first step (hydrolysis), the organic matter is enzymolyzed externally by

extracellular enzymes (cellulose, amylase, protease and lipase) of micro-organisms.

Bacteria decompose the long chains of the complex carbohydrates, proteins and lipids

into shorter parts. For example, polysaccharides are converted into monosaccharide.

Proteins are split into peptides and amino acids.

2.10.2 Acidification

Acid-producing bacteria, involved in the second step, convert the

intermediates of fermenting bacteria into acetic acid (CH3COOH), hydrogen (H2) and

carbon dioxide (CO2).

These bacteria are facultative anaerobic and can grow under acid conditions.

To produce acetic acid, they need oxygen and carbon. For this, they use the oxygen

solved in the solution or bounded-oxygen. Hereby, the acid-producing bacteria create

an anaerobic condition which is essential for the methane producing microorganisms.

Moreover, they reduce the compounds with a low molecular weight into alcohols,

organic acids, amino acids, carbon dioxide, hydrogen sulphide and traces of methane.

From a chemical standpoint, this process is partially endergonic (i.e. only

possible with energy input), since bacteria alone are not capable of sustaining that

type of reaction.

2.10.3 Methane Formation

Methane-producing bacteria, involved in the third step, decompose

compounds with a low molecular weight. For example, they utilize hydrogen, carbon

24

dioxide and acetic acid to form methane and carbon dioxide. Under natural

conditions, methane producing micro-organisms occur to the extent that anaerobic

conditions are provided, e.g. under water (for example in marine sediments), in

ruminant stomach and in marshes. They are obligatory anaerobic and very sensitive to

environmental changes.

In contrast to the acidogenic and acetogenic bacteria, the methanogen bacteria

belong to the archaebacter genus, i.e. to a group of bacteria with a very heterogeneous

morphology and a number of common biochemical and molecular-biological

properties that distinguish them from all other bacterial general. The main difference

lies in the makeup of the bacteria‟s cell walls.

Fig 2.4: The Conversion Processes in Anaerobic System. Source: (GTZ, 1999)

2.11 Factors Affecting Biogas Production

There are many factors that can affect biogas production, some of which are:

25

2.11.1 Temperature range of anaerobic fermentation

Anaerobic fermentation is in principle possible between 3°C and

approximately 70°C.

Differentiation is generally made between three temperature ranges:

· The psychrophilic temperature range lies below 20°C,

· The mesophilic temperature range between 20°C and 40°C and

· The thermophilic temperature range above 40°C.

2.11.1a Minimal Average Temperature

The rate of bacteriological methane production increases with temperature.

Since, however, the amount of free ammonia also increases with temperature; the bio-

digestive performance could be inhibited or even reduced as a result. In general,

unheated biogas plants perform satisfactory only where mean annual temperatures are

around 20°C or above or where the average daily temperature is at least 18°C. Within

the range of 20-28°C mean temperature, gas production increases over-proportionally.

If the temperature of the bio-mass is below 15°C, gas production will be so low that

the biogas plant is no longer economically feasible.

2.11.1b Changes in Temperature

The process of bio-methanation is very sensitive to changes in temperature.

The degree of Sensitivity, in turn, is dependent on the temperature range. Brief

fluctuations not exceeding the following limits may be regarded as still un-inhibitory

with respect to the process of fermentation:

· Psychrophilic range: ± 2°C/h

· Mesophilic range: ± 1°C/h

26

· Thermophilic range: ± 0.5°C/h

The temperature fluctuations between day and night are no great problem for

plants built underground, since the temperature of the earth below a depth of one

meter is practically

constant.

2.11.2 Available Nutrient

In order to grow, bacteria need more than just a supply of organic substances

as a source of Carbon and energy. They also require certain mineral nutrients. In

addition to carbon, oxygen and hydrogen, the generation of bio-mass requires an

adequate supply of nitrogen and sulphur.

2.11.3 pH Value

The methane-producing bacteria live best under neutral to slightly alkaline

conditions. Once the process of fermentation has stabilized under anaerobic

conditions, the pH will normally take on a value of between 7 and 8.5. Due to the

buffer effect of carbon dioxide-bicarbonate (CO2 – HCO3 -) and ammonia-ammonium

(NH3 – NH4 +), the pH level is rarely taken as a measure of substrate acids and/or

potential biogas yield.

A digester containing a high volatile-acid concentration requires a somewhat

higher-than-normal pH value. If the pH value drops below 6.2, the medium will have

a toxic effect on the methanogen bacteria.

27

2.11.4 Retention Time

The retention time can only be accurately defined in batch-type facilities. For

continuous systems, the mean retention time is approximated by dividing the digester

volume by the daily influent rate.

Depending on the vessel geometry, the means of mixing, etc., the effective

retention time may vary widely for the individual substrate constituents. Selection of a

suitable retention time thus depends not only on the process temperature, but also on

the type of substrate used.

2.12 Review of Previous Work

Ioana and Cioabla (2010) carried out an experiment which were accomplished

using a temperature domain of 30 – 38 °C (mesophilic range) and the duration for

each batch extended over 45 days, which means that the process was fully under

control. The waste materials used for the experiments were maize bran and a recipe of

maize (40 %), corn cobs (40 %) and sunflower seeds (20 %), all percentage by mass.

These substrates determine the amount of energy that is transformed into biogas.

Before the experiments, preliminary determinations for each type of biomass were

completed and the results are presented in Tables 2.1 and 2.2

28

Tables 2.1: General Characteristics for the Biomass Batches

No. Sample

Hygroscopic

Humidity (%)

Ash

Content

(%)

Low Calorific

Value (kJ/kg)

1 Maize Bran 0.16 4.63 15.535

2

Recipe of Corn Maize

and Sunflower seeds

1.04 1.18 15.192

Source: (Ioana and Cioabla, 2010)

Table 2.2: Major Elements for the Biomass Batches

No. Element Maize bran

(mg/kg)

Recipe of corn, maize and sunflower seeds

(mg/kg)

1 Mg 1331 764

2 Al 71 61

3 Si 174 34

4 P 5855 2419

5 S 1165 925

6 Cl 370 388

7 K 9697 4359

8 Ca 1209 901

9 Mn 108 14

10 Fe 177 117

11 Zn 69 25

Source: (Ioana and Cioabla, 2010)

29

They reported that the nature of utilized biomass represents an important

factor in the production of biogas, supplementary to the quantity and quality of the

produced biogas using the anaerobic fermentation process. The main parameter to be

controlled during the anaerobic fermentation process is temperature, the chosen range

having a relevant impact on the characteristics of the resulted biogas.

Further parameters of influence on the anaerobic fermentation process are

complementary to the temperature at which the process is achieved: the pH of slurry,

the elementary chemical composition of the materials used and the biomass nature. As

it resulted from the details involved in the process of anaerobic fermentation, the

material can be decomposed partially, or totally, as a function of its nature and

properties. The main operations which were accomplished are: (i) preliminary size

reduction, (ii) transport and storage, (iii) removing of non-desired materials (iv)

reducing the ash content (v) total or partial drying and secondary size reduction, prior

to the use.

Huong (2012) demonstrated the use of Orange peel as a potential source for

biogas production. However, D-limonene present in the peel is known as an anti-

microbial agent which can decrease biogas production. Biogas production from the

orange peel was improved by solvent pre-treatment.

A simple pre-treatment procedure following solid-liquid technique for the

removal of D-limonene was designed. In addition, experimental design has been

employed as an important tool for conducting experiments efficiently and analysing

experimental results in a correct statistical manner.

The results showed that biogas production at 2% Volatile Solid concentration

increased from 0.061 m3 methane/kg VS to 0.217 m

3 methane/kg VS if the chopped

peel was treated using n-hexane as solvent at the condition of 20°C, 10 minutes and a

30

hexane/peel ratio (volume/weight) of 12. D-limonene in orange peel was partly

removed and the amount varied depending on pre-treatment conditions.

Four important factors which cause effect on pre-treatment step was studied,

including orange peel types (chopped peel and homogenized peel), pre-treatment

temperature, pre-treatment time, hexane/peel ratio so that the pre-treatment step can

be improved. Two level factorial designs were employed to conduct experiments in

the experimental series.

The results showed that only factor of peel type gave significant effect. The

chopped peel gave higher methane production compared to that of homogenized peel.

N-hexane was the most interesting solvent since it showed higher extraction

efficiency toward D-limonene and orange peel treated by n-hexane gave higher

methane production than the peel treated by other solvents. Behaviour of n-hexane

can be due to either its high extraction efficiency or its less toxicity to bacteria.

Further experiments should be focused on pre-treatment using n-hexane as

solvent and the peel treated by n-hexane for biogas production. In addition, the pre-

treatment step should be improved and the conditions for pre-treatment should be

investigated so that biogas production from treated orange peel will increase in

comparison with untreated one.

Rungvichaniwat (2003) used residue from fruit and vegetable wastes mixed

with cow manure by using a low-solids anaerobic digester to determine the biogas

production as well as the efficiency in total solids (TS) and volatile solids (VS)

reduction from fruit and vegetable wastes (FVW) mixed with cow manure (CM) by

using a low-solids anaerobic digester.

The four bench-scale digesters were operated at the same hydraulic retention

time of 31.25 days with a digester volume of 12.5 litres. The various ratios of mixed

31

wastes to the volatile solids of FVW and CM were 100:0, 80:20, 60:40 and 40:60 and

were used as waste-feed for the digesters.

The results indicated that the efficiency in total solids reduction at various

ratios of the mixed wastes were from 36.84-73.12 %, whereas, the volatile solids

reduction were in the range of 43.83-80.63 %. The amount of biogas production was

varied from 0.67-0.73 m3/m

3 of digester-day or the equivalent of 0.12-0.30 m

3/kg of

VS feed-day.

The composition of the biogas consisted of methane from 48.64-53.26 % and

carbon dioxide was in the range of 29.84-41.28 %. Furthermore, the methane

production varied from 0.16-0.37 m3/m

3 of digester-day or the equivalent of 0.07-0.15

m3/kg of VS feed-day. In all cases, the digesters could be operated without addition of

chemicals or nutrients into the system.

The results clearly demonstrated that the digester, which was fed with mixed

waste, of FVW and CM, of 80:20 could produce the highest biogas production (0.73

m3/m

3 of digester-day or 0.30 m

3/kg of VS feed-day). In addition, this digester also

produced a large amount of methane (0.37 m3/m

3 of digester-day or 0.15 m

3/kg of VS

feed day). With a TS and VS reduction of 60.61 % and 66.77 %, respectively.

Periyasamy and Nagarajan (2011) used jatropha deoiled cake and orange peel

waste for biogas production which was carried out in the batch scale (500 ml serum

bottle) under anaerobic condition at ambient temperature (at various mixing ratios of

two substrate).

The experimental data showed a maximum gas output of 1140 ml of gas

production at (1:2) ratio of jatropha deoiled cake with orange peel waste obtained for

a period of 17 days. The modified Gompertz equation was used to adequately describe

the cumulative biogas production for this reactor.

32

The CH4 content was 75%, CO2 content was 16% and CO content was 9%.

The biogas production was measured by liquid displacement system on daily basis.

The total solids content of feed materials were determined as per the standard

method. The initial weight of the samples of 50 g biomass with pre-weighed porcelain

boxes were taken by using an electronic balance with least count of 0.001 g. The

samples were first heated at 60°C for 24 h and then at 103°C for 3 h using a hot air

oven. The final weight or dried samples weight with pre-weighed porcelain boxes

were recorded. The percentage total solids content of the sample was then calculated

using the formula:

(

)

Where, TS is the total solids in percentage (%); Wd is the weight of oven dried

sample and Ww is the weight of wet sample in gram (g).

The volatile solids and non-volatile solids content of feed materials were determined

as per the standard method. The oven dried samples used for the determination of

total solids content were further dried at 550 ± 50°C temperature for 1 h in a muffle

furnace and allowed to ignite completely. The dishes were then transferred to

desiccators for final cooling. The weight of the cooled porcelain dishes with ash were

taken by the electronic balance. The volatile solids content and non-volatile solids

content of the sample were calculated using the formulas:

(

)

(

)

33

Where, VS is the volatile solids in dry sample, %; NVS is the non-volatile solids in

dry sample, %; Wd is the weight (g) of oven dried sample; Wa is the weight (g) of dry

ash left after igniting the sample in a muffle furnace.

Figure 2.5: Schematic diagram for methanogenic activity test and reactor setup.

Source: (Periyasamy and Nagarajan, 2011).

Biogas production from jatropha deoiled cake and orange peel waste was

established here to be feasible at room temperature. The application of the modified

Gomperzt equation in studying the biogas production was able to predict the pattern

of biogas production with time.

It was observed that the maximum biogas production could be obtained from

the reactor 1 (2g jatropha deoiled cake + 4 g orange peel waste (1:2). In reactor 2, the

biogas production was fewer amounts than the reactor 1. Likewise reactor 3 and 4

34

produced less amount of biogas than the reactor 2. He concluded that biogas

production varied due to various substrate concentrations of the reactors.

Wantanee and Sureelak (2004) used starch-rich tubers of cassava plant in the

production of biogas which was investigated in the laboratory scale using the simple

single-state digesters of 5- and 20-litre working volumes. The digesters were fed on a

batch basis with the slurry of dry cassava tuber containing the average moisture

content of 18%, and operated at ambient temperature (29-31°C) for 30 days. When

operating the single-state digester of 5-liter working volume fed with the optimal

concentrations of carbon and nitrogen sources, 1.00% (w/v) total solids and 0.04%

(w/v) urea, the gas yield of 1.95 litres/day containing the maximum methane content

of 67.92% was achieved at 10-day retention time.

The fermentation reactions were ceased after 16-day operation. The

fermentation volume was then scaled up to 20 litres. The gas yield of 5.50 litres/day

containing 55.70% methane was obtained at 10-day retention time. Whereas the

methane content of 67.57% and the gas yield of 3.88 litres/day were obtained at 14-

day retention time. The fermentation reactions were ceased after 24-day operation.

Biogas containing 67% methane content could be achieved from the digestion of

cassava tubers using simple single-state digesters.

The production of biogas from raw cassava tuber was performed using the

simple single-state digesters with working volumes of 5 and 20 litres. The digesters

were fed on a batch basis with the slurry of dry cassava tuber containing the average

moisture content of 18% and 10% (v/v) of seed cultures. The biogas fermentation was

then operated in triplicate at ambient temperature for 30 days.

35

Table2.3: Physical Characteristics of 5-L and 20-L Working Volume Digesters

Parameter 5L 20L

Digester height (cm) 25.00 35.00

Liquid height (cm) 13.50 41.30

Empty Volume (L) 7.50 26.00

Filled Volume (L) 5.00 20.00

Source: (Wantanee and Sureelak, 2004)

Since the amount of main nutrients (carbon and nitrogen sources) affects the

growth of micro-organisms and the production of biogas, the optimal concentrations

of TS (carbon source) and nitrogen source added were determined. The high carbon-

to-nitrogen ratio (approximately 80:1) of cassava root (dry weight) has been reported.

The optimum ratios for the maximum biogas generation have been suggested to be

20-30:1.

In the study, various TS concentrations: 0.25, 0.50, 1.00, 2.00, 4.00, and

8.00% (w/v), were applied to the 5-L reaction volume to obtain the optimum TS

content. Then the addition of urea (46% of nitrogen) as a nitrogen source at 0.00,

0.02, 0.03, 0.04, 0.10, and 0.20% (w/v) was investigated.

For stabilizing pH of cassava slurry during the anaerobic digestion, the

addition of sodium bicarbonate (0.25%, w/v) was considered whenever the volatile

fatty acids-to-alkalinity ratio was greater than 0.8. The volume of biogas produced in

the digester was measured by the displacement of water in the gas holder

compartment.

The pH of water in this holder was adjusted to 2 to avoid carbon dioxide

dissolution. Gas production was measured daily. The composition of biogas collected

over water, was analysed using the Gas Analyser equipped with a thermal

36

conductivity detector (TCD) and 1-M Porapak Q (80-100 mesh) column. Helium was

used as a carrier gas at a flow rate of 25 mL/min. The oven, injector, and detector

temperatures were 80, 120, and 120°C respectively.

Biogas containing the methane content of 67% could be efficiently produced

from cassava tuber slurry (1%, w/v, TS) and the supplement of urea (0.04%, w/v) in

the simple single-state digester with both 5-L and 20-L reaction volumes. Cassava

tubers used to prepare the slurry contain the average contents of 81% of TS, 40% of

total carbon, 38% of starch, and 0.5% of total nitrogen.

37

CHAPTER THREE

3.0 MATERIALS AND METHODS

3.1 Choice of Feedstock

The choice of feedstock for this project was cow dung and rumen fluid as co-

substrate due to the excess abundance of cattle in Nigeria and its numerous

advantages. Cow dung is the ideal substrate for bio-digesters because it is not acidic

according to Karanja and Kiruiro (2003).

3.2 Material Procurement

The cow dung and rumen fluid used in this research was obtained from

slaughterhouse located at Ogbomoso, Oyo state, Nigeria. The fresh cow dung was

obtained from animal holding pen unit while rumen fluid was collected from

evisceration unit.

3.3 Material Preparation

Rumen fluid was prepared as follows: rumen content was poured to 25 litre

tank and 20 litre tap water added. Solid content was separated from slurry by filter

cloth. Before using, all of cow dung and rumen fluid collected was homogenized by

mixing with propeller mixer. Cow dung and rumen fluid sample was analysed based

on its dry matter (DM) content by mean heating at 105oC and 550

oC, respectively.

38

3.4 Materials and their Uses

Table 3.1: Materials and Uses

Materials Uses

9mm diameter rubber hose Used to connect the digester to the gas collector

Clip made of metal plates, bolt and nut To clip the hose at various point as required

during the experimental procedure

Rubber motorcycle tyre tube Used for collection of the gas yielded

Weighing scale Used for weighing of material needed

Cow dung (raw material) Used as feedstock into the digester

Rumen fluid (raw material) Used as co-substrate

Maggots Used to exhaust oxygen enclosed in the digester

Chemical reagent Caustic soda used to absorb co2

Rubber seal Used to ensure the digester is airtight

Poly filler Used for sealing welded joint to avoid leakages

Water Used for preparing the slurry

Thermometer

Galvanized steel sheet (1.2 mm)

Welding machine

Sheet metal cutter

Hand drilling machine

Thermometer duct cork (x2)

6201 bearings (x2)

Meter rule

Used for measuring the ambient temperature of digester

Used for the fabrication of the digester

Used for joining the galvanized steel sheet together

Used for cutting of the sheet metal into size and shape

Used to create bolt and nut holes on the digester

Used for closing the thermometer duct

Makes the agitator statically and dynamically balanced

Used for making measurements

39

3.5 The following are the component parts of the digester

i. The Manual Agitator

ii. The manual agitator handle (L-shaped)

iii. The thermometer duct

iv. Galvanized steel lid

v. 15 bolts, nuts and washers for the steel lid

vi. 6 bolts, nuts and washers for the substrate inlet cover

vii. The gas outlet duct

viii. The substrate inlet duct

ix. The digestion chamber

x. The slurry outlet duct

3.6 Design of Biogas Digester

40

41

Plate 3.1:- A Cylindrical Drum Digester

42

Fig. 3.1: Cross-section of a digester

43

3.7 Fabrication Process of the Digester

i. Cutting of galvanized sheet metal into dimension required

ii. Rolling of sheet metal into shape

iii. Welding of sheet metal

iv. Grinding of welded joints of sheet metal

v. Making indentation to the top lid and the substrate inlet cover

vi. Drilling of holes for the bolt and nuts on the top lid and the substrate inlet

cover

vii. Application of poly filler to the welded joint to seal off every hole left over by

the welding and grinding process

viii. Painting of the digester

3.8 The Experimental Procedures

Cow dung to rumen fluid with ratio 3:2 and water to the feedstock (cow dung

and rumen fluid) mixing ratio was 2:1 as research variables was fed to digester and

homogenized with manual stirrer. The inlet of the digester was covered tightly by bolt

and nuts and it was padded with rubber seal to ensure the anaerobic condition was

maintained. One end of the rubber hose was connected to the digester gas outlet

located at the top of the digester and the other end of the rubber hose was connected

to the tyre tube for gas storage.

The digester was stirred thrice daily to avoid scum formation in the digester. The

experiment was on for 42 days and reading taken for this retention period. The

temperature was measured thrice daily. The daily readings were taken every day for 6

weeks and the average weekly temperature was recorded.

44

The temperatures were taken with the aid of a mercury-in-glass thermometer via the

thermometer duct provided. The temperature readings were taken three times daily

around 8:00a.m, 2:00p.m and 6:00p.m of the day. This was done in order to determine

the temperature changes during the day and also the effect of sunlight on the digester.

Observation shows that, the body of the digester received so much heat, especially

around 2:00p.m and 6:00p.m as a result of reduced relative humidity in the air, and

this could be related to the black paint used to coat the outside body of the digester.

The average temperature readings taken from the measurement was 31.75oC.

3.9 Characterization of the wastes

The wastes used for this experiment were collected in two separate compartments and

water was also collected in another compartment. The total volume of digester used

for the experiment was 105 litres. The total wastes comprising of cow dung and

rumen fluid mixed in the ratio of 60:40 respectively, and water to substrate ratio of

2:1 was used. This is an indication that total waste of 23kg was used along with 47kg

of water, making the overall substrate quantity in the digester 70kg which represent

66.7% of the digester volume and does not exceed 2/3 of digester volume.

The experiment include the preparation of substrate (cow dung and rumen fluid) to

water mixture, feeding of the digester, daily temperature reading, collection of the gas

after 42 days, and running of laboratory analysis to determine the proximate

composition of generated gas. The daily temperature readings was taken and

recorded.

45

3.10 Biogas Purification

If the gases were to be purified before use ,then the main requirement would

be the removal of acid gases (i.e. CO2 and H2S) provided the hydrogen sulphide level

are low, and then it can be removed by passing the gas through heated iron oxide (iron

sponge). The carbon dioxide forms calcium carbonate and is precipitated. However,

this is only applicable in small scale operations, in large installations full scale Alkali

or organic scrubbers maybe necessary.

3.11 Cost Analysis

Cost analysis is the breakdown of the cost of construction of the biogas

digester, comprising of the labour cost and the material cost. The total estimated cost

is N52, 650 which is reckoned to be a bit expensive based on the quality of material

used for the construction of the digester. Hence, other materials which are cheaper

could be adopted for digester construction by medium scale farmers and household

utilization. The table below shows the breakdown of the materials used.

46

Table 3.2: Cost Analysis of Materials Used for Construction

S/N Material

Description

Quantity of

Material

Specification of

Material

Unit

Cost (N)

Total

Cost (N)

1 Galvanized steel

sheet

2 1.2 mm thickness

(8X6) ft

10,000 20,000

2 Mild steel

shaft/rod

1 12mm diameter 2,500 2,500

3 Roller bearing 2 40mm Diameter 600 1,200

4 Bolt and nut 21 12mm 40 840

5 Valve 1 - 400 400

6 Rubber packing 1 1.5 thickness 1,300 1,300

7 Workmanship - - 5,000 5,000

8 Thermometer 1 Mercury-in-glass 450 450

9 Cork 2 Wooden 100 200

10 Hose 5 yards 8mm diameter 200 1000

11 Clip 2 Round 30 60

12

13

14

Tube

Laboratory

Analysis

Logistics

1

2

-

Vehicle size 14

-

-

700

-

-

700

14,000

5,000

Total 52,650

47

CHAPTER FOUR

4.0 RESULTS AND DISCUSSIONS

4.1 Results

The table below shows the chemical composition of the substrate (cow dun

and rumen fluid) and indicating all parameters determined from the analysis of the

substrate.

Table 4.1: Chemical composition of the substrate

Parameters Determined 1 2 Average

% D.M @ 105oC 23.85 23.83 23.84

% O.D.M @ 550oC 72.34 72.36 72.35

% M.C 76.18 76.14 76.16

NH4-N (g/kg) 17.84 17.89 17.86

Nitrogen(g/kg) 41.18 41.13 41.15

%K on DM. 1.56 1.58 1.57

Phosphorus (g/kg) 3759.0 3756.0 3757.5

%C.F 11.48 11.51 11.495

%Lignin 4.8 4.6 4.7

%O.C 31.56 31.59 31.575

pH 5.67 5.63 5.65

48

D.M: Dry Matter

O.D.M: Organic Dry Matter

NH4-N: Ammonium – Nitrogen

K: Potassium

C.F: Crude fibre

O.C: Organic Content

Table 4.2: Average Weekly Temperature Readings for Biogas Production

HRT: Hydraulic Retention Time

HRT (Weeks) Temperature (oC)

1 30.50

2 31.00

3 33.50

4 32.50

5 33.00

6 30.00

Average 31.75

49

Table 4.3: Percentage Composition of Biogas

Fig.4.1:- Graph of temperature (oC) against HRT (weeks)

29.5

30

30.5

31

31.5

32

32.5

33

33.5

34

0 1 2 3 4 5 6 7

Tem

per

atu

re,

oC

HRT, (Weeks)

Average Weekly Temperature Profile

Component 1 (%) 2 (%) Average (%)

Methane (CH4) 57.99 58.00 57.99

Carbon dioxide (CO2) 39.98 40.00 39.99

Oxygen (O2) 2.00 2.00 2.00

Hydrogen Sulphide

(H2S)

0.01 0.01 0.01

Water Vapour 0.01 0.01 0.01

50

4.2: Discussion of Results

Table 4.1 shows the result of the chemical composition of the substrate. The

percentage of dry matter at 105oC was found to be 23.84%, the organic dry matter

was found to be 72.35%, the moisture content was 76.16%, the ammonium – Nitrogen

content was 17.86 (g/kg), the nitrogen content was 41.15 (g/kg), the amount of

potassium in dry matter was 1.57%, and Phosphorus content was 3757.5 g/kg. The

crude fibre content was found to be 11.495%, Lignin component was 4.7%, the

organic content was 31.575% and pH of the substrate mixture was 5.65.

The result shows that the dry matter yield of 23.84% appears to be close with the

work of Budiyono et al., (2011), where the dry matter obtained from the proximate

analysis of cattle manure was 20.23%. However, the value obtained for lignin from

this work deviate from the work of (Budiyono et al., 2011), where the value 25.97%

was obtained from cattle manure.

The implication of this is that the result obtained is dependent on the kind of substrate

used, its chemical constituent, quality and operating condition.

Table 4.2 shows the average weekly temperature reading, beginning from the first

week the digester was loaded.

Observation also shows from fig. 4.1 that as the hydraulic retention time (HRT) in

weeks increases, the temperature (o

C) increases to a maximum point which shows

increase in the rate of biogas production and the temperature later falls which shows

decrease in the volume of biogas production, that is; decrease in the production rate of

the substrate (cow dung and rumen fluid) because the substrate has reached the

maximum biogas yield point.

51

Table 4.3 shows the composition of the biogas produced. It can be seen that, the

production of biogas yielded 57.99% of methane (CH4), 39.99% of carbon dioxide

(CO2), 2.00% of oxygen (O2), 0.01% of hydrogen sulphide (H2S) and 0.01% of water

vapour. The result shows that the methane has the highest yield (57.99%) follow by

CO2 (39.99%), oxygen yielded 2.00% which shows that the process was carried out

under anaerobic condition(absence of oxygen) before biogas can be produced and the

oxygen composition of the water used in the preparation of the feedstock.

The 2.00% of oxygen is in contrast with the work of (Budiyono et al., 2011) that also

carryout the production of biogas from cattle dung and rumen fluid which got 0%

oxygen composition of biogas. The high percentage of methane (CH4) represents the

main source of energy. The implication of this is that the percentage yield of product

of biogas produced depends on the type of substrate used and its chemical

constituents. The methane produced can be used for generation of electricity, thermal

energy for cooking and heating and also as transportation fuel.

52

CHAPTER FIVE

5.0 CONCLUSION AND RECOMMENDATION

5.1 Conclusions

From the study, the following conclusions can be made:

i. Biogas can be produced by the microbial digestion of organic matter in the

absence of air. Various wastes, such as municipal wastes, kitchen waste,

animal waste and crop residue can also be used in the production of biogas.

ii. Biogas production technology has established itself as a technology with great

potential which could exercise major influence in the energy scene in rural

areas.

iii. Biogas production took place within the retention period of six weeks from

microbial digestion of cow dung and rumen fluid in an anaerobic condition.

iv. The percentage yield of products of biogas produced depends on the type of

substrate used and its chemical constituents.

v. A biogas digester that is air-proof was constructed for this to ensure the

breaking down of cow dung and rumen fluid by anaerobic bacteria.

vi. The total average retention period for the experiment was 42 days (6 weeks)

before gas production started and the collection was done immediately and

stored in tyre tube for further analysis.

5.2 Recommendations

Based on the results and findings of this study, the following

recommendations were suggested for future experiment:

53

i. More research bodies and organizations should be created by the government

or tertiary schools to translate this study into a high performing technology.

ii. A means of sustaining mesophilic temperature should be developed, as

productivity of biogas is higher at this temperature region.

iii. Low cost design should be developed to suite the adoption of biogas

technology especially in rural areas.

iv. The produced bio fertilizer should be used on farm, most especially, small

farms like family unit.

v. To maintain the temperature of digester, it should be thermally insulated to

prevent loss of heat and the material for the construction should be non-heat

reflector.

54

REFERENCES

Akinbami, J.F.K., Ilori, M.O., Oyebisi, T.O., Akinwuni, I.O., Adeoti, .O., (2001).

“Biogas Energy use in Nigeria: current status, future prospects and policy

implications”. Renew. Sustain. Energy.Rev. 5: 97-112.

Bejan, M., and Rusu, T., (2007) “A Source of Renewable Energy – Biogas from

Organic Residues” AGIR Bulletin, Issue 1, pp. 13 – 19.

Budiyono, Widiasa, I. N., & Johari, S., (2011)"Study on Slaughterhouse Wastes

Potency and Characteristic for Biogas Production", 1(5), 4–7.

Cioablă, A., E., (2009) “Theoretical and Experimental Contributions Concerning

Biogas Production from Biomass residues” PhD Thesis, Politehnica

Publishing House, Timisoara.

Daxiong, Q., (1990) “Diffusion and Innovation in the Chinese Biogas Program”.

Tsinghua University Beijing. World Development Vol 18, p 555-563.

Deublein, D., and Steinhauser A., (2008) “Biogas from Waste and Renewable

Resources, an Introduction” Wiley-VCH Publishing House.

El-Saeidy, E. A., (2004) “Technology Fundamentals of Briquetting Cotton Stalks as

Biofuel” an unpublished Ph.D Thesis, Faculty Agriculture and Horticulture,

Humboldt University, Germany.

Enweremadu, C.C., Ojediran, J.O., Oladeji, J.T., and Afolabi, I.O., (2004)

“Evaluation of Energy Potential of Husks from Soy-beans and Cowpea”

Science Focus vol. 8 pp.18-23.

55

Faaij, A., (2006) “Modern Biogas Conversion Technologies” Mitigation and

Adaptation Strategies for Global Change Journal, Vol. 11, Number 2, pp. 335

– 367.

Financing for Development (FMO) and SNV Provide Farmers in Cambodia with

Biogas Installation and Microloan (in Dutch). Available on the internet:

http://www.fmo.nl/en/recent/newsitem.php?id=201&archive=1&PHPSESSID=baa

Accessed on 29-01-2007

Girod, j., and Jacques, P., (1998) “Reforms in sub-Saharan Africa's power industries”.

Energy Policy 26.1 : 21-32.

GTZ, (1999).“Biogas Digest Volume II.Biogas - Application and Product

Development. Information and Advisory Service on Appropriate Technology”

http://www.gtz.de/de/dokumente/en-biogas-volume2.pdf (accessed February

8, 2008).

Huong, N., (2012) “Biogas Production from Solvent Pre-treated Orange Peel”

Chalmers University of Technology SE-412 96 Goteborg, Sweden

Ioana, L., and Cioabla A., E., (2010) “Biogas Production based on Agricultural

Residues” Wseas Transactions on Environment and Development Issue 8, vol.

6, pp 1-13

Kalia, A.K., and Kanwar, S. S., (1998) “Long term Evaluation of a Fixed dome Janata

Biogas Plant in HillY condition” Department of Agricultural Engineering,

H.PKrishi Vishvaviduyalaya, Bioresource Technology 61-63

Kaliyan, N., and Morey, R. V., (2009) “Factors Affecting Strength and durability of

densified Biomass products” Biomass and Bioenergy 33, 337-359.

56

Karanja, G.M., and Kiruiro, E.M., (2003) “Biogas Production” KARI Technical Note

No. 10.

Kozo, I., Hisajima, S., Dangh R.J., (1996). “Utilization of Agricultural Wastes for

Biogas Production in Indonesia, In: Traditional Technology for Environmental

conservation and Sustainable Development in the Asia Pacific Region” 9th

Ed., pp 134-138.

Nazir, M., (1991) “Biogas Plants Construction Technology for Rural Areas”

Biotechnology and Food research Centre PCSIR Laboratories Complex.

Bioresource Technology 35 p283- 289

Okafor., N., (1998). An integrated Bio-system for the disposal of Cassava Wastes. In

Proceedings: Internet conference on Integrated Bio-systems in Zero Emissions

Applications.

Okoye, j.K., (2007) “Background study on water and energy issues in Nigeria to

inform the National Consultative Conference on Dams and Development.” P

6-7.

Oladeji, J.T., Enweremadu, C.C., and Olafimihan, E.O., (2009) “Conversion of

Agricultural Residues into Biomass Briquettes” International Journal of

Applied Agricultural and Apicultural Research (IJAAR) vol. 5 No. 2 pp 116-

123.

Periyasamy, E., and Nagarajan, p., (2011) “Biogas Production from Co-digestion of

Orange Peel Waste and Jatropha De-oiled Cake in an Anaerobic Batch Reactor”

African Journal of Biotechnology Vol. 11(14), pp. 3339-3345

Practical Action Org., (2006). “Biogas and liquid befouls.”

57

Quaak, P., Stephen, G., and Johnson, T., B., (2001).“Biogas and liquid fuels”.

Intermediate Technology Development Group (ITDG) publ. pp. 46-52.

Rilwanua, L., (2003). Energy Commision of Nigeria “National Energy Policy”

Federal Republic of Nigeria.

Rungvichaniwat, J., (2003) “Biogas Production from Fruit and Vegetable Wastes

Mixed with Cow Manure by Using Low-Solids Anaerobic Digester” Faculty

of Graduate Studies Mahidol University.

Sharma, N., and Giuseppe, P., (1991) “Anaerobic Biotechnology and Developing

countries – technical status” Energy Conversions 32, 447-469.

Stalin, N., (2007) “Performance evaluation of Partial Mixing Anaerobic Digester”.

ARPN Journal of Applied Sciences.Vol 2, No3. p1-6

Wantanee, A., and Sureelak, R.,(2004)“Laboratory Scale Experiments for Biogas

Production from Cassava Tubers”.The Joint International Conference on

Sustainable Energy and Environment (SEE) 1-3, HuaHin, Thailand.