Abstract
This study was aimed at investigating microorganisms associated with biogas production using cassava peel as substrates. Cassava peels obtained after peeling cassava roots were anaerobically digested using a 5 litre capacity fermentor. The peels were blended and mixed with water, in the ratio of 1:2. Standard microbiological methods and anaerobic biodigester were used to screen the isolates and the wastes substrate for biogas production. The mean flammable biogas yield of the cassava peels was 13.7Litre/total mass of slurry. Analysis revealed that the temperature of raw substrates ranged between 26°C and 30°C while the pH varied between 4.04 and 6.86 during digestion. The results of the total heterotrophic and anaerobic microbial counts during the digestion period showed a steady variation in the anaerobic bacteria and fungal counts as fermentation progressed. The load obtained for the total heterotrophic bacteria and anaerobic bacteria were within 2.9x104cfu/ml to 9.4x104cfu/ml and 1.8x103cfu/ml to 6.9x103cfu/ml respectively. Similarly the fungal count obtained through the digestion period ranged from 1.1x10cfu/ml to 3.9x10cfu/ml. The bacterial isolates were identified as Pseudomonas sp, Escherichia coli, Bacillus sp, Clostridium sp, and Methanococcus sp, while fungi isolated were identified as Saccharomyces cerevicae, Aspergillus sp and Penicillium sp.
TABLE OF CONTENT
Title
page i
Certification ii
Declaration iii
Dedication iv
Acknowledgement v
Table
of content vi
List
of Table vii
List
of Figures viii
Abstract ix
CHAPTER 1:
INTRODUCTION
1.1 Introduction 1
1.2
Aim and Objectives 4
CHAPTER 2:
LITERATURE REVIEW
2.0
Literature Review 5
2.1. Biogas 5
2.2 Biogas
Composition 5
2.3 Chemical
Characteristics of Biogas 6
2.4 Physical
Characteristics of Biogas 6
2.5 Methane
as a Component of Biogas 6
2.6 Collection
of Biogas 7
2.7 Types
of Biogas bioreactor 7
2.8 Substrate (Cassava Peels ) 7
2.9 Microbial
Floral Present in Production of Biogas 8
2.10 Microbiology
and Biochemistry of Biogas Production 8
2.10.1 Hydrolysis 10
2.10.2 Acidification/Acetogenesis 10
2.10.3 Methane
Formation 10
2.11 Interactions
between the Various Microbial Groups 11
2.12 Factors
Influencing Biogas Production. 11
2.12.1
Temperature 11
2.12.2
pH (Hydrogen Concentration) 12
2.12.3 Substrate
Quality and Characterization 13
2.12.4
Loading Rate 13
2.12.5 Bioreactor
Design 14
2.13 Benefit
of Biogas Technology 14
2.14 Domestic
and Industrial Uses 15
2.15
Other Uses of Biogas 15
CHAPTER 3:
3.0 MATERIALS AND METHODS
3.1 Construction
of Anaerobic Digester 16
3.2 Sample
Collection 16
3.3 Pretreatment
of Cassava Peels 16
3.4 Charging
of the Digester 16
3.5 Determination
of Quantity of Biogas Produced 16
3.6 Determination
of Physiochemical Analysis of the Slurry in the Bioreactor. 17
3.6.1 Hydrogen
Ion Concentration (pH) 17
3.6.2 Temperature 17
3.6.3 Dissolved
Oxygen (DO) 17
3.7 Determination
of Biogas Flammability 17
3.9
Collection of Sample for Isolation 17
3.9 Media
Preparation 18
3.10 Isolation
Of Microorganisms (Fungi And Bacteria) 18
3.13
Isolation And Identification Of Bacterial Isolates 19
3.14
Gram Staining 19
3.14
Biochemical Identification of the Isolates 19
3.14.1 Catalase test 20
3.14.2
Coagulase Test 20
3.14.3
Oxidase Test 20
3.14.4 Indole Test 20
3.14.5
Citrate Utilization Test 21
3.14.6 Urease Test 21
3.14.7 Methyl Red Test 21
3.14.8 Voges- Proskauer Test 21
3.14.9 Sugar
Fermentation Test 21
CHAPTER 4:
RESULTS
4.0
Results of Biogas Produced and microbial isolates 23
4.1
Results 23
CHAPTER 5:
DISCUSSION, CONCLUSION AND RECOMMENDATION
5.1
Discussion 29
5.2 Conclusion 31
5.3
Recommendations 32
REFERENCES 47
LIST OF TABLES
Table Title Pages
4.1 The
Temperature pH, Dissolved oxygen level and conductivity
readings
of the bioreactor at two days interval 24
4.2 colonial
Description and Biochemical characteristics of the bacterial isolates 27
4.3 lag
period, Cumulative gas yield and mean volume of gas 28
LIST OF FIGURES
Figure Title pages
1. Conversion of fermentative substrate to
biogas 11
2. Total Viable count, Anaerobic count and Total
Fungal count measured in cfu/ml. 29
3. Diagram showing fabricated bioreactor 37
CHAPTER
ONE
1.1 INTRODUCTION
The demand for
renewable fuel is increasing with growing concern about climate change, air
quality, energy import dependence and the depletion of fossil fuels. Biogas is
one of the versatile renewable fuels which can be used for power and heat/cool
production or it can be upgraded to biomethane to be used as vehicle fuel.
Biogas is produced by anaerobic digestion of biological wastes such as cattle
dung, cow dung, food waste, sheep and
poultry droppings, plantain peels, municipal solid waste, industrial waste
water and landfill to give mainly methane (50-70%), carbon dioxide (20-40%) and
traces of other gases such as nitrogen, hydrogen, ammonia, hydrogen sulphide,
water vapour etc (Ofoefule and Ibeto, 2010). The composition of the mixture
depends on the source of biological waste and management of digestion process
(Yadar and Hesse, 2001).
The anaerobic fermentation of organic
materials has long been used to generate useful resources which have been
harnessed for the use of mankind (Uri, 1992; US Environmental Protection
Agency, 2001). As early as the 18th Century, anaerobic process of
decomposing organic matter was known, and in the middle of the 19th
century, it became clear that anaerobic bacteria are involved in the
decomposition process. Methanogens (methane producing bacteria) are the last
component in a chain of microbes which degrade natural material and return the
decay products in the environment. Hydrogen and carbon dioxide or acetate is
used by methanogenic archea for the fructification of methane (also termed
methanation) (Aisha and Shagufta, 2013). In this series of action biogas is generated
and the methane is finally reformed to electricity. Although it is burdensome
to detect attenuated organisms in very distinct communities acting as those in
anaerobic digesters, defining community morphology can provide good information
concerning the functional potential of the community (Aisha and Shagufta,
2013).
The energy in plant vegetation,
animals, industrial and domestic waste matter can be released in terms of a
useful gas when fermented anaerobically, that is in the absence of oxygen the
biogas formed after the decomposition of organic wastes is channeled or
transported to homes for use for cooking, running engines, electrical power
generation and heating with virtually little or no pollution at all (Ozor et al; 2014). As demand for energy is
increasing astronomically, and the fossil based fuels become scarce and more
expensive and carbon dioxide emission levels become of more concern; Biogas a
by-product of anaerobic fermentation and a renewable energy source have
currently been recognized globally as a means of solving the problem of rising
energy prices, waste treatment/management and creating sustainable development (Rao
and Seenayya, 1994; Ofoefule and Uzodinma, 2004).
Hashimoto and Varriel, (1981),
defined Biogas as a colourless, flammable gas produced through anaerobic
fermentation (digestion) of animal, plant, food, human, industrial and
municipal waste to produce methane (50-70%), carbon dioxide (30-40%) and traces
of other gases such as hydrogen (1-10%). Nitrogen (1-3%), oxygen (0.1%), carbon
monoxide and trace of hydrogen sulphide. However, the composition of the mixture
depends on the source of biological waste and management of digestion process
(Yadar and Hesse, 2001).
The natural generation of biogas is
an important part of biochemical reaction which takes place under anaerobic
condition in the presence of highly pH sensitive microbiological catalyst that
are mainly bacteria (Uzodinma and Ofoefule, 2009). The production of Biogas
comprises of three bio chemical processes; or steps: hydrolysis,
acidogenesis/acetogenesis and methanogenesis (Nagamani and Ramasamy, (1999).
Biogas is formed solely through the activity of bacteria. Bacteria have a
temperature range which they are most productive in term of production rates,
growth rates and substrate degradation performance. Several groups of bacteria
are involved in anaerobic digestion and they also have different optimum
temperature. This results in two main temperature ranges at which digestion
usually can be done optimally and most economically. These ranges from 30-450C
and it is termed mesophilic range and 45-700C called the
thermophilic range (BTG, 2003; Ezeonu et
al., 2005).
The rate of bacteriological methane
production increase with digester temperature, retention time and with the
percentage of total solid/volatile solid in the slurry (Dioha et al., 2006, Kalia and Singh, 1996).
This is because temperature and the addition of innocula affects the enzymatic
activities of the microorganisms (anaerobic) responsible for the conversion of
organic materials into biogas (Kelper, 2006, Maurya et al., 1994).
One of the main environmental problems
of today’s society is the continuous increase in production of organic wastes
which are harmful to human existence. Some of these waste which are posing
serious environmental threats to human and animal existence in these nations
come from agriculture due to their degradable nature and lack of profitable
technique to convert these “wastes” to better manure quality or other useful
means such as energy (Okoroigwe et al., 2013).
Cassava (Manihot
exculenta) is one of the major root crops produced in sub-Saharan Africa.
It is a very important crop grown for food and industrial purposes in several
parts of the world. According to NPC (2008), Nigeria has the largest production
of the crop of 49million tonnes of cassava. The processing of cassava results
in the production of peels, chaff, fibre, and spoilt or otherwise unwanted
tubers which is feed directly to ruminants. However, the much larger remaining
proportion of cassava solid wastes are indiscriminately discharged into the
environment and amassed as waste dumps on sites where cassava is processed.
With increased production of peels and other cassava derived wastes, this constitutes
an enhanced risk of pollution to the environment (Adelikan and Bangboye; 2009).
This is also a need to find an alternative productive use of the peels. One
area of possibility is to investigate the potential of cassava peels for the
production of biogas and by so doing, it will reduce the nuisance value it
creates in the environment.
1.2 AIM AND OBJECTIVES
This study was
aimed at:
1. Producing
combustible biogas from cassava peels
2. Isolating
and characterizing the microbes responsible for the biodegradation of cassava
peels in biogas production.
3. Evaluating
the physicochemical parameters of the slurry during biogas production
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