MICROORGANISMS ASSOCIATED WITH BIOGAS PRODUCTION USING CASSAVA PEELS, PIG DUNG AND COW RUMEN FLIUD

ABSTRACT

This study was carried out to investigate the microorganisms associated with the co-digestion of cassava peel, pig dung and cow rumen fluid for the production of biogas. These wastes were collected between July and August 2018 while the experimental studies were carried out between September and October 2018. The animal wastes were used as collected without further treatment. The blending ratio was 1:1:1 (10kg of each) and was initially mixed with water in the ratio of 1:2 (10kg of waste 20kg of water) and fed into a 15 liters laboratory scale anaerobic digester using improved rubber water dispensers (35cm diameter, 55cm high). The anaerobic digestion process was batch operated for 30 days under room temperature conditions. In order to achieve homogeneity of the slurry and discourage scum formation in the system, daily stirring was carried out using the inbuilt manual stirring mechanism in the digester. The physicochemical and microbial parameters of the slurry samples analyzed using prescribed equipments and standard methods. Daily biogas production was monitored and volume of gas measured using downward displacement method. The maximum biogas production was 1.90 Ld-1 for total anaerobic count of 3.61 x 106 cfu/mL and mean fungal count of 2.11 x 106 cfu/mL observed at the 16th day of biodigestion. The  results  indicate the incidence of Clostridium sp; Streptococcus sp, Lactobacillus sp; Bacillus sp, Micrococcus sp, Pseudomonas sp, Enterobacter sp, Fusarium sp, Aspergillus sp and Mucor sp were  isolated and identified in slurry of the codigestion of a cassava peel, pig dung and cow rumen fluid.

TABLE OF CONTENTS

Title Page                                                                                                                                i

Certification                                                                                                                           ii

Dedication                                                                                                                              iii

Acknowledgements                                                                                                                iv

Table of Contents                                                                                                                   v

List of Tables                                                                                                                          vii

List of figures                                                                                                                         viii

Abstract                                                                                                                                  ix

CHAPTER 1

INTRODUCTION

1.1       Aim and Objectives of the Study                                                                               3

CHAPTER 2

LITERATURE REVIEW

2.1       History of Anaerobic Digestion (AD)                                                                        5

2.2       Anaerobic Co-digestion of Organic Wastes                                                               7

2.3       Anaerobic Digestion Technology                                                                               8

2.3.1    Types of anaerobic digesters                                                                                      9

2.3.2    System of anaerobic digesters                                                                                    9

2.3.3    Modes of anaerobic digester                                                                                       10

2.4       Maximizing Biogas Production through Co-digestion                                               11

2.4.1    Factors Affecting Anaerobic Digestion Efficiency                                                    13

2.4.1.1 pH Level                                                                                                                     13

2.4.1.2 Temperature                                                                                                                13

2.4.1.3 Mixing                                                                                                                        14

2.4.1.3 Total Solid (TS)                                                                                                          15

2.4.1.4 Carbon to Nitrogen Ratio (C/N)                                                                                 15

2.4.2    Advantages of Anaerobic Digestion to the Society                                                    16

2.4.2.1 Odour Control                                                                                                             16

2.5       Literature Study on Various Feedstock                                                                      16

CHAPTER 3                                     

MATERIALS AND METHODS

3.1       Study Area and Sample Collection                                                                            19

3.2       Materials                                                                                                                     19

3.3       Methods                                                                                                                      19

3.4       Microbial Analysis                                                                                                     20

3.4.1    Biochemical Tests                                                                                                      21

3.5       Physicochemical Analysis                                                                                          23

3.6       Determination of Biogas Production                                                                          26

3.7       Data Analysis and Confirmation of Results                                                               27

CHAPTER 4

RESULTS AND DISCUSSION

4.1 RESULTS                                                                                                                         28

4.2       DISCUSSION                                                                                                             33

CHAPTER 5

5.1       CONCLUSION                                                                                                           35

REFERENCE

APPENDIX I

APPENDIX II

LIST OF TABLES

Table 4.1 Substrate and Microbial Composition                                                                    29

Table 4.2 Mean Anaerobic and Fungal Count                                                                       30

Table 4.3 Physicochemical Characteristics of Slurry For 30 Days                                        31

Table 4.4: Mean Volume Of The Biogas Produced                                                               32

CHAPTER 1

INTRODUCTION

There is an increasing interest in biogas and bioenergy production across the world for environmental and economic reasons. The production of biogas contributes to the production of renewable and sustainable energy since biogas works as a flexible and predictable alternative for fossil fuel (Igoni et al., 2008).

Biogas can be produced from various organic wastes types. Besides energy production, the degradation of organic waste through anaerobic digestion offers other advantages such as the prevention of odor release and decrease of pathogens (Derbal et al., 2008). Moreover the nutrient rich digested residues can be utilized as fertilizer for recycling the nutrients back to the fields.The production of biogas via anaerobic digestion of large quantities of agricultural residues and organic waste benefit the society by providing clean fuel from renewable sources and help end energy poverty. As a renewable high quality fuel biogas can be utilized for various energy services.  This would reduce dependence on fossil derived energy and reduce environmental impact including global warming and pollution, improve sanitation and provide high quality fertilizer. It has been evaluated as one of the most energy efficient technology for bioenergy production (Fehrenbach et al., 2008). It can reduce green house gas emissions compared to fossil fuels by utilization of locally available resources (Olowolafe, 2008).

Anaerobic digestion consists of several interdependent complex, sequential and parallel biological reactions during which the products from one group of microorganisms serve as the substrates for the next resulting in the transformation of organics mainly into a mixture of methane and carbon dioxide with minor quantities of nitrogen, hydrogen, ammonia and hydrogen sulphide (Olayiwola et al., 2011).

Anaerobic fermentation of organic wastes is a complex process which can be divided into four phases, hydrolysis, acidogenesis, acetogenesis/dehydrogenation and methanation. The individual fermentation steps are carried out by different consortia of microorganisms which mostly stand in syntrophic interrelation and place different requirements on the environment (Angelidak et al., 1993). Hydrolyzing microorganisms are responsible for the initial attack on organic polymers and reduce mainly acetate, hydrogen and varying amounts of volatile fatty acids into acetate and hydrogen, completing acidiogenesis acetogenesis and dehydrogenation. At the end of the degradation chain methanogens produce methane from acetate or hydrogen and carbondioxide (Angelidak et al., 1999). The whole anaerobic fermentation for biogas production is difficult to describe by reliable kinetics since hydrolysis, acidogenesis, acetogenesis and gas production through complex insoluble substrate depends on many different parameters such as size, production of enzymes pH and temperature.

All types of organic waste can be used as substrate for biogas production as long as it contains carbohydrate, proteins, fats, cellulose and hemicelluloses as constituents. The composition of biogas yield depends on the organic substrate, the digestion system and retention/incubation time (Charles et al., 2009).

Anaerobic digestion has mainly been associated with the treatment of animal manure and sewage sludge from aerobic wastewater treatment. Today, most biogas production plants digest waste from pigs, cow and other animals with the addition co-substrates to increase the content of organic materials for achieving a higher gas yield. Typical co-substrates are plants residues e.g. peels, leaves of food crops, organic wastes food waste and energy crops. The biogas yield of the individual substrates varies considerably dependent on their origin content of organic substance and substrate composition, fats provide the highest biogas yield but require a long retention time due to their poor bioavailability carbohydrates and proteins show much faster conversion rates but lower gas yields. The contents of nutrients respectively the carbon/nitrogen ratio should be well balanced to avoid process failure by ammonia accumulation. The carbon/nitrogen (C/N) ratio should be in the range between 15 and 30 (Ward et al., 2008). In Nigeria identified feedstock substrate for feasible biogas production include water lettuce, water hyacinth, dung, cassava leaves and processing wastes, urban refuse, solid waste agricultural waste, residues and sewage. It has been estimated that Nigeria produce about 227,500 tons of fresh animal waste daily. Since 1kg of fresh animal waste produces about 6.8 million m³ of biogas everyday from animal waste only (Akinbami, et al., 2001).

In order to fill some gaps existing in previous studies of the codigestion of cassava peel with other waste types, there is the need to study the effect of the addition of cow rumen fluid into the feed stock blends in a 1:1:1 mix ratio with cassava peels and pig dung. However the microbial diversity and especially possible the interactions between the microbial communities in waste blends of cassava peels, cow rumen fluid  and pig dung has not yet received much attention. This knowledge however is required to identify the key microorganisms of use for efficient organic degradation and biogas production.

1.1       Aim and Objectives of the Study

This research work aims at investigating the microorganisms associated with the co-digestion of cassava peel, cow rumen fluid and pig dung for the production of biogas.

The objectives of the study include:

·       To isolate, identify and characterize the microorganisms involved in the anaerobic co-digestion of the substrates.

·       To determine the mean anaerobic and fungal load of the substrate slurry for 30 days.

·       To analyse the physicochemical characteristics of substrates during digestion.

·       To measure the daily biogas volume produced.

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