Variation of Methane and Carbon dioxide Yield in a biogas ... › smash › get › diva2:604559 › FULLTEXT02.pdfmethane in the biogas will determine the thermal dynamic property

Variation of Methane and Carbon dioxide Yield in a biogas plant

By Chrish Kavuma (821231-A172)

MSc. Thesis Report

2013

Department of Energy Technology

Royal Institute of Technology

Stockholm, Sweden

ii

Master of Science Thesis EGI 2012

Variation of Methane and carbon dioxide Yield in a biogas plant

Chrish Kavuma

Approved

Date 29/01/2013

Examiner

Torsten Fransson

Supervisor

1. Peter Hagström 2. Kucel Samuel Baker

Commissioner

Contact person

i

Abstract According to Lawbury, 2001, approximately 60% methane and 40% carbon dioxide is produced with traces of other gases. However the time required to produce the highest amount and quality of the combustible methane gas is not known. Biogas is produced from different substrates which give varying quantities and quality of the gas. This makes exploitation of the gas as a fuel and control of its adverse effects difficult. The objective of this research was to assess the variation of methane and carbon dioxide yield with retention time and substrate in a biogas plant. Many biogas systems are too small to handle the available supply of substrate, therefore knowing the time at which maximum methane is produced will help in selecting the best substrates during co-digestion so that one does not require a big volume of the substrate to produce methane.

The selected substrates was mixed with water in appropriate proportion before feeding and checked for stones or other unnecessary materials. The mixture was then placed in the five litter containers. Pig manure, cow dung and mixture of pig and cow dung in the ratio of 1:1 substrates were considered. Each container had a thermometer to monitor temperature variation. The samples were then tested for methane and carbon dioxide yields during the laboratory scale batch experiment.

A good productivity of methane for mixture of pig and cow dung was found to be 61.2% by volume and it occurred on the 18th day of digestion. When all the substrates were anaerobically digested, treatment with 50% cow dung and 50% pig dung produced the highest methane. The production of methane was also hindered by the presence of some trace gases such as hydrogen sulphide which limited the methane producing bacteria. Key words: Methane, Carbon dioxide, Biogas

ii

Table of Contents CHAPTER 1: INTRODUCTION................................................................................................... 1

1.1 Background ................................................................................................................................. 1

1.2 Problem statement ..................................................................................................................... 1

1.3 Research Objectives .................................................................................................................. 2

1.3.1 Main objective ...................................................................................................................... 2

1.3.2 Specific objectives ............................................................................................................... 2

1.4 Hypothesis testing ...................................................................................................................... 2

1.4.1 Initial hypothesis .................................................................................................................. 2

1.5 Justification ................................................................................................................................. 2

1.6 Scope .......................................................................................................................................... 2

CHAPTER 2: LITERATURE REVIEW .......................................................................................... 3

2.1 Introduction ................................................................................................................................. 3

2.2 Biogas Digesters ........................................................................................................................ 4

2.2.1 Batch-feeding ....................................................................................................................... 4

2.2.2 Continuous-load digesters .................................................................................................. 4

2.2.3 Fixed dome digester ............................................................................................................ 4

2.2.4 Floating drum ....................................................................................................................... 5

2.3 Substrate types and management ............................................................................................ 6

2.3.1 Cattle dung and manure ..................................................................................................... 6

2.3.2 Pig dung and manure .......................................................................................................... 7

2.3.3 Goat dung ............................................................................................................................ 7

2.3.4 Chicken droppings ............................................................................................................... 8

2.3.5 Plant Wastes ........................................................................................................................ 8

2.4 Methanogenesis ......................................................................................................................... 8

2.5 Factors affecting biogas production.......................................................................................... 8

2.5.1 Temperature ........................................................................................................................ 9

2.5.2 Hydraulic retention time ...................................................................................................... 9

2.5.2 Loading rate ......................................................................................................................... 9

2.5.4 pH value ............................................................................................................................. 10

2.5.5 C/N ratio ............................................................................................................................. 10

2.6 Gas analysis in biogas plants.................................................................................................. 11

iii

CHAPTER 3: METHODOLOGY ................................................................................................ 12

3.1 Introduction ............................................................................................................................... 12

3.2 Materials and methods ............................................................................................................ 12

3.3 Materials and equipment used ................................................................................................ 12

3.4 Preparation of samples for biogas production ....................................................................... 13

3.5 Determining the volume of methane and carbon dioxide at a given time interval .............. 14

3.7 Evaluation of the trace gases variation in the selected substrates. ..................................... 14

CHAPTER 4: RESULTS AND DISCUSSION.............................................................................. 16

4.1 Introduction ............................................................................................................................... 16

4.3 variation of the volumes of methane and carbondioxide with time ...................................... 18

4.2 Mixture that gives the highest yield of methane .................................................................... 17

4.4 Variation of trace gases ........................................................................................................... 20

4.5 Hypothesis Testing................................................................................................................... 22

CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS ............................................... 23

5.1 Conclusions .............................................................................................................................. 24

5.2 Recommendations ................................................................................................................... 24

REFERENCES ............................................................................................................................... 26

APPENDICES ................................................................................................................................ 29

iv

INDEX OF TABLES TABLE 2- 1: POTENTIAL FOR BIOGAS PRODUCTION FROM ANIMAL WASTE ....................................................... 7 TABLE 2- 2: C/N RATIO OF SOME ORGANIC MATERIALS ................................................................................ 11 TABLE 2- 3: BIOGAS COMPOSITION ............................................................................................................ 11 TABLE 3- 1: PROPORTIONS FOR DIFFERENT TREATMENTS ............................................................................ 13 TABLE 4- 1: MEAN VALUES OF METHANE AND CARBON DIOXIDE WITH TIME FOR TREATMENTS A, B AND C .......... 16 TABLE 4- 2: PH FOR THE DIFFERENT TREATMENTS ...................................................................................... 17 TABLE 4- 3: COMPOSITION OF TRACE GASES ............................................................................................... 20 TABLE 4- 4: RESULTS OF METHANE FOR THE THREE TREATMENTS ................................................................ 22 TABLE 4- 5: GENERAL ANOVA SUMMARY TABLE FOR A COMPLETELY RANDOMIZED DESIGN ........................... 23

INDEX OF FIGURES FIGURE 2- 1: BIO-DIGESTER .................................................................................................................................. 3 FIGURE 2- 2: FIXED DOME DIGESTER ..................................................................................................................... 5 FIGURE 2- 3: FLOATING DRUM DIGESTER ............................................................................................................... 5 FIGURE 3- 1: GA2000PLUS GAS ANALYZER USED IN EXPERIMENT WORK ............................................................ 12 FIGURE 3- 2: EXPERIMENTAL SET UP IN THE LABORATORY ................................................................................... 13 FIGURE 4- 1: VARIATION OF METHANE PRODUCTION WITH TIME FOR DIFFERENT TREATMENTS ............................. 18 FIGURE 4- 2: VARIATION OF METHANE FOR VARIOUS TREATMENTS ...................................................................... 19 FIGURE 4- 3: PROPORTIONS OF CARBON DIOXIDE (CO2) FOR VARIOUS TREATMENTS WITH TIME ......................... 19 FIGURE 4- 4: VARIATION OF CARBON MONOXIDE WITH TIME FOR DIFFERENT TREATMENTS .................................. 21 FIGURE 4- 5: PROPORTIONS OF HYDROGEN SULPHIDE WITH TIME FOR VARIOUS TREATMENTS ............................ 21

v

NOMENCLATURE

C/N – Carbon Nitrogen ratio

ANOVA – Analysis of variance

RT – Retention time

1

CHAPTER 1: INTRODUCTION

1.1 Background Biogas is an environmentally friendly fuel which is part of nature’s own cycle. It consists of a mixture of methane and carbon dioxide which are produced naturally when organic materials such as animal, agricultural, domestic, and industrial wastes decompose under anaerobic conditions (wellinger, 2000). Worldwide biogas is used to provide energy for cooking, lighting, and even running internal combustion engines. The combustible portion of the biogas is methane. The rest of the gas is carbon dioxide, with small amounts of nitrogen, oxygen, hydrogen, water, hydrogen sulphide and trace elements. The percentage of methane to carbon dioxide varies depending on the feedstock and the completeness of the process (World Energy Council, 1994). The biogas produced contains usually 50-65% methane, 35-50% carbon dioxide (World Energy Council, 1994). However the proportions of methane and carbon dioxide keep on varying with the duration and extent of biomethanation over retention time. In order to determine the thermal capacity of the biogas, it is important to know when and how much methane is produced at a given time. It is also important to determine the composition of the other gases in order to keep track of the quality of the gas as well as assessing its green house effects.

1.2 Problem statement According to Lawbury, 2001, approximately 60% methane (CH4) and 40% carbon dioxide is produced with traces of other gases such as hydrogen, nitrogen and hydrogen sulphide. However the time required to produce the greatest amount and quality of the combustible methane gas is not known. Biogas is produced from different substrates which give varying quantities and quality of the gas. This makes exploitation of the gas as a fuel and control of its adverse effects difficult.

2

1.3 Objectives

1.3.1 Main objective

To assess the variation of methane and carbon dioxide yield with retention time and substrate composition in a biogas plant.

1.3.2 Specific objectives

To find out the mixture that gives the highest yield of methane at a given time. To determine the volume of methane and carbon dioxide at a given time interval. To evaluate the variation of the trace gases in the selected substrates.

1.4 Hypothesis testing

1.4.1 Initial hypothesis

The quantity of methane and carbon dioxide varies with the substrate constituents and the retention time.

1.5 Justification Fuel resources are quite scarce such that increasing the production of methane is urgently needed. Many biogas systems are too small to handle the available supply of substrate, therefore knowing the time at which maximum methane is produced will help in selecting the best substrates during co-digestion and when to load the digester so that one does not require a big volume of the substrate to produce methane. It is thus necessary to determine the percentage of these components, since the proportions of methane in the biogas will determine the thermal dynamic property of the gas as a whole. Also know whether to use single substrate or co-digest since co-degestion does not necessarily mean increased methane production.

1.6 Scope The substrates considered in this study included cow dung, pig dung and mixture of both cow and pig dung.

3

CHAPTER 2: LITERATURE REVIEW

2.1 Introduction Biogas is a mixture of methane and carbon dioxide, produced by the breakdown of organic waste by bacteria without oxygen (anaerobic digestion). Production of methane-rich biogas through anaerobic digestion of organic materials provides a versatile carrier of renewable energy, as methane can be used in replacement for fossil fuels in both heat and power generation and as a vehicle fuel, thus contributing to cutting down the emissions of greenhouse gases and slowing down the climate change (LBS, 2002). The anaerobic digestion process is a simple and applied energy source. A simple digester consists of a digestion chamber, a dome, an inlet, an outlet for biogas and an outlet for slurry. The biogas trapped by the dome flows under pressure through the outlet, where it can be used as an energy source. Figure 2.1 shows a simple lay-out for the anaerobic digester.

Figure 2- 1: Bio-digester (Robles, 2001)

Anaerobic degradation or digestion involves the breakdown of biomass by a concerted action of a wide range of microorganisms in the absence of oxygen. The general principle of biomass is the degradation of organic materials (e.g. carbohydrates, protein and fats) under anaerobic condition, where bacteria convert the organic material to methane, carbon dioxide and water. Acetate is the most important source of methane in the anaerobic environment; it forms approximately 70% of the methane, while the remaining 30% of methane is formed directly from hydrogen and carbon dioxide (Robles, 2001). The first step in the anaerobic digestion is the hydrolysis of organic compounds into smaller units, that is; the hydrolysis of proteins into amino acids. The second step is

4

fermentation, where the hydrolysis products are absorbed by the fermentative bacteria. The products of fermentation process are acetate, fatty acids, alcohols and hydrogen. The third step is the oxidization of fermentative products to acetate and the reduction of proteins to hydrogen. This reaction is called Acetogenesis. In the fourth step, hydrogen-consuming organisms and hydrogen-producing organisms are presented in the biomass (Tafdrup, 2000). Both hydrogen-consuming reactions and the hydrogen-producing reactions will yield energy. Growth of bacteria in flocks increases the absorption of nutrients compared with free-living organisms and thus make the energy utilization more effective. This is followed by methane formation. Methane potential fraction differs and ranges between 40%-80% do the basis of the digester type, substrate quality and digesting bacteria (Stewart et al., 1984).

2.2 Biogas Digesters With biogas technology, waste is stored in specially constructed containers while being digested. There are a number of technologies used to accomplish this:

2.2.1 Batch-feeding A full charge of raw material is placed into the digester which is then sealed off and left to ferment as long as gas is produced. When gas production has ceased, the digester is emptied and refilled with a new batch of raw materials. Batch digesters have advantages where the availability of raw materials is limited to coarse plant wastes which contain undigestible materials that can be conveniently removed when batch digesters are reloaded. Also, batch digesters require little daily attention. Batch digesters have disadvantages, however, in that a great deal of energy is required to empty and load them; also gas and sludge production tend to be quite sporadic (Singh, 1971).

2.2.2 Continuous-load digesters A small quantity of raw material is added to the digester every day. In this way the rate of production of both gas and sludge is more or less continuous and reliable. Continuous-load digesters are especially efficient when raw materials consist of a regular supply of easily digestible wastes from nearby sources such as livestock manures (Sasse et al, 1991).

2.2.3 Fixed dome digester The fixed dome digester model is the most widely used type in Uganda. It consists of an underground brick masonry compartment with a dome on top for gas storage as shown in Figure 2.2. In this design, the fermentation chamber and gas holder are combined in one unit.

5

Figure 2- 2: Fixed dome digester (Cheng and Liu, 2002)

A well and a dome are made out of concrete. This is called the digester tank T. The dome is fixed and hence the name given to this type of plant is fixed dome type of biogas plant. The function of the plant is similar to the floating holder type biogas plant. The used slurry expands and overflows into the overflow tank F (Cheng and Liu, 2002).

2.2.4 Floating drum

Figure 2- 3: Floating drum digester (Cheng and Liu, 2002)

A well is made out of concrete. This is called the digester tank T. It is divided into two parts. One side has the inlet, from where slurry is fed to the tank as shown in Figure 2.3. The tank has a cylindrical dome H made of stainless steel that floats on the slurry and collects the gas generated. Hence the name given to this type of plant is floating gas holder type of biogas plant. The slurry is made to ferment for about 50 days. More gas is made by the bacterial fermentation, leading to the pressure inside H to increase. The

6

gas can be taken out through outlet pipe V. The decomposed matter expands and overflows into the next chamber in tank T. This is then removed by the outlet pipe to the overflow tank and is used as manure for cultivation purposes (Cheng and Liu, 2002).

2.3 Substrate types and management The amount and characteristics of organic materials available for digestion vary widely. In rural areas, the digestible material will depend upon the climate, the type of agriculture practiced, the animals used and their degree of confinement, the methods of collecting wastes. There are also degrees of quality and availability unique to urban wastes (Braun, 2007).

2.3.1 Cattle dung and manure Cattle dung is the most suitable material for biogas plants because of the methane producing bacteria already contained in the stomach of ruminants. The specific gas production, however, is lower and the proportion of methane is around 65% because of pre-fermentation in the stomach. Its homogenous consistency is favourable for use in continuous plants as long as it is mixed with equal quantities of water. Fresh cattle dung is usually collected and carried to the system in buckets or baskets. Upon arrival it is hand-mixed with about an equal amount of water before being fed into the digester (Maramba, 1978). Liquid cattle manure, a mixture of dung and urine, requires no extra water. However, the simple animal housing found on most farms in developing countries normally does not allow the collection of all animal excrement. Hence, most of the urine with its valuable plant nutrients is lost. The main advantage to animal manure, with respect to continuous digesters, is that it is easy to collect and easy to mix as slurry and load into digesters. Successful continuous digesters have been set up using pig manure (Taiganides, 1963). Table 2.1 shows the potential biogas production from animal waste.

7

Table 2- 1: Potential for Biogas Production from Animal Waste (TACIS, 1997)

Number Biomass source

Total amount, Thousand Heads

Biomass, kg/Day per unit

Total biomass, Tonnes/Day

Biogas Amount obtained from 1kg of biomass,m3

Total biogas production, thousand m3/Day

1 Livestock 916 45 41260 0.04 1650 2 Pigs 328 9 2955 0.06 177.3 3 Sheep,

Goats 580 4 2321 0.06 139.2

4 Poultry 7580 0.17 1288 0.07 90.1 5 Horses 22 35 786 0.04 314

2.3.2 Pig dung and manure When pigs are kept in unpaved areas or pens, only the dung can be collected. It must be diluted with water to the requisite consistency for charging the digester. This could result in considerable amounts of sand being fed into the digester, unless it is allowed to settle in the mixing vessel. Once inside the digester, sand and soil accumulates at the bottom and has to be removed periodically. Some form of mechanical mixer should be used to dilute the dung with water, since the odor nuisance makes manual mixing so repulsive that it is usually neglected. Similar to cow stables, a cemented floor, sloping towards the mixing pit, is a preferable solution. Compared to cattle, pigs are more frequently kept on concrete floors. The water used for washing out the pens yields liquid manure with low solids content. Thus, whenever the topography allows, the liquid manure should be allowed to flow by gravity into the digester. Wash-water should be used as sparingly as possible in order to minimize the necessary digester volume. Very frequently, the pig manure is collected in pails, which is advantageous, even though a sand trap should be provided to prevent sand from entering the digester (Fry, 1961).

2.3.3 Goat dung

For goats kept on unpaved floors, the situation is comparable to that described for pig dung. Since a goat farm is practically the only place where any substantial amount of goat dung can accumulate, and then only if the animals are kept on straw bedding, the available feedstock for a biogas system will usually consist of a mixture of dung and straw bedding. Most such systems are batch-fed versions into which the dung and an appropriate quantity of water are loaded without being pre-mixed. The feed-stock is usually hauled to and from the digester in wheelbarrows or baskets (Werner, 1989).

8

2.3.4 Chicken droppings Chicken droppings can only be used if the chickens settle above a suitable dung collecting area of limited size. Otherwise, the sand or sawdust fraction would be disproportionately high. Chicken droppings can be fed into plants which are primarily filled with cow dung without any problem. There is a latent danger of high ammoniac concentration with pure chicken dung, but despite this there are many well functioning biogas plants combined with egg or meat producing factories. The collected droppings are hard and dry, so that they have to be pulverized and mixed with water before they can be loaded into the digester. Mechanical mixing is advisable. The proportion of methane in biogas from chicken excrement is up to 60% (Fry, 1961). 2.3.5 Plant Wastes The primary advantage to plant wastes is their availability. Their disadvantage for a small farm operation is that plant wastes can often be put to better use as livestock feed or compost. Also, plants tend to be bulky and to accumulate lignin and other indigestible materials that must be regularly removed from digesters. This severely limits the use of plant wastes in continuous-feeding digesters (Anderson, 1972).

2.4 Methanogenesis Methanogenesis is a microbial process, involving many complex, and differently interacting species, but most notably, the methane-producing bacteria. The biogas process consists of three stages; hydrolysis, acidification and methane formation.

In the first stage of enzymatic hydrolysis, the extracellular enzymes of microbes, such as cellulase, protease, amylase and lipase, externally enzymolize organic material. Bacteria decompose the complex carbohydrates, lipids and proteins in cellulosic biomass into more simple compounds.

During the second stage, acid-producing bacteria convert the simplified compounds into acetic acid (CH3COOH), hydrogen (H2), and carbon dioxide (CO2). In the process of acidification, the facultatively anaerobic bacteria utilise oxygen and carbon, thereby creating the necessary anaerobic conditions necessary for methanogenesis (Gate, 1999).

In the final stage, the obligatory anaerobes that are involved in methane formation decompose compounds with a low molecular weight, (CH3COOH, H2, CO2), to form methane (CH4) and CO2 (Gate, 1999).

2.5 Factors affecting biogas production According to Dhevagi, 1992, various factors such as biogas potential of feedstock, design of digester, inoculum, nature of substrate, pH, temperature, loading rate,

9

hydraulic retention time, C: N ratio, volatile fatty acids, and other trace gases influence the biogas production as explained below

2.5.1 Temperature

Temperature affects the production of biogas. The temperature at which the stages of biogas formation take place is very important and needs to be kept constant. The methanogenic bacteria, which facilitate the formation of biogas, are very sensitive to temperature changes (Lawbury, 2001). The optimum temperature is 350C. Temperatures below this slow down the biogas production process, a higher temperature than necessary kills the biogas producing bacteria. The methonogens are inactive in extreme high and low temperatures. When the ambient temperature goes down to 100C, gas production virtually stops. Satisfactory gas production takes place in the mesophilic range between 250 to 300C.Proper insulation of digester helps to increase gas production in the cold season. When the ambient temperature is 300C or less, the average temperature within the dome remains about 40C above the ambient temperature (Lund, 1996). Therefore in areas of temperature changes, such as mountainous regions, or winter conditions that may be more accentuated inland, mitigating factors need to be taken into account, such as increased insulation (Kalia, 1988), or the addition of heaters to maintain temperatures (Lichtman, 1983).

2.5.2 Hydraulic retention time Hydraulic retention time is the average time spent by the input slurry inside the digester before it comes. Since it is very difficult to load straight manure into a digester it is usually necessary to dilute it with water into slurry. If too much water is added, the mixture will become physically unstable and settle quickly into separate layers within the digester, thus inhibiting good fermentation. The general rule-of-thumb is slurry about the consistency of cream. The important point here is that as you dilute the raw material you reduce its retention time. In tropical countries retention time varies from 30-50 days while in countries with colder climate it may go up to 100 days (Zennaki et al., 1996).

2.5.2 Loading rate

Loading rate is also important considerations. In the floating drum model, retention ranges between 30-55 days (KVIC, 1983), depending upon climatic conditions, and will decrease if loaded with more than its rated capacity which may result in imperfectly digested slurry. KVIC state that maximum gas production occurs during the first four weeks, before tapering off, therefore a plant should be designed for a retention that exploits this feature. Retention period is found to reduce if temperatures are raised, or more nutrients are added to the digester. Human excreta, due to its high nutrient content, needs no more than 30 days retention in biogas plants (KVIC, 1983). If the

10

plant is overfed, acids will accumulate and methane production will be inhibited. Similarly, if the plant is underfed, the gas production will also be low (Lagrange, 1979).

2.5.4 pH value

The optimum biogas production is achieved when the pH value of input mixture in the digester is between 6 and 7. The pH in a biogas digester is also a function of the retention time. In the initial period of fermentation, large amounts of organic acids are produced by acid forming bacteria, the pH inside the digester to below 5. This inhibits or even stops the digestion or fermentation process. Methanogenic bacteria are very sensitive to pH and do not thrive below a value of 6.5. Later, as the digestion process continues, concentration of ammonia increases due to digestion of nitrogen which can increase the pH value to above 8. When the methane production level is stabilized, the pH range remains buffered between 7.2 and 8.2. A pH higher than 8.5 will start to show toxic effect on methanogen population (Karki and Dixit, 1984).

2.5.5 C/N ratio The relationship between the amount of carbon and nitrogen present in organic materials is expressed in terms of the carbon/nitrogen ratio (C/N). A C/N ratio ranging from 20 to 30 is considered optimal for anaerobic digestion. If the C/N ratio is very high, the nitrogen will be consumed rapidly by methanogens for meeting their protein requirements and will no longer react on left over carbon content of the material. As a result, gas production will be low. On the other hand, if the C/N ratio is very low, nitrogen will be liberated and accumulated in the form of ammonia. Ammonia will increase the pH value of the content in the digester. Animal waste, particularly cattle dung, has an average C/N ratio of about 24 (Karki and Dixit, 1984). The plant materials such as straw and sawdust contain a higher percentage of carbon. The human excreta has a C/N ratio as low as 8 (Karki and Dixit, 1984). C/N ratio of some of the commonly used materials are presented in Table 2.2.

11

Table 2- 2: C/N Ratio of some organic materials (Karki and Dixit, 1984)

Raw materials C/N Ratio

Duck dung 8

Human excreta 8

Chicken dung 10

Goat dung 12

Pig dung 18

Sheep dung 19

Cow dung/ Buffalo dung 24

Water hyacinth 25

2.6 Gas analysis in biogas plants A biogas plant must be continuously monitored with respect to gas composition, temperature, dwell time in the fermenter and the addition of substrate to ensure optimum operation of the biological process and achieve as high a methane yield as possible. It is important to check the concentration of hydrogen sulphide as this residual gas is toxic and corrosive and can disrupt the biological process above a specific concentration level (Rakican, 2007). Table 2.3 is a summary of composition of biogas within the digester. Table 2- 3: Biogas composition (Rakican, 2007)

Gas component Concentration range Mean value

Methane (CH4) 45 - 70% 60%

Carbon dioxide (CO2) 25 - 55% 35%

Water vapour 0 - 10% 3-10%

Nitrogen (N2) 0.01 – 5% 1%

Oxygen (O2) 0.01 – 2% 0.3%

Hydrogen (H2) 0 - 1%

12

CHAPTER 3: METHODOLOGY

3.1 Introduction The project was conducted in the laboratory and experiments were carried out in assessing the variation of methane and carbon dioxide yield with time, where three replicates were carried out for each sample.

3.2 Materials and methods The literature review and background research was carried out in order to provide an initial overview of biogas. These sources described what biogas was, how it was produced, and used. The literature reviewed also transcribed what studies had been done in reference to biogas and current projects using biogas technology.

3.3 Materials and equipment used The materials and equipment used in the study included; substrates such as cow dung, pig manure, five liter containers, GA2000Plus Gas analyzer (shown in Figure 3.1), and thermometers.

Figure 3- 1: GA2000Plus Gas analyzer used in the experimental work

13

3.4 Preparation of samples for biogas production The substrates were checked for stones or other unnecessary materials before feeding in the digesters. Weighing of the substrates was done using a digital weighing scale. The pig manure and cow dung were each mixed with water in a ratio of 1:1 by volume before being mixed in varying proportions indicated in Table 3.1. The mixture was then placed in the five liter containers. Pig manure, cow dung and mixture of pig and cow dung in the ratio of 1:1 substrates were considered. Each container had a thermometer to monitor temperature variation. The pH of the mixtures was measured with a digital pH meter. Table 3- 1: Proportions for different treatments

Mixture proportions Treatment 100% cow dung A 50% cow dung and 50% pig dung B 100% pig dung C Figure 3.2 shows the experimental set up for treatments A, B, and C each replicated three (3) times.

Figure 3- 2: Experimental set up in the laboratory

14

3.5 Determining the volume of methane and carbon dioxide at a given time interval

The samples were tested for gas yield (methane and carbon dioxide) during the laboratory scale batch experiment. Methane and carbon dioxide proportions were measured using GA2000Plus Gas analyzer. The tube from the sample (treatment) was connected to the gas inlet port shown in Figure 3.1. After each reading, the GA200plus Gas analyzer was switched off by a long press on the on/off button for about 15 seconds. At this point a clean air purge is carried out. The mixture that gives the highest yield of methane at a given time was found out and noted.

3.7 Evaluation of the trace gases variation in the selected substrates. The trace gases, that is; hydrogen sulphide, and carbon monoxide, were measured using a GA2000 Plus gas analyzer.

3.8 Hypothesis testing The samples were randomly selected in an independent manner from the number of treatment populations. This was accomplished by randomly assigning the experimental units to the treatments.

3.8.1 Analysis of variance (ANOVA) Analysis of Variance (ANOVA) is a statistical test used to determine if more than two population means are equal. The region of rejection of Test statistics was obtained from the F-table in appendix B with alpha and degrees of freedom. Test statistics (F) The test uses the F-distribution (probability distribution) function and information about the variances of each population and grouping of populations to help decide if variability between and within each populations are significantly different. The test statistic was computed using equation 3.1 (Gomez, 1976).

(EMS) Square Mean Error(TMS) Square Mean Treatment(F)statistic Test

(3.1) But Error mean square which is one of many ways to quantify the difference between values implied by an estimator and the true values of the quantity being estimated was calculated using equation 3.2.

15

(SST) Squares of Sum Treatment(SS) squares of Sum TotalSSE

, (df) freedom of degee Error

SSEEMS

(3.2)

where SSE is the error sum of squares

)freedom(df of DegreeSST(TMS) square Mean Treatment

(3.3) where SST is the Treatment sum of squares

3.8.2 Degree of freedom Since each sample has degrees of freedom equal to one less than their sample sizes, then treatment and error degrees of freedom were calculated using equation 3.4 and 3.5 respectively (Gomez, 1976). Degree of freedom (df) = T-1 (3.4)

1)T(rdf Error (3.5)

Sum of squares for treatments (SST) = (Sum of squares of treatments totals with each square divided by the number of observations for that treatment) - Correction for mean

N

GTr

SSTt

ii

2

1

21 (3.6)

Total sum of squares (SS) = (Sum of squares of all observations)

NGySS

t

i

r

jij

2

1 1

2

)( (3.7)

16

CHAPTER 4: RESULTS AND DISCUSSION

4.1 Introduction The results that are presented in Figures 4-1 and Tables 4-1 were the mean of the three replicates for each sample. The temperature of the digester (container) was noted every day. The results were analyzed using Microsoft Excel, and null hypothesis was tested using the ANOVA. Table 4- 1: Mean values of methane (%) and carbon dioxide (%) with time for treatments A, B and C

Substrates A(100% cow dung) B(50%cow dung & 50% pig) C(100% pig dung)

Time (Days)

CH4 (%)

CO2 (%)

Temperature OC

CH4 (%)

CO2 (%)

Temperature OC

CH4 (%)

CO2 (%)

Temperature OC

1 0.0 0.0 26.0 0.0 0.0 26.0 0.0 0.0 26.0

2 0.0 0.0 26.0 0.0 0.0 26.0 0.0 0.0 26.0

3 3.0 10.7 26.0 22.8 9.3 26.0 17.7 14.0 26.0

4 11.7 10.0 28.0 27.0 15.9 28.0 26.1 19.9 28.0

5 17.1 19.8 27.3 35.7 19.8 26.3 29.4 22.2 26.3

6 22.8 22.3 29.0 42.9 24.1 28.0 36.3 26.0 28.7

7 23.1 18.2 25.0 46.2 26.8 24.0 36.0 26.1 25.3

8 24.0 20.6 30.0 48.9 28.5 30.0 38.7 27.2 30.0

9 26.7 21.0 26.0 48.6 29.3 26.0 42.0 29.8 26.0

10 35.1 25.8 26.0 50.4 30.8 26.0 44.4 30.4 26.0

11 24.6 17.3 23.0 53.1 31.2 22.7 43.2 28.9 23.0

12 33.0 24.0 24.0 57.3 32.9 24.0 45.9 30.5 24.0

13 36.0 24.4 27.0 54.3 30.4 27.0 47.1 30.0 27.3

14 30.0 19.2 25.3 56.7 33.2 25.0 44.4 27.0 25.0

15 38.1 23.9 28.0 55.4 33.7 28.0 45.9 29.6 28.0

16 40.2 24.3 24.0 56.9 32.2 24.0 41.7 27.0 24.0

17 42.9 26.3 30.0 58.1 31.8 30.0 39.0 26.0 30.0

18 45.3 26.8 32.0 61.2 30.8 32.0 40.8 27.0 32.0

19 43.2 27.4 30.0 60.9 29.7 30.0 29.4 14.9 30.0

20 40.6 25.1 29.5 58.4 26.6 29.5 18.6 14.5 29.5

17

From Table 4.1 temperatures within the digester ranged between 24 and 320C. This was due to constant rain which greatly reduced the production of methane since the optimum temperature (350C) was not reached although satisfactory gas production took place in the mesophilic range which is between 250 to 350C according to Lund, A, 1996.

Table 4- 2: pH for the different treatments

Treatment Initial PH Final PH

A 6.8 5.9

B 6.6 6.1

C 6.7 5.6

Since the pH for the initial slurry varied within the range of 6.6 and 6.8, the final ranged between 5.6 and 6.1 (Table 4.2). Thus, the experiment was conducted within the pH range for optimum methane production, but measuring the final pH of the substrates, it indicated that treatments A and C were below 6. Free-ammonia concentration is strongly dependant on pH and temperature, but it depends more severely on pH since there is always little temperature variation throughout the experiment. If pH falls below 6, free-volatile fatty acids become toxic to methane forming bacteria. Above a pH of 8, free-ammonia becomes toxic to methane forming bacteria. Therefore, the recommended pH of digester should be mainly from 7.0 to 7.4, which is the healthy environment for methane forming bacteria, in order to minimize the toxicity of both free-ammonia and free-volatile fatty acids (NiJi-Qin, 1993).

4.2 Mixture that gives the highest yield of methane Treatment B which is a mixture of 50% cow dung and 50% pig dung produced more methane than the rest of the treatments and its highest methane yield by volume was 61.2%. This was followed by treatment C obtained from 100% pig dung with methane yield of 47.1%.The lowest methane rate was 45.3% obtained from treatment A which is 100% cow dung. Cumulative methane yields by volume were shown in Figure 4-1.

18

Figure 4- 1: Variation of Methane production with time for different treatments

4.3 Variation of the volumes of methane and carbon dioxide with time Graphs of methane and carbon dioxide against retention time (RT) were generated as shown in Figures 4-2 and 4-3. Generally methane production increased with time. From Table 4.1 and Figure 4-2, maximum methane production was harnessed between the 15th to the 18th days of digestion. Treatment B produced more methane than the rest of the treatments and its proportion by volume was 61.2% and it occurred on the 18th day of digestion. It was followed by treatment C with 47.1% and it occurred on the 13th day of digestion. Lastly was treatment A with 45.3% methane by volume on the 18th day of digestion.

19

Figure 4- 2: Variation of Methane for various treatments

The yield and composition of biogas from different substrates were evaluated and the cumulative curves for the three treatments were estimated as shown in Figure 4-3. Carbon dioxide production increased for the first days of digestion and observed to be at its peak on the 15th day of digestion, there after it reduced significantly. Treatment B produced the highest emission of carbon dioxide with 33.7% by volume and it occurred on the 15th day of digestion. It was followed by Treatment C with 30.5% which was noticed on the 12th day of digestion and least was A with 27.4% which happened on the 19th day.

Figure 4- 3: Proportions of Carbon dioxide (CO2) for various treatments with time

20

4.4 Variation of trace gases The trace gases identified included carbon monoxide, hydrogen sulphide and hydrogen as shown in the Table 4.3. Hydrogen was extremely low in that it could not be identified by the gas analyzer and because of this it was left out in the analysis. Some numerical values of hydrogen are indicated in Appendix A.

Table 4- 3: Composition of trace gases

Substrates A(100% cow dung) B(50% cow dung & 50% pig)

C(100% pig dung)

Time (Days)

CO (ppm)

H2S (ppm)

Temperature 0C

CO (ppm)

H2S (ppm)

Temperature 0C

CO (ppm)

H2S (ppm)

Temperature 0C

1 0.0 0.0 26.0 0.0 0 26.0 0.0 0.0 26.0

2 0.0 0.0 26.0 0.0 0 26.0 0.0 0.0 26.0

3 51.3 95.0 26.0 10.3 1 26.0 1.0 101.0 26.0

4 29.5 187.0 28.0 7.0 164.3 28.0 7.0 271.0 28.0

5 6.0 141.3 27.3 6.3 256.3 26.3 5.0 399.0 26.3

6 5.7 172.0 29.0 4.3 291.3 28.0 3.0 124.0 28.7

7 3.3 160.0 25.0 1.7 172.3 24.0 3.0 368.0 25.3

8 4.7 86.7 30.0 4.3 380.7 30.0 3.3 828.7 30.0

9 2.3 154.3 26.0 2.0 232.3 26.0 2.5 >> 26.0

10 2.3 86.3 26.0 3.7 169.7 26.0 3.0 >> 26.0

11 1.3 84.7 23.0 2.7 219 22.7 0.7 >> 23.0

12 11.0 115.0 24.0 1.3 241 24.0 0.7 198.0 24.0

13 2.0 140.7 27.0 1.7 144.7 27.0 2.7 175.0 27.3

14 0.7 159.3 25.3 2.0 232.7 25.0 1.5 355.0 25.0

15 1.7 172.7 28.0 2.0 205 28.0 3.7 422.7 28.0

16 2.7 283.0 24.0 4.0 161.7 24.0 2.0 328.7 24.0

17 3.0 292.0 30.0 2.3 234.7 30.0 1.3 299.3 30.0

18 2.7 272.0 32.0 4.0 258 32.0 2.7 225.0 32.0

19 4.0 257.0 30.0 3.3 258 30.0 1.7 351.5 30.0

20 2.0 242.2 29.5 2.2 258.3 29.5 1.2 278.0 29.5

21

Figure 4- 4: Variation of Carbon monoxide with time for different treatments

From the Figure 4.4, carbon monoxide production was high between days 2 and 5 but substrate A had a greater generation than the rest. It was followed by treatment B and C generated the least percentage of carbon monoxide. After day 5, the production of carbon monoxide generally reduced.

Figure 4- 5: Proportions of Hydrogen sulphide with time for various treatments

From Figure 4.5, hydrogen sulphide increases with time up to day 8 and thereafter starts to reduce significantly. Treatment C generated a lot of hydrogen sulphide followed

22

by B and the least being A. Measuring hydrogen sulfide levels makes it possible to keep the concentration of this toxic and corrosive gas as low as possible by taking appropriate action (The Biogas Technology in China, 1989). Substrate C has a high hydrogen sulphide emission and this resulted in low methane yield since the gas adversely affect both the generation of biogas and downstream processes. Also high levels of hydrogen sulphide wear down the anaerobic digester and high concentration of it has a toxic effect which hinders bacteria growth.

4.5 Hypothesis Testing Analysis of Variance was used since the experiment involved three or more means as summarized in Table 4.4. The F-test was used to show only if a difference existed among the three means as shown in Table 4.5. Table 4- 4: Results of methane (%) for the three treatments

Substrates A B C Time (Days) CH4 CH4 CH4

1 0.0 0.0 0.0 2 0.0 0.0 0.0 3 3.0 22.8 17.7 4 11.7 27.0 26.1 5 17.1 35.7 29.4 6 22.8 42.9 36.3 7 23.1 46.2 36.0 8 24.0 48.9 38.7 9 26.7 48.6 42.0

10 35.1 50.4 44.4 11 24.6 53.1 43.2 12 33.0 57.3 45.9 13 36.0 54.3 47.1 14 30.0 56.7 44.4 15 38.1 55.4 45.9 16 40.2 56.9 41.7 17 42.9 58.1 39.0 18 45.3 61.2 40.8 19 43.2 60.9 29.4 20 40.6 58.4 18.6

Treatment Totals (T)[%Volume] 537.4 894.8 666.6

Grand total (G) = 537.4 + 894.8 + 666.6 = 2098.8%Volume

23

There were three (3) treatments (T), 20 runs(r) and total number of observations (N) =3x20=60 Using equation 3.7, the total sum of squares (SS) = 17676.6

From equation 3.6 sum of squares for treatments (SST) = 3275.044

Sum of squares for error (SSE) = SS – SST (3.2) SSE = 14401.55 Table 4-5 summarizes the computation of the F-value at 1% and 5% level of significance. Table 4- 5: General ANOVA Summary Table for a Completely Randomized Design for methane Source of Variation

Df Sum of Squares

Mean square (MS)

Calculated F

F1% F5%

Treatment 2.0 3275.04 1637.52 6.5 5.01 3.16 Error 57.0 14401.55 252.66 Total 59.0 17676.60 From F-tables at 1% level of significance as attached in Appendix B, 5.01F[2,57] Since the computed F-value was larger than the tabular F-value at 1% level of significance, it implied that the treatment difference (substrates) was highly significant. This therefore implied that methane production varied with the type of substrate being digested.

Following the above procedure, the calculated and tabulated values of F for CO2 were obtained and recorded in table 4-6.

Table 4- 6: General ANOVA Summary Table for a Completely Randomized Design for carbon dioxide

Source of Variation

Df Sum of Squares

Mean square (MS)

Calculated F

F1% F5%

Treatment 2.0 304.62 152.31 1.73 5.01 3.16

Error 57.0 5029.99 88.25

Total 59.0 5334.61

24

CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions A batch mixed laboratory anaerobic digester (5 liter bottles) was designed and built to evaluate methane and carbon dioxide from different substrates: cow dung, pig dung and mixture of pig and cow dung in the ratio of 1:1. A good productivity of methane for mixture of 50% pig and 50% cow dung was found to be 61.2% by volume. It was followed by treatment with 100% pig dung and lastly treatment with 100% cow dung. When all the substrates were anaerobically digested, maximum methane production was harnessed between the 15th to 18th days of digestion. Treatment B with 50% pig dung and 50% cow dung produced more methane than the rest of the treatments on the 18th day of digestion. Even if co-digestion is reported to increase biogas production, as stated by several researchers (Kasisira et al., 2009; World Energy Council, 1994), the percentage of methane and CO2 largely depend on the feedstock. The production of methane was hindered by the presence of some trace gases such as hydrogen sulphide which limited the methane producing bacteria. Since the computed F-value was larger than the tabular F-value at 1% level of significance, it implied that the treatment difference was highly significant. This therefore implied that methane production varied with the type of substrate being digested and this implied that the initial hypothesis was accepted.

5.2 Recommendations 1) Biogas users need to understand the process of methanogenesis. This allows

manipulation, which can serve to maximize gas production in the field. Since the temperatures in the digester become reduced during the rainy season, it is better for biogas users to insulate their digesters in order to maintain the mesophilic temperatures.

2) Users should also make sure that the pH of the substrates within the digester is between 6 and 8. This is because above a pH of 8, free-ammonia becomes toxic to methane forming bacteria and below 6, free-volatile fatty acids become toxic for the methane forming bacteria.

25

Areas for further research 3) Research should be carried out in determining the effect of co-digestion on

methane and carbon dioxide yield in a biogas plant. Co-digestion increases the production of biogas but does not necessarily mean increased yield of methane.

26

REFERENCES

Anderson, L. (1972), Energy Potential from Organic Wastes: A Review of the Quantities and Sources. Bureau of Mines Information Circular 8549, U.S. Dept. Interior.

Braun, R. (2007). Anaerobic digestion: a multi-faceted process for energy, environmental management and rural development, In: Improvement of Crop Plants for Industrial End Uses, P. Ranalli (Ed.), 335-416, Springer, ISBN 978-1-4020-5485-3, Dordrecht, The Netherlands.

Cheng, J. and B. Liu. (2002), Swine wastewater treatment in anaerobic digesters with floating media. Transactions of the ASAE 45(3):799-805.

Dhevagi, P., Ramasamy, K. and Oblisami, G. (1992), Biological Nitrogen Fixation and Biogas Technology (eds Kannaiyan, S., Ramasamy, K., Ilamurugu, K. and Kumar, K.), Tamil Nadu Agricultural Unveristy, Coimbatore, pp. 149–153.

Fry, J. (1961), Manure Smell Furnishes Farmstead's Power Needs. National Hog Farmer 6:3.

Fulford, D. (1985), Fixed Concrete Dome Design. Biogas - Challenges and Experience from Nepal. Vol I. United Mission to Nepal, pp. 3.1-3.10.

GATE (Deutsches Zentrum fur Entwicklungstechnologien)(1999), Biogas technology in Sangli, India. Eschborn, Germany.

Gomez Kwanchai,A. (1976), Procedures for Agricultural Research, International rice research institute, Philippines,

Kalia, AK, (1988), Development and evaluation of a fixed-dome plug flow anaerobic digester. Biomass 16 (1988) 225-235.

Karki, A.B. and K, Dixit (1984), Biogas fieldbook. Sahayogi press, Kathamandu. Nepal

Kasisira L.L and Muyiiya N.D, 2009, “Assessment of the Effect of Mixing Pig and Cow Dung on Biogas Yield”. Agricultural Engineering International: the CIGR Ejournal. Manuscript PM 1329, Vol. XI.

KVIC (1993), Khadi and V.I Commission and its Non-Conventional Energy Programmes. KVIC, Bombay, India.

27

Lagrange, B. (1979), Biomethane 2: principles-Techniques Utilization. EDISUD, La Calade,13100 Aix-en-Provence, France.

Lawbury, J. ( 2001), Biogas technology in India: More than Gandhi’s dream? Online at www.ganesha.co.uk/Articles.htm as accessed 03.02.2012

LBS. (2002), GM Well-to-Wheel analysis of energy use and greenhouse gas emissions of advanced fuel/vehicle systems A European Study. 133 p., L-B-Systemtechnik GmbH, Ottobrunn Germany.

Lichtman, RJ, (1983), Biogas Systems in India. VITA (Volunteers in Technical Assistance). Virginia, USA.

Lund, M. S., S.S. Andersen and M. Torry-Smith (1996), Building of a flexibility Bag Biogas Digester in Tanzania, student report. Technical university of Denmark, Copenhagen.

Maramba Felix, (1978), Production and Utilization of Biogas in Rural Areas of Industrialized and Developing Countries, Schriftenreihe der gtz, No. 97, pg. 63, after; Biogas and Waste Recycling - The Phillipine Experience; Metro Manila, Phillipines.

NiJi-Quin and E. J. Nyns (1993), Biomethanization: A developing technology in Latin America. Catholic University of Louvain, Belgium. pp67-68.

Rakican. K, Murska Sobota (2007), Biogas for farming, energy conversion and environment protection Department of Agroenergetics Lithuanian University of Agriculture Studentu 11, LT-53361, Akademija, Kaunas distr. Lithuania.

Robles-Gil, S. (2001), Climate Information for Biomass Energy Applications, report on solar energy Commission for Climatology World Metrological Organization. La Paz, Mexico, Feb 21.

Sasse, L, Kellner, C, Kimaro, A, (1991), Improved Biogas Unit for Developing Countries. (GATE) Deutsches Zentrum fur Entwicklungstechnologien. Eschborn, Germany.

Singh, Ram Bux. (1971), Bio-Gas Plant. Gobor Gas Research Station. Ajitman, Etawah (U.P.) India.

TACIS, (1997), Assessment of Market Potential of Home-Made and Industrial Biogas Equipment in Georgia. TACIS Technical Assistance to the Commonwealth of Independent States(TACIS), Tbilisi.

28

Tafdrup, S., Hjort-Gregersen, K. (2000), Centralized Biogas Plants, Centre for Biomass Technology Danish Bioenergy Solutions - reliable & efficient, (www.videncenter.dk) last updated 06, january,2004

The Biogas Technology in China (1989), Chengdu Biogas Research Institute, Chengdu, China.

Wellinger, A. (2000), Process design of agricultural digesters. AD-Nett Anaerobic digestion: Making energy and solving modern waste problems. rtenblad H.ed. Herning municipal utilities. Denmark.

Werner, U., Stöhr, U., Hees, N. – GATE (1989), Biogas Plants in Animal Husbandry – A Practical Guide. Friedr. Vieweg & Sohn, Braunschweig/Wiesbaden (Germany), 153 P., ISBN 3-528-02048-2

World Energy Council (1994), New Renewable Energy Resources: a guide to the future: London Kogan page limited

Zennaki, B.Z., Zadi, A., Lamini, H., Aubinear, M., Boulif, M. (1996), Methane Fermentationof cattle manure: effects of hydraulic retention time, temperature and substrate concentration. Tropicultural 14 (4), 134-140.

29

APPENDICES APPENDIX A: DAILY DATA COLLECTION SHEET

Day 3 sample Temp OC CH4 (%) CO2 (%) O2 (%) Balance (%) CO (ppm) H2 (ppm) H2S (ppm)

A1 26 3.1 12.6 0.1 84.2 74 low 125 A2 26 2.8 8.4 7.1 81.6 66 low 82 A3 26 3.1 11.0 0.1 85.9 14 low 78

B1 26 20.8 8.7 0.4 70.0 10 low 1 B2 26 25.1 9.6 0.2 65.1 12 low 1 B3 26 22.5 9.7 0.2 67.6 9 low 1

C1 26 C2 26 18.6 13.5 0.1 67.7 1 1 20 C3 26 16.7 14.5 0.2 68.6 1 low 182


A1 28 A2 28 12.2 3.9 0.2 83.6 52 low 201 A3 28 11.2 36.1 0.5 52.3 7 low 173

B1 27 28.7 29.2 0.1 42.0 7 low 101 B2 28 15.6 34.0 1.1 49.3 6 low 156 B3 29 36.7 32.3 0.3 30.8 8 low 236

C1 28 24.6 40.3 1.6 33.5 7 low 24 C2 28 28.2 36.6 4.1 31.2 6 low 255 C3 28 25.5 42.5 0.2 31.8 8 low 534

Comment: Even if methane is increasing, carbon dioxide was increasing too.

30


A1 28 18.6 19.8 2.0 59.6 5 low 152 A2 28 17.1 17.9 1.2 63.8 8 low 120 A3 26 15.6 21.6 2.3 60.5 5 low 152

B1 26 36.3 18.7 0.7 44.3 7 low 314 B2 27 38.0 20.6 0.9 40.5 6 low 262 B3 26 32.8 20.2 1.1 45.9 6 low 193

C1 27 30.5 24.6 1.3 43.6 6 low 402 C2 26 27.4 20.0 0.6 52.0 4 low 435 C3 26 30.3 22.0 0.7 47.0 5 low 360

Day 6

sample Temp OC CH4 (%) CO2 (%) O2 (%) Balance (%) CO (ppm) H2 (ppm) H2S (ppm) A1 29 24.2 21.5 0.3 54.0 6 low 209

A2 29 22.4 20.4 0.4 56.8 6 low 162

A3 29 21.8 25.1 1.9 51.2 5 low 145

B1 27 40.7 23.2 1.3 34.8 3 low 249

B2 29 43.8 24.3 0.4 31.2 5 low 349

B3 28 44.2 24.7 0.3 30.6 5 low 276

C1 29 30.8 26.4 4.3 32.2 2 low 124

C2 29 28.9

C3 28 49.2 25.6 0.2 37 4 low >>

Comment: Treatment C2 was leaking.

31

Day 7

sample Temp OC CH4 (%) CO2 (%) O2 (%) Balance (%) CO (ppm) H2 (ppm) H2S (ppm) A1 25 20.1 14.3 8.0 57.6 2 low 45

A2 25 22.6 14.2 2.0 61.2 4 low 287

A3 25 26.6 26.1 1.0 46.3 4 low 148

B1 25 47.6 25.1 2.0 25.3 1 low 164

B2 25 44.8 27.8 1.8 25.6 2 low 209

B3 25 46.2 27.5 1.8 24.5 2 low 144

C1 26 37.1 28.3 1.9 32.7 3 low 377

C2 25 36.0 24.6 1.9 37.5 3 low 360

C3 25 34.9 25.3 1.3 38.5 3 low 421

Comment: The oxygen concentration is too high. This explains the low methane production


A1 30 24.1 21.4 0.4 54.1 9 low 79 A2 30 23.8 18.8 1.3 56.1 2 low 14 A3 30 24.1 21.7 8.2 46.0 3 low 167

B1 30 48.9 26.9 0.5 23.7 5 low 517 B2 30 49.3 29.0 0.6 21.1 4 low 371 B3 30 48.5 29.5 0.1 21.9 4 low 254

C1 30 39.4 29.7 0.9 30.0 3 low 882 C2 30 38.7 26.1 0.5 34.7 4 low 860 C3 30 38.0 25.8 0.9 35.3 3 low 744

32


A1 26 26.8 12.6 9.2 51.4 0 low 140 A2 26 28.9 22.4 0.5 48.2 3 low 173 A3 26 24.4 27.9 0.5 47.2 4 low 150

B1 26 48.9 30.6 0.5 20.0 2 low 362 B2 26 50.1 31.8 0.5 17.6 4 low 303 B3 26 46.8 25.6 6.9 20.7 0 low 32

C1 26 43.2 31.3 1.5 24.0 3 low C2 26 42.3 28.2 0.5 29.0 2 low C3 26 40.5 59.5


A1 26 36.5 23.2 1.1 39.2 2 low 6 A2 26 34.6 22.7 1.1 41.6 1 low 4 A3 26 34.2 31.5 1.1 33.2 4 low 249

B1 26 51.4 27.1 2.8 18.7 3 low 1 B2 26 49.0 32.5 0.9 17.6 4 low 276 B3 26 50.8 32.7 0.5 16.0 4 low 232

C1 26 45.4 32.4 0.5 21.7 3 low >> C2 26 48.1 29.3 0.5 22.1 3 low >> C3 26 39.7 29.4 0.4 30.5 3 low >>

33

Day 11

sample Temp OC CH4 (%) CO2 (%) O2 (%) Balance (%) CO (ppm) H2 (ppm) H2S (ppm) A1 23 24.6 14.8 9.5 51.1 0 low 100 A2 23 28.1 9.4 12.1 50.4 0 low 33 A3 23 21.1 27.6 0.9 50.4 4 low 121

B1 22 50.1 32.7 1.4 15.8 3 low 270 B2 24 48.9 27.5 4.8 18.8 2 low 192 B3 22 60.3 33.3 1.1 5.3 3 low 195

C1 23 39.2 27.1 4.0 29.7 1 low >>>> C2 23 44.2 29.9 1.4 24.5 1 low >>>> C3 23 46.2 29.7 0.6 23.5 0 low >>>>

Comment: The vacuum in sample A1 was removed by letting the gas to escape.


A1 24 33.8 23.1 0.5 42.6 1 low 140 A2 24 36.5 23.0 0.9 39.6 1 low 143 A3 24 28.7 25.9 2.0 43.4 1 low 62

B1 24 56.7 33.3 0.3 9.7 2 low 312 B2 24 60.2 31.9 0.7 7.2 1 low 219 B3 24 55.0 33.5 0.6 10.9 1 low 192

C1 24 46.9 31.7 0.3 21.1 2 low 82 C2 24 40.3 30.5 0.2 29.0 0 low 314 C3 24 50.5 29.4 0.0 20.1 0 low >>

34


A1 27 36.1 23.8 1.3 38.8 2 low 222 A2 27 27.8 22.8 1.1 48.3 3 low 159 A3 27 44.1 26.6 1.7 27.6 1 low 41

B1 27 56.4 33.4 2.3 7.9 2 low 245 B2 27 50.3 27.7 4.5 17.5 2 low 77 B3 27 56.2 30.2 3.6 10.0 1 low 112

C1 27 47.5 32.0 2.7 17.8 4 low 389 C2 28 50.7 29.8 2.2 17.3 3 low 68 C3 27 43.1 28.1 0.6 28.2 1 low 68


A1 25 30.6 7.2 14.1 48.1 0 Low 88 A2 26 28.7 23.6 1.0 46.7 2 Low 345 A3 25 30.7 26.7 3.7 38.9 0 Low 45

B1 25 58.6 34.1 0.8 6.5 2 Low 276 B2 25 50.5 31.4 1.6 16.5 2 Low 238 B3 25 61.0 34.2 1.8 3.0 2 Low 184

C1 25 45.9 26.4 4.5 23.2 Low C2 25 43.2 29.6 0.9 26.3 2 Low 305 C3 25 44.1 25.0 3.1 27.8 1 Low 405

35


A1 28 39.1 20.1 3.7 37.1 1 Low 285 A2 28 36.5 23.4 0.5 39.6 4 Low 141 A3 27 38.7 28.2 0.7 32.4 0 Low 92

B1 28 56.2 34.2 0.2 9.4 2 Low 322 B2 28 59.1 32.8 0.3 7.8 2 Low 34 B3 28 50.9 34.2 0.3 14.6 2 Low 259

C1 28 47.3 30.5 0.7 21.5 7 Low 295 C2 28 48.9 29.7 0.3 21.1 3 Low 503 C3 28 41.5 28.6 1.2 28.7 1 Low 470

Comment: The vacuum in treatment C3 was removed by letting the gas to escape.


A1 24 42.4 20.1 4.5 33.0 3 Low 333 A2 24 36.6 24.5 2.5 36.4 3 Low 250 A3 24 41.6 28.4 1.2 28.8 2 Low 266

B1 24 58.5 32.6 0.4 8.5 7 Low 25 B2 24 59.9 30.9 0.5 8.7 4 Low 201 B3 24 52.3 33.1 0.7 13.9 1 Low 259

C1 24 42.7 29.0 0.5 27.8 3 Low 341 C2 24 41.6 28.9 0.4 29.1 1 Low 418 C3 24 40.8 23.2 3.2 32.8 2 Low 227

36


A1 23 43.9 25.4 3.0 27.7 3 Low 330 A2 23 49.1 24.6 0.5 25.8 4 Low 302 A3 23 35.7 29.0 0.6 34.7 2 Low 244

B1 23 59.3 32.6 0.3 7.8 5 Low 221 B2 23 58.1 29.1 2.0 10.7 2 Low 229 B3 23 56.9 33.8 0.4 8.9 0 Low 254

C1 23 40.1 25.8 0.5 33.5 1 Low 174 C2 23 35.6 25.7 0.4 38.3 1 Low 193 C3 23 41.3 26.6 0.0 32.1 2 Low 531


A1 28 46.3 25.3 0.8 27.5 3 Low >> A2 28 41.1 25.6 0.5 32.8 3 Low >> A3 28 48.5 29.6 0.5 21.4 2 Low 272

B1 28 61.8 32.8 0.6 4.8 4 Low 336 B2 28 59.0 26.5 0.3 14.3 5 Low 154 B3 28 62.8 33.0 0.4 3.8 3 Low 284

C1 28 45.2 29.1 1.0 24.7 3 Low >> C2 28 48.0 29.6 0.6 21.8 1 Low >> C3 28 29.2 22.3 0.2 48.3 4 Low 225

37

Day 19 sample Temp OC CH4 (%) CO2 (%) O2 (%) Balance (%) CO (ppm) H2 (ppm) H2S (ppm) A1 32.0 44.2 26.2 0.9 28.3 4.0 Low >> A2 32.0 44.8 26.0 0.4 28.6 4.0 Low >> A3 32.0 40.6 30.1 0.4 28.9 4.0 Low 257 B1 32 61.5 32.1 0.4 6.0 4 Low 350 B2 32 58.9 26.3 0.4 14.4 3 Low 201 B3 32 62.3 29.5 0.3 7.8 3 Low 223 C1 32 28.6 17.6 9.3 44.5 2 Low 385 C2 32 30.1 15.2 10.2 44.6 2 Low >> C3 32 29.5 11.9 9.5 49.1 1 Low 318

38

APPENDIX B: PERCENTAGE POINTS OF THE INVERTED BETA (F)

Documents

Variation of Methane and Carbon dioxide Yield in a biogas ... › smash › get › diva2:604559 › FULLTEXT02.pdfmethane in the biogas will determine the thermal dynamic property