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Transcript of Scientific Project
Ahmed Hussein
ANAEROBIC DIGESTION OF CHICKEN MANURE, OLIVE POMACE AND WINE POMACE
Written by:
Ahmed Hussein, Student ID#: 173666, 3rd
Semester, 2012
Course of Study:
Energy Conversion and Management (International Program of ECM)
College Supervisor:
Prof. Dr.-Ing. Joachim Jochum
Company Name, Department and Internship Duration:
MT-Energie GmbH (Biogas-Technologie)
Department of Sales & Project Management (East Europe)
From April 16th till September 30
th
Company Supervisor:
Mr. Jan Ludeloff
Director Sales & Project Management (East Europe)
Hochschule Offenburg
Badstraße 24, 77652 Offenburg
Department: Mechanical- and Process-Engineering
Study course: Energy Conversion and Management
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Scientific Project ‘A.D. of Chicken Manure, Olive and Wine Pomace’
Ahmed Hussein Page II
Abstract
The Anaerobic Digestion; used in its both Ecological and Industrial terminologies,
has been a bright solution for both environmentalists and engineers in the last couple
of decades. The liaison between the rise of the Earth’s temperature; known as the
Green House Effect and the world’s race against time to find renewable and clean
resources for energy has framed the objectives for using this methodology to con-
front with the depletion of the world’s both Oil and Coal resources and reserves by
the next 50-75 years (according to the American Petroleum Institute). The Anaerobic
Digestion (AD) is an appropriate technique for the treatment of almost any biode-
gradable wastes. Unlike both Wind and Solar energies which are vulnerable to extra-
neous variables (biggest being weather conditions), the Anaerobic Digestion is
known to be more reliable. On different scales, the biodegradable wastes could be
simple kitchen wastes or wastes that reckon on both agricultural and livestock in-
vestments. Throughout this scientific report, a hands-on practical trial will be dis-
cussed as a field experiment for feeding dry chicken manure, olive pomace and wine
pomace into 750 and 950-liter trial wet fermenters with daily observations for the A.D.
process in the mesophilic range and in a run of 6 Months. (© 2012 MT-Energie and
Ahmed Hussein All Rights Reserved)
Hochschule Offenburg Mt-Energie GmbH
Scientific Project ‘A.D. of Chicken Manure, Olive and Wine Pomace’
Ahmed Hussein Page III
Table of Contents
Table of Contents .......................................................................................... III
List of Figures and Illustrations .................................................................. V
List of Equations.............................................................................................. V
List of Tables ................................................................................................. VII
Nomenclature (Latin Symbols) ............................................................... VIII
Nomenclature (Greek Symbols) ................................................................. IX
List of Abbreviations ..................................................................................... IX
1 Introduction ................................................................................................. 10
2 Basics ............................................................................................................ 11
2.1 History of Anaerobic Digestion ............................................................................. 11
2.2 What is Anaerobic Fermentation? ....................................................................... 12
2.3 Formation of Gas Mixture ..................................................................................... 13
14
2.4 Ambient Conditions ............................................................................................... 15
2.4.1 Oxygen ........................................................................................................... 15
2.4.2 Temperature ................................................................................................... 16
2.4.2.1 Psychrophilic Temperature Range ............................................................ 16
2.4.2.2 Mesophilic Temperature Range ................................................................ 16
2.4.2.3 Thermophilic Temperature Range ............................................................ 17
2.4.3 pH Value ........................................................................................................ 18
2.4.4 Nutrients and Trace Elements Supply ............................................................ 18
2.4.5 Inhibitors ........................................................................................................ 19
2.4.6 FOS (Volatile Organic Acids) ........................................................................ 21
2.4.7 TAC (Total Alkalinity) ................................................................................... 21
2.4.8 FOS/TAC Ratio .............................................................................................. 21
2.5 Operating Parameters ........................................................................................... 21
2.5.1 Loading Rate and Hydraulic Retention Time of the Fermenter ..................... 21
2.5.2 Productivity, Recovery and Degradation Efficiency ...................................... 24
2.5.3 Mixing ............................................................................................................ 25
2.5.4 Gas Formation, Potential and Methanogenic Activity ................................... 26
2.5.4.1 Possible Gas Yield .................................................................................... 26
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2.5.4.2 Gas Quality ............................................................................................... 27
3 Experiments ................................................................................................. 28
3.1 Anaerobic Digestion of Chicken Manure ............................................................. 29
3.1.1 Introduction .................................................................................................... 29
3.1.2 Acquisition and Properties of Chicken Manure ............................................. 30
3.1.3 The Experiment .............................................................................................. 32
3.1.3.1 Building up the trial Fermenter ................................................................ 32
3.1.3.2 Putting the fermenter into operation ......................................................... 38
3.1.3.3 Feeding and measuring ............................................................................. 41
3.1.3.4 Observations (results) ............................................................................... 53
3.1.3.5 Conclusion ................................................................................................ 56
3.2 Anaerobic Digestion of Olive Pomace .................................................................. 58
3.2.1 Introduction .................................................................................................... 58
3.2.2 Acquisition and properties of Olive Pomace .................................................. 58
3.2.3 The Experiment .............................................................................................. 60
3.2.4 Observations (results) ..................................................................................... 60
3.2.5 Conclusion ...................................................................................................... 63
3.3 Anaerobic Digestion of Wine Pomace .................................................................. 64
3.3.1 Introduction .................................................................................................... 64
3.3.2 Acquisition and properties of Wine Pomace .................................................. 64
3.3.3 The Experiment .............................................................................................. 66
3.3.4 Observations (results) ..................................................................................... 66
3.3.5 Conclusion ...................................................................................................... 69
4 Acknowledgement ....................................................................................... 70
5 Bibliography ................................................................................................ 71
6 Appendix ...................................................................................................... 72
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List of Figures and Illustrations
Figure 1: Biogas in ancient China ....................................................................................... 11
Figure 2: Decomposition in absence of Oxygen ................................................................. 12
Figure 3: Formation of Biogas and trace gases ................................................................... 13
Figure 4: Fermentation Process ........................................................................................... 14
Figure 5: Mesophilic bacteria .............................................................................................. 16
Figure 6: Thermophilic bacteria .......................................................................................... 17
Figure 7: Relation between loading rate and hydraulic retention time by different ODM
concentrations ........................................................................................................................... 23
Figure 8: Dry Chicken Manure Barrels ............................................................................... 30
Figure 9: Dry Chicken Manure 1………………………………………………………. 30
Figure 10: Dry Chicken Manure 2……………………………………………………… 30
Figure 11: Prototyping the actual Biogas fermenter…………………………………… 32
Figure 12: Inside the trial fermenter……………………………………………………. 33
Figure 13: Temperature control valve…………………………………………………... 33
Figure 14: Main components of the trial fermenter……………………………………… 33
Figure 15: Upper components on the fermenter…………………………………………. 34
Figure 16: Impeller coupled with the motor……………………………………………… 34
Figure 17: The module’s control panel…………………………………………………… 34
Figure 18: TFT screen interface…………………………………………………………...34
Figure 19: 1st Gasline auxiliaries…………………………………………………………. 35
Figure 20: Input and output syphon to the gas counter………………………………….. 35
Figure 21: Gas counter box………………………………………………………………. 35
Figure 22: Pressure retaining Syphon……………………………………………………. 36
Figure 23: Surge chamber…………………………………………………..…………… 37
Figure 24: Creating head difference…………………………………………………..…. 38
Figure 25: Pumping the maize silage…………………………………………………….. 38
Figure 26: The silage being pumped into the fermenter………………………………… 38
Figure 27: The fermenter’s upper part immersed with water……………………………. 40
Figure 28: A gas leak found from the fermenter’s hatch………………………………... 40
Figure 29: The hole for Temperature sensing…………………………………………… 42
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Figure 30: Temperature Probe…………………………………………………………… 42
Figure 31: Wöhler digital pressure gauge……………………………………………….. 43
Figure 32: Laser distance meter…………………………………………………………. 44
Figure 33: Silicone based defoamer……………………………………………………... 44
Figure 34: Fermenter’s operating volume vs. distance………………………………….. 45
Figure 35: Density meter………………………………………………………………… 46
Figure 36: Dräger device………………………………………………………………… 47
Figure 37: Gas quality measurement…………………………………………………….. 47
Figure 38: Fermenter’s feeding hole……………………………………………………. 48
Figure 39: Scale…………………………………………………………………………. 48
Figure 40: Manual agitator………………………………………………………………. 48
Figure 41: pH meter……………………………………………………………………… 49
Figure 42: Titrator………………………………………………………………………... 49
Figure 43: Sample preparation…………………………………………………………… 49
Figure 44: Drying Oven…………………………………………………………………. 50
Figure 45: Muffle Furnace………………………………………………………………. 50
Figure 46: Nitrogen titration device…………………………………………………...… 51
Figure 47: Dräger Ammonia vial………………………………………………………… 51
Figure 48: Liquid chromatography………………………………………………………. 52
Figure 49: The Rheometer……………………………………………………………….. 52
Figure 50: pH values……………………………………………………………………... 53
Figure 51: FOS/TAC ratio……………………………………………………………….. 53
Figure 52: FOS and TAC in comparison………………………………………………… 54
Figure 53: Volumetric gas production…………………………………………………… 54
Figure 54: Volumetric Methane quantity………………………………………………… 55
Figure 55: HRT vs. DM…………………………………………………………………. 55
Figure 56: Sand in chicken manure substrate……………………………………………. 56
Figure 57: Gas production per kg ODM…………………………………………………. 57
Figure 58: Olive pomace barrels…………………………………………………………. 58
Figure 59: Olive pomace………………………………………………………………… 58
Figure 60: pH values…………………………………………………………………….. 60
Figure 61: FOS/TAC ratio………………………………………………………..……… 61
Figure 62: FOS and TAC in comparison………………………………………………… 61
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Figure 63: Volumetric gas production…………………………………………………… 62
Figure 64: Volumetric Methane quantity………………………………………………… 62
Figure 65: Gas production per kg ODM………………………………………………… 63
Figure 66: Wine pomace barrels…………………………………………………………. 64
Figure 67: Wine pomace………………………………………………………………… 64
Figure 68: pH values…………………………………………………………………….. 66
Figure 69: FOS/TAC ratio……………………………………………………………….. 67
Figure 70: FOS and TAC in comparison………………………………………………… 67
Figure 71: Volumetric gas production…………………………………………………... 68
Figure 72: Volumetric Methane quantity……………………………………………….. 68
Figure 73: Gas production per kg ODM………………………………………………… 69
List of Equations
Equation 1: Loading rate ..................................................................................................... 22
Equation 2: Hydraulic retention time .................................................................................. 23
Equation 3: Methane productivity ....................................................................................... 24
Equation 4: Methane recovery ............................................................................................. 25
Equation 5: Degradation efficiency ..................................................................................... 25
Equation 6: Ideal Gas Law .................................................................................................. 42
List of Tables
Table 1: Permissible concentration for different trace materials ......................................... 19
Table 2: Inhibitors and their harmful concentrations .......................................................... 22
Table 3: Specific Biogas and Methane contents in corresponding groups of materials ...... 26
Table 4: Average compositions in Biogas ........................................................................... 27
Table 5: DM and ODM values for Chicken Manure ........................................................... 31
Table 6: Agrolab analysis results......................................................................................... 39
Table 7: DM and ODM values for Olive Pomace ............................................................... 59
Table 8: DM and ODM values for Wine Pomace ............................................................... 65
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Nomenclature (Latin Symbols)
Symbol Unit Description
.
V / max
.
V - Charge
.
V h
m3
volume flow
Pab kW power output
Pzu kW power consumption
p mbar Pressure
n min
1 rotation speed
M Nm Torque
.
m s
kg mass flow
Nl litre Norm litre
J mechanical work
s
m relative inlet velocity of the water jet
s
m relative outlet velocity of the water jet
s
m absolute velocity of the jet flow
s
m absolute inlet velocity of the jet flow
s
m absolute outlet velocity of the jet flow
U s
m circumferential speed
T °C Temperature
m kg mass
g 2s
m gravitational acceleration
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Nomenclature (Greek Symbols)
Symbol Unit Description
α ° angle of the relative outlet velocity vector with the
horizontal datum
η - degree of efficiency
ρ 3m
kg density
ω s
1 angular frequency
List of Abbreviations
Abbreviation Description
Fig. Figure
FOS Flüchtige Organische Säuren
TAC Total Alkalinity
HRT Hydraulic Retention Time
TS Trockensubstanz
oTS Organische Trockensubstanz
DM Dry Material
ODM Organic Dry Material
PLC Programmable Logic Control
TFT Thin Film Transistor
R.H.S. Right Hand Side
L.H.S. Left Hand Side
C.P. Centrifugal Pump
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1 Introduction
Historically, the Bio wastes were considered as an agricultural resource due to its
beneficial effects to the soil. Particularly, the chicken manure was used as a natural
fertilizer for cropping soils while both olive and wine pomace were disposed by either
inhumation or incineration. After the considerable growth in production of Bio wastes
due to the huge dimension of the modern and intensive farmhouses and the great
daily productions in both wine and olive oil industries, odour problems and
contamination of the underground water and soil and other negative consequences in
different environmental sectors have been spotted as a point of interest for many
scientists (Burton et al., 2003). Industrialization has set the start for a new technology
named Biogas. Biogas production was not of a great importance till the problem of oil
and coal resources’ depletion has arisen. Although the Biogas production using an-
aerobic digestion could be a new and reliable source of Energy, firm regulations and
legislations have been set to control the bio by-products and bio sludge that are pro-
duced in the end phase of this technology.
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2 Basics
2.1 History of Anaerobic Digestion
It has been reported that the Chinese were the first to extract and use the Biogas
from the fermentation process. Information about the first Biogas installations in
China refers back to yearly 16th century BC. However, it was first reported in the 17th
century by both Robert Boyle and Stephen Hale who have noticed that a flammable
gas would be released by disturbing the sediment of the streams and lakes1. In 1808,
Sir Humphry Davy has realised that the Methane was present in the cow manure23. It
has also been thought that the ancient Egyptians were the first to use the solidified
cow manure for flaming up their ovens.
4
Figure 1: Biogas in ancient China
1 Fergusen, T. & Mah, R. (2006) Methanogenic bacteria in Anaerobic digestion of biomass, p49, 29 May, 2012
2 Anaerobic digestion, waste.nl. Retrieved 19.08.07.
3 Cruazon, B. (2007) History of anaerobic digestion, web.pdx.edu. Retrieved 17.08.07.
4 http://www.onetoremember.co.uk/xcart/images/P/chinese-biogas-plant.gif, 29 May, 2012
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2.2 What is Anaerobic Fermentation?
As the upper headline states, the Anaerobic digestion is the biological process
where the decomposition of the organic wastes or products will take place in the
absence of oxygen. In the contrary with the aerobic digestion which is done under
“aerated” conditions, the anaerobic fermentation are usually done in oxygen-free,
sealed and heated environments. In both types, different kinds of decomposing
bacteria tends to break down fats, protiens and carbohydrates into simpler
constituent materials.
5
Figure 2: Decomposition in absence of Oxygen
5 http://www.skyrenewableenergy.com/wp-content/uploads/2009/05/digester.jpg, 11 June, 2012
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2.3 Formation of Gas Mixture
Since the anaerobic digestion is originally an exothermal biological reaction, it
produces heat in addition with Biomass (substrate or base material) and Biogas. The
Biogas produced consists of Methane 50-75 Vol.-percent, Carbon dioxide 25-50 Vol.-
percent, gases like (Hydrogen, Hydrogen Sulphide and Ammonia) and other trace
gases. Generally, the composition of the gas mixture will depend on the fed base
material, the processing of the fermentation and other technical parameters. Since
the development of the Biogas can be divided into several sub-steps, these steps
should be processed in an optimal sequence and without any interruptions.
The first step is called, the ‚Hydrolysis’, when all the complex compounds of the
feedstock (e.g. Carbohydrates, Proteins and Fats) are biochemically decomposed in
to simple organic compounds (e.g. Amino acids, Sugar and Fatty acids) by the effect
of an enzyme released by the bacteria.
The resulting intermediate products will then be degraded in a second step by the
fermentation (acid-forming) bacteria in the so called ‚acidification phase’
(acidogenesis) into lower fatty acids (Acetic, propionic and butyric acids) as well as
carbon dioxide and hydrogen.
6
Figure 3: Formation of Biogas and trace gases
6 http://water.me.vccs.edu/courses/ENV149/lesson4.htm, 11 June, 2012
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In addition to that, a small amount of lactic acids and alcohols will be formed. The
nature of the formed products in this stage is influenced by the concentration of the
intermediately formed hydrogen.
The third step is called the ‚Acetogenesis’. In this ‘Acetic acid formation’ process,
these products (acetic acid, hydrogen and carbon dioxide) will; subsequently, be im-
plemented by the acetogenic bacteria as Biogas precursors.
In this context, the hydrogen partial pressure plays an important role. As the hy-
drogen content rises in the biological process, it will obstruct the implementation of
the Acetogenesis process’s intermediates. As a result, the concentration of the or-
ganic acids (propionic, iso-butyric, iso-valeric and caproic acids) will rise and hence
will reduce the methane production.
In the subsequent ,Methanogenesis’ process; the last step of the Biogas for-
mation, all the acetic acids as well as the Hydrogen and carbon dioxide will be con-
verted from the strict anaerobic methanogens to methane.
Figure 4: Fermentation Process
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2.4 Ambient Conditions
Since the anaerobic fermentation is basically a biological reaction, maintaining
reliable and convenient conditions for this reaction is indispensable. Speaking about
the environmental conditions, parameters like the Temperature, amounts of Oxygen,
PH value, Nutrients and Inhibitors are worth to be mentioned.
2.4.1 Oxygen
The methanogenic archaea are among the oldest living beings on earth which
were created about three to four billion years ago, long before the atmosphere has
been formed the way we know nowadays. For this reason, these microorganisms are
still surviving in savage living environments where oxygen does not exist. Most
methanogenic species are killed with even small amount of oxygen. In general, the
oxygen entry inside the fermenters cannot be avoided completely.
The reason that methanogenic archaea are not immediately inhibited in their
activity or even die entirely lies in the fact that they live together with oxygen-
consuming bacteria from the previous reduction steps.
Some of them are called facultative anaerobic bacteria. These bacteria can
equally survive in the presence of oxygen and in its absence. As long as the oxygen
is not too large, they use up the oxygen before it damages the methanogenic
archaea, which depend on an oxygen-free environment.
Also for the biological desulphurization which is done in the gas space of the
fermenter and with the assistance of small amounts of atmospheric oxygen, the
methane production will not be harmfully affected by these amounts of oxygen.
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2.4.2 Temperature
In principle, the higher the ambient temperature, the faster the chemical reaction.
But this cannot be constantly applied to biological degradation and transformation
processes where optimum operating temperatures should be maintained for the
microorganisms. Therefore, the microorganisms involved in the wastes degradation
process can be divided according to their optimal operating temperature into 3
groups.
2.4.2.1 Psychrophilic Temperature Range
The psychrophilic microorganisms have their optimum degree at temperatures
below 25 °C. At such temperatures, there is no need to heat up the substrate or the
fermenter because the performance of the degradation process as well as the gas
production will be, however, low.
2.4.2.2 Mesophilic Temperature Range
Most of the known methanogens has its growth optimum degree in the mesophilic
temperature range 37-42 °C. Biogas plants operating in the mesophilic range are; in
practice, the most widely used. It has been observed that in this temperature range,
relatively high gas yields can be achieved as well as good process stability.
7
7 http://aretusa.ice.it/SchemaSite/images/UserImageDir/177/EN/Presentations/Biogas.pdf, 25 July, 2012
Figure 5: Mesophilic bacteria
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2.4.2.3 Thermophilic Temperature Range
In order to facilitate faster reaction rates and; hence faster gas yields, a
Thermophilic temperature range is maintained at 50-60 °C. Although Thermophilic
digestion systems are considered to be less stable with higher energy input, they
facilitate greater sterilization for the digestate. In contrary to the Thermophilic
species, the Mesophilic species are more tolerant to changes in the environmental
conditions and more stable.
8
Practice has shown in this context, that the distinctions are blurred between the
temperature ranges. Primarily, a rapid change in temperature may lead to a damage
for the microorganisms, whereas the methanogenic microorganisms can adapt to
slower temperature changes at different temperature levels.
8 http://aretusa.ice.it/SchemaSite/images/UserImageDir/177/EN/Presentations/Biogas.pdf, 25 July, 2012
Figure 6: Thermophilic bacteria
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2.4.3 pH Value
Similar to the temperature range, the pH value will have the same coherence with
the execution and optimization of the biological process. The microorganisms require
different pH values with which they could increase and develop. The optimum pH
value for the hydrolytic and acidogenic bacteria should lie between 5.2-6.3. The
Acetic acid-forming bacteria and the methanogenic archaea require an optimal pH
value range from 6.5-8. The pH value inside the fermenter will be automatically
changed through the alkaline and the acidic metabolites which are produced during
the anaerobic digestion. At the time when the fermenter is fed with too many organic
materials or the methane production; for some reason, has dropped down, so the
acidic metabolite of the acidogenesis should be increased. Normally, the pH values
are manually adjusted when it arises by using either carbonate or ammonia buffer
solutions.
2.4.4 Nutrients and Trace Elements Supply
The microorganisms of the anaerobic digestion have a typal demand of macro and
micro-nutrients as well as vitamins. The concentration and the availability of these
components influence both activity and growth rate of the assorted populations. For a
stable processing, the ratio between the macro and micro-nutrients should be
balanced.
Right after the carbon, nitrogen is the most needed nutrient. Nitrogen will be used
for the production of the enzymes which will be used later for the production of the
metabolites. The C/N-ratio also plays a vital role in the methane production. When
the C/N-ratio increases (more carbon and less nitrogen), the present carbon amount
cannot be fully implemented by the lack of the metabolism and hence the maximum
gas yield is not achieved. For a stable process flow, the C/N-ratio should be main-
tained in the range of 10-30. Another nutrients (phosphorus and sulphur) should be
taken into consideration so that, the C:N:P:S ratio should be kept within the range of
600:15:5:3 for stable reactions.
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Besides the nutrients supply, there are some trace elements which are essential
for the microorganisms to stay alive and productive.
a. Absolute minimum concentration by the Biogas system
b. Recommended optimal concentration
2.4.5 Inhibitors
Inhibitors are meant to be those materials which can stop or even reduce the
progression of the gas yield production. Inhibition and reduction of the gas production
could be caused by different reasons. It could be either of a technical or Biological
reason. By feeding the fermenter, it should be considered that the overfeeding
amounts of the substrate could have an inhibiting effect on the biological process
since the concentration of the different elements within the substrate will rise
harmfully to stop the reaction. This includes substances such as antibiotics,
disinfectants, solvents, herbicides, heavy metals or salts that can inhibit; even in
small amounts, the degradation process (see Table 2). The existence of antibiotics is
due to the feeding of manure or fats that are excreted by animals being given
antibiotics, however the inhibitory effect of certain antibiotics varies widely. Not only
antibiotics in high concentrations could be harmful but also some essential trace
elements in slight higher concentrations could be toxic for the microorganisms.
Inhibitors could also result from the interaction of different substances within the
substrate. Heavy metals; for example, can act as an inhibitor when they are
dissolved rising up the potential of forming hydrogen sulphide as a paired, undesired
but acceptable gas within the produced methane.
9 http://www.fnr-server.de/ftp/pdf/literatur/pdf_208-leitfaden_biogas_2010_neu.pdf, p. 25, 15 August, 2012
Trace ele-ments
Concentration range [mg/l]
For [2-18] For [2-19] For [2-16]a For [2-17]b
Co 0.003-0.06 0.003-10 0.06 0.12
Ni 0.005-0.5 0.005-15 0.006 0.015
Se 0.08 0.08-0.2 0.008 0.018
Mo 0.005-0.05 0.005-0.2 0.05 0.15
Mn N/A 0.005-50 0.005-50 N/A
Fe 1-10 0.1-10 1-10 N/A9
Table 1: Permissible concentration for different trace materials
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This is not applied for the copper compounds, which due to their antibacterial
effect even at very low concentrations (40-50 mg/L) are very toxic.
During the fermentation process, a series of materials will be produced which can
inhibit the methane production. Along within this context, the high adaptation
capability of the bacteria should be observed since it is not allowed to exceed the
concentration limits of these materials.
Especially, the free Ammonia (NH3) will act harmfully; even in small amounts,
against the bacteria. High temperatures as well as pH values will affect directly on
the tolerated amounts of the free Ammonia within the substrate since the amount of
the free Ammonia will increase by the increase of temperature and pH value. For ex-
ample, an increase for the pH value from 6.5 to 8 will lead to an increase in the con-
centration of free Ammonia by 30 times. Also by higher temperatures, the concentra-
tion of free Ammonia should not exceed the safe limits. For a stable Ammonia con-
centration, the NH3 should stay within the range of 80-250 mg/l. With higher Ammo-
nia contents, adding distilled water inside the fermenter would reduce the ammonia
concentration but increases the fermenter’s volume and decreases the HRT as well
as the gas yield.
Depending on the pH value and the temperature, this corresponds to an Ammonia
concentration of 1.7-4 g/l. Practical experience has limited an overall concentration of
Ammonium nitrogen (NH3-N) by 3000-3500 mg/l with an expected nitrogen inhibition
effect for the Biogas process.
Another product of the fermentation process is the hydrogen sulfide (H2S), which
acts in the undissolved or undissociated form as a cytotoxic inhibitor and in a concen-
tration of about 50 mg/l can stop the degradation process. With decreasing pH val-
ues, increases the proportion of H2S, and hence increases the risk of inhibition. It
could also condense in the flue gas system of the CHP stations and form sulphuric
acid (H2SO4) which causes corrosion and also reduces the service life of the engine’s
lube oil.
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2.4.6 FOS (Volatile Organic Acids)
The volatile organic acids are simply the sum of all acids present in the acetic ac-
ids without distinction of possible different types. This value should be maintained
lower than 10000.
2.4.7 TAC (Total Alkalinity)
The Total Alkalinity measures the ability of a solution to neutralize acids to the
equivalence point of carbonate or bicarbonate. TAC value or buffer includes all buffer
substances, as if they were all carbonates. This value should be maintained over
10000.
2.4.8 FOS/TAC Ratio
FOS / TAC ratio is an indicator for rapid assessment of the fermenter’s condition.
This value should be maintained in the range from 0.2-0.6.
2.5 Operating Parameters
2.5.1 Loading Rate and Hydraulic Retention Time of the Fermenter
By building the Biogas systems, the economic considerations would stand in the
foreground. Thus, in the choice of the fermenter size, the maximum gas yield as well
as the potential of the complete degradation of the organic material in the substrate
might not necessarily be taken into consideration.
If a complete degradation of the organic material is required to be achieved, some-
times very long hydraulic retention periods should be maintained and hence, a rela-
tively larger container volumes will be used cause some ingredients within the sub-
strate will require longer times to be degraded. Another way to achieve this is to build
up a large number but with smaller size containers in order to decrease the hydraulic
retention time of the substrate but this will be an expensive alternative.
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In this regard, the loading rate is an important operating parameter. It indicates
how many kilograms of organic dry material per m3 working volume can be supplied
per unit time.
10
Equation 1: Loading rate
Inhibitor Inhibitory con-
centration
Notes
O2 >0.1 mg/l Inhibition of the obligate anaerobic
methanogenic archaea.
H2S >50 mg/l H2S Inhibition effect increases with decreased pH-
value.
Volatile fatty
acids
>2.000 mg/l HAc
(pH=7.0)
Inhibition effect increases with lowered pH-
value. High adaptation activity for bacteria.
NH4-N >3.500 mg/l NH4+
(pH=7.0)
Inhibition effect increases with the increase of
the pH-value and temperature. High adapta-
tion ability of bacteria.
Heavy metals Cu > 50 mg/l
Zn > 150 mg/l
Cr > 100 mg/l
Only dissolved metals act as inhibitors.
Detoxication by sulfide precipitation.
Disinfectants
antibiotics
N/A Inhibition effect is product-specific. 11
Table 2: Inhibitors and their harmful concentrations
10 http://www.fnr-server.de/ftp/pdf/literatur/pdf_208-leitfaden_biogas_2010_neu.pdf, p. 27, 17 August, 2012
11 http://www.fnr-server.de/ftp/pdf/literatur/pdf_208-leitfaden_biogas_2010_neu.pdf, p. 27, 17 August, 2012
Loading rate
Substrate mass flow rate
Concentration of organic dry material
Fermenter’s volume
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The loading rate can be specified for each stage (gas-tight, insulated and heated
fermenters), for the entire system (the sum of all working volumes at all levels), with
and without inclusion of material back feeding. By changing the dimensions of the
reactor, different values for the loading rate shall be expected. For a descriptive
comparison of loading rates for different Biogas plants, it is advisable to determine
these parameters for the overall system and without consideration of material recy-
cling into the fermenter. By determining the right speed of degrading the Bio wastes,
the hydraulic retention time will be calculated successfully.
Another important parameter for dimensioning the reactor’s size is the hydraulic
retention time. It is simply the time duration when the fed substrate will remain inside
the fermenter till it is discharged. This value should be daily calculated during the op-
eration.
12
Equation 2: Hydraulic retention time
13
Assuming a uniform substrate composition, the increasing loading rate will
require more input material to be fed in to the fermenter and thus the hydrau-lic retention time will be reduced.
12 http://www.fnr-server.de/ftp/pdf/literatur/pdf_208-leitfaden_biogas_2010_neu.pdf, p. 27, 18 August, 2012
13 http://www.fnr-server.de/ftp/pdf/literatur/pdf_208-leitfaden_biogas_2010_neu.pdf, p. 27, 18 August, 2012
Fermenter’s working volume
Daily feed
0
20
40
60
80
100
120
140
160
1 1.5 2 2.5 3 3.5 4 4.5 5
Hyd
rau
lic r
ete
nti
on
tim
e [
d]
Loading rate [kg oTS/(m3 d)]
50 kg oTS/mᵌ
100 kg oTS/mᵌ
150 kg oTS/mᵌ
Figure 7: Relation between loading rate and hydraulic retention time by different ODM concentrations
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In order to obtain a proper fermentation process, the hydraulic retention time
should be calculated in such a way that through the constant exchange of the sub-
strate inside the digester, there will no longer be growing microorganisms that might
be flushed away and lost at this time. On the other hand, if the hydraulic retention
time was miscalculated to be too short, then the microorganisms will not be able to
fully produce the methane out of the substrate. In order to maintain a proper retention
time with increasing loading rate, mostly more than one fermenter is being used but
that will definitely increase the construction cost.
2.5.2 Productivity, Recovery and Degradation Efficiency
When stating the performance of a certain Biogas plant, Productivity (P(CH4)), Re-
covery (A(CH4)) and Degradation efficiency (ηoTS) are of a great importance to be men-
tioned.
Productivity is what simply describes the relation between the Biogas production
and the volume of the fermenter. It should be considered as the quotient of the daily
gas production from the fermenter which is absolutely influenced by the effectiveness
of the fermentation process. The productivity will be based on both the amount of
Biogas produced (P(Biogas)) and the methane production (P(CH4)).
14
Equation 3: Methane productivity
Since the gas production also depends on the input materials, so it also affects the
gas recovery (gas yield). The gas recovery can also depend on the Biogas (A(Biogas))
and the methane production (A(CH4)). It is defined as the quotient of the produced gas
quantity and the fed organic substance.
14 http://www.fnr-server.de/ftp/pdf/literatur/pdf_208-leitfaden_biogas_2010_neu.pdf, p. 28, 20 August, 2012
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The gas recovery simply indicates the efficiency of the Biogas as well as the me-
thane production out of a specific substrate. Being only a single parameter makes it
very low informative, since it doesn’t conceive the loading rate of the fermenter. Be-
cause of that, mentioning the gas yield should always be accompanied with the load-
ing rate.
15
Equation 4: Methane recovery
The degradation efficiency (ηoTS) refers to the efficiency of the substrate utilization.
The degradation efficiency can; by means of the organic dry substance or the chemi-
cal oxygen demand, be determined. Due to practical experience, it is advisable be-
fore carrying out the analysis to determine the ODM degradation efficiency.
16
Equation 5: Degradation efficiency
Organic dry substance content in the fresh fed materials [kg/t FM].
Organic dry substance content in the fermenter [kg/t FM].
Mass weight of the fed material [t].
Mass weight of the digestate [t].
2.5.3 Mixing
In order to achieve a maximum Biogas production, a sufficient contact should be
maintained between the bacteria and the substrate inside the fermenter which would
be achieved by an efficient mixing. In a non-mixed fermenter for some time, a sepa-
ration of contents will be observed with concomitant formation of layers indicating the
differences in density between the individual ingredients of the substrate and the
buoyancy caused by gas formation. In such case and due to the difference in densi-
ties, a layer that separates the fresh substrate from those where the bacteria are
highly concentrated will be formed reducing the amount of gas yield.
15 http://www.fnr-server.de/ftp/pdf/literatur/pdf_208-leitfaden_biogas_2010_neu.pdf, p. 28, 21 August, 2012
16 http://www.fnr-server.de/ftp/pdf/literatur/pdf_208-leitfaden_biogas_2010_neu.pdf, p. 28, 21 August, 2012
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Also by clustered substrate due to poor mixing, the formed floating solids will im-
pede the mixture from being pumped. It is also important to maintain a direct contact
between the microorganisms and the substrate, while a strong mixing could be really
harmful depending on the substrate’s viscosity.
2.5.4 Gas Formation, Potential and Methanogenic Activity
2.5.4.1 Possible Gas Yield
What is the amount of Biogas that might be produced out of a specific type of sub-
strate?. A question that will only be answered by performing pretests on the sub-
strate. Another way to know is to calculate the total gas output as long as there are
no resources to rely on.
Name Biogas content [l/kg oTS] Methane content [Vol.-%]
Digestible protein 700 71
Digestible fat 1.250 68
Digestible carbohydrate 790 5017
Table 3: Specific Biogas and Methane contents in corresponding groups of materials
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2.5.4.2 Gas Quality
Biogas is a formation of many gases which consists mainly of Methane (CH4) and
Carbon dioxide (CO2) as well as water vapor and other different trace gases. The
most important product among these products is the Methane gas. The composition
of the produced gas is totally depending on the fed material as well as the formerly
mentioned operating parameters. The concentration of the trace gases also plays an
important role in defining the gas quality, since the concentration of the Hydrogen
Sulphide (H2S) will act as an inhibitor for the Biogas production process when ex-
ceeding the permissible limits.
Component Concentration
Methane (CH4) 50-70 Vol.-%
Carbon dioxide (CO2) 25-45 Vol.-%
Water (H2O) 2-7 Vol.-% (20-40 °C)
Hydrogen Sulphide (H2S) 20-20000 ppm
Nitrogen (N2) ˂ 2 Vol.-%
Oxygen (O2) ˂ 2 Vol.-%
Hydrogen (H2) ˂ 1 Vol.-%18
Table 4: Average compositions in Biogas
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3 Experiments
Rules of the Thumb
Before approaching with the experiments, some rules of thumb shall be known.
The first rule to cohere with is to keep the FOS/TAC ratio in a range from 0.2-0.4 for
stable operation and due; the amount of the feed can be increased. In the range from
0.5-0.6, a slight correction; under circumstances, should be done in the operation of
the trial fermenter. When it exceeds 0.7, the feed should be stopped. At higher critical
values, Slaked Lime (Calcium Hydroxide Ca(OH)2) could be used to increase the to-
tal alkalinity and hence, reduce the FOS/TAC ratio. In cases when a secondary fer-
menter is used (in large scale plants), a recirculated substrate can be mixed together
with a new fresh wastes and pumped back to the primary fermenter to improve the
flowability. Another advantage is to make use of the “hungry” bacteria that are still
active and ready to work immediately with breaking down the organic matters. If a
drop down with the Methane production is noticed, so it is probably a problem with
the measuring process or the fed amounts were larger than enough. The Ammonium
level should remain in the range of 1000-3000 mg/L. In high Ammonia content mate-
rials, the level should be observed not to reach 5000 mg/L. In some cases, a me-
chanical drying mechanism could be used to reduce the NH4 content, but that would
produce offensive odors and be expensive. The ration between the propionic and the
acetic acid should be 1:3. The viscosity also is an important parameter to be consid-
ered, to be noticed that a value from 5000 mPas, the substrate won’t be steerable.
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3.1 Anaerobic Digestion of Chicken Manure
3.1.1 Introduction
The Poultry farms in many countries all over the world represent a very high percent-
age of this country’s animal wealth (in the so called Broiler Belt in the United States,
chickens have outnumbered people by as much as 400 to 1)19. With the fact that the
Poultry wastes (represented mainly in the chicken manure) are of a Toxic nature, the
laying hens will tend frequently to excrete it and in high amounts. With this very vast
amounts of chicken manure (could reach sometimes to 0.02 million cubic meter per
year for a poultry farm contains around 10 million chickens), an appropriate tech-
nique for both treatment and disposal should be embraced. As for the direct usage of
the chicken wastes with high ammonia content for fertilizing crops would lead to both
soil and ground water contamination, a solution has been proposed to use mechani-
cal dryers in order to reduce the ammonia content, but due to its high initial costs and
production of offensive odors makes it a controversial solution and sometimes inapt.
The AD in its current consolidation between waste treatment and Biogas production
will have a Surpass to dissolve both disposal and treatment problems accompanied
with the production of chicken manure.
19 http://www.pewenvironment.org/uploadedFiles/PEG/Publications/Report/PEG_BigChicken_July2011.pdf, 29 May, 2012
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3.1.2 Acquisition and Properties of Chicken Manure
The fresh and dry chicken manure has been obtained from a neighboring Biogas
plant that belongs to Ernst Schnakenberg which lies in Tarmstedt (a municipality in
the district of Rotenburg in lower Saxony). The manure has been shoveled and
stored in big blue plastic barrels so that to be used later for the manual feeding oper-
ations (see figs. 8, 9&10).
Figure 9: Dry Chicken Manure 1
Figure 10: Dry Chicken Manure 2
Figure 8: Dry Chicken Manure Barrels
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Both the dry substance and organic dry substance contents in the manure were
measured gradually (once per week) to concern the effect of the ambient conditions
(hot, cold, humid and rainy days) as well as the influence of storing method (some
barrels were kept in shadow and some in sun).
TS = 60.7 % Analyzed on: Applied till: oTS = 43.9 % 31/07/2012 06/08/2012
TS = 58.5 % Analyzed on: Applied till: oTS = 42.4 % 06/08/2012 13/08/2012
TS = 53.8 % Analyzed on: Applied till:
oTS = 45.5 % 13/08/2012 20/08/2012 TS = 59.1 % Analyzed on: Applied till: oTS = 45.4 % 21/08/2012 28/08/2012 TS = 57.5 % Analyzed on: Applied till: oTS = 48.8 % 03/09/2012 10/09/2012 TS = 62.2 % Analyzed on: Applied till: oTS = 39.5 % 10/09/2012 17/09/2012 TS = 55.7 % Analyzed on: Applied till: oTS = 41.9 % 17/09/2012 25/09/2012
TS = 58.5 % Analyzed on: Applied till: oTS = 47.3 % 26/04/2012 07/05/2012
TS = 61.0 % Analyzed on: Applied till: oTS = 42.6 % 13/06/2012 TS = 55.7 % Analyzed on: Applied till: oTS = 42.6 % 20/06/2012 TS = 58.7 % Analyzed on: Applied till: oTS = 40.0 % 13/07/2012 TS = 56.1 % Analyzed on: Applied till:
oTS = 43.9 % 17/07/2012 23/07/2012 TS = 59.4 % Analyzed on: Applied till: oTS = 41.9 % 23/07/2012 30/07/2012
Table 5: DM and ODM values for Chicken Manure
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The test of the dry substance and organic dry substance would usually last for 3
days (the dry substance test lasts for 48 hrs. and the organic dry substance test lasts
for about 6 hrs.) and that to be done once per week.
3.1.3 The Experiment
3.1.3.1 Building up the trial Fermenter
This experiment has taken place on the 1st of May, 2012 in the R&D Biogas plant
of MT-Energie in Rockstedt, Kyffhäuserkreis, Thüringen under the supervision of
Prof. Dr.-Ing. Joachim Jochum as my university’s supervisor and Mr. Jan Ludeloff as
my company’s supervisor. A 750-liter stainless steel container has been modified to
simulate the large fermenters used by MT-Energie Biogas power plants (see fig. 11).
Figure 11: Prototyping the actual Biogas fermenter
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Figure 14: Main components of the trial fermenter
A stainless steel hot water hoses have been rotated on the inner round surface of
the container and along with its circumference to assure an equally distributed heat
to the substrate (see fig. 12). The heating system has used hot tap water as a work-
ing fluid and a house-used ordinary thermostatic valve for temperature control (see
fig. 13), whilst the temperature inside the fermenter was observed using an analogue
temperature gauge (see fig. 14). Also to retain the heat, a sheet of glass wool insula-
tor has been wrapped around the fermenter. The trial fermenter has been fitted with
three big ball valves at different levels for either filling up or emptying out the fer-
menter.
Figure 12: Inside the trial fermenter Figure 13: Temperature control valve
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At the top of the fermenter we could notice the existence of a 3.0 kW Electric Mo-
tor (69Nm, 500/min) with a gear box which is coupled with an impeller protracted
deep down inside the fermenter to maintain an appropriate mixing for the substrate
for optimal gas production (see fig. 15&16). The Motor is riveted with a welded steel
support which is eventually fixed to the fermenter’s body using screw bolts.
The power control for the Mixer is done by a small 7-Input PLC unit which enables
us to either manually or automatically switch ON/OFF the fermenter. Also the Module
has been programmed to automatically switch ON/OFF the Mixer at different time
intervals through the whole day (see fig. 17&18).
Figure 15: Upper components on the fermenter Figure 16: Impeller coupled with the Motor
Figure 17: The module's control panel Figure 18: TFT screen interface
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From the other components on the upper side of the fermenter, there are two
Gaslines. The first Gasline (on the R.H.S) is branched into two paralleled sections;
the first section is connected with two black Gas Sacs which act as pressure indica-
tors when inflated or deflated (see fig. 15), while the other branch is connected with a
sludge filter (with a fine-meshed net) preceded with two ball valves, the first is used
as a Gas outlet port for gauging both pressure inside the fermenter and the Gas
Quality, whilst the other is used as a control valve (see fig. 19).
After the water condensate out of the produced gas due to the temperature differ-
ence between inside and outside the fermenter is being trapped in the sludge filter,
the dry gas is then routed through the syphon gas pipes directly to the gas counter to
measure the daily gas production in cubic meters (see fig. 20&21).
Figure 19: 1st Gasline auxiliaries
Figure 20: Input and output syphon to the gas counter Figure 21: Gas counter box
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Complementary to the sludge filter for trapping the condensate, the syphon has a
further line extension with a small attached condensate tab for wasting out the water.
The output syphon line from the gas counter is also branched into two sections, the
first line extension is for draining out the condensate (if there is any left) and the other
is connected to a pressure retaining siphon shown in fig. 22.
The concept of the pressure retaining Syphon is simply dependable on the length
of the water column inside the internal capillary tube where the pressurized gas has
to overcome the water to escape to the atmospheric pressure. Therefore, the pres-
sure inside the fermenter is easily controlled by the amount of water poured inside
the Syphon. Generally, the pressure inside the fermenter should be regulated in ac-
cordance with the maximum allowable Hydrogen partial pressure for a stable gas
production (see section 2.3, Formation of Gas Mixture, p. 13). However the pressure
inside the fermenter (whether in Big or Trial versions) could sometimes not be of a
significant importance (it always oscillates between 3-4.5 mbar), but it could be used
to create some points of pressure difference within the route where the Biogas
should be directed; in our case, the gas should build enough pressure to function the
gas counter.
Figure 22: Pressure retaining Syphon
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The second Gasline (on the L.H.S.) is directly attached to an over pressure/under
pressure safety device (see fig. 23). This device is quite similar to the pressure re-
taining Syphon (both for working concept and design). It is simply constructed from a
small capillary tube inside a bigger surge chamber filled with water (the water column
here is much higher than in the pressure retaining Syphon) which acts like a relief
valve for over pressurized gas. The excessively pressurized gas will simply be re-
lieved to the atmosphere. This device should have the ability to compensate for neg-
ative pressure situations but that would be done manually by adding more water
through the water inlet port shown in fig. 23.
Figure 23: Surge chamber
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3.1.3.2 Putting the fermenter into operation
In order to specify the optimal HRT value for the chicken manure (one of the main
purposes of this experiment), the working volume of the fermenter has been fixed on
600 liters (with a maximum permissibility to reach up to 700 liters) leaving 150 liters
from the total fermenter volume for the gas accumulation. Around 600 liters of maize
silage out of the bigger fermenters have been pulled out and pumped inside the trial
fermenter as an inoculum (see fig. 24, 25&26).
Figure 24: Creating head difference Figure 25: Pumping the maize silage
Figure 26: The silage being pumped into the fermenter
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The inoculum has been then tested in the main laboratories in Zeven using the
Agrolab Analysis giving the following results:
Parameter
Unit Value i.d. OS Value i.d. DS
Dry substance % 59.1
Water content % 40.9
Total Nitrogen content % 1.5 2.5
Ammonium (NH4-N) % 0.48 0.81
Total Phosphate (P2O5) % 1.2 2.1
Total Potassium (K2O) % 1.0 1.7
Total Magnesium (MgO) % 0.59 1.0
Calcium (CaO) % 4.13 6.98
Sulphur (S) % 0.19 0.32
Molybdenum (Mo) mg/kg 1.20 2.03
Selenium (Se) mg/kg 0.288 0.487
Total Iron (Fe) mg/kg 1590 2690
Cupper (Cu) mg/kg 35.2 59.6
Manganese (Mn) mg/kg 178.8 302.6
Zink (Zn) mg/kg 155.6 263.2
Cobalt (Co) mg/kg 1.01 1.71
Nickel (Ni) mg/kg 1.94 3.28
Table 6: Agrolab analysis results
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The agitator has been then programmed to work in intermittent time intervals
through the day. The inoculum has been left for around a week (30.04-06.05) without
feeding to see how stable the gas production was. Before starting the feed of the
chicken manure and after enough amount of gas being generated, a gas leak test
has been done to the fermenter (see fig, 27&28).
Also all the threaded pipe connections have been tested for leakage using a gas
leak testing solution and after the leakages have been repaired the tests have been
done one more time for confirmation of repair.
Figure 27: The fermenter’s upper part immersed with water Figure 28: A gas leak found from the fermenter's hatch
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3.1.3.3 Feeding and measuring
Referring to the law of the loading rate (see section 2.5.1, loading rate and hydrau-
lic retention time of the fermenter, p. 21) and with both the fermenter’s working vol-
ume (constant) and the concentration of the organic dry substance being measured
once per week, a feeding plan is generated at the beginning of each week for the
fermenter with the BR being defined with correspondence to the amount of kilograms
chicken manure fed per day.
The feed has started with BR = 1.5 from 07.05 to 13.05 and due to the significant
rise in the FOS/TAC ratio (from 0.27 to 0.53), the BR has been reduced to 0.1 from
14.05 to 20.05 which led to a decrease in the FOS/TAC ratio from 0.53 to 0.43 leav-
ing it in a relative stable range. On the 21st calendar week, the BR has been decided
to be 1 and that to be carefully increased in accordance with the increase in the
FOS/TAC ratio and the fluctuations with other biological parameters.
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From 21st of May till 30th of September 2012, the following activities have been
done daily to the trial fermenters as follows:
Temperature measurement (°C)
The temperature reading is written down out of the analogue temperature sensor
which has significance on the type of fermentation (always kept at 40 °C for
Mesophilic digestion) as well as its importance to measure the standard values of
daily gas productions at standard atmospheric pressure and temperature accord-
ing to the combined ideal gas law.
Equation 6: Ideal Gas Law
For even more precise temperature values and since the temperature sensor
mounted inside the fermenter is leveled too low to measure the gas temperature in-
side the gas accumulation room (which is the temperature required), a hole in the
outlet gas line out of the gas counter has been made and the gas temperature has
been measured using an analogue temperature gauge with probe (see fig. 29&30).
Figure 29: The hole for Temperature sensing Figure 30: Temperature Probe
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It has been constantly noticed that the temperature of the produced gas is always
4 degrees lower than the temperature of the substrate inside the fermenter.
Gas meter reading (m3)
The reading out of the Gas meter has been noted down every day to calculate the
daily gas production and compare it with the frequent changes in the biological
parameters. These daily values are then corrected to the standard values for the
standard pressure and temperature.
Internal pressure (mbar)
The internal pressure has also been measured through the Gas outlet port (see
fig. 15) using a digital pressure gauge (see fig. 31).
The pressure values have been used later for calculating the standard daily gas
production values at standard pressure and temperature. Also, the pressure values
have been an indicator for a stable technical operations as well as biological pro-
cessing.
Figure 31: Wöhler digital pressure gauge
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Digester Gas space (cm)
The distance between the top of the fermenter (represented at the surface of the
sight glass in the fermenter’s hatch) and the surface level of the substrate inside
the fermenter, has given the significance of the digester gas space as well as the
operating volume of the fermenter which was always kept constant at 600 liters
(around 26 cm). The lower the reading is, the more occupied volume in the fer-
menter. The distance has been measured using a laser distance meter shown in
fig. 32.
Some problems have been accompanied with measuring the distance using the
device mentioned above like the accumulation of foam sometimes on the surface of
the substrate as well as the existence of buoyant particles which could give false
measured values. It could be simply solved by switching on the agitator continuously
for a period of time till the foam disappears or to use an antifoam solution (silicone
based defoamers) with calibrated amount at the cases of severe foam accumulation.
Figure 32: Laser distance meter
Figure 33: Silicone based defoamer
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The liaison between the fermenter’s occupied volume and the distance meas-
ured using the laser distance meter has been plotted as follows:
Figure 34: Fermenter's operating volume vs. distance
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At the cases when the volume of the substrate inside the fermenter increases or
when it is necessary to add water to the fermenter (in the case when the DM con-
tent arises), more substrate should be taken out of the fermenter before feeding to
keep the level at equilibrium. In order to determine the exact volume of the sub-
strate taken out, the quantity is first scaled by kg and the density is measured us-
ing density meter (see fig. 35).
Figure 35: Density meter
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Gas quality measurement
Since the Methane (CH4), Carbon dioxide (CO2), Oxygen (O2) and Hydrogen Sul-
phide (H2S) are the main constituent gases in the produced gas (see table 4, Av-
erage Compositions in Biogas, P. 26), they have been daily measured through the
outlet gas port using the gas quality measuring device called “Dräger”.
Figure 36: Dräger device Figure 37: Gas quality measurement
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Feeding the fermenters
After calculating the appropriate value of loading rate and the correspondent
amount of chicken manure in kg, the amount is scaled and fed manually in to the
fermenter through the fermenter’s feeding hole (see fig. 38).
The amount of chicken manure is shoveled out of the barrels and scaled using the
scale (see fig. 39) and then mixed with around 10 liters of substrate out of the fer-
menter using the manual agitator (see fig. 40) and then fed back in. This process
would be done usually in stages and in more than one time.
Figure 38: Fermenter's feeding hole
Figure 39: Scale Figure 40: Manual agitator
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Figure 41: pH meter
Figure 42: Titrator
Sometimes when the mixture seems to be dense and heavy, and after the feeding
is done, more 10 liters out of the fermenter would be taken and poured back in just to
sweep down the mixture into the fermenter.
Measuring the pH and FOS/TAC ratio
For the periodic measurement of pH and FOS/TAC ratio, a daily fresh sample is
taken out of the fermenter and measured using pH meter (see fig. 41) and biologi-
cal titration device (see fig. 42).
Figure 43: Sample preparation
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Measuring the DM and ODM
Both DM and ODM for the substrate and the fed chicken manure are measured
gradually for the process control. Normally for such a test, a daily (could also be
weekly) samples are taken to the lab in Zeven. The samples taken are weighted
in the lab and then dried using the oven (see fig. 44) under an approximate tem-
perature of 100 °C and weighted after drying to calculate the moisture. After dry-
ing, all we have is a dry material with a ratio of organic material. The sample is
then roasted under higher temperatures (around 330 °C) using a muffle furnace
(see fig. 45) for about 48 Hours long and then weighted to determine the dry and
burnt leftovers (ash) with which the Organic Dry Material could be calculated.
Figure 44: Drying Oven Figure 45: Muffle Furnace
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Measuring the Ammonia content
The amount of nitrogen inside either the substrate (in the form of Ammonium Hy-
droxide NH4OH) or in the produced gas (in the form of free Ammonia NH3) is
measured gradually due to its inhibitory effect. The Ammonia in the substrate is
measured as the total Nitrogen content (N, mg/L) using the device shown in fig.
46. The free Ammonia in the produced gas is measured manually using the
Dräger vials shown in fig. 47.
Figure 46: Nitrogen titration device Figure 47: Dräger Ammonia vial
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Measuring the lower fatty acids (Acetic, propionic and butyric acids)
As the increase of the lower fatty acids could be of an inhibitory effect, they have
been scaled once per week using the device shown in fig. 48.
Measuring the substrate viscosity
Viscosity is a property that is significant to how easy and efficient the mixing of the
substrate inside the fermenter will be. The Rheometer (see fig. 49) is used for meas-
uring the dynamic viscosity.
Figure 48: Liquid chromatography
Figure 49: The Rheometer
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3.1.3.4 Observations (results)
pH value
FOS/TAC ratio
7.4
7.5
7.6
7.7
7.8
7.9
8
8.1
8.2
8.3
pH
-val
ue
Date
pH-value
pH
0
0.1
0.2
0.3
0.4
0.5
0.6
FOS/
TAC
Date
FOS/TAC-ratio
FOS/TAC
Figure 50: pH values
Figure 51: FOS/TAC ratio
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FOS and TAC in comparison
Gas production
0
5000
10000
15000
20000
25000
30000
35000
FOS,
TA
C in
mg/
l
Date
FOS and TAC in comparison
FOS TAC
Figure 52: FOS and TAC in comparison
Figure 53: Volumetric gas production
000
000
000
000
000
001
001
001
001
001
Date
Gas production Nm³/d
Gasertrag Nm³/d
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Methane quantity
HRT vs. DM
Figure 55: HRT vs. DM
HRT vs. DM
DM (%)
HRT (d)
0
10
20
30
40
50
60
70
CH
4 in
%
Date
Methane quantity
CH4
Figure 54: Volumetric Methane quantity
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3.1.3.5 Conclusion
After monitoring all the vital parameters throughout the experiment, it has been
observed that the DM content inside the digester along with the high viscosity was
the main challenge (see fig. 56). According to the periodical DM tests performed on
the substrate, it has been observed that the manure is mixed with high ratio of fine
sand grains. Due to the fact that when designing a new Biogas plant, the optimal
HRT for the specific type of digestate to be fully digested and the exact amount of
added water to make it steerable are already known as well as the available amounts
of organic material fed per day, the correct fermenter’s volume can be easily calcu-
lated. While in this experiment, the fermenter’s volume has been set to be constant
and that the amounts of fed manure will change accordingly with the contained
amounts of ODM and loading rate. Therefore, the HRT should be calculated satisfy-
ing the amounts of added water (to overcome the DM problem) along with stable Me-
thane production.
As the hydraulic retention time was actually decreasing with the increase of the
DM content inside the fermenter and since the gas production was decreasing re-
spectively, so the fermenter’s volume should be whether increased or a secondary
fermenter is to be added for an appropriate and stable Methane production. Another
solution is to treat the manure before feeding by involving some separation technolo-
gy for the contained sand.
Figure 56: Sand in chicken manure substrate
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The FOS/TAC ratio has shown an average value of 0.36 and the ammonia content
of about 4800 mg/L which according to the rules of the thumb should be acceptable.
Considering the amount of DM % and ODM % inside the chicken manure as well
as its price and the Methane content inside the total gas production in Nm3/t and the
total gas production per kg ODM (around 500 Nl/kg ODM), the Chicken manure
should be considered as commercially feasible (see fig. 57).
0
1000
2000
3000
4000
5000
6000
18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 2 4 6 8 10 12 14 16
Gas
pro
du
ctio
n in
Nl/
kg O
DM
Calender week
Gas production Nl/kg ODM
Gasertrag Nl/kg oTS
Figure 57: Gas production per kg ODM
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3.2 Anaerobic Digestion of Olive Pomace
3.2.1 Introduction
Olive trees have been a traditional crop in so many countries in the Mediterranean
over long ages. The production of the Olive oil has been disseminated in the Mediter-
ranean basin as a leading industry in countries like Spain, Greece, Italy, Tunisia,
Egypt and Turkey. The production process of the Olive oil usually yields an oily
phase residue, a solid residue (pomace or husk) and aqueous phase from the water
content. With the fact that there are huge amounts of waste out of the olive oil pro-
duction industry, so it makes it a good and smart way to invest their wastes in Biogas
production.
3.2.2 Acquisition and properties of Olive Pomace
The olive pomace has been imported from some olive oil manufacturer in Greece
(see fig. 58 & 59) and the inoculum used was the same used for the chicken manure
experiment to start the fermentation process.
Figure 58: Olive pomace barrels Figure 59: Olive pomace
Hochschule Offenburg Mt-Energie GmbH
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Both the dry substance and organic dry substance contents in the pomace were
measured gradually (once per week) to concern the effect of the ambient conditions
(hot, cold, humid and rainy days) as well as the influence of storing method (some
barrels were kept in shadow and some in sun).
TS = 46.2 % Analyzed on: Applied till: oTS = 97.2 % 08/05/2012 14/05/2012
TS = 38.7 % Analyzed on: Applied till: oTS = 96.8 % 13/06/2012 TS = 46.4 % Analyzed on: Applied till: oTS = 83.2 % 13/07/2012 TS = 42.4 % Analyzed on: Applied till: oTS = 94.9 % 19/07/2012 26/07/2012 TS = 39.9 % Analyzed on: Applied till:
oTS = 94.8 % 23/07/2012 30/07/2012 TS = 38.9 % Analyzed on: Applied till: oTS = 94.7 % 31/07/2012 06/08/2012
TS = 36.8 % Analyzed on: Applied till: oTS = 95.2 % 06/08/2012 13/08/2012
TS = 49.8 % Analyzed on: Applied till: oTS = 96.8 % 13/08/2012 20/08/2012
TS = 46.5 % Analyzed on: Applied till:
oTS = 97.7 % 21/08/2012 28/08/2012 TS = 37.8 % Analyzed on: Applied till: oTS = 92.4 % 03/09/2012 10/09/2012
TS = 47.4 % Analyzed on: Applied till: oTS = 92.4 % 11/09/2012 11/09/2012 TS = 47.1 % Analyzed on: Applied till: oTS = 97.8 % 10/09/2012 17/09/2012 TS = 42.8 % Analyzed on: Applied till: oTS = 97.3 % 17/09/2012 25/09/2012
Table 7: DM and ODM values for Olive Pomace
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3.2.3 The Experiment
The experiment of the Olive Pomace was quite similar to the Chicken Manure
when talking about Building up the fermenter and ending with the feeding and meas-
uring procedures. Unlike the Chicken Manure experiment, the DM test where done in
long time intervals as it didn’t have a great influence to the liquidity since the viscosity
of the substrate was reasonably low.
3.2.4 Observations (results)
pH value
6.8
7
7.2
7.4
7.6
7.8
8
8.2
pH
-val
ue
Date
pH-value
pH
Figure 60: pH values
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FOS/TAC ratio
FOS and TAC in comparison
0 0.05
0.1 0.15
0.2 0.25
0.3 0.35
0.4 0.45
0.5
FOS/
TAC
Date
FOS/TAC-ratio
FOS/TAC
0 2000 4000 6000 8000
10000 12000 14000 16000 18000 20000
FOS,
TA
C in
mg/
l
Date
FOS and TAC in comparison
FOS TAC
Figure 61: FOS/TAC ratio
Figure 62: FOS and TAC in comparison
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Gas production
Methane Quantity
000
000
000
001
001
001
001
001
Date
Gas production Nm³/d
Gasertrag Nm³/d
Figure 63: Volumetric Gas Production
0
10
20
30
40
50
60
70
80
CH
4 in
%
Date
Methane quantity
CH4
Figure 64: Volumetric Methane Quantity
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3.2.5 Conclusion
Unlike the Chicken Manure experiment, this experiment has shown more stability
with the DM content along with the quite low viscosity (around 1000 mPa.s). Except
for some operating problems and troubleshooting, Methane production has been ob-
served to be stable. Some operating troubles like Gas leakage and Oxygen seepage
inside the fermenter has affected the Gas yield but under stable and airtight opera-
tion conditions, the Gas production should be stable.
According to the Gas yield and investment potentials, the anaerobic digestion of
the olive pomace can be considered commercially feasible (see fig. 65) but it has
shown a lower gas production per kg of ODM (around 250 Nl/kg ODM) than the
chicken manure would have.
The FOS/TAC ratio has shown an average value of 0.36 and the ammonia content
of about 2280 mg/L.
0
50
100
150
200
250
300
350
18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 2 4 6 8 10 12 14 16
Gas
pro
du
ctio
n in
Nl/
kg O
DM
Calender week
Gas production Nl/kg ODM
Gasertrag Nl/kg oTS
Figure 65: Gas production per kg ODM
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3.3 Anaerobic Digestion of Wine Pomace
3.3.1 Introduction
The production of Wine has been disseminated in all Europe as a traditional indus-
try since a long time ago. The production process of the Wine usually yields a solid
residue (pomace or husk) and aqueous phase from the liquid content. With the fact
that there are huge amounts of waste out of the Wine production industry especially
in Germany, so it makes it a good and smart way to invest their wastes in Biogas
production.
3.3.2 Acquisition and properties of Wine Pomace
The wine pomace has been gotten from Neustadt, Germany (see fig. 66 & 67) and
the inoculum used was the same used for the chicken manure and olive pomace ex-
periment.
Figure 66: Wine pomace barrels Figure 67: Wine pomace
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Both the dry substance and organic dry substance contents in the pomace were
measured gradually (once per week) to concern the effect of the ambient conditions
(hot, cold, humid and rainy days) as well as the influence of storing method (some
barrels were kept in shadow and some in sun).
TS = 35.7 % Analyzed on: Applied till: oTS = 93.9 % 22/05/2012 05/07/2012
TS = 32.8 % Analyzed on: Applied till: oTS = 92.8 % 18/07/2012 26/07/2012 TS = 36.9 % Analyzed on: Applied till: oTS = 95.6 % 23/07/2012 30/07/2012 TS = 34.2 % Analyzed on: Applied till: oTS = 94.9 % 30/07/2012 06/08/2012 TS = 36.9 % Analyzed on: Applied till:
oTS = 95.4 % 06/08/2012 13/08/2012 TS = 35.6 % Analyzed on: Applied till: oTS = 93.4 % 13/08/2012 20/08/2012
TS = 33.6 % Analyzed on: Applied till: oTS = 94.8 % 21/08/2012 27/08/2012
TS = 37 % Analyzed on: Applied till: oTS = 90.2 % 03/09/2012
TS = Analyzed on: Applied till:
oTS = TS = Analyzed on: Applied till: oTS =
TS = Analyzed on: Applied till: oTS = TS = Analyzed on: Applied till: oTS = TS = Analyzed on: Applied till: oTS =
Table 8: DM and ODM values for Wine Pomace
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3.3.3 The Experiment
The experiment of the Wine Pomace was quite similar to the Chicken Manure and
the Olive Pomace when talking about Building up the fermenter and ending with the
feeding and measuring procedures. Unlike the Chicken Manure experiment, the DM
test where done in long time intervals as it didn’t have a great influence to the liquidi-
ty since the viscosity of the substrate was reasonably low.
3.3.4 Observations (results)
pH value
Figure 68: pH values
7.3
7.4
7.5
7.6
7.7
7.8
7.9
8
8.1
pH
-val
ue
Date
pH-value
pH
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FOS/TAC ratio
FOS and TAC in comparison
Figure 69: FOS/TAC ratio
Figure 70: FOS and TAC in comparison
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
FOS/
TAC
Date
FOS/TAC-ratio
FOS/TAC
0
2000
4000
6000
8000
10000
12000
14000
16000
FOS,
TA
C in
mg/
l
Date
FOS and TAC in comparison
FOS TAC
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Gas production
Methane Quantity
Figure 71: Volumetric Gas Production
Figure 72: Volumetric Methane Quantity
000 000 000 000 000 001 001 001 001 001 001
Date
Gas production Nm³/d
Gasertrag Nm³/d
0
10
20
30
40
50
60
70
CH
4 in
%
Date
Methan quantity
CH4
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3.3.5 Conclusion
According to the Gas yield and investment potentials, the anaerobic digestion of
the wine pomace can be considered commercially feasible (see fig. 73). It has shown
a relative equal gas production to what the olive pomace does have.
The FOS/TAC ratio has shown an average value of 0.28 and the ammonia content
of about 2370 mg/L which is considered to be within the safe operational range.
Figure 73: Gas production per kg ODM
The feed has started in the middle of the 27th
calender week
0
200
400
600
800
1000
1200
1400
1600
1800
2000
23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
Calender week
Gas production Nl/kg ODM
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4 Acknowledgement
This report owes very much to all MT-Energie staff for their tremendous contribu-
tion and support in all means towards the completion of this project. I am also grate-
ful to my company’s supervisor Mr. Jan Ludeloff who without his help and guidance
this project would not have been completed. I also show my gratitude to my friends
and all who contributed in one way or another in the course of this work.
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5 Bibliography
Leitfaden Biogas von der Gewinnung zur Nutzung, Fachagentur Nachwachsende Rohstoffe e.V. (FNR), ISBN 3-00-014333-5, 05.2012.
Biogas production from olive pomace, Ali R. Tekin, A. coskun Dalgis, 07.2012.
1 Fergusen, T. & Mah, R. (2006) Methanogenic bacteria in Anaerobic digestion of bio-mass, p49, 29 May, 2012
1 Cruazon, B. (2007) History of anaerobic digestion, web.pdx.edu. Retrieved 17.08.07.
1 http://www.onetoremember.co.uk/xcart/images/P/chinese-biogas-plant.gif, 29 May, 2012 1 http://aretusa.ice.it/SchemaSite/images/UserImageDir/177/EN/Presentations/Biogas.pdf, 25 July, 2012 1 http://aretusa.ice.it/SchemaSite/images/UserImageDir/177/EN/Presentations/Biogas.pdf, 25 July, 2012 1 http://www.fnr-server.de/ftp/pdf/literatur/pdf_208-leitfaden_biogas_2010_neu.pdf, p. 25, 15 August, 2012 1 http://www.fnr-server.de/ftp/pdf/literatur/pdf_208-leitfaden_biogas_2010_neu.pdf, p. 27, 17 August, 2012 1 http://www.fnr-server.de/ftp/pdf/literatur/pdf_208-leitfaden_biogas_2010_neu.pdf, p. 27, 17 August, 2012 1 http://www.fnr-server.de/ftp/pdf/literatur/pdf_208-leitfaden_biogas_2010_neu.pdf, p. 27, 18 August, 2012 1 http://www.fnr-server.de/ftp/pdf/literatur/pdf_208-leitfaden_biogas_2010_neu.pdf, p. 27, 18 August, 2012 1 http://www.fnr-server.de/ftp/pdf/literatur/pdf_208-leitfaden_biogas_2010_neu.pdf, p. 28, 20 August, 2012 1 http://www.fnr-server.de/ftp/pdf/literatur/pdf_208-leitfaden_biogas_2010_neu.pdf, p.
28, 21 August, 2012
1 http://www.fnr-server.de/ftp/pdf/literatur/pdf_208-leitfaden_biogas_2010_neu.pdf, p.
28, 21 August, 2012
1 http://www.fnr-server.de/ftp/pdf/literatur/pdf_208-leitfaden_biogas_2010_neu.pdf, p. 29, 22 August, 2012 1 http://www.fnr-server.de/ftp/pdf/literatur/pdf_208-leitfaden_biogas_2010_neu.pdf, p. 31, 21 August, 2012 1 http://www.pewenvironment.org/uploadedFiles/PEG/Publications/Report/PEG_BigChicken_July2011.pdf, 29 May, 2012 1 http://water.me.vccs.edu/courses/ENV149/lesson4.htm, 11 June, 2012 1 Anaerobic digestion, waste.nl. Retrieved 19.08.07. 1 http://www.skyrenewableenergy.com/wp-content/uploads/2009/05/digester.jpg, 11 June, 2012
Hochschule Offenburg Mt-Energie GmbH
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6 Appendix
The MT-Energie GmbH in Lower Saxony Zeven is a leading manufacturer of
complete biogas plants of all sizes, and biogas-engineered components. The
company has been founded in the small town of Rockstedt by Christoph Martens in
1995. In 1997 Martens invented the so-called air-supported membrane cover for
biogas plants. This technology has now become the market-leading standard and is
used by various manufacturers of biogas plants.
According to a study by the German Agricultural Society, MT-Energie is highly
respected in the field of renewable energies. The society’s “image barometer 2010”
awarded the company 87.5 of 100 possible points, positioning it in second place in
this field. In the sector of renewable energies “we can distinguish two image leaders
in the agricultural field: Enercon, Germany’s leading supplier of wind energy plants,
and MT-Energie, the supplier of biogas plants.
Beside my own activities in the R&D Biogas plants in Rockstedt performing this
experiment, I was associated with other new projects in Australia, Russia and
Pakistan. As an intern in the department of Sales and Project Management, I had to
contribute in preparing both feasibility and technical studies. Receiving orders from
customers, supplying both engineering and Biotechnological consultations,
Engineering Drawings preparation, cost estimates, looking for shareholders and
partners were all a part of my job.
The Biogas project of Landhi, Karachi, Pakistan was one of my direct Burdens. A
multi stream set of 12 Biogas plants with a total output of 22 mW electricity as the
world’s biggest Biogas plant. With 250000 Water Buffalos producing around 8000
tons/day of manure along with vegetable and restaurant wastes makes this project
very unique. Challenges like separation of solid bodies, logistics of waste collection,
dealing with high DM content in the feeding wastes, green water recovery techniques
and fertilizers’ production have risen in the horizon. By the time I was facing these
problems; my experiment in Rockstedt was solving most of them.