introduction into digester biology - bioenergyfarm 2 · introduction into digester biology 1...
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Introduction into Digester
Biology
1
Workshop for international experts
Oberschleißheim, 12 October 2015
Katrin Kayser
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Conversion process…
… dependent on efficiency factors!
- Efficiency factor of the digesterProductivity [m³ CH4/(m³RV d)]
- Efficiency factor of the inputsYield [m³ CH4/t oTS]
- Electrical efficiency factor [%]
- Thermal efficiency factor [%]
2. physical1. biochemical
CHP
biogasOrganic
matter
Digester
Electricity
Heat
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Principles of the biogas process
1 The biogas process
2 Environmental conditions
3 Engineering process parameter
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The 4 stages of the fermentation gas formation
Acidification Biogas formation
Hydrogen H2
Methane CH4
Carbon dioxide
CO2
1. Stage
Hydrolysis
2. Stage
Acidogenesis
3. Stage
Acetogenesis
4. Stage
Methanogenesis
acetic acid H2
Hydrolytic
bacteria
Acidogenic
bacteria
Acetogenic
bacteria
Methanogenic
bacteria
Biomass
Polysaccharides
Proteins, Fats
Acetic acid
H2
Sugar,
Amino acids,
fatty acids
H2/CO2
Biogas
CH4/CO2
Fatty acids
(propionic acid)
alcohols
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Generation time of different bacteria
Anaerobe Microorganisms
Acid producing bacteria
Methanogenic bacteria
Bacterioides < 24 h.
Clostridien 24 - 36 h.
Acetogenic bacteria 80 - 90 h.
Methanosarcina barkeri 5 - 15 d
Methanococcus ca. 10 d
Aerobe microorganisms Escherichia coli 20 Min.
Activated sludge bacteria 2 h.
!
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The different degradation processes…
• … occur at the same time simultaneously In agricultural biogas plants the separation of the degradation stages plays a
minor role
• … strongly depend on each otherIntermediate products are needed for following processes
• … can cause mutual inhibition ▪ Intermediate products may not accumulate ▪ Product inhibition
• … develop slowly in advanced stages Hydrolysis hydrolysis is the fastest, methane formation the slowest
one-stage process
biogas digestate
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Environment conditions of anaerobic degradation
W0104124CDREnvironmental requirements for the fermentation of raw – and residual
substrates
FAL – TB
Essential: Ni, Co, Mo, SeNo specific requirementsTrace elements
600 : 15 : 5 : 3500 : 15 : 5 : 3Nutrient demand
C:N:P:S
< -250 mV+400 – 300 mVRedox - potential
< 30 % DM< 40 % DMSolid content
20 - 3010 - 45C:N-Relation
6,7 – 7,55,2 – 6,3pH value
Mesophilic: 32 – 42 ºC
Thermophilic: 50 – 58 ºC
25 – 35º CTemperature
Methane formationHydrolysis/acidificationMeasured variable
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The most important requirements
for the biogas process
• Temperature
• pH-value
• Salt content
• Trace elements
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Temperature ranges
• Psychrophil (< 25 °C)
low growth rate long retention times
inefficient for biogas production no longer in use
• Mesophil (32 - 45 °C)
stable biocoenosis satisfying gas yield with acceptable retention time
common, particularly in wet fermentation processes
• Thermophil (50 - 60 °C)
high gas yield after short retention time
sensitive biocoenosis caution with rapid degradable substrates,
(hydrolysis develops too fast)
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pH-Value and CO2-solubility
sampling
approx. 40 Vol-% CO2
0,03 Vol-% CO2
insideoutside
Immediately after
taking a sample,
outside the digester
CO2 begins to escape.
pH-value rises
pH-value in the
digester is lower than
measured outside the
digester!
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pH-value
• Metabolites would reduce the pH-value, but:
– Plants with manure have normally good buffering systems:
– Carbonate buffer, Ammonium buffer, ...
• pH-value as sole parameter is not suited to evaluate the
process
Attention: H+ H2≠
Hydrogen ion (H+)- concentration
It‘s a question of buffer!
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pH-stability through buffer systems
Source: Novatech GmbH Support program
Säureanalyse
0
1
2
3
4
5
6
7
8
9
10
KW 5
1/05
KW 0
1 / 0
6
KW 0
6 / 0
6
KW 0
7 / 0
6
Säu
re in
[g
/ l F
MI]
n-Valeriansäure
n-Buttersäure
Propionsäure
Essigsäure
pH 7,7 pH 7,6 pH 7,6 pH 7,8
Acidity analysis
Ac
idit
y i
n [
g/l
FM
]
Acidification
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Salt content or electric conductivity
• Simple measurement
– Should be always included in case of inexplicable changes
• High salt content dry up the bacteria
– Osmotic pressure
• Unit: mS/cm
– Values > 60 mS/cm are critical
– Correction on a temperature of 25°C
• If value is critical: add water
Usually no problem during
fermentation of energy crops,
BUT
You have to analyse during
fermentation of food-waste (e.g.
canteens, grease separator,
salted matter)
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Principles of the biogas process
1 The biogas process
2 Environmental conditions
3 Engineering process parameter
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Functional principle
Overflow system
communicating vessels• Through hydrostatic pressure, liquid level is at
the same height in the connecting pipe
• Liquid levels balance themselves
• Overflow works
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Fundamental process engineering parameters
• Hydraulic retention time; T (HTR)
• Dry Matter; DM (oDM)
• Organic loading rate; BR
Input
Output
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Solid matter contentW
et/
Fre
sh
mass (
FM
)
Mineral solids = ash (minerals)
Water content
So
lid
s
Solid content
= Dry Matter [DM]
= organic Dry Matter or
Volatile solids [oDM;
VS]
(FM = fresh matter)
Organic solids = Volatile solids [from % FM or % DM ]
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(Hydraulic) Retention time T, HRT
Digester volume = Work volume (gross volume without gas storage space)
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(Hydraulic) Retention time T, HRT
Digester volume = Work volume (gross volume without gas storage space)
• central parameter in the case of liquid manure plants
• less important in the case of plants operating with energy crops
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Organic loading rate BR
• Solids (DM, oDM) – load per m³ work volume and day
• Tendency for higher load
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Example for calculation: Organic loading rate BR
Work volume = 800 m³
Daily feeding of organic DM = 1926 kg
Process sensitivity increases with a larger organic loading rate
Substrate Substrate [t/a] oDM [%FM] oDM [t/a] oDM [kg/d]
Cattle manure 2200 9,0% 198 542
Leftovers 700 17,0% 119 326
Chicken dry manure 500 34,0% 170 466
Grease waste 800 27,0% 216 592
Total 4200 703 1926
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Critical organic loading rate and retention time
Organic loading rate [kg oDM/(m³*d)]
Hydraulic retention time [d]G
as p
rod
uctivity
[m³
Gas/(
m³ F
er.*
d)]
Ga
s y
ield
[m³
Gas /k
g o
DM
]
1
21
2
Critical hydraulic retention
time and organic loading rate
Thank you for your attention!
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Speaker:
Dipl.-Ing. Katrin Kayser
IBBK Fachgruppe Biogas GmbH,
Am Feuersee 6
74592 Kirchberg / Jagst, Germany
Credentials: Birgit Pfeifer, bioreact GmbH