BIOLOGIA DA DIGESTÃO ANAEROBIA

1. UMWEKO GmbH, Dr Konrad Schleiss
3. Biology of anaerobic digestion
(after Peter Weiland, Institute of Technology and Biosystems Engineering
Federal Agricultural Research Centre, Braunschweig, Germany)
• Microbiology and biochemistry of anaerobic
digestion
• Physical and chemical parameters
• Substrates
• Setting up and managing the process
• Synthesis and outlook

2. UMWEKO GmbH, Dr Konrad Schleiss
Microbiology and biochemistry of AD
1st stage
Hydrolysis
2nd stage
Acido-
genesis
3rd stage
Aceto-
genesis
4th stage
Methano-
genesis
Biomass
Polysaccharides
Proteins
Fats
Sugars
Amino acids
Fatty acids
H2/CO2
Carbonic
acids:
Acetate
Propionate
Butyrate
Succinate
Alcohols
Acetate
H2, CO2
Biogas
CH /CO4 2
Acetogens
Methanogens
Fermentative
bacteria
Hydrolytic
bacteria

3. UMWEKO GmbH, Dr Konrad Schleiss
Microbiology and biochemistry of AD
ca. 70% ca. 30%

4. UMWEKO GmbH, Dr Konrad Schleiss
Microbiology and biochemistry of AD
In anaerobic digestion, the microorganisms can only make use
of a small part of the chemical energy bound in the substrates
they digest. Most of the energy is lost to them as “useless”
biogas.
A direct consequence of this low energy yield is the small
amount of bacterial biomass which is formed.
Another consequence is the small amount of waste heat
released: AD is an isothermic process.

5. UMWEKO GmbH, Dr Konrad Schleiss
Physical and chemical parameters
Comparative formation of bacterial biomass during aerobic degradation (with
oxygen) and anaerobic degradation (digestion)
aerobic degradation
anaerobic degradation
C fraction
(100%)
C fraction
(100%)
biomass biomass

6. UMWEKO GmbH, Dr Konrad Schleiss
Physical and chemical parameters
Generation times of different microorganisms
Anaerobic microorganisms
Acidogenic bacteria
Bacterioides < 24 hours
Clostridium 24 - 36 hours
Acetogens 80 - 90 hours
Methanogens
Methanosarcina barkeri 5 – 15 days
Methanococcus ca. 10 days
Aerobic microorganisms
Escherichia coli 20 minutes
Belebtschlamm 2 hours

7. UMWEKO GmbH, Dr Konrad Schleiss
Physical and chemical parameters
Medium requirements for the anaerobic digestion of input materials and waste
Parameter Hydrolysis / Acidogenesis Methanogenesis
Temperature 25 - 35°C
mesophilic: 32 - 42°C
thermophilic: 50 - 58°C
pH 5.2 – 6.3 6.7 – 7.5
C:N ratio 10 - 45 20 - 30
Total solids < 40 %TS < 30 % TS
Redox potential +400 – -300 mV < -250 mV
Nutrients: C:N:P:S ratio 500 : 15 : 5 : 3 600 : 15 : 5 : 3
Trace elements no special requirements essential: Ni, Co, Mo, Se

8. UMWEKO GmbH, Dr Konrad Schleiss
Physical and chemical parameters
Comparison between mesophilic and thermophilic digestion
Range of application
Range of application
Mesophilic
methanogenesis
Thermophilic
methanogenesis

9. UMWEKO GmbH, Dr Konrad Schleiss
Physical and chemical parameters
Inhibiting and toxic factors
Inhibitor Inhibiting concentration Comment
Oxygen > 0,1 mg/l O2 Inhition of the methanogens (obligatory
anaerobes).
Hydrogen sulphide > 50 mg/l H2S Inhibitory effect increases as pH decreases.
Volatile fatty acids > 2000 mg/l HAc (pH = 7,0) Inhibitory effect increases as pH decreases.
The bacteria exhibit high adaptability to
this factor.
Ammonium-N > 3500 mg/l NH (pH = 7,0) Inhibitory effect increases as pH decreases
and temperature rises. The bacteria exhibit
high adaptability to this factor.
Heavy metals Cu > 50 mg/l
Zn > 150 mg/l
Cr > 100 mg/l
Only dissolved metals are inhibitory.
Deztoxification by precipitation as
sulphides.
Desinfectants
Antibiotics
n.d. Inhibitory effect is product spezific.

10. UMWEKO GmbH, Dr Konrad Schleiss
Physical and chemical parameters
Inhibition by ammonia
Inhibition of methanogenesis by NH3
(methane formation from acetic acid)
Inhibition [%]

11. UMWEKO GmbH, Dr Konrad Schleiss
Physical and chemical parameters
Inhibition by sulphides
Inhibition of methanogenesis
(methane formation from acetic acid)
Inhibition [%]

12. UMWEKO GmbH, Dr Konrad Schleiss
Physical and chemical parameters
Inhibition by carbonic acids
Inhibition of methanogenesis
Inhibition [%]
mg/l acids (undiss.)
Propionic acid
Acetic acid

13. UMWEKO GmbH, Dr Konrad Schleiss
Substrates
Theoretical gas yield of various classes of substances
Fats Proteins Starch
Gas yield Nl/kg org. TS

14. UMWEKO GmbH, Dr Konrad Schleiss
Substrates
Composition of the biogas according to the digestion substrate
Class of substances Biogas yield
[l/kg oDM]
Methane content
[Vol.-%]
Calorific value
[kWh/m³]
Carbohydrates 700 - 830 50 - 55 5.0 – 5.5
Proteins 700 - 900 70 - 75 7.0 – 7.5
Fats 1.000 - 1.400 68 - 73 6.8 – 7.3
Biowaste 350 - 500 55 - 68 5.5 – 6.8
Renewable raw materials 500 - 700 50 - 62 5.0 – 6.2

15. UMWEKO GmbH, Dr Konrad Schleiss
Substrates
Composition of the biogas according to the average oxidation level of
the carbon
oxalic acid
formic acid
citric acid
carbohydrates, acetic acid
propionic acid
butyric acid
proteins
fats
methanol
Mean oxidation level of the C

16. UMWEKO GmbH, Dr Konrad Schleiss
Substrates
Biogas yields of various digestion substrates
Agricultural waste Agricultural raw materials Non-agricultural waste
Cowmanure25
Pigmanure36
Fodderbeet95
Silagemaize190
Raygrass110
Biowaste120
Foodwaste240
Greaseseparatorresidue400
Wastefat800
Biogas yield [m3 gas/t substrate]

17. UMWEKO GmbH, Dr Konrad Schleiss
Synthesis and outlook
• Knowledge of the microbial metabolic processes is
indispensable to operate a biogas plant.
• Operational stability is only possible if account is taken of the
microbial requirements and chemical parameters.
• Sustainable biogas production is only economically feasible in
the long term if the full value can be extrated from the biomass
by optimising the digestion process and using all the energy.