1 Chapter Chapter 3 Microbiology Microbiology of of Anaerobic Digestion Anaerobic Digestion Response to free molecular O 2
1
Chapter Chapter 33
MicrobiologyMicrobiology of of
Anaerobic DigestionAnaerobic Digestion
Response to free molecular O2
2
Electron transport
Electron transport molecules (e- acceptors) used in degradation of
soluble substrate
Electron transport
Depending upon the
molecule used
(O2, NO3-, SO4
2-, CO2,
or soluble cBOD)
by bacteria to remove
electrons from the cell,
a variety of substrates
are produced.
Sulfate
reduction
Denitrification
Methanogenesis
Ferm
entation
Aerobic
oxidation
e-e- e- e- e-e-
3
ORP vs Cellular activity
Final ElectronAcceptor (carrier)
Energy yield and sludge production
Final ElectronAcceptor (carrier)
kg VSS Produced per kg COD Degraded
Methane producing archaea
4
Microorganisms in AD
Higher FattyAcids, Alcohols
Monosaccharides, Amino acids
Intermediates (Propionate,
butyrate, alcohols)
CH4 + CO2
H2 + CO2 Acetate
1
2
2
2
3 3
4 4
3
1
2
Complex Organics(Carbohydrates, proteins, lipids)
H2S + CO25
5
5
1. Hydrolytic bacteria
2. Fermentation bacteria
3. Acetogenic bacteria4. Methanogic archaea
5. Sulfate reducing bacteria
Hydrolysis
Cell membrane
Cell wallInsoluble
substrates
Extracellularenzymes
Intracellularenzymes
Soluble substrates
8
Substrates of methanogens
acetoclastic methanogens
hydrogenotrophic methanogens
methyltrophic methanogens
Habitats of methanogens
9
Acetoclastic Methanogens
Methanosarcina acetivorans
Methanosaeta sp.Methanosaeta concilii
Methanogens
Mixed cultureSubstrate: Sucrose
MethanosaetaSubstrate: Acetate
10
Competition: SRB vs Methanogens
Sulfate reducingbacteria
Methanogenicarchaea
Competition: SRB vs Methanogens
Model of kinetic and thermodynamic competition among sulfatereducing bacteria and methanogenic archaea
11
Minimum Minimum doubling times of major doubling times of major
microbialmicrobial groups in ADgroups in AD (Mosey, 1989)(Mosey, 1989)
Days2.6Methanogens growing on acetate
Days2.5Acetogenic bacteria fermenting propionate
Days1.4Acetogenic bacteria fermenting butyrate
Hours6Methanogens growing on hydrogen
Min30Sugar-fermenting, acid forming bacteria
Sludge Granulation
Anaerobic sludge granules from a UASB reactor treating effluent from a recycle paper mill (Roermond, The Netherlands).
Millimeter paper indicating the
size of the granules.
Gas vents in the granules,
where biogas is released