Post on 01-Apr-2015
Biogas production
Biomas in Biomas out (Digestate)Gas out
Where are we?Why do we want?
How do we manage?What do we need?
From where should we start?What do we want to know?
Biogas knowledge piramide
Biogas plant concept
Pig slurryFeBiomas out (Digestate)
Additional income for the farmersClean energy (kitchen)Digestate is an excellent fertilizerLess odourSanitaion
The microbiology process
Biomasse:Animal manureOrganic waste
Hydrolysis
Dissolved substrate
Acidogenesis
H2+CO2
Acetognesis
VFA>C2
CH4+H2O+ CO2
CH3-COOH
Methanogenesis
Methane produktion
Biomasse:Animal manureOrganic waste
Hydrolysis
Dissolved substrate
Acidogenesis
H2+CO2
Acetognesis
VFA>C2
CH4+H2O+ CO2
CH3-COOH
Methanogenesis
Hydrolysis is process rate controlling
VFA transformation reduced due to:
•High NH3
•Sudden changes in environment
•High H2 concentration
Feedback:
High VFA conc. reduces hydrolysis
Physical process
COMPOSITE MATERIAL
MACROMOLECULES
Physical process: Disintegration
• Lysis• Non enzymatic decay• Phase separation• Physical breakdown (shearing)
Biological and chemical process
MACROMOLECULES
SIMPLE SUBSTRATES
Hydrolysis (chemical)A→B1+B2 (H2O is used)
Hydrolytic enzymes (biological/chemical)Made by micro-organisms – same outcome
SIMPLE SUBSTRATES
VOLATILE FATTY ACIDS
ACETATE & HYDROGEN
Acidogenesis: (biological)Volatile fatty acids are generated from monosaccarides, fat and aminoacids.(sugar-degraders & aminoacid-degraders)
Acetogenesis: (biological)Acetate is generated from LCFAs. (lcfa-degraders) and from sugar (sugar-degraders)
ACETATE & HYDROGEN
BIOGAS
Methanogenesis (biogas production)
Acetoclastic methanogenesisCH3COOH → CH4 + CO2
Hydrogenotrophic methanogenesisCO2 + 4H2 → CH4 + 2H2O
Biogas knowledge pyramideInhibition
H2inhibitionReaction
)()(3)(3)( 3233223 aqHCOaqHOHaqCOOCHOHaqCOOCHCH
)()()( 423 gCHaqCOaqCOOHCH )()(3)()(3)( 3224223 aqHCOaqHaqCOaqCHOHaqCOOCHCH
O2H(aq)CH(aq)4H(aq)CO 2422 -130.4
1
VFA component Acetic acid
Ammonia inhibition
• Ammonia inhibition: 1,5 – 2,5 g N/L, after adaptation inhibition at 4 g N/L (Angelidaki og Ahring 1998)
Ammonia chemistry OHNHOHNH NK
3324
)(
)()(
4
33
NH
OHNHKN
)(
)(
3
43 OH
NHKNH N
pH= -log(H+)•Thus if the concentration of [H+] is •Neutral: 10-7 mol then pH = –log(10-7)=7•Acid: 10-2 mol then pH = –log(10-2)=2•Basic: 10-10 mol then pH = –log(10-10)=10
Ammonia-ammonium equilibrium
pH
7 8 9 10 11 12
NH
4+, N
H3,
TA
N (
mol
l-1)
0.00
0.02
0.04
0.06
0.08
0.10 TAN
NH4+ NH3
Ammonia inhibition
• In literature ammonia inhibition has been assessed relating biogas production to
• Reactive ammonium (NH3)
• Total Nitrogen• AmmoniumHow is NH3 related to NH4
+
How would you recommend that the inhibition is expressed (reactive ammonium, total nitrogen or ammonium
Inhibition at high and low pH
SH2 NH3
VFA inhibition
• Inhibition at a ratio of propionic acid to acetic acid at 1.4:1
• Inhibition at 2 g VFA Ltr-1
TemperatureBacteria adaptation
Batstone et al. 2002
SIMPLE SUBSTRATES
VOLATILE FATTY ACIDS
ACETATE & HYDROGEN
Acidogenesis: (biological)Volatile fatty acids are generated from monosaccarides and aminoacids.(sugar-degraders & aminoacid-degraders)
Acetogenesis: (biological)Acetate is generated from LCFAs. (lcfa-degraders) and from sugar (sugar-degraders)
What happens if the temperature suddenly drops?
Metane production as affected by NH4+
koncentration interacting with temperature
20 days retention time in CSTR digester
0
100
200
300
400
0 10 20 30 40 50 60 70
Temperature oC
Lite
r C
H4/
kg V
S
NH4-N<3 g/l
NH4-N>3 g/l
Biogas knowledge piramideDigestibilty
Definitioner
• VS (Volatile solids):– The fraction of dry matter (DM) in slurry that is
transformed to gas at high temperature/incineration (550oC) for one hour
– How would you measure VS?
• Methane productivity:– CH4 production pr. unit VS
– CH4 production pr. unit COD
Source of energy in animal slurry
Fermented slurry
Digestible
Non-digestible
Transformed to CH4
Energy production
Concentration, %
0
20
40
60
80
100
Concentration, %
0
1
2
3
4
5
6
Water
Volatile solids
Ash
Volatile solids
Ash
Untreated slurry
Digestible
Non-digestible
Biogas plant
CH4 - source
Biogas, CH4 +CO2
Characterisation of biogas potential• In the biological process the maximum biogas production BMP• (liter CH4 kg(VS)-1)
– Volume of methane produced when residence time is in principle very long
Inoculum
Biomas
BMP is estimated in batch fermentation at 35oCFermentation time 70-100 daysDays
0 10 20 30 40 50 60 70CH
4 pr
oduc
tion
, lit
er C
H4
kg(V
S)-1
0
100
200
300
400
Pig slurry
Cattle slurry
Anaerobic Digestibility The theoretical biogas production can be calculated from knowing the chemical
composition of the biomass:TBMP In the biological process the maximum biogas production: BMP Anaerobic digestibility =BMP/TBMP• • Question • - BMP/TBMP ↑ digestibility??• - BMP/TBMP ↓ digestibility ??
•
Biodegradability (BMP/TBMP) examples
Low digestibility Low digestibility
lignin : Non degradable in anaerobic environments
hydrolysis of cellulose blocked by lignin.
Lignin Lignin glue to hold lignocellulosic
matrix protective coat used to assess digestibility of
feed in animal science
LignocelluloseLignocellulose
Lignocellulose in VS (volatile solid) Lignocellulose in VS (volatile solid)
Fermentation result - animal manure Fermentation result - animal manure
Digestability of the biomass
CH4 L kg(VS)-1
Energy potential of biomassDry matter Volatile
solids in pct of dry matter (DM)
Total energy content
Energy production in biogas plant
% % MJ/ kg DM MJ/kg DM
Pig slurry 6 80 16,3 9,8
Cattle slurry
10 80 15,3 7,6
Clover grass
20 90 18,3 14,6
Straw 90 90 19,1 9,6
Why is biogas energy production of straw so low
Methane produkcion crops and organic waste
0100200300400
Gra
ssM
aize
Whea
t stra
w
Slaug
hter
was
tes
Flotta
tions
slud
ge
Bleac
hing
clay
Whey
Mun
icipa
l sol
id was
teNm
3 C
H4/
ton
ne
s
Biogas production estimates
With the Hashimoto equation one can assess production of biogas as affected by:
•temperature, •hydraulic retention time, •micro-organism activity•biomass composition
Hashimoto equation
HRT or θ Hydraulic retention timeSRT Solid retention timeΓ Is the specific gas yield
B0 The ultimate or specific methane yield, measured with batch fermentation at more than 60 days and at 35oC.
µ maximal specific growth rate of the micro organisms, µm a
function of temperature and residues feed to the reactor K is a kinetic parameter depending of the rate of feed, feed
composition and bacterial consortium,
S0 Concentration of organic components in feed to the reactor
Nm3 The volume CH4 produced, calculated at 0oC (273oK)
Hashimoto model predictions’
Summarising
• Biogas is efficient in producing energy from biomasses with a high water content
• Biogas transform the biomas reducing VS and thus reduced GHG emission potential of the slurry
• Biogas transform biomas organic N into ammonium that is an efficient fertilizer