ConfidentialA European Project supported within the Seventh Framework Programme for Research and Technological Development
Castro (LE), Italy, September 22nd 2011Speaker : Alessandro Spagni (ENEA)
EuroBioRef Summer School 18-24 Sep 2011
From lab scale to full scale biogas plants(R. Farina – A. Spagni)
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Outline● General
● What can be used to used as substrate?
● Pretreatment
● Design criteria
● Reactor for biogas production from biomass
● Reactor for biogas production from wastewater
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Substrates
● Several substrates can be used:● Biomass● Energy crops●Waste●Wastewater● Biogas production can be designed as the “final
treatment” (or last step) in the biorefinery concept
● How can we evaluate the biogas potential?● The Biochemical methane potential
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Example of a biorefinery
Algae
biodisel Glycerin
H2
H2
CH4
CH4
MFC
OFMSW
wastes
biomass
PHA
Ethanol
Wastewater
H2
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Process and oxygen
● Respiration
● Anoxic respiration
422291918 NHO8H18COHO17.5NOHC
OHOHCONOHCHNO 2222
136
5
67
65
3
CH3COO- CH4 + CO2 .
● FermentationHCO3- + 4H2 CH4 + 2H2O + OH-
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Process and oxygen
● Aerobic condition● If oxygen is present
● Anoxic conditions● oxygen absent but other inorganic electron acceptors are
present● Anaerobic digestion
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Organic matter CO2+H2O
Synthesis New biomassGrowth
Energy
Bacterial cell
O2
Yield
1-Yield
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Kinetics and environmental conditions
● Aerobic microorganisms● Growth rate = 6 d-1● Yield up to 67%
● Anoxic● both 10-20% smaller than aerobic● Anaerobic
● Growth rate < 1 d-1● Yield up to 10%
● Hydrolysis: no big differences
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Kinetics and environmental conditions
● Methanogens are strictly anaerobic
● Competition
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Ammonia inhibitionAmmonia usually accumulates in the reactors
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OHNHOHNH 3324
Sulphate reductionCompete for substrates
SHSSO 222
4
Not appropriate when sulphate conc is high
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75%
28%72%
23%52%
Organic matter
Acetogenic bacteria
Homoacetogenic bacteria
Lipids, Alchols, etc.
ACETATE H2 + CO2
Acetoclastic methanogenic
bacteria
Methanogenic
bacteria
CH4 + CO2 CH4 + H2O
carbohydratesproteins
lipids
5%20%
100%
Hydrolytic fermentative bacteria
Disintegration
Hydrolysis
Acidogenesi
Methanogenesis
Rat
e
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Several different microorganisms work togheter to produce methane
● Can we use pure cultures?●Substrate characteristics limits●Process limits
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Process conditions
● Temperature●Psychrophilic: no heating ●Mesophilic 35-37°C●Thermophilic 55°C
● pH● Nutrients?●Add micronutrients●Waste design
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COD (chemical oxygen demand)is an estimation of the electrons involved
Organic matter CO2+H2O
Synthesis New biomassGrowth
Energy
Bacterial cell
O2
Yield
1-Yield
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Biodegrabality
● What does “biodegradable” means when you want to treat a substrate with microorganism?
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Estimate the methane productionBMP (biochemical methane potential) Test
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InoculumSubstrate(Water)BufferN2
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BMP
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LVs
LgVS
LbVsVg
LBMP
VS
CHnCHCH
VS
CHn
4444
10035.0
%4
4
deg
COD
CHn
VS
COD
VS
CHn
radability
gL
gg
VSCOD
gL
BMPBMP
1g of DEGRADED COD produce approx. 350 mL of methane
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PretreatmentsNote: several substrates do not require pretreatment for methane production
● Mechanical● The most used (mills, extrusions)● Reduce size (important for biological activity)
● Biological ● Enzymes
● Chemical● Acids or alkali
● Thermal● sometimes used in combination
● it is much better to do not use27
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Cellulosepolysaccharide consisting of a linear chain of several hundred to over ten thousand β(1→4) linked D-glucose units
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Design – important parameters● HRT: hydraulic retention time● SRT: solids retention time● For plant for biogas production from solids (or semisolids)
HRT=SRT● For wastewaters SRT>>HRT
● OLR: organic loading rate
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QVHRT
Q, Cin
V
VCinQOLR *
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Design
● V: volume of the reactor (m3)● HRT (d)● Q = flow of the materials to be treated (m3/d)
● Referenced HRT or can be estimated by lab-scale experiments
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QHRTV *
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Cumulative and specific biogas production at different HRT in batch test (LfU, 2007) modified
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A
B
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Design
● V: volume of the reactor (m3)● Mom: mass of organic matter, as SV or COD, introduced in the unit of
time (kg/d )● OLR: mass of organic matter, as SV or COD, introduced in the unit of
time (kgm3/d)
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OLRMV om
OLRCinQV *
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Plants Classification according● Water content of the substrate
● Wet - dry solids < 15%● Semiwet – 15 < d.s. < 20 ● Dry – dry solids > 20%
● Temperature ● Psychrophilic: no heating ● Mesophilic 35-37°C● Thermophilic 55°C
● Solids management (if HRT is equal or not to SRT)● Feeding regime (continuous or discontinuous)● Stages of the process: single or multiple
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How to chose for
● Temperature● Solids management (HRT and SRT)● Feeding regime?
● Stages of the process
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75%
28%72%
23%52%
Organic matter
Acetogenic bacteria
Homoacetogenic bacteria
Lipids, Alchols, etc.
ACETATE H2 + CO2
Acetoclastic methanogenic
bacteria
Methanogenic
bacteria
CH4 + CO2 CH4 + H2O
carbohydratesproteins
lipids
5%20%
100%
Hydrolytic fermentative bacteria
Disintegration
Hydrolysis
Acidogenesi
Methanogenesis
Rat
e
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Biogas from wastewaters● The most important difference of the biogas production plant from
wastewater compared with solids materials is the retention of the microbial community.
Some strategies or apparatus are addedIn order of separating the HRT from SRT
SRT high enough to allow the retention of the slowest growing bacteria (methanogens)
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Type of wastewater
● Usually for high concentrated wastewater● Temperature: enough energy production for
heating the system● This is not a so big problem for Solids substrate treatment
● Industrial WW (e.g. agro-industrial)● COD > 5,0 g/L
● Soluble and particulate COD
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Ammonia concentration inside a reactor for methane production from biomass from the production of antibiotics (yeast waste)
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Biogas productivity (waste from antibiotics production)
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0
200
400
600
800
1000
1200
1400
1600
1800
2000
0 50 100 150 200
Biog
as (
mL/
gior
no)
giorni
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Biogas production using a membrane anaerobic reactor
72Time (d)0 50 100 150 200 250
Bio
gas
prod
uctio
n (L
/d)
0
10
20
30
40
50
60
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HR
T (d
)0
20406080
100120140
CO
D (g
/L)
051015202530
CODinCODout
Time (d)0 50 100 150 200 250
OLR
[gC
OD
/(L*d
)]
02468
10121416
(a)
(b)
(c)
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Time (d)0 50 100 150 200 250
Vol
atile
fatty
aci
ds (g
/L)
0
2
4
6
8
10
12AceticPropionicn-butyric
Time (d)0 50 100 150 200 250
pH
5.5
6.0
6.5
7.0
7.5
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Biological hydrogen production via dark fermentation
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75%
28%72%
23%52%
Organic matter
Acetogenic bacteria
Homoacetogenic bacteria
Lipids, Alchols, etc.
ACETATE H2 + CO2
Acetoclastic methanogenic
bacteria
Methanogenic
bacteria
CH4 + CO2 CH4 + H2O
carbohydratesproteins
lipids
5%20%
100%
Hydrolytic fermentative bacteria
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Select for H2 production● Thermal treatment of the inoculum
● pH
● HRT
● Reactor temperature
CSTR
VFABIOMASS
H2
VFA
BIOMASS
Heat
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0 1 2 3 4 5 10 20 30 40 50 60 70 80
CG
P (L
/kgC
OD
)
050
100150200250300
BHP BMP
0 1 2 3 4 5 6 7 10 20 30 40 50 60
CG
P (L
/kgC
OD
)
050
100150200250300
H2 CH4
BMPBHP
0 1 2 3 4 5 6 7 10 20 30 40 50 60 70 80 90
CG
P (L
/kgC
OD
)
050
100150200250300
BHP BMP
a
b
c
0 1 2 3 4 5 6 7 10 20 30 40 50
CG
P (L
/kgC
OD
)
050
100150200250300
BHP BMP
Time (d)0 1 2 3 4 5 6 7 10 20 30 40 50
CG
P (L
/kgC
OD
)
050
100150200250300
BHP BMP
d
e
Cumulative gas production (CGP) with glucose (a), common wheat (b), durum wheat (c), mashed potato (d) and steam peeling potato (e) wastes.
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PHA
83
75%
28%72%
23%52%
Organic matter
Acetogenic bacteria
Homoacetogenic bacteria
Lipids, Alchols, etc.
ACETATE H2 + CO2
Acetoclastic methanogenic
bacteria
Methanogenic
bacteria
CH4 + CO2 CH4 + H2O
carbohydratesproteins
lipids
5%20%
100%
Hydrolytic fermentative bacteria
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PHA
● Some bacteria accumulate PHA from organic acids ● it happens when this is a competitive advantage● A nutrient limitation● Alternation of environmental conditions