Innovative methods for biogas upgrading by the addition
of hydrogen to anaerobic reactor
Gang Luo, Postdoc
Irini Angelidaki, Professor
BioEnergy Research Group
Biogas production and utilization
Electricity
Biogas
50-70% CH4
30-50% CO2
Heat
CH4>95%
Digested
substrate
Organic
substrate
Vehicle fuels
Natural gas
Anaerobic reactor
• Biogas can be produced from all kinds of organic wastes/residues
• Biogas utilization as vehicle fuel or natural gas is very promising
2
Biogas upgrading
• Current industrial biogas upgrading technology
–
–
–
–
Chemical absorption
Pressure swing adsorption
High pressure water scrubbing
Membrane separation
• Physical and chemical technologies
• High pressure or chemical addition
• 0.15-0.28 Euro/m3 biogas treated
• 0.1%-15% methane loss
An alternative method for biogas upgrading is needed!
3
Biological method for biogas upgrading
• CO2 together with H2 could be used by hydrogenotrophic methanogens for
methane production.
4H2+CO2=CH4+2H2O
• In Denmark, H2 could be obtained by electrolysis of water using the
surplus electricity from wind mills.
Water
electrolysis
H2
CO2, CH4
Wind mill
Biogas reactor
CH4
4
Advantages
• Increased CH4 production and no CH4 loss
• Minimal chemical and energy requirments
• Storage of wind power as CH4
– Wind power is not stable
– Water electrolysis for H2 production
– High cost for H2 storage and transportation
– CH4 is easier to be stored and distribution
5
Concept 1: In-situ biogas upgrading
Biogas with high
CH4 content
Water
Electrolysis
Organic wastes
H2
Biogas reactor
Effluent
• Very simple process for biogas upgrading
6
Manure as substrate
7
Manure as substrate
Methane production (ml/d)
2000
Reactor with H2
Control
pH
8.3±0.1
8.0±0.1
Acetate (mM)
24±0.93
7.2±0.73
CH4 (%)
65±3.3
62±2.5
H2 (%)
20±2.5
0
CO2 (%)
15±2.1
38±3.2
1600
1200
Reactor with hydrogen
Control
800
400
0
50
55
60
65
70
75
80
85
Time (d)
• The addition of H2 significantly decreased the CO2 concentration
• pH was increase upon the addition of H2
• Around 80% H2 was consumed, but still some left in the biogas
8
Technical Challenge 1
Increase of pH to higher than 8.0
Solutions: Co-digestion
On-line pH control
Parameters
Cattle manure
Whey
pH
7.15±0.11
4.33±0.13
COD (g/L)
40.4±2.3
150±5.7
TKN (mg/L)
1092±210
460±78
NH4 +-N (mg/L)
540±56
89±25
• Whey is a kind of byproduct from cheese factory
• Whey has lower pH and contains lower amount of nitrogen
9
Technical Challenge 1
Reactor with H2
Control Reactor
1200
30
Biogas
Acetate
Propionate
Butyrate
Valerate
800
400
15
0
0
0
20
40
60
2000
50
1600
40
1200
30
800
20
400
10
0
80
0
0
20
Time (d)
60
80
80
100
8
60
pH
7
40
6
20
5
0
0
20
40
60
80
60
7
6
40
5
0
20
Time (d)
Time (d)
pH 7.8
68% CH4
8% CO2
24% H2
40
pH 7.3
55% CH4
45% CO2
60
80
Biogas composition (%)
CO2
Biogas composition (%)
80
pH
8
10
40
Time (d)
pH
CH4
H2
VFA concentration (mM)
1600
VFA concentration (mM)
Biogas production rate (mL/L/d)
45
Biogas production rate (mL/L/d)
2000
Technical Challenge 2
Lower gas-liquid mass transfer rate of hydrogen
Solutions: Hollow fiber membrane
Biogas
H2
H2
Influent
Hollow Fiber
Membrane
Membrane module
11
Liquid
H2
Liquid
Effluent
Membrane
module
Technical Challenge 2
• Bubbleless diffusion of
hydrogen could be
achieved by using hollow
fiber membrane
• There was no detectable
H2 left in the produced
biogas, and CH4 content
was as high as 90-95%
12
On-going Research
Biogas
• In-situ biogas upgrading in UASB
H2
Effluent
Membrane
module
• Microbial community characterization
Liquid
recirculation
Influent
UASB
13
Concept 2: ex-situ biogas upgrading
H2
Biogas with high
CH4 content
Water
Electrolysis
Biogas
Mixed
hydrogenotrophic
culture
Biogas reactor
Organic wastes
14
Effluent
Enriched mixed cultures
Mesophilic
Thermophilic
• Enrichment at thermophilic temperature (55 oC) resulted in CO2 and H2 bioconversion rate of 320
mL CH4/(gVSS·h), which was more than 60% higher than that under mesophilic temperature
(37oC).
15
Reactor performance
1h
Gas flow rate (L/(Ld))
25
Gas loading rate
Biogas production rate
20
15
2h
10
4h
5
Upgraded Gas Composition (%)
0
100
80
CH4
60
H2
CO2
40
20
0
0
20
40
60
80
100
120
140
Time (d)
• Higher CH4 (90-95%) content could be achieved with lower gas retention time
16
Conclusions
• Innovative methods for biogas upgrading has been developed
• pH increase and gas-liquid mass-transfer are the two main challenges for in-situ
biogas upgrading
• CH4 content between 90-95% could be obtained by co-digestion of manure and
whey when using hollow fiber membrane for H2 diffusion
• For ex-situ biogas upgrading, thermophilic enriched culture is more effective
• CH4 content as high as 95% could be obtained under lower gas retention time (2h)
• Surplus electricity from wind mill could be stored as biomethane in this process
17
Achievements
1 Funding from Danish Agency for Science, Technology and Innovation
An innovative process for simultaneous utilization of hydrogen and in-situ
biogas upgrading, 3,240,000 DKK
2 Publication
Gang Luo, Sara Johansson, Kanokwan Boe, Li Xie, Qi Zhou, Irini Angelidaki.
Simultaneous hydrogen utilization and in-situ biogas upgrading in an
anaerobic reactor. Biotechnology and Bioengineering, 2012,109, 1088-1094
Gang Luo, Irini Angelidaki. Integrated biogas upgrading and hydrogen
utilization in an anaerobic reactor containing enriched hydrogenotrophic
methanogenic culture. Biotechnology and Bioengineering, 2012, In press.
1 Patent
Irini Angelidaki, Poul Lyhne, Gang Luo. Methods and apparatus for hydrogen
based biogas upgrading, US patent, Application number：61/563,247
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• Irini Angelidaki
• Gang Luo
19
Email: iria@env.dtu.dk
Email: gangl@env.dtu.dk