Innovative methods for biogas upgrading by the addition

of hydrogen to anaerobic reactor

Gang Luo, Postdoc

Irini Angelidaki, Professor

BioEnergy Research Group

2

Biogas production and utilization

• Biogas can be produced from all kinds of organic wastes/residues

• Biogas utilization as vehicle fuel or natural gas is very promising

Organic

substrate

Digested

substrate

Biogas

50-70% CH4

30-50% CO2

Anaerobic reactor

Electricity

Heat

CH4>95%

Vehicle fuels

Natural gas

Organic

substrate

Digested

substrate

Biogas

50-70% CH4

30-50% CO2

Anaerobic reactor

Organic

substrate

Digested

substrate

Biogas

50-70% CH4

30-50% CO2

Anaerobic reactor

Electricity

Organic

substrate

Digested

substrate

Biogas

50-70% CH4

30-50% CO2

Anaerobic reactor

Heat

Electricity

Organic

substrate

Digested

substrate

Biogas

50-70% CH4

30-50% CO2

Anaerobic reactor

CH4>95%

Vehicle fuels

CH4>95% CH4>95%

Vehicle fuels

CH4>95%

Natural gas

Vehicle fuels

CH4>95%

Natural gas

Vehicle fuels

CH4>95%

Natural gas

Vehicle fuels

CH4>95%

Natural gas

Vehicle fuels

CH4>95% CH4>95%

Vehicle fuels

CH4>95%

Natural gas

Vehicle fuels

CH4>95%

Natural gas

Vehicle fuels

CH4>95%

Natural gas

Vehicle fuels

CH4>95%

Natural gas

Vehicle fuels

CH4>95%

3

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!

4

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

5

• 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

Advantages

6

Concept 1: In-situ biogas upgrading

• Very simple process for biogas upgrading

Organic wastes

Biogas with high

CH4 content

Effluent

Water

Electrolysis

H2

Biogas reactor

7

Manure as substrate

8

Manure as substrate

• 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

50 55 60 65 70 75 80 850

400

800

1200

1600

2000

Met

han

e pro

du

ctio

n (

ml/

d)

Time (d)

Reactor with hydrogen

Control

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

9

Increase of pH to higher than 8.0

Solutions: Co-digestion

On-line pH control

Technical Challenge 1

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

10

0 20 40 60 800

400

800

1200

1600

2000

Time (d)

Bio

gas

pro

du

ctio

n r

ate

(mL

/L/d

)

0

10

20

30

40

50

VF

A co

ncen

tration

(mM

)

0 20 40 60 805

6

7

8

Time (d)

pH

40

60

80

Bio

gas co

mp

ositio

n (%

)

0 20 40 60 805

6

7

8

pH

CH4

H2

CO2

Time (d)

pH

0

20

40

60

80

100

Bio

gas co

mp

ositio

n (%

)

0 20 40 60 800

400

800

1200

1600

2000

Biogas

Acetate

Propionate

Butyrate

Valerate

Time (d)

Bio

gas

pro

du

ctio

n r

ate

(mL

/L/d

)

0

15

30

45

VF

A co

ncen

tration

(mM

)

Technical Challenge 1

Reactor with H2 Control Reactor

pH 7.8

68% CH4

8% CO2

24% H2

pH 7.3

55% CH4

45% CO2

11

H2

Liquid

Liquid

Membrane module

H2

Hollow Fiber

Membrane

Influent Effluent H2

Biogas

Membrane

module

Technical Challenge 2

Lower gas-liquid mass transfer rate of hydrogen

Solutions: Hollow fiber membrane

12

• 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%

Technical Challenge 2

13

• In-situ biogas upgrading in UASB

• Microbial community characterization

On-going Research

Influent

Effluent H2

Biogas

Liquid

recirculation

Membrane

module

UASB

14

Concept 2: ex-situ biogas upgrading

Organic wastes Effluent

Water

Electrolysis

Biogas reactor

H2

Biogas

Biogas with high

CH4 content

Mixed

hydrogenotrophic

culture

15

• Enrichment at thermophilic temperature (55oC) 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).

Enriched mixed cultures

Mesophilic Thermophilic

16

Reactor performance

• Higher CH4 (90-95%) content could be achieved with lower gas retention time

0

5

10

15

20

25

0 20 40 60 80 100 120 1400

20

40

60

80

100

1h

2h

Gas

flo

w r

ate

(L/(

Ld

))

Gas loading rate

Biogas production rate

4h

Upgra

ded

Gas

Com

posi

tion (

%)

Time (d)

CH4

H2

CO2

17

• 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

Conclusions

18

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

Achievements

19

• Irini Angelidaki Email: iria@env.dtu.dk

• Gang Luo Email: gangl@env.dtu.dk