23 April 2014

Challenge the future

Delft University of Technology

Biomass Energy Addressing the rate limiting step

Prof.dr.ir. Jules B. van Lier

2

Biomass COD is created by the photosynthetic reduction of

CO2.

Biomass Energy: how does it start?

CODtheo. = 8(4n+a-2b-3d)/(12n+a+16b +14d) mg COD/mg CnHaObNd

CnHaObNd + ¼ (4n+a-2b-3d) O2 nCO2 + ½(a-3d)H2O + dNH3

+ Energy!!!!

CO2 CnHaObNd

N, P, K

3

Energy Recovery? Anaerobic Digestion!!

(heat, carriers, electricity)

Anaerobic

conversions COD

“heat”

Sludge

Reduced liquid

compounds: VFA,

alcohols, LCFA,

alkanes??*

*Zengler et al., ’99, Nature 401,

266-269: alkanes→CH4

Electrons:

MFC/BES

Energy content

biomass:

13.5 MJ/kg COD

3.8 kWh*/kg COD

(theoretical)

“Conservation of electrons”

Reduced gases:

CH4, H2, (H2S)

4

Drivers and Application of AD

• Most widespread AD application worldwide: manure & slurry digestion:

• Biogas

• Fertiliser

•Most frequently applied scale: farm-scale digestion / domestic biogas

plants. E.g. India, China, Nepal:

• Nepal: 50,000 digesters

• China: > 30 million domestic biogas plants

• Current growing interest: industrial size biogas plants for green energy

generation and waste stabilisation

5

EU success developed in Denmark: spread out over Europe!

Germany, Austria, Sweden are leading (Germany > 3.000 manure digesters)

Note: China: > 25.000 large scale digesters for agricultural wastes!

Centralised manure (co-)digestion /

energy crops Holsworthy plant (UK),

commissioned in 2002

(Courtesy: Nova Energie).

Bio-Energy Production!

6

Crop /

residue

High value feed/

chemicals

Bioethanol/Biodiesel

Food

Biogas

Fertilizer/ Soil

conditioner Residues

valorization

Biorefinery Energy Food Industry

Anaerobic Digestion

(Pabon et al., 2013)

Role of AD for energy crops (residues)

in the bio-based economy

“Biomass cascading”

7

What energy can we expect?

Assessing the biomethane potential

Oxitop: measuring P increase:

AMPTS: Online CH4 production:

See e.g. Angelidaki et al, 2008: IWA Task group

Large volume batch digesters:

8

Manure

OFMSW

Industrial

waste

Crop

residues

Aerobic

sludge

Substrate BMP

(L CH4/ g VS)

Methane yield

(m3 CH4/ton ww)

Slaughterhouse waste 0.57 150

OFMSW 0.5-0.6 100-150

Energy crops 0.30-0.50 30-100

Straws, sugar beet

tops 0.2 - 0.4 36-145

Pig manure 0.29 - 0.37 17-22

Cow manure 0.11 - 0.24 7-14

Energy

crops

Biomethane Potential (BMP) of organic

substrates

(Lehtomaki et al, 2005)

BMP range: 0.1 - 0.6 L CH4/gVS

9

• Substrate (1): exact species, time of harvest

• Substrate (2): pre-treatments (particle size, storage,

blending)

• Inoculum: Type (source, structure), age, concentration (S/I)

• Buffer solution: type, concentration

• Macronutrients and trace elements: accessibility

• Equipment: type of bioassay (batch, continuous)

• Operating conditions: temperature, pH, sampling frequency.

(Hansen et al , 2004);(Rozzi and Remigi, 2004);

(Muller, 2004);(Colleran et al. 1992)

Intrinsic values?

Large variability in BMP literature data:

(PhD thesis Claudia Pabon (2009)) EU Cropgen project

(Banks, Univ. South., UK)

10

Up to 31%

difference in

BMP

0,41

0,35

0,31

0,34

0,31

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0,40

0,45

Mixture S/I 0.5 Mixture S/I 1.5 Mixture S/I 2.5 Granular S/I 0.5 Granular S/I 2.5

BM

P (

l C

H4

ST

P/g

VS

)BMP: Impact Substrate/Inoculum

ratio and inoculum type: Inoculum type:

Digested primary sludge

Methanogenic granular sludge S/I ratios: 0.5 – 1.5 – 2.5

(Pabon-Pereira et al, WST 2012)

sludge mixture methanogenic

granular sludge

11

101% 100%

85%

78%

86% 100%

69% 73%

0.00

0.20

0.40

0.60

0.80

1.00

1.20

5 mM 20 mM 30 mM 50 mM

BM

P (

l C

H4 -

ST

P/g

VS

0%

20%

40%

60%

80%

100%

120%

BMP not corrected blank BMP

BMP: Impact phosphate buffer

concentration..!

Max. conc.: 20 mM

Also blank test was

impacted…

(Pabon-Pereira et al, WST 2012)

12

BMP: Impact substrate pre-treatment

Increase in BMP:

Freezing: No

significant influence

Blending: Up to 40%

Dry grinded: Up to

50%

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Mustard Endive Green beans

BM

P (

l C

H4 -

ST

P/g

VS

)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Fib

er

co

nte

nt

(%V

S)

Fresh 1 cm Frozen 1 cm Frozen blended Dry grinded Fiber content

Impact blending and

grinding apparently

dependent on fibre

content

(Pabon-Pereira et al, WST 2012)

13

BMP: impact drying and grinding

depends on fibre content:

-10%

0%

10%

20%

30%

40%

50%

60%

70%

Braken Mustard Spartina Triticale Winter

bean

Endive Green

beans

% B

MP

in

cre

ase

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

Lig

nin

+C

ell

ulo

se (

g/g

VS

)

Dry grinded

Lignin+cellulose

(Pabon-Pereira et al, WST 2012)

14 14

First step AD conversion process (extent determines BMP)

Generally the overall rate limiting step

Conversion of polymeric compounds into soluble monomeric or

dimeric substrates.

Extra-cellular conversion by hydrolytic enzymes excreted by microbs

(dissolved compounds are taken up by biomass). Rate dependent

on surface availability and presence of refractory fibres!

Generally modeled using first order kinetics

Hydrolysis of particulate organic

substrates; “recap”

Batch digestion:

P= P0.e-kh.t

ln(P/P0)= -kh.t

CSTR digestion:

-kh.P + (P0-P)/SRT=0

(P0-P)/P= kh.SRT

dP/dt = -kh.P

(Eastman and Ferguson, 1991;

Hobson 1983; Noike et al. 1985).

15 15

Lignin: 15-25%

- Complex aromatic structure

- high energy content

- anaerobic non-biodegradable

Hemi-cellulose: 23-32%

- Polymer of C5 and C6 sugars

- easy to hydrolyse

Cellulose: 38-50%

- Polymer of glucose

- easy to hydrolyse

Fibres limiting hydrolysis:

Ligno-cellulosic matter

16

kh vs total fibre CROPGEN 2

y = -0,7915x + 0,8224

R2 = 0,695

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7

Total fiber (g/gVS)

-kh

kh vs lignin CROPGEN 2

y = -2,0655x + 0,6689

R2 = 0,8589

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0 0,05 0,1 0,15 0,2 0,25

lignin (g/gVS)

-kh

kh vs lignin + cellulose CROPGEN 2

y = -0,9537x + 0,7879

R2 = 0,7932

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0 0,1 0,2 0,3 0,4 0,5 0,6

lignin + cellulose (g/gVS)

-kh

Slope R2

Total fibre - 0.79 0.695

Lignin+cellulose - 0.95 0.793

Lignin -2.06 0.858

Impact fibre content hydrolysis rate

(Claudia Pabon, PhD thesis, 2009)

(EU-Cropgen)

Batch digestion:

ln(P/P0)= -kh.t

17

CSTR; hydrolysis is rate limiting; COD: 100g/l; BMP=80%

Impact hydrolysis rate on CH4

production at fixed SRT/HRT

Effect hydrolyis rate on CH4-production

0

5

10

15

20

25

0 20 40 60 80 100 120

HRT (days)

CH

4-p

rod

ucti

on

(m

3/m

3)

kh=0,05/daykh=0,2/dayBMP

G. Zeeman, WUR

CSTR digestion:

(P0-P)/P= kh.SRT

18

Observed problems in industrial

scale digesters:

• Less biogas than expected

• Production of non-stabilised digestates

• pH drops with energy rich substrates

• High effluent VFAs

ΔCH4 /Δt determined by BMP of substrate and SMA of methanogenic

biomass. Possible retardation caused by:

- inadequate mixing (drop in SMA)

- substrate overloading (drop in SMA)

- presence of refractory fibres (drop in BMP)

- inhibition of hydrolysis step (drop in BMP)

Angelidaki (2005): evaluation of 18 centralised scale biogas plants:

A large residual CH4 potential remains in main reactor…

19

Pretreatment of lignocellulose

Improved AD by pre-treating lignocellulosic biomass

- Improved accessibility of (hemi-)cellulose (higher BMP)

- Digestion of additional intermediates formed during pre-treatment (VFA,

aldehydes)

- Possibility to apply AD at high solid concentrations; no product inhibition.

Figure 1: Bonding of cellulose, hemicellulose and lignin (Keeton

et al., 1994)

(e.g. Moisier et al, 2005)

Thermo-chemical

20

A novel approach for bio-methanation

of agro-industrial residues:

Enzymatic pretreatment and subsequent high-rate bio-

methanation in EGSB reactors

Hydrolysis Simple

organic

compounds

Enzyme

addition

BSG = Brewer’s spent grain

BSG hydrolysate:

85 g COD/L!

15-20 g sugars/L

Haoyu et al., 2013, 2014

21

Start-up of EGSB reactor with pre-

hydrolysed BSG: risk of overloading!

VFA accumulation, sludge wash-out

Haoyu et al., 2013, 2014

22

Two-stage versus one-stage BSG

methanation: granule conservation

• HRT: 8h

• pH: 4.3~4.9

Influent

Pre-acidification

tank

Recyclin

g

Effluent

EGSB

Influent

One-stage, Day 16

One-stage, Day 55

One-stage, Day 70

Two-stage, Day 16

Two-stage, Day 55

Two-stage, Day 70

Haoyu et al., 2013, 2014

23

End of One-stage

Two-stage versus one-stage BSG

methanation: max. OLR 5-7 times CSTR

loading capacities

Haoyu et al., 2013, 2014

24

Sugar VF

A

CH4 Fibre

H A M

lignin

cellulose

Hemi-

cellulose

Hydrolysis rate assessed by analysing

fermentation products and biogas

Hydrolysis inhibition causing

disappointing CSTR performances?

25

0

2

4

6

8

10

12

14

16

18

20

9 10 11 12

HRT (days)

Hyd

roly

sis

(%)

Cow manure

0

2

4

6

8

10

12

14

16

18

20

0 1000 2000 3000 4000 5000 6000

NH4 (mg N/l)

Hyd

roly

sis

(%

)

1000 mg NH4+-N >4000 mg NH4

+-N

Hydrolysis at different NH4+-N

manure digestion in CSTR systems (mesophilic)

HRT = 10 days

(Zeeman,1991)

26

Lipid hydrolysis rates in relation to

NH4+

0

20

40

60

80

100

0 1 2 3 4

Time (days)

H (%

)

2000 mg NH4+-N 7000 mg NH4

+-N

Digestion of Tributyrin at

varying [NH4+]

Increase of [NH4+] did not

decrease hydrolysis rate

27

0

10

20

30

40

50

60

0 2000 4000 6000 8000 10000

Inert dissolved COD (mg/l)

Hyd

roly

sis

(%

)

Cow manure HRT 10 days

Pig manure 1 HRT 15 days

Pig manure 2 HRT 10 days

Pig manure 2 HRT 15 days

Relation between inert dissolved COD

and Hydrolysis?

Ligno-cellulosic

biomass

limiting

hydrolysis??

28

What are humic compounds: humic acids (HA) and fulvic

acids (FA)? End product of the biological decay of biota residues

• Hardly degradable organic acids

• Behave like weak polyelectrolytes

• HA higher MW than FA

• HA soluble at pH > 3.5

• FA soluble at all pH

(Engebretson & Wandruszka, 1994)

(Schulten and Schnitzer,1993) C308H328O90N5

MW = 5540Da

A closer look to humic compounds:

29

Reactivity of humic compounds? - Bind cations and other molecules

- Oxygen containing functional groups responsible for reactivity

O

OH R

OH

OH

OH

O

O

O

O

OH

O

R’ R O R R`

Phenolic & Carboxyl

Main source of binding

Humic compounds’ reactive groups:

30

Humic & Fulvic acids extraction

Fresh cow manure silage energy maize

HA FA

Fernandes et al., 2010

31

-1

1

3

5

7

0 25 50 75 100 125 150Time (hours)

Hy

dro

lysi

s (%

)

0 g/l

0.5 g/l

1 g/l

2.5 g/l

5 g/l

HA manure

-1

1

3

5

7

0 50 100 150 200 250Time (hours)

Hy

dro

lysi

s (%

)

0 g/l

0.5 g/l

1 g/l2.5 g/l

5 g/l

HA maize

Cellulose Hydrolysis

Humic Acids affecting cellulose hydrolysis

Results:

Fernandes et al., 2010 - Cellulases

- Fibrobacter succinogenes

- pH = 7

32

-1

1

3

5

7

0 25 50 75 100 125 150 175 200

Time (hours)

Hy

dro

lysi

s (%

)

0 g/l

0.5 g/l1 g/l

2.5 g/l5 g/l

FA manure

-1

1

3

5

7

0 5 10 15 20 25Time (hours)

Hyd

roly

sis

(%)

0 g/l0.5 g/l1 g/l2.5 g/l5 g/l

FA maize

Cellulose Hydrolysis

Fulvic Acids affecting cellulose hydrolysis

Results:

Fernandes et al., 2010

33

0

20

40

60

80

100

0 10 20 30 40 50Time (hours)

Hyd

roly

sis

(%)

0 g/l

0.5 g/l

1 g/l

2.5 g/l

5 g/l

HA manure

0

20

40

60

80

100

0 25 50 75 100 125Time (hours)

Hy

dro

lysi

s (%

)

0 g/l 0.5 g/l

1 g/l 2.5 g/l

5 g/l

HA maize

Tributyrin Hydrolysis

Humic Acids affecting tributyrin hydrolysis

Results:

Fernandes et al., 2010

34

What is the possible effect?

C

O

O-

O-

enzyme

cellulose

Ca 2+ Ca2+

- Cellulolytic enzymes scavenged by reactive functional

groups of humic substances (hydrolysis inhibition)

- Bivalent cations (Ca2+) mitigate inhibiting effect ? (Brons et

al., 1985; Ladd & Butler, 1970)

Effect of humic compounds on the

hydrolysis of lignocellulosic biomass?

35

How humic acid interfere cellulolytic

activity? (current research)

May Inhibit

Microbial Activity

May Inhibit Enzymatic

Activity

May Inhibit Functional

Gene Expression

May cover substrate to prevent microbial adhesion

Only hydrolysis? or more methanogenic subpopulations??

36

Turning biomass energy into a

gaseous fuel:

37

Na+ (CH3COO-)

CH4 HCO3

-

CO2

Na+

CO32-

Long live Henry’s law!!

Autogenerative high pressure digestion

(AHPD): Integrate biogas upgrading with

digestion in a single step

r = % of non-dissolved biogas

n = stoichiometric coefficient

P in bar

R = 8.3145*10-2 L Bar K-1mol-1

4 2( )* * *( )

lr

t l

VP nCH nCO R T

V V

Ralph Lindeboom, PhD thesis, 2014

38

Pre

ssure

(bar)

4

0

5

10

15

20

25

30

0 20 40 60 80 100 120

hours

6

6.2

6.4

6.6

6.8

7

7.2

7.4

7.6

7.8

Pressure pH

Which pressures are needed?

Lindeboom et al, 2012

Production of high pressure CH4 gas:

- Negligible water vapor

- Little CO2 (> 5 bar < 10%)

- Little if any H2S

- Injection in gas grid ? !!

39

Pre

ssure

(bar)

4

0

5

10

15

20

25

30

0 20 40 60 80 100 120

hours

6

6.2

6.4

6.6

6.8

7

7.2

7.4

7.6

7.8

Pressure pH

With active inoculum:

- 30 bars within few days

- Methanogenesis up to 100 bar!

Which pressures are needed?

Lindeboom et al, 2012

Production of high pressure CH4 gas:

- Negligible water vapor

- Little CO2 (> 5 bar < 10%)

- Little if any H2S

- Injection in gas grid ? !!

40

Pre

ssure

(bar)

4

0

5

10

15

20

25

30

0 20 40 60 80 100 120

hours

6

6.2

6.4

6.6

6.8

7

7.2

7.4

7.6

7.8

Pressure pH

With active inoculum:

- 30 bars within few days

- Methanogenesis up to 100 bar!

Which pressures are needed?

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200

Time (h)

Pre

ss

ure

(b

ar)

NaAc as feed

Lindeboom et al, 2012

Production of high pressure CH4 gas:

- Negligible water vapor

- Little CO2 (> 5 bar < 10%)

- Little if any H2S

- Injection in gas grid ? !!

41

Limiting factor: acidification (CO2)…

• Digestion of neutral, non-acidified compounds: pH ↓ • C6H12O6 + 2H2O 2CH3COO- + 2H+ + 4H2 + 2CO2

• VFA production and CO2 accumulation both lowers pH!

‘normal pH range CH4

production: 6-8 !’

pCO2 acidification

VFA acidification

Lindeboom et al, 2012, 2013

42

pH control using natural minerals

In-situ mineral

weathering

No need for NaOH dosing!

Wollastonite:

CaSiO3

Olivine:

Mg1.8Fe0.16Ni0.04SiO4

Lindeboom et al, 2013

4

5

6

7

8

0 24 48 72 96 120 144

pH

Time (h)

43

Addition of silicate minerals

88% CH4 + 12% CO2

50% CH4+ 50% CO2

Acetic acid

Glucose

CaSiO3(s)

Ca2+ + SiO2

CaCO3(s)

-H+

-CO2

Lindeboom et al, 2013

44

- influent feed pomp? - ΔP for membrane processes - ‘free’ injection in gas grid - etc.

Zagt et al., H2O, 2010-4

Pressure as additional energy source?

45

Conclusions

Maximising BMP requires better understanding hydrolysis

Cellulolytic and methanogenic (?) activity retarded by humic compounds

High pressure digestion technological feasible for biogenic CH4 production

AD technology world wide accepted for biomass energy recovery

Thanks for your attention!!

46

Acknowledgement

Claudia Pabon

Ralph Lindeboom

Tania Fernandes

Grietje Zeeman

Environmental Technology Lettinga Associates

Fondation

The TU Delft Group: