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BAGRUP DE RECERCA EN

BIOTECNOLOGIA AMBIENTALDEPARTAMENT D’ENGINYERIA QUÍMICA

ANAEROBIC DIGESTION

Mass balance

Sergi Astals & Joan Mata

EPROBIO - Foggia - June 2011

ITXARXA DE CENTRESDE SUPORT A LAINNOVACIÓ TECNOLÒGICA

ITXARXA DE CENTRESDE SUPORT A LAINNOVACIÓ TECNOLÒGICA

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INDEX OF CONTENTS

Oxidation state of carbon

Chemical oxygen demand

COD balance

Specific biological methane potential

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Oxidation state

• A measure of the degree of oxidation of an atom in a substance:

The oxidation state is the difference between the number of electronsassociated with an atom in a compound as compared with the number of electrons in an atom of the element.

H H+ + 1 e-

N + 3 e- N3- Reduction (a gain of electrons)

Oxidation (a loss of electrons)

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Oxidation state (OSc) of carbon

• Hydrogen +1

• Oxygen -2

• Nitrogen -3

• Phosphor +5

• Sulphur +6

• Carbon variable!!! and balance the molecular charge

Propionate C3H6O2 OSc = [-(6·+1) – (2·-2)]/3 = -2/3

AA (asparagine) C4H8N2O3OSc = [-(8·+1) – (2·-3) – (2·-2)]/4 = 1/2

Palmitic acid C16H32O2 OSc = [-(32·+1) – (2·-2)]/16 = -7/4

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Biomass yield (Y)

Aerobic conditions

C3H7O2N* CO2

NO3- N2

Anoxic conditions

C3H7O2N CO2

Anaerobic conditions

C3H7O2N CO2

O2 CO2

0 +4

0 -2

0 +4

+5 0

C3H7O2N CH4

0 +4

0 -4

CnHaObNc + H20 CH4 + CO2 + NH3

In AD only carbon change its oxidation state

* Alanine is an amino acid

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• COD is an indirect measure of the organic matter.

Chemical Oxygen Demand (COD)

• It is defined as the amount of oxygen required to oxidize the matter present in the sample, using a strong oxidizing agent under acidconditions.

• COD is expressed in terms of mg O2 L-1.

AD mass balances must be done on COD-basisAD mass balances must be done on COD-basis

Because in AD system COD is not destroyed only re-distributed

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COD classical calculation without nitrogen

OH4aCOnO

2b

4anOHC 222ban +→⎟

⎠⎞

⎜⎝⎛ −++

322b

4an/mol)O (g COD 2 ⋅⎟

⎠⎞

⎜⎝⎛ −+=

16ba12n

322b

4an

)g/ O (g COD compound2 ++

⋅⎟⎠⎞

⎜⎝⎛ −+

=

2.71Lauric acid (C12H24O2)

4Methane (CH4)

1.07Acetic acid (C2H4O2)COD (g O2 / gcompound)Compound

* Molecular formula of acetic acid is C2H4O2 while its classical representation is CH3COOH

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COD classical calculation with nitrogen

3222dban NH d OH4aCOnOd

43

2b

4anNOHC ++→⎟

⎠⎞

⎜⎝⎛ −−++

3243

2b

4an/mol)O (g COD 2 ⋅⎟

⎠⎞

⎜⎝⎛ −−+=

14d 16ba12n

3243

2b

4an

)g/ O (g COD compound2 +++

⋅⎟⎠⎞

⎜⎝⎛ −−+

=

* Molecular formula of acetic acid is C2H4O2 while its classical representation is CH3COOH

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Another way to calculate COD

+ 48g COD / mol SSO4-2S Sulphur

+ 40g COD / mol PPO3-4P Phosphorous

- 24g COD / mol NNH4+N Nitrogen

- 16g COD / mol OH2OO Oxygen

+ 8g COD / mol HH2OH Hydrogen

+ 32g COD / mol CCO2C Carbon

Equivalent CODReference compoundElement

+ 8g COD / mol chargeZero chargeCharge (+ / -)

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COD / molecompound = Σ (Mi · CODi)

• Mi: mole of element i in the compound

• CODi: theorecial COD of element i

COD / gcompound = CODcompound / MWi

• MWi: molecular weight

Another way to calculate COD

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• The methane production is related with the amount of substrate stabilized.

COD balance

• Influent COD can be divided in:

- Particulate > CODp

- Soluble > CODs

Both fraction have biodegradable and non-biodegradable compounds.

• Effluent COD can be divided in:

- Methane CODm

- Particulate > CODp

- Soluble > CODs

Microorg. are included in the particulate fraction.

COD of CO2 is 0

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COD balance

CODCH4 64 gCOD / molCH4

1 molgas 22.4 LSTP

0.35 LCH4 / g CODeliminated

COD influent

Anaerobic

Digester

CODeffluent

CODgas

CODsludge

COD influent

Anaerobic

Digester

Anaerobic

Digester

CODeffluent

CODgas

CODsludge

Biomass C5H7O2N

1.42 g COD / gnew biomass

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COD balance

CODinfluent = CODgas + CODeffluent + CODsludge

COD influent

Anaerobic

Digester

CODeffluent

CODgas

CODsludge

COD influent

Anaerobic

Digester

Anaerobic

Digester

CODeffluent

CODgas

CODsludge

CODin = CODoutSince in AD system COD is not destroyed only re-distributed

Degraded COD ends up in:

- Methane

- New biomass or sludge

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COD balance

CODi

Anaerobic

Digester

CODe

CODm

CODremoval = CODi - CODe

Methanisation = CODm / CODi * 100

Microorg.

Non-biodegradable OM

Biodegradable OM

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COD balance for an easy biodegradable waste

CODi = 100

CODremoval = 100 – 5*

Methanisation = 90%

Anaerobic

Digester

CODe = 5

CODm = 90

CODbiom = 5

* 5 COD have been degraded and converted to new biomass. However, it is taken into account when you measure the effluent COD. Methane represent between a 85 and a 95% of the degraded COD.

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COD balance for a low biodegradable waste

CODi = 100

CODremoval = 100 – 45*

Methanisation = 50%

Anaerobic

Digester

CODe = 45

CODm = 50

CODbiom = 5

* 5 COD have been degraded and converted to new biomass. However, it is taken into account when you measure the effluent COD. Methane represent between a 85 and a 95% of the degraded COD.

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Specific biological methane potential (B0) without nitrogen

242ban CO4b

8a

2nCH

4b

8a

2nOH

2b

4a -nOHC ⎟

⎠⎞

⎜⎝⎛ +−+⎟

⎠⎞

⎜⎝⎛ −+→⎟

⎠⎞

⎜⎝⎛ −+

⎟⎟⎠

⎞⎜⎜⎝

⎛

++

⋅⎟⎠⎞

⎜⎝⎛ −+

=compoundg

CHLSTP16ba12n

22.44b

8a

2n

B 40 ⎟⎟

⎠

⎞⎜⎜⎝

⎛

⋅⎟⎠⎞

⎜⎝⎛ −+

⋅⎟⎠⎞

⎜⎝⎛ −+

=CODgCHLSTP

322b

4an

22.44b

8a

2n

B 40

100n

4b

8an

%CH4 ⋅⎟⎠⎞

⎜⎝⎛ −+

=

Biogas composition

100n

4b

8an

%CO2 ⋅⎟⎠⎞

⎜⎝⎛ +−

=

* STP are standard temperature and pressure conditions 1 atm and 0 ºC

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Specific biological methane potential (B0) with nitrogen

3242dban dNHCO8

3d4b

8a

2nCH

83d

4b

8a

2nOH

43d

2b

4a -nNOHC +⎟

⎠⎞

⎜⎝⎛ ++−+⎟

⎠⎞

⎜⎝⎛ −−+→⎟

⎠⎞

⎜⎝⎛ +−+

⎟⎟⎠

⎞⎜⎜⎝

⎛

+++

⋅⎟⎠⎞

⎜⎝⎛ −−+

=compound

40 g

CHLSTP14d16ba12n

22.48

3d4b

8a

2n

B ⎟⎟⎠

⎞⎜⎜⎝

⎛

⋅⎟⎠⎞

⎜⎝⎛ −−+

⋅⎟⎠⎞

⎜⎝⎛ −−+

=CODgCHLSTP

328

3d2b

4an

22.48

3d4b

8a

2n

B 40

100n

83d

4b

8an

%CH4 ⋅⎟⎠⎞

⎜⎝⎛ −−+

=

Biogas composition

100n

83d

4b

8an

%CO2 ⋅⎟⎠⎞

⎜⎝⎛ ++−

=

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Specific biological methane potential (B0) with nitrogen and sulphur

SHfNHdCO4f

83d

4b

8a

2nCH

4f

83d

4b

8a

2nOH

2f

43d

2b

4a -nSNOHC s3242fdban ++⎟

⎠⎞

⎜⎝⎛ +++−+⎟

⎠⎞

⎜⎝⎛ ++++→⎟

⎠⎞

⎜⎝⎛ ++++

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Total organic carbon (TOC)

dban NOHC

⎟⎟⎠

⎞⎜⎜⎝

⎛

+++=

compoundgCg

14d16ba12n12TOC n

COD / TOC ratio

⎟⎟⎠

⎞⎜⎜⎝

⎛⋅⎟

⎠⎞

⎜⎝⎛ −−+

=COD g

Cg12n

328

3d2b

4an

TOC / COD

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Summary:

Compund Molecular formula C H O NMethane CH4 1 4 0 0Amino acid (Leucine) C3H13O2N 3 13 2 1Ethanol C2H60 2 6 1 0Palmitic acid C16H32O2 16 32 2 0Oleic acid C18H34O2 18 34 2 0Lipid C57H10406 57 104 6 0Valeric acid C5H10O2 5 10 2 0Butyric acid C4H8O2 4 8 2 0Glycerol C3H8O3 3 8 3 0Amino acid (Lysine) C6H14O2N2 6 14 2 2Propionic acid C3H6O2 3 6 2 0Protein (Collagen) C254H377O75N65 254 377 75 65Carbohydrate (Lactose) C12H22O11 12 22 11 0Glucose C6H12O6 6 12 6 0Acetic acid C2H4O2 2 4 2 0Lactic acid C3H6O3 3 6 3 0Biomass C5H7O2N 5 7 2 1Pyruvic acid C3H4O3 3 4 3 0Carbon dioxide CO2 1 0 2 0

Exercise 2:Calculate the: (1) OSc; (2) g COD / gcompound; (3) g C / gcompound; (4) g COD/ g C; (5) B0 (mL CH4 / gcompound & mL CH4 / g COD); (6) %CH4 of each compound

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Summary: Exercise 2:Compund Molecular formula OSc g COD / gcompound g C / gcompound g COD / g C B0 (LCH4/ gcompound) B0 (LCH4/ g COD) % CH4

Methane CH4 -4,00 4,00 0,750 5,333 1,400 0,350 100,0Amino acid (Leucine) C3H13O2N -2,00 1,52 0,379 4,000 0,531 0,350 75,0Ethanol C2H60 -2,00 2,09 0,522 4,000 0,730 0,350 75,0Palmitic acid C16H32O2 -1,75 2,88 0,750 3,833 1,006 0,350 71,9Oleic acid C18H34O2 -1,67 2,89 0,766 3,778 1,013 0,350 70,8Lipid C57H10406 -1,61 2,90 0,774 3,743 1,014 0,350 70,2Valeric acid C5H10O2 -1,20 2,04 0,588 3,467 0,714 0,350 65,0Butyric acid C4H8O2 -1,00 1,82 0,545 3,333 0,636 0,350 62,5Glycerol C3H8O3 -0,67 1,22 0,391 3,111 0,426 0,350 58,3Amino acid (Lysine) C6H14O2N2 -0,67 1,53 0,493 3,111 0,537 0,350 58,3Propionic acid C3H6O2 -0,67 1,51 0,486 3,111 0,530 0,350 58,3Protein (Collagen) C254H377O75N65 -0,13 1,51 0,551 2,751 0,530 0,350 51,6Carbohydrate (Lactose) C12H22O11 0,00 1,12 0,421 2,667 0,393 0,350 50,0Glucose C6H12O6 0,00 1,07 0,400 2,667 0,373 0,350 50,0Acetic acid C2H4O2 0,00 1,07 0,400 2,667 0,373 0,350 50,0Lactic acid C3H6O3 0,00 1,07 0,400 2,667 0,373 0,350 50,0Biomass C5H7O2N 0,00 1,42 0,531 2,667 0,496 0,350 50,0Pyruvic acid C3H4O3 0,67 0,91 0,409 2,222 0,318 0,350 41,7Carbon dioxide CO2 4,00 0,00 0,273 0,000 0,000 -- --

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Summary: Exercise 2:

0,000

0,200

0,400

0,600

0,800

1,000

1,200

1,400

1,600

-4,00 -3,00 -2,00 -1,00 0,00 1,00 2,00 3,00 4,00

OSc

L C

H 4 /

g com

poun

dMethane

Pyruvic acid

AA Leucine

Ethanol Valeric acidButyric acid

LipidOleic acid

Palmitic acid

Glycerol

AA LycinePropionic

ProteinBiomass

Acetic acidLactic acidGlucose

CH Lactose

Compounds with low OSc, more reduced, can bound more oxygen so the higher is the COD.

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Summary: Exercise 2:

0,0

10,0

20,0

30,0

40,0

50,0

60,0

70,0

80,0

90,0

100,0

-4,00 -3,00 -2,00 -1,00 0,00 1,00 2,00 3,00 4,00

OSc

% C

H 4

Methane

Pyruvic acid

AA Leucine; Ethanol

Valeric acidButyric acid

LipidOleic acid

Palmitic acid

Glycerol; AA Lycine; Propionic acidProtein

CH Lactose; Glucose; Lactic & Acetic acid; Biomass

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Summary: Exercise 2:

0,000

0,200

0,400

0,600

0,800

1,000

1,200

1,400

1,600

0,000 1,000 2,000 3,000 4,000 5,000 6,000

g COD / g C

L C

H 4 /

g com

poun

d

Butyric acid

Methane

AA Leucine

EthanolValeric acid

Glycerol

Propionic

Acetic acidLactic acidGlucose

AA Lycine

Pyruvic acid

Lipid Oleic acid

Palmitic acid

ProteinBiomass

CH Lactose

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Summary: Exercise 2:

0,0

10,0

20,0

30,0

40,0

50,0

60,0

70,0

80,0

90,0

100,0

0,000 1,000 2,000 3,000 4,000 5,000 6,000

g COD / g C

% C

H 4

AA Leucine; Ethanol

Valeric acidButyric acid

LipidOleic acid Palmitic acid

Glycerol; AA Lycine; Propionic acid

ProteinCH Lactose; Glucose; Lactic & Acetic acid; Biomass

Methane

Pyruvic acid