1. biochemical process - uni oldenburg · project planning for ... the 1907 nobel prize in...

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Henri SpanjersLettinga Associates FoundationLeAF

Biogas Compact Workshop

Project Planningfor

Biodigesters in Developingand

Industrialized Countries

26 – 28 April, 2011University of Oldenburg, Germany

From Waste to Energy – The Bio-Chemical Process

Postgraduate Programme RenewableEnergy (PPRE)

LeAFLettinga Associates Foundation 1

Content

• History• Definitions• Biochemical processes

– Hydrolysis

– Acidogenesis

– Acetogenesis

– Methanogenesis

• Reactors

2


8 ppm O 2

AIR

Interface

Water

20% O2

- organic matter

20% O2

+ organic matter

8 ppm O 2

0 ppm O 2

Natural Anaerobic Environments

LeAF

Carbon cycle

Lettinga Associates Foundation 3

Anaerobic respiration Fermentation

Respiration:plants, animals,microorganisms

Organic compounds

Photosynthesis:AlgaeGreen -plantsCyanobacteria

(Methylcompounds)

sedimentation

Aerobic

Anaerobic

(CO2)

(CH2O)n

Organic compounds

(CH2O)n

CH4

Methane-oxidizingbacteria

Methanogenicbacteria

Phototrophicbacteria

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Hey, there is a flammable gas coming out of rotting marshes and swamps!!!

ALESSANDRO VOLTAItaly

1770

� First to report about natural methane production

Some history


Figure 1 Natural gas and the chemist. John Dalton (1766–1844) collecting marsh gas by poking a stick into pond sediments (Picture by Ford Madox Brown). Marsh gas (methane, CH4, the simplest alkane) is the main component of natural gas. As shown by the work of Zengler et al. new aspects of this economically important bacterial process are still being revealed.

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Fermentation

Fermentation: process of deriving energy from the oxidation of organic compounds, such as carbohydrates, and using an endogenous electron acceptor, usually an organic compound

German chemist and zymologist, Eduard Buchner, winner of the 1907 Nobel Prize in chemistry, determined that fermentation is actually caused by a yeast secretion that he termed zymase.


Fermentation Products

• Microbial cells or biomass (single cell protein, bakers yeast, lactobacillus, E. coli, etc.)

• Microbial enzymes: catalase, amylase, protease, pectinase, glucose isomerase, cellulase, hemicellulase, lipase, lactase, streptokinase, etc.

• Microbial metabolites:– Primary metabolites – ethanol, citric acid, glutamic acid, lysine,

vitamins, polysaccharides etc. – Secondary metabolites: all antibiotic fermentation

• Recombinant products: insulin, HBV, interferon, GCSF, streptokinase

• Biotransformations: phenyl acetyl carbinol, steroid biotransformation, etc.

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Fermentation Products (cont’d)

• Alcoholic fermentation: sugars (glucose, fructose, sucrose) are converted into Ethanol and carbon dioxide

• Dark fermentation is the fermentative conversion of organic substrate to H2


Anaerobic biodegradation

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Anaerobic biodegradation

• Anaerobic biodegradation or anaerobic digestion: very complex biological and biochemical process performed by various different species of bacteria working together

• End products of anaerobic digestion are “biogas” and more bacteria that grow out of the consumed organic matter


living organisms

eukaryotes prokaryotes

archaebacteria eubacteria

extreme halophiles thermoacidophiles

Archaebacteria were the first living organisms on earth. Before there was oxygen in the atmosphere!

Methanogenicbacteria

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Reaction C6H12O6 + 6O2 → 6CO2 + 6H2O C6H12O6 → 3CO2 + 3CH4

Energy release ∆G°’ = -2840 kJ/mol glucose ∆G°’ = -393 kJ/mol glucose

Carbon balance 50% → CO2 50% → biomassa

95% → CH4 + CO2 (= biogas)

5% → biomassa Energy balance 60% → biomassa

40% → heat production 90% retained in CH4 5% → biomassa 5% → heat production

Biomass production

Fast growth of biomass, Resulting in a sewage sludge problem

Slow growth of biomass

Characteristic Aerobic Anaerobic

Comparison Aerobic - Anaerobic


Anaerobic digestion

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Scheme anaerobic biodegradationPolymers

(proteins, polysaccharides, lipids)

Monomers(sugars, amino acids, peptides)

butyratePropionate

H2 + CO2 acetate

CH4 + CO2

h

h

111

1

2 2

2

3

3

44

4Hydrolytic enzymesFermentative bacteriaSyntrophic acetogenic bacteria

Homoacetogenic bacteriaMethanogens

Methanogenic Consortium

From www.uasb.org


ADM1 Model Structure Overview

Death

Complex particulate waste and Inactive

biomass

CH4

6 7

Inert soluble

Inert particulate

Carbohydr. Proteins Lipids

Sugars Amino acids LCFA

Propionate HVa, HBu

Acetate H2

3

5

2

4

1

9


CH4 / CO2

MethanogenesisMethanogens

AcetogenesisSyntrophic acetogenic bacteria

Mono- and oligomersamino acids, sugars, fatty acids

Organic Polymersproteins carbohydrates lipids

HydrolysisHydrolytic enzymes

AcidogenesisFermentative bacteria

Volatile Fatty AcidsLactate Ethanol

AcetateH2 / CO2

Anaerobic Conversion of Organic Matter

Homoacetogenic bacteria


Hydrolysis

CH4 / CO2




AcetateH2 / CO2 Homoacetogenic bacteria

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Hydrolysis: Characteristics

• Polymeric compounds � monomer or dimeric components

• By extra-cellular enzymes• Slow process (rate limiting): dS/dt = -Kh•S• Retention time and particle size rate determining • Optimum pH = 6• Cellulose/hemicellulose degradation depends on lignin

fraction • Hydrolysis of fats hardly proceeds <15-20°C (rate limit ing)• (Product) inhibition by: LCFA. NH3, amino acids, H2?


Hydrolysis: Enzymes

• Hydrolysis of suspended solids is surface-related process

• The more specific surface, the faster the process

• Individual enzymes work at constant rate (constant T, pH)

• Number of enzymes determines the total rate

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Hydrolysis: Surface related

Rate increases

Particlebreakdown or “lysis”

More enzymes“attack” the substrate

From: Wendy Sanders

� Hydrolysis as a surface-related process


Long Chain Fatty Acids (LCFA)

Hydrolytic enzymes

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From Dr. Wendy Sanders

• Cellulose is hydrolysed by cellulase (mixture of exo-glucanases, endo-glucanases and cellobiases)

• The hydrolysis of starch is performed by a mixture of amylases that is able to hydrolyse the α-1,4 bonds and α-1,6 bonds of the amylose and amylopectin.

Hydrolysis: Carbohydrates



Hydrolysis: Proteins

• Proteinases (Peptidases + Proteases)

• Protein � polypeptides � peptides � amino acids

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� most lipids in waste(water) are present as triacylglycerides


Hydrolysis: Lipids


Bio-degradation of cellulitic matter versus lignin content

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Digestible part of wood


Acidogenesis

CH4 / CO2




AcetateH2 / CO2

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Acidogenesis: Sugars

• Release of protons (H+) and reaction products (proton acceptors)

• H2 formation (catalyzed by the enzyme hydrogenase)

• Performed by a very large group of bacteria (about 1% of all bacteria facultative fermenters)

C12H22O11 + 9 H2O → 4 CH3COO- + 4 HCO3- + 8 H+ + 8 H2

C12H22O11 + 5 H2O → 2 CH3CH2CH2COO- + 4 HCO3- + 6 H+ + 4 H2


Acidogenesis: Sugars

End products depend on circumstances, e.g.:

• Glucose fermentation in a two-step system– more reduced products like ethanol, lactate, propionate, butyrate,

CO2 and H2

• Glucose fermentation in a one-step system– acetate, H2 and CO2

• Production of acids proceeds up to pH = 4(product inhibition)

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Kinetic Properties Acidifiers / Methanogens

Process RxgCOD/gVSS/d

Yg VSS/g COD

Ksmg COD/l

µ-maxday-1

Tddays

Acidogenesis 13 0.15 200 2.0 0.35

Methanogenesis 3 0.03 30 0.12 5.8

Overall 2 0.03 –0.18 - 0.12 5.8

Acidogenesis of sugars: most rapid step!


dtdS

YdtdX

XdtdX

⋅−=

⋅µ=

Substrate availability and bacterial growth

Where: dS/dt = substrate utilisation rateY = yield coefficient

SKS

smax +

⋅µ=µ µ

S

µµµµmax

Ks

Monod’s equation:

At S = Ks → µ = ½ µmax

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Methane Capacity Exceeded

Poor BufferingCapacity

VFAincreases

pHdecreases

Unionized VFAincreasing

Methanogenic ToxicityIncreasing

Acidogenesis: Acidification


Acidogenesis: Proteins

• Organically bound N (amino acids) is released as NH4+

(Stickland reaction: oxidation-reduction)

Alanine: CH3CHNH2COO- + 3 H2O → CH3COO- + HCO3- + NH4

+ + 2 H2

Glycine: 2 CH2NH2COO- + 2 H2 → 2 CH3COO- + 2 NH3

alanine + glycine + 3 H2O → 3 acetate + 2 NH3 + NH4+ + HCO3

-

(2 NH3 + 2 H2O + 2 CO2 → 2 NH4+ + 2 HCO3

-)

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Stickland reaction

Alanine Glycine

acetate, CO2, NH4 2 acetate, 2 NH4

4 e-ATP

(ATP)

Oxidative branch Reductive branch


Acidogenesis: Long Chain Fatty Acids

• Anaerobic degradation of LCFA proceeds via β-oxidation

CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COO-

• Palmitic acid: CH3-(CH2)14-COO- + 14 H2O → 8 CH3COO- + 7 H+ + 14 H2

• With uneven numbers: acetate + propionate are formed:CH3-(CH2)14-CH2COO- + 14 H2O → 7 CH3COO- + CH3CH2COO- 7 H+

+ 14 H2

• Unsaturated LCFA are firstly hydrogenated before degradation

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Acetogenesis

CH4 / CO2




AcetateH2 / CO2 Homoacetogenic bacteria


Acetogenesis (Acetate formation)

• Conversion of fermentation products into acetic acid, CO2, and H2

• Mainly from propionic acid, butyric acid and ethanol

propionate- + 3H2O → acetate- + HCO3- + H+ + 3H2 ∆ G0’ = + 76.1 kJ/mole

butyrate- + 2H2O → 2 acetate- + H+ + 2H2 ∆ G0’ = + 48.1 kJ/mole

ethanol + 2H2O → acetate- + H+ + 2H2 ∆ G0’ = + 9.6 kJ/mole_______________________________________________________________________________________________

4 H2 + CO2 → CH4 + 2H2O ∆ G0’ = -138.9 kJ/mole

Need for syntrophic associations !!!

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0

50

-50

-100

∆G’ (kJ/mole)

pH2=-log (H2)

propionate- + 3H2O → acetate- + HCO3- + H+ + 3H2

2 4 6

4 H2 + CO2 → CH4 + 2H2O

butyrate- + 2H2O → 2 acetate- + H+ + 2H2Reactionpossible

Reactionimpossible

Methanogenic niche

High H2pressure

Low H2pressure

8

ba

dc

BA

DCRTGG

][][

][][ln'' 0 ⋅

⋅+∆=∆

Impact of pH2 on thermodynamics


Methanogenesis

CH4 / CO2




AcetateH2 / CO2

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Methanogenesis

• Aceticlastic methanogenesis (70%):

CH3COOH → CH4 + CO2

• Hydrogenotrophic methanogenesis (30%):

CO2 + H2 → CH4 + CO2


∆G0 (kJ/mole CH4)

4H2 + CO2 => CH4 + 2H2O -130.4

4HCOOH => CH4 + 3CO2 + 2H2O -119.5

4CO + 2H2O => CH4 + 3CO2 -185.5

4CH3OH => 3CH4 + CO2 + 2H2O -103.0

CH3OH + H2 => CH4 + H2O -112.5

4CH3NH3 + 2 H2O => 3CH4 + CO2 + 4NH4+ - 74.0

2(CH3) 2NH2 + 2H2O => 9CH4 + 3CO2 + 4NH4+ - 74.0

CH3COOH => CH4 + CO2 - 32.5

Most important substrates: hydrogen and acetate

Furthermore: formate, carbon monoxyde, methanol and methylamines

Methanogenesis: Substrates

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Maximum Production of Biogas

0,86

0,400,50

0,00

0,20

0,40

0,60

0,80

1,00

1,20

1,40[N

m³/k

g]

Lipids Carbohydrates Proteins

production of biogasproduction of methane

(ATV-DVWK M 363)

LeAFLettinga Associates Foundation 43Biochemical processes and biogas

Animal manure

Inorganic Organic

Compounds of Cu, P, K, Zn, Mn, Co, Ca, Fe, H, O

Phosphorous Nitrogenous Carbonaceous Sulphurous

Inositiol phosphate,

phospholipids, nucleic acids,

ATP

Inorganic phosphates

Proteines

Peptides

Amino acids

N, NH4

Lipids

Glycerol

Fatty acids

Sugars

Alcohols

Carbohydrates

Fibers

Sulphites

Volatile acids

H2O CH4 CO2

Celluloselignin HsS

Biogas Practice AreaBiogas Practice AreaBiogas Practice Area

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Take-home message

• Anaerobic microbial conversion differs from aerobic

• Anaerobic digestion is a complex process

• Ultimate COD removal via production of CH4

• Anaerobic bacteria have a narrow substrate spectrum: complex consortia are needed for complete COD removal

• Environmental factors affect the process


Reactors

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Water content in the reactor

�wet (TS <= 10%)�dry (TS = 30-35%)

Process management

�Continuous Stirred�Plug-Flow

Temperature�Mesophilic (35-37ºC)�Thermophilic (55-60ºC)

Steps of process�Single-stage�Multi-Stage

Operational mode�Semi-continuous�Discontinuous (Batch)

Form of reactor�vertical (conventional, oval, etc.)�horizontal

Mixing process�Agitation�Circulation�Percolation

Different Technologies of Process Management


Fixed Dome Domestic Digester

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Digester: SchematicDigester with rubber membrane cover > 50 % of

all digesters


Biogas plant in the UK

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Completely mixed

(Bio)gas

influent effluent

Relative capacity: 1

Physical retention


Immobilised biomass


Enhanced contact


Development of “high-rate” anaerobic treatment systems


UASB and EGSB

Auto immobilization / granulation

UASB

EGSB

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Reactor Technologies for Liquids

influent

influent influentinfluent

influent

influent

effluent

effluent

effluent

effluent

effluenteffluent

gas

gasgas

gas gasgas

UASB-Reactor

Fluidized bed Reactor Fixed bed Reactor Anaerobic Contact Reactor

Biobed-Reactor IC-Reactor

second stage

first stage

sludge bed

reci

rcul

atio

n

reci

rcul

atio

n

reci

rcul

atio

n

(loop

)

(loop

)


UASB Reactor: Sewage

Bucaramanga, Colombia, 12000 m3/d

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UASB reactors: Sewage

Mirzapur, India, 14 m3/d plant


UASB: Sewage

Accra, Ghana

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Anaerobic Industrial Wastewater TreatmentAnaerobic UASB-Reactor CSM


(Kraul & Wilkening u. Stelling)

IC-Reactor: Distillery Hanover

1. biochemical process - uni oldenburg · project planning for ... the 1907 nobel prize in...

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