ConfidentialA European Project supported within the Seventh Framework Programme for Research and Technological Development

Castro (LE), Italy, September 22nd 2011Speaker : Alessandro Spagni (ENEA)

EuroBioRef Summer School 18-24 Sep 2011

From lab scale to full scale biogas plants(R. Farina – A. Spagni)

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Outline● General

● What can be used to used as substrate?

● Pretreatment

● Design criteria

● Reactor for biogas production from biomass

● Reactor for biogas production from wastewater

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Substrates

● Several substrates can be used:● Biomass● Energy crops●Waste●Wastewater● Biogas production can be designed as the “final

treatment” (or last step) in the biorefinery concept

● How can we evaluate the biogas potential?● The Biochemical methane potential

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Example of a biorefinery

Algae

biodisel Glycerin

H2

H2

CH4

CH4

MFC

OFMSW

wastes

biomass

PHA

Ethanol

Wastewater

H2

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Process and oxygen

● Respiration

● Anoxic respiration

422291918 NHO8H18COHO17.5NOHC

OHOHCONOHCHNO 2222

136

5

67

65

3

CH3COO- CH4 + CO2 .

● FermentationHCO3- + 4H2 CH4 + 2H2O + OH-

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Process and oxygen

● Aerobic condition● If oxygen is present

● Anoxic conditions● oxygen absent but other inorganic electron acceptors are

present● Anaerobic digestion

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Organic matter CO2+H2O

Synthesis New biomassGrowth

Energy

Bacterial cell

O2

Yield

1-Yield

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Kinetics: Growth and hydrolysis

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Bs

XKS

SVV

max

Bhh XXsKr

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Kinetics and environmental conditions

● Aerobic microorganisms● Growth rate = 6 d-1● Yield up to 67%

● Anoxic● both 10-20% smaller than aerobic● Anaerobic

● Growth rate < 1 d-1● Yield up to 10%

● Hydrolysis: no big differences

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Kinetics and environmental conditions

● Methanogens are strictly anaerobic

● Competition

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Ammonia inhibitionAmmonia usually accumulates in the reactors

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OHNHOHNH 3324

Sulphate reductionCompete for substrates

SHSSO 222

4

Not appropriate when sulphate conc is high

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75%

28%72%

23%52%

Organic matter

Acetogenic bacteria

Homoacetogenic bacteria

Lipids, Alchols, etc.

ACETATE H2 + CO2

Acetoclastic methanogenic

bacteria

Methanogenic

bacteria

CH4 + CO2 CH4 + H2O

carbohydratesproteins

lipids

5%20%

100%

Hydrolytic fermentative bacteria

Disintegration

Hydrolysis

Acidogenesi

Methanogenesis

Rat

e

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Several different microorganisms work togheter to produce methane

● Can we use pure cultures?●Substrate characteristics limits●Process limits

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Process conditions

● Temperature●Psychrophilic: no heating ●Mesophilic 35-37°C●Thermophilic 55°C

● pH● Nutrients?●Add micronutrients●Waste design

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Cumulative biogas production of methane and biogas at different temperatures

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Organic matter measurement

● Volatile solids (VS) ● COD (chemical oxygen demand)

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COD (chemical oxygen demand)is an estimation of the electrons involved

Organic matter CO2+H2O

Synthesis New biomassGrowth

Energy

Bacterial cell

O2

Yield

1-Yield

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Biodegrabality

● What does “biodegradable” means when you want to treat a substrate with microorganism?

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Estimate the methane productionBMP (biochemical methane potential) Test

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InoculumSubstrate(Water)BufferN2

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Gas measurement systems

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Example of a cumulative biogas production graph

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Example of a cumulative biogas production graphcu

mul

ativ

e bi

ogas

ml

days

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BMP

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LVs

LgVS

LbVsVg

LBMP

VS

CHnCHCH

VS

CHn

4444

10035.0

%4

4

deg

COD

CHn

VS

COD

VS

CHn

radability

gL

gg

VSCOD

gL

BMPBMP

1g of DEGRADED COD produce approx. 350 mL of methane

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PretreatmentsNote: several substrates do not require pretreatment for methane production

● Mechanical● The most used (mills, extrusions)● Reduce size (important for biological activity)

● Biological ● Enzymes

● Chemical● Acids or alkali

● Thermal● sometimes used in combination

● it is much better to do not use27

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Extrusion

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Structure of a ligno-cellulosic compound

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Cellulosepolysaccharide consisting of a linear chain of several hundred to over ten thousand β(1→4) linked D-glucose units

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Cellulose and starch

StarchAlpha

CelluloseBeta

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Cellulose, hemicellulose

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Lignin

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Design – important parameters● HRT: hydraulic retention time● SRT: solids retention time● For plant for biogas production from solids (or semisolids)

HRT=SRT● For wastewaters SRT>>HRT

● OLR: organic loading rate

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QVHRT

Q, Cin

V

VCinQOLR *

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Design

● V: volume of the reactor (m3)● HRT (d)● Q = flow of the materials to be treated (m3/d)

● Referenced HRT or can be estimated by lab-scale experiments

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QHRTV *

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Example of a cumulative biogas production graph

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Cumulative and specific biogas production at different HRT in batch test (LfU, 2007) modified

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A

B

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Design

● V: volume of the reactor (m3)● Mom: mass of organic matter, as SV or COD, introduced in the unit of

time (kg/d )● OLR: mass of organic matter, as SV or COD, introduced in the unit of

time (kgm3/d)

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OLRMV om

OLRCinQV *

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Plants Classification according● Water content of the substrate

● Wet - dry solids < 15%● Semiwet – 15 < d.s. < 20 ● Dry – dry solids > 20%

● Temperature ● Psychrophilic: no heating ● Mesophilic 35-37°C● Thermophilic 55°C

● Solids management (if HRT is equal or not to SRT)● Feeding regime (continuous or discontinuous)● Stages of the process: single or multiple

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How to chose for

● Temperature● Solids management (HRT and SRT)● Feeding regime?

● Stages of the process

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75%

28%72%

23%52%

Organic matter

Acetogenic bacteria

Homoacetogenic bacteria

Lipids, Alchols, etc.

ACETATE H2 + CO2

Acetoclastic methanogenic

bacteria

Methanogenic

bacteria

CH4 + CO2 CH4 + H2O

carbohydratesproteins

lipids

5%20%

100%

Hydrolytic fermentative bacteria

Disintegration

Hydrolysis

Acidogenesi

Methanogenesis

Rat

e

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CSTR, (Continuous Stirred-Tank Reactor,

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Chines type reactor (Gunnerson C.G., 1986)

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Indian type reactor

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Scheme of the DRANCO process (De Baere, 2010)

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Biogas from wastewaters● The most important difference of the biogas production plant from

wastewater compared with solids materials is the retention of the microbial community.

Some strategies or apparatus are addedIn order of separating the HRT from SRT

SRT high enough to allow the retention of the slowest growing bacteria (methanogens)

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Kinetics: Growth and hydrolysis

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Bs

XKS

SVV

max

Bhh XXsKr

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Biogas from wastewaters

WATER

SOLIDS

HRT of h or dSRT of months

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Type of wastewater

● Usually for high concentrated wastewater● Temperature: enough energy production for

heating the system● This is not a so big problem for Solids substrate treatment

● Industrial WW (e.g. agro-industrial)● COD > 5,0 g/L

● Soluble and particulate COD

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Anaerobic wastewater treatment processes

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CSTRSludge retention

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Anaerobic wastewater treatment processes

54Sequencing batch reactor

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Scheme of (Up flow) Anaerobic Filter

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Different types of packing material for anaerobic filters

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Anaerobic granules scheme of UASB reactor

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UASB

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EGSB, expanded granular sludge bed

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Pilot-plantUASB

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Some comments about process management

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Ammonia concentration inside a reactor for methane production from biomass from the production of antibiotics (yeast waste)

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Biogas productivity (waste from antibiotics production)

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0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 50 100 150 200

Biog

as (

mL/

gior

no)

giorni

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Membrane

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Membrane

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Membrane

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Biogas production using a membrane anaerobic reactor

72Time (d)0 50 100 150 200 250

Bio

gas

prod

uctio

n (L

/d)

0

10

20

30

40

50

60

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HR

T (d

)0

20406080

100120140

CO

D (g

/L)

051015202530

CODinCODout

Time (d)0 50 100 150 200 250

OLR

[gC

OD

/(L*d

)]

02468

10121416

(a)

(b)

(c)

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Time (d)0 50 100 150 200 250

CO

D re

mov

al (%

)

20

40

60

80

100

120

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Time (d)0 50 100 150 200 250

Vol

atile

fatty

aci

ds (g

/L)

0

2

4

6

8

10

12AceticPropionicn-butyric

Time (d)0 50 100 150 200 250

pH

5.5

6.0

6.5

7.0

7.5

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Anaerobic processes and wastewater treatment

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Biological hydrogen production via dark fermentation

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75%

28%72%

23%52%

Organic matter

Acetogenic bacteria

Homoacetogenic bacteria

Lipids, Alchols, etc.

ACETATE H2 + CO2

Acetoclastic methanogenic

bacteria

Methanogenic

bacteria

CH4 + CO2 CH4 + H2O

carbohydratesproteins

lipids

5%20%

100%

Hydrolytic fermentative bacteria

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Select for H2 production● Thermal treatment of the inoculum

● pH

● HRT

● Reactor temperature

CSTR

VFABIOMASS

H2

VFA

BIOMASS

Heat

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H2 production Dark fermentation and anaerobic digestion

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CSTR

VFA

H2

CSTR

CH4

Waste

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0 1 2 3 4 5 10 20 30 40 50 60 70 80

CG

P (L

/kgC

OD

)

050

100150200250300

BHP BMP

0 1 2 3 4 5 6 7 10 20 30 40 50 60

CG

P (L

/kgC

OD

)

050

100150200250300

H2 CH4

BMPBHP

0 1 2 3 4 5 6 7 10 20 30 40 50 60 70 80 90

CG

P (L

/kgC

OD

)

050

100150200250300

BHP BMP

a

b

c

0 1 2 3 4 5 6 7 10 20 30 40 50

CG

P (L

/kgC

OD

)

050

100150200250300

BHP BMP

Time (d)0 1 2 3 4 5 6 7 10 20 30 40 50

CG

P (L

/kgC

OD

)

050

100150200250300

BHP BMP

d

e

Cumulative gas production (CGP) with glucose (a), common wheat (b), durum wheat (c), mashed potato (d) and steam peeling potato (e) wastes.

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Biological hydrogen productionDark fermentation and photo-fermentation

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PHA

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75%

28%72%

23%52%

Organic matter

Acetogenic bacteria

Homoacetogenic bacteria

Lipids, Alchols, etc.

ACETATE H2 + CO2

Acetoclastic methanogenic

bacteria

Methanogenic

bacteria

CH4 + CO2 CH4 + H2O

carbohydratesproteins

lipids

5%20%

100%

Hydrolytic fermentative bacteria

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PHA

● Some bacteria accumulate PHA from organic acids ● it happens when this is a competitive advantage● A nutrient limitation● Alternation of environmental conditions

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PHB metabolism

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Anaerobic conditions

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Aerobic conditions

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And now… a movie to finish