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Biochar Production by

Pyrolysis and its effects on plant

growth & Carbon sequestration

Roger S Swift1 and Michael H B Hayes2 1Queensland Alliance for Agriculture and Food Innovation, University of Queensland, Australia

2Carbolea Research Group, University of Limerick, Ireland

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Why the interest in Biochar?

Biochar can be made from a wide range of organic residues (mainly derived from agriculture & forestry)

Also from urban wastes & residues remaining after biofuel production processes

Biochar is very stable and can last for ~1000 yr or more (depending on chemical composition)

Therefore it can be used to

Sequester Carbon from the atmosphere for a long time

But what do you do with it?

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Carbon Sequestration in Soil

An attractive possibility is the addition of Biochar to soils as an ‘improver’

Soil is the largest terrestrial reservoir of C (~3x atmosphere & ~2.5x vegetation) and has a large storage potential capacity

The biochar must be at least benign or preferably beneficial to plant growth (but must not be harmful to plants, micro-organisms or the environment)

There is growing evidence that it can increase plant production when prepared and used correctly

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How is biochar made? – pyrolysis

Table: Typical product yields (dry wood basis) obtained by different modes of pyrolysis of wood

Mode Conditions Liquid Gas Char

Fast pyrolysis moderate temperature, around 500°C, short hot vapour residence time ~1 s

75 % 13 % 12 %

Intermediate pyrolysis

moderate temperature, around 500°C, moderate hot vapour residence time ~10-20 s

50 % 30 % 20 %

Slow pyrolysis (carbonisation)

low temperature, around 400°C, very long solids residence time

30 % 35 % 35 %

Gasification high temperature, around 800°C, long vapour residence time

5 % 85 % 10 %

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Pyrolysis Conditions Used

Slow pyrolysis: low heating rate

Biochar, from Miscanthus x giganteus chips and other plant sources using a lab-scale pyrolyser (1 dm3) @ atmospheric pressure.

Various temperatures & residence times

Biochars also produced from other types of organic waste (eg sugar trash & bagasse, green urban waste etc)

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Characterisation of biochars

Conditions

400°C for

10 min

500°C for

30 min

600°C for

60 min

Yield of biochar

(Miscanthus @ 10% H2O)

30% 25% 20%

Surface area, m2/g 1.4-1.7 3.9-7.9 50.9-51.1

C 74.8 79.7 85.1

H 4.3 3.2 2.4

Volatile/fixed C

content

70/30% nd 40/60%

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Scanning Electron Micrograph

Miscanthus

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Effects of temperature of biochar

pyrolysis on biochar morphology

400°C 600°C

800°C

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Loss of cellular structure following

biorefining and pyrolysis of residue

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13CNMR spectroscopy- Miscanthus

Carbohydrate

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13C NMR spectroscopy-biochars

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NMR - Biomass vs biochar

Carbohydrate

Aromatic C

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21st day 5% biochar

10% biochar

1% biochar

Control

Effect of Biochars on plant growth

Control

Control

Miscanthus biochar Miscanthus biochar

Miscanthus biochar

Control biochar

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Effect of biochars on plant

growth

Conditions 400°C

for

10 min

500°C

for

30 min

600°C

for

60 min

Yield of dry matter as

weight % of control

76.6 135 165

Growth of maize seedlings in soils amended with biochars (3% w/w),

prepared under different conditions.

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Effect on maize growth–different

char sources

Biochar source Control Willow Pine Miscanthus

Yield of dry

matter after 28

days as weight %

of control

100 128 135 153

Growth of maize seedlings in soils amended with biochars (5% w/w),

prepared at 500ºC for 10 mins.

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Effect of amount of added Biochar

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Treatments

Sand + B

ioch

ar 0 t/

ha

Sand + B

ioch

ar 10 t/

ha

Sand + B

ioch

ar 30 t/

ha

Sand + B

ioch

ar 50 t/

ha

Sand + B

ioch

ar 100 t/

ha

Weig

ht

(g)

0

10

20

30

40

50

Fresh leaf weight

SEM: 1.36; CV%: 23.23

Effect of Biochar on plant growth

Lettuce

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Biochar pores provide a benign, protected

location for beneficial microbial activity

bacteria

fungi

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Arbuscular mycorrhizal fungi –

Enhanced Phosphate Utilisation

a) b)

Plant roots from pot trial

no biochar added

Plant roots from pot trial

biochar added

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Biochar - Important aspects

Level of porosity

Pore size distribution & continuity

Surface area & surface properties

(hydrophobicity, surface functional

groups, charge)

Composition of starting material

Preparation conditions (temp & time)

Minimal residual condensate & volatiles

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Biochar and Carbon Sequestration

Under the right conditions (location,

availability of material etc) production of

biochar using unwanted or under-

utilised wastes followed by addition of

biochar to soil (where plant growth is

enhanced) has the potential to sequester

large amounts of atmospheric carbon

for a long period using existing and

relatively cheap technologies

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SOIL AMENDMENT

BIOCHAR

Chemical conversions

BIO-OIL

Pyrolysis

Chemical industry

GAS

GasificationCatalytical

gasification

BIO SYNGAS-

Thermo-chemical conversion

FEEDSTOCK PRE-TREATMENT

THERMAL CONVERSION

FEEDSTOCK

3

C C

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Thank you for your Attention

Contributors

Ireland

Michael Hayes

J.J. Leahy

C. Byrne

W. Kwapinski

A. Piterina

Australia

Roger Swift

J. Kochanek

K. Upadhyay

J. Fleming