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1
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
2
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?
3
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
4
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 %
5
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)
6
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%
13
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
14
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.
15
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.
17
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
18
Biochar pores provide a benign, protected
location for beneficial microbial activity
bacteria
fungi
19
Arbuscular mycorrhizal fungi –
Enhanced Phosphate Utilisation
a) b)
Plant roots from pot trial
no biochar added
Plant roots from pot trial
biochar added
20
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
21
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
22
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