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Effect of biochar application at a trace-elements polluted area on soil carbon stability
Paloma Campos1, Ana Z. Miller2, Heike Knicker1, Águeda Sánchez-Martín1,
Elena Fernández-Boy3, José María De la Rosa1
1. Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS-CSIC), Av. Reina Mercedes 10, 41012, Sevilla, Spain
2. HERCULES Laboratory, University of Évora, Évora, Portugal.
3. Facultad de Química, Universidad de Sevilla. Profesor García González St. 41012, Seville, Spain
pcamposdm@irnas.csic.es
Session SSS5.5Tuesday, 5 May 2020
BIOCHAR
Bio-oilCondenser
Air
Combustion
chamber
Gases(syngas) (CH4)
Pyrolysis
reactor
(O2 < 2%)
Heat
Biochar (BC) is the carbonaceous solid residue produced through the thermochemical conversion (pyrolysis) of
biomass under low O2 atmosphere.
What is biochar?
Soil
Soilremediation
Management of organic
wastes
pcampos@irnas.csic.es
Biochar applicationsDifferent applications:
Biochar potential to immobilize trace elements
Direct mechanisms
Chemisorption
• Adsorption in oxygenated functional groups (release H+)
• Cationic exchange (Na, Ca, S, K, Mg)
Physisorption
• Electrostatic attraction (π electrons)
Precipitation
• Mineral fraction / biochar ash
Indirect mechanisms
Changes in pH
Organic matter and soluble C
• Priming effect and DOC
Availability of P
Competition with As
Redox
Improvement of soil fertility, plant growth
Reduction of soil nutrient leaching
Mitigation of green house gases
C sequestration
Soil remediation
Biochar properties:
pcampos@irnas.csic.es
Biochar stability?Stability of biochars under debate
De la Rosa et al. (2018)
Main objetive: Determine the effects of biochar on C stability in trace
element polluted soils.
MRTbiochar>1000 years, when H/Corg<0.4
MRTbiochar>500, when 0.4<H/Corg<0.7
(Lehmann and Joseph, 2015)
Reference Scale of
estimated
MRT
MRT (years)
Masiello and Druffel (1998) Millennial 2400-13900
Cheng et al. (2006) Millennial 1000
Kuzyakov et al. (2009) Millennial 2000
Novak et a. (2010) Millennial 1400-51000
Zimmerman (2010) Centennial to
millennial
100-100000
MRT2 (years)
Pure Cambisol 5.7
Biochars+Cambisol 7.9-43.9
MRT2 (years)
Pure Cambisol 15.7
Biochar+Cambisol 17.4
Pure biochar 87
Dos Anjos Leal et al. (2019)
pcampos@irnas.csic.es
Respiration experiment – C stability
Respicond apparatus IV
(25°C)
10-20 g soil; 0.5-4 g chars
60% WHC, inoculated
Incubation vessel
KOH
CO2
Multimeter
pcampos@irnas.csic.es
Respiration experiment – C stability
KOH-solution
Electrodes
Sample
1. CO2 released by the sample is
absorbed in the KOH-solution and
forms carbonate, which decrease the
conductivity.
2. This change is conductivity is
measured by the respirometer.
3. From these values can be calculated:
- Cumulative carbon loss
- Degradation rates
- Mean residence time.
pcampos@irnas.csic.es
Respiration experiment – C stability
Re
ma
inin
gC
r(%
ofC
tota
l)
Incubation time (h)
94
95
96
97
98
99
100
101
0 500 1000 1500 2000 2500
Degradation rate constant
Fast pool Slow pool
Cr (%) =Cf*e(-kf*t)+ CS*e(-ks*t)
R2 =0.998
pcampos@irnas.csic.es
HPS - Highly Polluted SoilMPS - Moderately Polluted Soil
Green Corridor of Guadiamar (25 km north Seville)
2 soil (Typic Xerofluvent):
MPS: Moderately Polluted Soil
HPS: High Polluted Soil
WHC (%) Bulk density (g/ml) pH (CaCl2) EC (S/cm) % C
HPS 32.73 1.1 3.62 3610 0.8
MPS 51.45 1.2 6.47 1809 1.7
Materials: soilsThe Aznalcóllar Mine Accident
pcampos@irnas.csic.es
MPS
HPS
Materials: soilspcampos@irnas.csic.es
Location:
-Iberian Pyrite Belt (SW Spain-Portugal)
-Aznalcóllar (30 km from Seville)
25th April 1998 (3:30 am)
• 4 millions m3 acidic water
• 2 millions m3 toxic mud
The Aznalcóllar Mine Accidentpcampos@irnas.csic.es
Pyrolysis conditions• Temperature 500 ºC
• Time 2 h
• N2 atmosphere
• Heating rate 20 °C min-1
Batch reactor
N2
NaOH-water-oil
Reactor
Materials: biocharsFeedstock Biochar production
Rice Husk(RH)
Olive Pit(OP)
AlmondShell (AS)
Certified biochar (B1)• Material: Mixed wood sieving from
wood chip
• Pyrolysis: 20 min, 620 ºC
• Swiss Biochar, Laussane, Switzerland
pcampos@irnas.csic.es
One-exponential model
Underestimation of biochar stability?
Leng et al. (2019), Sci. Total Environ. 664, 11-23
Biochars – C stability
99.65
99.7
99.75
99.8
99.85
99.9
99.95
100
100.05
0 1000 2000 3000 4000
Rem
ain
ing
C (
% o
f in
itia
l C
)
Incubation time (h)
RHB500_2
OPB500_2
ASB500_2
B1
RHB
B1
ASB
OPB
No fast pool
𝐴 = 𝐴2 · ⅇ−𝑘2𝑡
Results pcampos@irnas.csic.es
Greater stability
of biochars
Effects of biochar in MPS – C stability
90
92
94
96
98
100
102
0 1000 2000 3000 4000
Rem
ain
ing
C (
% o
f in
itia
l C
)
Incubation time (h)
C_MPS
10%RHB500_2_MPS
10%OPB500_2_MPS
10%ASB500_2_MPS
10%B1_MPS
Control
RHBB1ASBOPB
𝐴 t = 𝐴1 · ⅇ−𝑘1𝑡 +𝐴2 · ⅇ
−𝑘2𝑡
Results pcampos@irnas.csic.es
Greater stability of biochar
amended soilThe curves were fitted by the following equation:
The curves were fitted by the following equation:
Except C_HPS and 10%OPB500_2_HPS that
were fitted by one-exponential model:
Effects of biochar in HPS – C stability
96.5
97.0
97.5
98.0
98.5
99.0
99.5
100.0
100.5
0 1000 2000 3000 4000
Rem
ain
ing
C (
% o
f in
itia
l C
)
Incubation time (h)
C_HPS
10%RHB500_2_HPS
10%OPB500_2_HPS
10%ASB500_2_HPS
10%B1_HPS
RHB
B1
ASBOPB
Control
Results pcampos@irnas.csic.es
𝐴 t = 𝐴1 · ⅇ−𝑘1𝑡 +𝐴2 · ⅇ
−𝑘2𝑡
Greater stability of biochar
amended soil
Experiment long enough?
Underestimation of C stability?
Leng et al. (2019), Sci. Total Environ. 664, 11-23
𝐴 = 𝐴2 · ⅇ−𝑘2𝑡
Conclusions
All biochars showed MRT > 100 years, being greater for OPB and ASB than RHB and the certified B1.
In moderately polluted soil, biochars:
• Did not modified the labile C fraction of soil.
• Increased MRT2 in 2-10 times in comparison to the control soil.
In highly polluted soil, biochars :
• Enhanced the degradation of a small fraction of labile C.
• Increased in 2.8-13.1 times the MRT2 of the more recalcitrant C fraction of soil.
Longer experiments would be recommended in order to distinguish if the C fraction found in control HPS was the labile fraction or all C in this soil has this degradability.
pcampos@irnas.csic.es
Acknowledgements:Grupo MOSS (IRNAS-CSIC)
MINEICO: CGL2016-76498-R and CGL2015-64811-P projects
Fundación Tatiana Pérez de Guzmán el Bueno
Thank you for your attention
pcampos@irnas.csic.es
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