11.3 Biochar Characteristics
Biochar is a carbon-rich solid material formed through the combustion process of
organic material or biomass without or with little oxygen (pyrolysis) at the temperatures of 250–700
C and can be used as a soil amendment (Sohi et al. 2009;
Lehmann and Joseph 2009). The complete pyrolysis process leaves only carbon,
but in making biochar it often leaves other nutrients. In contrast to organic matter,
biochar is stable for hundreds to thousands of years when it is mixed into the soil and
is capable of sequestering carbon in the soil (Lehmann 2007; Renner 2007; Fraser
2010).
The physical and chemical characteristics of biochar affect its quality. The
characteristics of biochar depend on the feedstock and pyrolysis conditions such as
temperature, pyrolysis duration, and oxygen or air supply (Sohi et al. 2009). Physical
characteristics include pore distribution, pore size, surface area; while chemical
properties include CEC, pH, macro- and micro-nutrient, and ash content.
11.3.1 Biochar Physical Properties
The amount and distribution of mineral elements in biochar and biochar pores vary
greatly depending on feedstock and pyrolysis temperature (Brewer 2012; Amonette
and Joseph 2009). Physical characteristics also depend on biochar treatment after
pyrolysis (Downie et al. 2009). The chemical composition of the biomass of
feedstock has direct influence on the physical properties of biochar. Lua et al.
(2004) showed that raising pyrolysis temperatures from 250
C to 500
C increases
the surface area of biochar because of the increased volatile evolution of feedstock
and results in the development of pores in biochar. The physical properties of
biochar are also influenced by the time of activation and the amount of steam used
for activation, where the surface area develops with an increase in activation time
(Stavropoulos 2005; Zhang et al. 2004).
The pressure of gas during pyrolysis also has influence on the structure of
biochar. Cetin et al. (2004) stated that biochar produced at 5 bar pyrolysis pressure
at a heating rate of 500
C to 950
C has been shown to have a larger cavity with
thinner cell walls than biochar produced at a pressure of 1 atmosphere.
The size of particle produced at the heating rate of 400
C was not much different
from the particle size of the feedstock before pyrolysis. However, some volatile
substances are lost during pyrolysis, so that biochar becomes more porous (Brewer
2012). Scanning Electron Microscopy (SEM) analysis can describe the pore space in
biochar. Based on SEM analysis, there are differences in biochar pore size
depending on the types of biochar (Maftuah and Sosiawan 2018) (Fig. 11.1).
Based on SEM image, coconut shell biochar has more micro-, meso-, and macropore space composition compared to bamboo biochar, Eleocharis dulcis biochar, and
palm midrib biochar. Rice husk biochar showed more particles than pores.
11 Biochar for the Improvement of Peatland and Suboptimal Land
341
Biochar is a carbon-rich solid material formed through the combustion process of
organic material or biomass without or with little oxygen (pyrolysis) at the temperatures of 250–700
C and can be used as a soil amendment (Sohi et al. 2009;
Lehmann and Joseph 2009). The complete pyrolysis process leaves only carbon,
but in making biochar it often leaves other nutrients. In contrast to organic matter,
biochar is stable for hundreds to thousands of years when it is mixed into the soil and
is capable of sequestering carbon in the soil (Lehmann 2007; Renner 2007; Fraser
2010).
The physical and chemical characteristics of biochar affect its quality. The
characteristics of biochar depend on the feedstock and pyrolysis conditions such as
temperature, pyrolysis duration, and oxygen or air supply (Sohi et al. 2009). Physical
characteristics include pore distribution, pore size, surface area; while chemical
properties include CEC, pH, macro- and micro-nutrient, and ash content.
11.3.1 Biochar Physical Properties
The amount and distribution of mineral elements in biochar and biochar pores vary
greatly depending on feedstock and pyrolysis temperature (Brewer 2012; Amonette
and Joseph 2009). Physical characteristics also depend on biochar treatment after
pyrolysis (Downie et al. 2009). The chemical composition of the biomass of
feedstock has direct influence on the physical properties of biochar. Lua et al.
(2004) showed that raising pyrolysis temperatures from 250
C to 500
C increases
the surface area of biochar because of the increased volatile evolution of feedstock
and results in the development of pores in biochar. The physical properties of
biochar are also influenced by the time of activation and the amount of steam used
for activation, where the surface area develops with an increase in activation time
(Stavropoulos 2005; Zhang et al. 2004).
The pressure of gas during pyrolysis also has influence on the structure of
biochar. Cetin et al. (2004) stated that biochar produced at 5 bar pyrolysis pressure
at a heating rate of 500
C to 950
C has been shown to have a larger cavity with
thinner cell walls than biochar produced at a pressure of 1 atmosphere.
The size of particle produced at the heating rate of 400
C was not much different
from the particle size of the feedstock before pyrolysis. However, some volatile
substances are lost during pyrolysis, so that biochar becomes more porous (Brewer
2012). Scanning Electron Microscopy (SEM) analysis can describe the pore space in
biochar. Based on SEM analysis, there are differences in biochar pore size
depending on the types of biochar (Maftuah and Sosiawan 2018) (Fig. 11.1).
Based on SEM image, coconut shell biochar has more micro-, meso-, and macropore space composition compared to bamboo biochar, Eleocharis dulcis biochar, and
palm midrib biochar. Rice husk biochar showed more particles than pores.
11 Biochar for the Improvement of Peatland and Suboptimal Land
341