to biochar has been reported in some earlier study. Zhang et al. (2013) reported that
the possibility of acetone/hexane extraction was not exhaustive enough to extract the
PAHs that were more strongly bound to the added soil amendments (biochar),
suggesting that these more strongly bound PAHs are not freely bioavailable and
thus unlikely to pose an environmentally toxic risk. Otherwise, the application of
biochar in contaminated soil could stimulate the biodegradation of PAH due to the
enhancement of soil microbial activity in amended soils (Rhodes et al. 2008;
Steinbeiss et al. 2009). According to Haritash and Kaushik (2009), the addition of
compost alone or with the combined form of biochar could increase the degradation
of PAH compounds as well as improve the soil texture and oxygen transfer and
provide energy to the microbial population that can actively participate in this
process. But Kaestner and Mahro (1996) found that the degradation process of
PAH can be increased due to the biochar amendments, but sorption of organic
matter in amended soil is unchanged. Biochar and compost (vermicompost and
farmyard manure, FYM) both could reduce PAH concentrations by different mechanisms in the soil. Furthermore, when the blend of biochar and compost is added in
combination, they generally worked less effectively than when added individually.
Zhang et al. (2013) reported that the reduced PAH bioavailability caused by the
addition of biochar may have an antagonistic relationship with the increased microbial activity caused by the addition of compost, by reducing the substrate available
for the microbes.
10 Biochar and Immobilization of Contaminants in Soils
Biochar is an important solid sorbent that immobilizes organic and inorganic
pollutants by various mechanisms in contaminated soil (Chen and Chen 2009;
Ahmad et al. 2014). According to the previous study, electrostatic attraction, polar
and nonpolar organic attraction to the carbonized stage of biochar, and partitioning
to the non-carbonized phase enhanced the attachment of biochar with organic
contaminants (Chen et al. 2008; Chen and Chen 2009; Huang and Chen 2010).
Soil contaminants are attached on biochar surface by the proficient mechanism of ion
exchange, anionic metal attraction, precipitation, and cationic metal attraction (Cao
et al. 2009; Qian and Chen 2013; Ahmad et al. 2014, Xu and Chen 2015). Cao et al.
(2009) reported that in some cases, biochar can be even more efficient than activated
charcoal to immobilize heavy metals; in a study, six times more Pb absorption was
detected in biochar-amended soil. Biochar could adsorb some herbicides (such as
simazine) in micropores or on the surface and prevents their accessibility to microbial cells, extracellular enzymes, and plants as well as prevents their leaching into the
groundwater (Jones et al. 2011). After the changes in biochar properties with the
treatment of iron oxide obtained such magnetic biochar with an efficient sorption
capability of organic and inorganic pollutants, which enables biochar a
multifunctional application in agricultural and environmental fields (Chen and
Yuan 2011; Qian et al. 2013), current research exposes the significant role of biochar
486
C. Singh et al.
the possibility of acetone/hexane extraction was not exhaustive enough to extract the
PAHs that were more strongly bound to the added soil amendments (biochar),
suggesting that these more strongly bound PAHs are not freely bioavailable and
thus unlikely to pose an environmentally toxic risk. Otherwise, the application of
biochar in contaminated soil could stimulate the biodegradation of PAH due to the
enhancement of soil microbial activity in amended soils (Rhodes et al. 2008;
Steinbeiss et al. 2009). According to Haritash and Kaushik (2009), the addition of
compost alone or with the combined form of biochar could increase the degradation
of PAH compounds as well as improve the soil texture and oxygen transfer and
provide energy to the microbial population that can actively participate in this
process. But Kaestner and Mahro (1996) found that the degradation process of
PAH can be increased due to the biochar amendments, but sorption of organic
matter in amended soil is unchanged. Biochar and compost (vermicompost and
farmyard manure, FYM) both could reduce PAH concentrations by different mechanisms in the soil. Furthermore, when the blend of biochar and compost is added in
combination, they generally worked less effectively than when added individually.
Zhang et al. (2013) reported that the reduced PAH bioavailability caused by the
addition of biochar may have an antagonistic relationship with the increased microbial activity caused by the addition of compost, by reducing the substrate available
for the microbes.
10 Biochar and Immobilization of Contaminants in Soils
Biochar is an important solid sorbent that immobilizes organic and inorganic
pollutants by various mechanisms in contaminated soil (Chen and Chen 2009;
Ahmad et al. 2014). According to the previous study, electrostatic attraction, polar
and nonpolar organic attraction to the carbonized stage of biochar, and partitioning
to the non-carbonized phase enhanced the attachment of biochar with organic
contaminants (Chen et al. 2008; Chen and Chen 2009; Huang and Chen 2010).
Soil contaminants are attached on biochar surface by the proficient mechanism of ion
exchange, anionic metal attraction, precipitation, and cationic metal attraction (Cao
et al. 2009; Qian and Chen 2013; Ahmad et al. 2014, Xu and Chen 2015). Cao et al.
(2009) reported that in some cases, biochar can be even more efficient than activated
charcoal to immobilize heavy metals; in a study, six times more Pb absorption was
detected in biochar-amended soil. Biochar could adsorb some herbicides (such as
simazine) in micropores or on the surface and prevents their accessibility to microbial cells, extracellular enzymes, and plants as well as prevents their leaching into the
groundwater (Jones et al. 2011). After the changes in biochar properties with the
treatment of iron oxide obtained such magnetic biochar with an efficient sorption
capability of organic and inorganic pollutants, which enables biochar a
multifunctional application in agricultural and environmental fields (Chen and
Yuan 2011; Qian et al. 2013), current research exposes the significant role of biochar
486
C. Singh et al.