has been found in the gastrointestinal tract of several earthworm species [153, 159]
and in soil disturbed by earthworms [160]. However, it has not been demonstrated if
the earthworm-induced carboxylesterase activity hydrolyses ester-containing APIs
as mammalian carboxylesterases do [156, 161].
The persistence of exoenzymes largely depend on the organomineral complexes
of soil [162]. Binding of exoenzymes to clays and organic matter protect them
from physic stress (soil desiccation or high temperature) and microbial foraging
[163]. With this premise, biochar technology has been proposed as an environmentally compatible approach to stabilise exoenzymes and concentrate their activity in
soil for agronomic and remediating purposes [164]. The next section discusses how
biochar may synergistically improve the earthworm-assisted bioremediation of
contaminated soils.
7 Biochar-Improved Vermiremediation
In the last decade, biochar technology has emerged as a remediating strategy to
eliminate a wide range of both organic and inorganic pollutants from water and soil
[165–168]. Biochar is simply charcoal, but it is used as a soil conditioner instead of
being used for energy generation [169]. This carbonaceous material is produced by
pyrolysing solid organic feedstocks (e.g. manure, wood chips, pine needles, spent
coffee grounds, municipal biosolids, nut shells, corncob, rice straw, switchgrass, and
many others) under anoxic environment and temperatures between 250 and 700
C
[169, 170]. Biochar has been used in the remediation of API-contaminated wastewater [171, 172]. Some studies even suggest that biochar may be an ideal material in
filtering drinking water because of its excellent capacity to adsorb many inorganic
and organic pollutants, including APIs [173]. However, the remediation capacity of
biochar depends on the type of feedstock and the pyrolysis temperature which, in
turn, have a strong influence on the physicochemical and structural properties of
biochar [174]. Pyrolysis temperatures above 450
C generally produce biochar
suitable to be used in bioremediation of contaminated soils because of its higher
specific surface area, open porosity, alkalinity, hydrophobicity, density of aromatic
groups and lower oxygenated functional groups on the surface compared to biochar
produced at temperatures below 450
C [175]. For example, wheat straw-derived
biochar produced at 700
C had a higher adsorption capacity for ketoprofen, atenolol
and carbamazepine than biochar produced at 300
C [176]; a marked difference in the
specific surface area between both biochars explained the biochar-specific adsorption of these APIs (605 m
2 /g for 700
C-biochar versus 6.47 m
2 /g for 300
Cbiochar). Moreover, physicochemical properties of biochar other than the specific
surface area seem to be involved in API adsorption. For instance, a laboratory study
that compared the sorption behaviour of sulfamethoxazole in eight types of biochar
(bamboo, Brazilian pepper wood, sugarcane bagasse and hickory wood, produced at
both 450 and 600
C) evidenced that only the biochars derived from sugarcane
bagasse and bamboo at 450
C had the highest capacity for retaining
Vermiremediation of Pharmaceutical-Contaminated Soils and Organic Amendments
359
and in soil disturbed by earthworms [160]. However, it has not been demonstrated if
the earthworm-induced carboxylesterase activity hydrolyses ester-containing APIs
as mammalian carboxylesterases do [156, 161].
The persistence of exoenzymes largely depend on the organomineral complexes
of soil [162]. Binding of exoenzymes to clays and organic matter protect them
from physic stress (soil desiccation or high temperature) and microbial foraging
[163]. With this premise, biochar technology has been proposed as an environmentally compatible approach to stabilise exoenzymes and concentrate their activity in
soil for agronomic and remediating purposes [164]. The next section discusses how
biochar may synergistically improve the earthworm-assisted bioremediation of
contaminated soils.
7 Biochar-Improved Vermiremediation
In the last decade, biochar technology has emerged as a remediating strategy to
eliminate a wide range of both organic and inorganic pollutants from water and soil
[165–168]. Biochar is simply charcoal, but it is used as a soil conditioner instead of
being used for energy generation [169]. This carbonaceous material is produced by
pyrolysing solid organic feedstocks (e.g. manure, wood chips, pine needles, spent
coffee grounds, municipal biosolids, nut shells, corncob, rice straw, switchgrass, and
many others) under anoxic environment and temperatures between 250 and 700
C
[169, 170]. Biochar has been used in the remediation of API-contaminated wastewater [171, 172]. Some studies even suggest that biochar may be an ideal material in
filtering drinking water because of its excellent capacity to adsorb many inorganic
and organic pollutants, including APIs [173]. However, the remediation capacity of
biochar depends on the type of feedstock and the pyrolysis temperature which, in
turn, have a strong influence on the physicochemical and structural properties of
biochar [174]. Pyrolysis temperatures above 450
C generally produce biochar
suitable to be used in bioremediation of contaminated soils because of its higher
specific surface area, open porosity, alkalinity, hydrophobicity, density of aromatic
groups and lower oxygenated functional groups on the surface compared to biochar
produced at temperatures below 450
C [175]. For example, wheat straw-derived
biochar produced at 700
C had a higher adsorption capacity for ketoprofen, atenolol
and carbamazepine than biochar produced at 300
C [176]; a marked difference in the
specific surface area between both biochars explained the biochar-specific adsorption of these APIs (605 m
2 /g for 700
C-biochar versus 6.47 m
2 /g for 300
Cbiochar). Moreover, physicochemical properties of biochar other than the specific
surface area seem to be involved in API adsorption. For instance, a laboratory study
that compared the sorption behaviour of sulfamethoxazole in eight types of biochar
(bamboo, Brazilian pepper wood, sugarcane bagasse and hickory wood, produced at
both 450 and 600
C) evidenced that only the biochars derived from sugarcane
bagasse and bamboo at 450
C had the highest capacity for retaining
Vermiremediation of Pharmaceutical-Contaminated Soils and Organic Amendments
359