48
Phytotechnology with Biomass Production
widely used for landfill covers to reduce water infiltration, but less so as a
means to control leachate, once it is formed. Gąbka & Wolski (2011) described
a successful study of active management of leachate by watering various turf
grasses with collected landfill leachate at a closed landfill in Poland. In warm
subtropical to tropical climates, vetiver grass has been used since 1994 and
shown to be highly effective for managing a wide range of leachates either
actively by irrigation, or passively by planting directly into the leachate
seepage path (Vetiver Network International, 2017). Miscanthus has suitable
characteristics for temperate climates including deep rooting where potential crop evapotranspiration exceeds normal precipitation (see Chapter 5 for
information on water usage by Miscanthus).
3.4 Phytoremediation of Organic
Contaminants with Miscanthus
Miscanthus is a C 4 grass related to sugarcane and sorghum, with a rich
microbiome. Thus, it is anticipated that it can facilitate rhizoremediation of
many organic compounds. Field data on its capacity to do so are not abundant because until recently cultivation of Miscanthus was of most interest
as a source of bioenergy, not remediation of contaminated sites. There are a
limited number of greenhouse pot studies with selected compounds. These
are discussed in reviews by Nsanganwimana et al. (2014) and Pidlisnyuk
et al. (2014). By that date only the work of Técher et al. (2012a) reported a
field study of significant organic [PAH] contamination. That same group
showed that exudates of Miscanthus roots stimulated microbial degradation of some PAHs in microcosm studies (Técher et al., 2012b), while an earlier study showed enhancement of degradation of diesel fuel also (Técher
et al., 2011).
One recent study (Wechtler et al., 2020) examined dissipation of PAHs from a
technosol (mixture of dredged sediments and contaminated soil). Plants used
were M. × giganteus, white clover (T. repens), and a co-culture of the two. After
a growing season of 263 days, there was a significant decrease of 16 priority
PAHs, with ~30% decrease in the monocultures and co-culture compared to
an unplanted technosol. This lowered the integrated average cancer risk from
about 4.3 to 3.4. The co-culture also lowered the predicted ecotoxicity more
than each monoculture, showing a greater decrease of anthracene and pyrene.
Miscanthus is known to have resistance to herbicides similar to that of
maize (Anderson, 2011), but mechanisms are undefined, whether by metabolic tolerance, deactivation of the herbicide or exclusion from the plant.
Anderson (2011) tested more than 20 herbicides, at several rates of application
for control of broad-leaf weeds or other grasses (pre-emergence). Many herbicides were tested in greenhouse studies and some at small scale in a field.
Phytotechnology with Biomass Production
widely used for landfill covers to reduce water infiltration, but less so as a
means to control leachate, once it is formed. Gąbka & Wolski (2011) described
a successful study of active management of leachate by watering various turf
grasses with collected landfill leachate at a closed landfill in Poland. In warm
subtropical to tropical climates, vetiver grass has been used since 1994 and
shown to be highly effective for managing a wide range of leachates either
actively by irrigation, or passively by planting directly into the leachate
seepage path (Vetiver Network International, 2017). Miscanthus has suitable
characteristics for temperate climates including deep rooting where potential crop evapotranspiration exceeds normal precipitation (see Chapter 5 for
information on water usage by Miscanthus).
3.4 Phytoremediation of Organic
Contaminants with Miscanthus
Miscanthus is a C 4 grass related to sugarcane and sorghum, with a rich
microbiome. Thus, it is anticipated that it can facilitate rhizoremediation of
many organic compounds. Field data on its capacity to do so are not abundant because until recently cultivation of Miscanthus was of most interest
as a source of bioenergy, not remediation of contaminated sites. There are a
limited number of greenhouse pot studies with selected compounds. These
are discussed in reviews by Nsanganwimana et al. (2014) and Pidlisnyuk
et al. (2014). By that date only the work of Técher et al. (2012a) reported a
field study of significant organic [PAH] contamination. That same group
showed that exudates of Miscanthus roots stimulated microbial degradation of some PAHs in microcosm studies (Técher et al., 2012b), while an earlier study showed enhancement of degradation of diesel fuel also (Técher
et al., 2011).
One recent study (Wechtler et al., 2020) examined dissipation of PAHs from a
technosol (mixture of dredged sediments and contaminated soil). Plants used
were M. × giganteus, white clover (T. repens), and a co-culture of the two. After
a growing season of 263 days, there was a significant decrease of 16 priority
PAHs, with ~30% decrease in the monocultures and co-culture compared to
an unplanted technosol. This lowered the integrated average cancer risk from
about 4.3 to 3.4. The co-culture also lowered the predicted ecotoxicity more
than each monoculture, showing a greater decrease of anthracene and pyrene.
Miscanthus is known to have resistance to herbicides similar to that of
maize (Anderson, 2011), but mechanisms are undefined, whether by metabolic tolerance, deactivation of the herbicide or exclusion from the plant.
Anderson (2011) tested more than 20 herbicides, at several rates of application
for control of broad-leaf weeds or other grasses (pre-emergence). Many herbicides were tested in greenhouse studies and some at small scale in a field.