Environmental Engineering Reference
In-Depth Information
17.4.6.6 Rhizodegradation
Rhizodegradation is a biological treatment of a contaminant by enhanced bacterial
and fungal activity in the rhizosphere of certain vascular plants. The rhizosphere is
a zone of increased microbial density and activity at the root surface, and was
described originally for legumes. Plants and microorganisms often have symbiotic
relationships making the root zone or rhizosphere an area of very active microbial
activity (bacteria and fungi) (Kirk et al.
2005
). Plant litter and root exudates
provide nutrients such as nitrate and phosphate that reduce or eliminate the need
for costly fertilizer additives. Plant roots penetrate the soil, providing zones of
aeration and stimulate aerobic biodegradation (Anderson et al.
1993
).
Many plant molecules released by root dies and this exudation resembles
common contaminants chemically and can be used as co-substrates. For example,
phenolic substances released by plants have been found to stimulate the growth of
PCB degrading bacteria (Fletcher and Hegde
1995
). Recent studies have described
enhanced degradation of pentachlorophenol in the rhizosphere of wheat grass
(Agropyron cristatum), increased initial mineralization of surfactants in soil-plant
cores, and enhanced degradation of TCE in soils collected from the rhizospheres
(Knabel and Vestal
1992
; Ferro et al.
1994
).
17.4.7 Biochar
It is environmental friendly, carbon rich, fine grained, and porous substance, which
is produced by thermal decomposition of several kinds of biomass under oxygen-
limited conditions and at a relatively low temperatures, and have the capability of
moisture and nutrients retention (Tang et al.
2013
). It can also mitigate climate
change by sequestrating C from atmosphere into the soil (Marris
2006
) and also
improve soil properties and enhance recycle of agricultural and forestry waste
(Luo et al.
2011
), and also microbial activity (Lehman et al.
2011
). Amendment by
adding biochar in the soil with poor fertility can improve the crop yield. It has been
reported by various studies that biochar acts as an efficient sorbent of various
organic and inorganic contaminants because of its increased surface area and
special structure. Biochar can also be used for heavy metal removal from con-
taminated soils. Several kinds of organic waste like animal manure, woodchips,
and crop waste can serve as source materials of biochar, thus showing a rela-
tionship among biochar, waste recycle, and soil decontamination.
Surface adsorbtion and partition of pollutant molecules in the micropores of
biochar enhances the bioremediation process .However, from different point of
view, further studies on the safety uses of biochar is needed to be carried out
(Beesley et al.
2011
).
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