Environmental Engineering Reference
In-Depth Information
Table 5.4
Typical plants used in various phytoremediation applications
Application
Media
Contaminants
Key plants
Phytotransformation
Soil, groundwater, land-
fill leachate, land applica-
tion of wastewater
Herbicides (atrazine, alachlor)
Aromatics (BTEX)
Chlorinated aliphatics (TCE)
Nutrients (NO
3
+
, NH
4
+
, PO
4
3−
)
Ammunition waste (TNT,
RDX)
Phreatophyte trees (pop-
lar, willow, cottonwood
aspen); grasses (rye, ber-
muda, sorghum, fescue);
legumes (clover, alfalfa,
cowpeas)
Rhizosphere bioremediation
Soil, sediments, land
application of wastewater
Organic contaminants (pesti-
cides, aromatics and poly-
nuclear aromatic hydrocarbons
(PAHs))
Phenolic releasers
(mulberry, apple, orange);
grasses with fibrous roots
(rye, fescue, Bermuda)
for contaminants 0-3 ft
deep; phreatophytes trees
for 0-10 ft; aquatic plants
for sediments
Photostabilization
Soil, sediments
Metals (Pb, Cd, Zn, As, Cr,
Cu, Se, U)
Hydrophobic organics (PAHs,
PCBs, dioxins, furans, PCP,
DDT, dieldrin)
Phreatophyte trees to
transpire large amount of
water for hydraulic con-
trol; grasses with fibrous
roots to prevent soil ero-
sion; dense root system to
sorb/bind contaminants
Phytoextraction
Soil, brownfields,
sediments
Metals (Pb, Cd, Zn, Ni, Cu)
with EDTA addition for Pb and
Se (volatilization)
Sunflowers, Indian
mustards, rapeseed plants,
barley, crucifers, serpen-
tine plants, dandelions
Rhizofiltration
Aquatic plants; Emer-
gents (billrush, cattail,
coontail, pondweed,
arrowroot, duckweed);
Submergents (algae,
stonewort, parrot feather,
Eurasian water milfoil,
Hydrilla
)
BTEX
benzene, toluene, ethylbenzene and xylene,
TCE
trichloroethylene,
TNT
2,4,6-trinitrotoluene,
RDX
Research
Department explosive,
PCB
polychlorinated biphenyl,
PCP
pentacholorophenol,
DDT
dichlorodiphenyltrichloroeth-
ane,
EDTA
ethylenediaminetetraacetic acid
Groundwater, water and
wastewater in lagoons or
created wetlands
Metals (Pb, Zn, Cu, Ni, Cd)
Radionuclides (
137
Cs,
90
Sr, U)
Hydrophobic organics
(1 mm) for transformation of organic contami-
nants. When plants are grown in soil or sediment
slurries, pH is buffered, metals are biosorbed or
chelated and enzymes remain protected inside
the plant or absorbed to plant surfaces. In US
Environmental Protection (EPA) studies of TNT
breakdown, plants like hornwort increase soil
water pH from 3 to 7 and sorb high concentra-
tions of metals that usually inhibit bacteria, while
the plants remain healthy and viable. Overall,
plants and their root systems can accommodate
mixed wastes (organic and metals) and other
harsh conditions (Schnoor et al.
1995
).
Shaw and Burns (
2007
) have demonstrated the
importance of biodegradation in the rhizosphere.
Plants are associated with microbial transforma-
tions in many ways, such as: mycorrhiza fungi
associated with plant roots metabolize the organ-
ic pollutants; plant exudates stimulate bacterial
transformations (enzyme induction); build-up of
organic carbon increases microbial mineraliza-
tion rates (substrate enhancement); plants pro-
vide habitat for increased microbial populations
and activity; oxygen is pumped to roots ensuring
aerobic transformations.
Narasimhan et al. (
2003
) have reported that
flavonoids and coumarin are released by root
turnover from trees like mulberry, orange and
apple that selectively stimulate polychlorinated
biphenyl (PCB)- and PAH-degrading organisms.
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