Agriculture Reference
In-Depth Information
incubation. The mixed starter culture #5 removed 47 % of aromatic compounds during 60
days of incubation. Bento et al. (2005) reported 72.7% light TPH fraction and 75.2% heavy
TPH fraction degradation in diesel contaminated soil bioaugmented with bacterial
consortium of
Bacillus cereus, Bacillus sphaericus, Bacillus fusiformis, Bacillus pumilus
Acinetobacter junii
and
Pseudomonas
sp. Ying et al. (2010) augmented a PAH-contaminated
soil with
Paracoccus
sp. strain HPD-2 and observed 23.2% decrease in soil total PAH
concentrations after 28 days, with a decline in average concentration from 9942 to 7638 µg
kg
-1
dry soil. They discovered percentage degradation of 3-, 4- and 5(+6)-ring PAHs was
35.1%, 20.7% and 24.3%, respectively.
The soil environment is very complicated and the degrading ability of exogenously added
microorganisms tends to be affected by the physicochemical and biological features of the
soil environment. Sometimes, the administration of petroleum degrading microorganisms
leads to a failure of bioaugmentation (Vogel 1996; Gentry et al., 2004). Bioaugmentation is
not always an effective solution for remediation of contaminated soil because in some cases
laboratory strains of microorganisms rarely grow and biodegrade xenobiotics compared to
the indigenous microbes (Thieman and Palladino 2009). Also Bioaugmentation is yet to gain
public acceptance, most especially the use of genetically engineered microbes due to the
believe that these microbes when seeded into contaminated soil may alter the ecology of the
environment as well as pose risk to the environmental health if they persist after the
remediation of the contaminated soil.
3.3 Phytoremediation of hydrocarbon and metal-contaminated soil
Phytoremediation is a remediation method that utilizes plants to remove, contain or
detoxify environmental contaminants (Palmroth, 2006). Phytoremediation appears attractive
because in contrast to most other remediation technologies, it is not invasive and, in
principle, delivers intact, biologically active soil (Wenzel, 2009). Some major advantages and
disadvantages of phytoremediation are shown in Table 1. The most common plant species
used in phytoremediation of organic and inorganic compounds includes willows, poplar
and different types of grasses. Comprehensive list of plants that has recorded positive
results in remediation of organic compounds are listed in Table 2.
On-site phytoremediation of petroleum hydrocarbons and heavy metals can be enhanced by
employing a combination of common agronomic practices (e.g. fertilizer application, tillage
and irrigation), this is because available nutrient reserves can be quickly depleted as the
microbial community begins to degrade the contaminants (Farrell and Germida, 2002).
Therefore fertilizer applications may enhance the degradation of petroleum hydrocarbons in
soil by reducing competition for limited nutrients. Cutright (1995) reported that increasing
the amount of nitrogen and phosphorus in soil under aerobic conditions increased the
degradation of PAHs by the soil fungus
Cunninghamella echinulata
var.
elegans.
Brown, (1998)
also observed loss of 2- and 3- rings of aromatic hydrocarbons from soil contaminated with
weathered petroleum compounds when the soil was amended with sludge compost high in
nitrogen compared to no amendment or low nitrogen amendment. Palmroth et al. (2002)
recorded 60% loss of diesel fuel in 30 days in diesel-contaminated soil planted with pine tree
and amended with NPK fertilizer. Also, Vouillamoz and Milke (2009) observed that
compost addition combined with phytoremediation, increases the rate of removal of diesel
