Environmental Engineering Reference
In-Depth Information
claimed to be less toxic to marine microorgan-
isms than in past. During Deepwater Horizon
blowout, more than 700,000 ga of dispersant
Corexit was applied directly at the wellhead. Co-
rexit was reported to have increased the toxicity
of oil by 52 times after 2 years of the incident
(Rico-Martinez et al.
2013
). The debate is still
active about the perceived success of Corexit as
oil spill response in Deepwater Horizon incident.
Current research in this area should focus to en-
hance our understanding about functional inter-
action of dispersants with different components
of oil and better technology to predict real-time
information on oil removal from water surface as
a result of dispersant application.
oxygen, nitrogen, and phosphate concentrations
in sea water. Therefore, P and N-based fertilizers
are applied to alleviate nutrient limitation, which
stimulates the growth of oil degrading bacteria. P
and N fertilizers such as ammonium phosphate,
nitrates, phosphates, and urea can be used. How-
ever, being highly soluble, they risk rapid dis-
solution and dispersion in open systems such as
seas. Water soluble fertilizers are best applicable
in low-energy fine-grained shorelines where
water transport is limited (Nikolopoulou and
Kalogerakis
2009
). Thus, efforts are being made
to provide a suitable alternative that can work on
other conditions.
Oleophilic (oil-loving) and slow-release fertil-
izers have been suggested as other alternatives.
Inipol EAP22 containing oleic acid, urea, and
lauryl phosphate has been utilized for oil spill
cleanup in the shoreline of Prince William Sound
(Zhu et al.
2001
). Inipol EAP22 was found to
be effective in sandy beaches with coarse sedi-
ments and not with fine sediments due to its in-
ability in penetrating fine sediments (Sveum and
Ladousse
1989
). Inipol EAP22 suffers from at
least three problems—oleic acid component con-
tributes as alternative carbon source, urea com-
ponent dissolves in water phase and is unavail-
able to microbes working at the oil phase, and
toxicity of 2-butoxy-ethanol component in Inipol
EAP22 (Ron and Rosenberg
2014
). Polymerized
urea and formaldehyde formulations have been
used successfully to remediate oil spill in sandy
beaches. However, they were found unsuitable in
open seas where they tend to sink due to their
high density.
Slow-release fertilizers provide continuous
source of nutrients in oil-contaminated areas,
overcome washout problems characteristic of
intertidal environments, and forgo the need for
frequent application of fertilizers. Slow-release
fertilizers are soild formulations containing
inorganic fertilizers coated with paraffin or veg-
etable oil. Customblen, a formulation of calcium
phosphate, ammonium phosphate, and ammo-
nium nitrate, coated with vegetable oil has been
used in oil spill cleanup in the shorelines of
Prince William Sound along with Inipol EAP22
with moderate success. Studies on slow-release
9.4.3
Biological Approaches
Biological approaches for biodegradation pri-
marily include bioremediation (biostimulation
and bioaugmentation) which enhances the rate
of natural biodegradation. Phytoremediation has
been suggested as one of the biological approach-
es. As the name suggests, biodegradation is the
conversion of complex compounds by biological
agents (fungi, bacteria, and yeasts) into simpler
compounds for obtaining energy and nutrients.
Addition of nutrients, enzymes, and naturally oc-
curring or genetically modified microorganisms
(GMOs) and application of phytoremediating
plants are key biological approaches for oil spill
cleanup. We will discuss bioremediation with
reference to biostimulation and bioaugmentation.
Biostimulation
Biostimulation is the addition of growth-limiting
nutrients and other cosubstrates to the contami-
nated environment for stimulating the growth of
indigenous oil degraders. Biostimulation is one
of the most environmentally safe methods for
combating oil spills. Indigenous oil degraders
generally subside on natural oil seeps and plant
synthesis; however, the rate of biodegradation is
slow (Fehler and Light
1970
). In case of natu-
ral and anthropogenic oil spills, indigenous oil
degrading bacteria are unable to degrade the oil
due to limiting abiotic factors such as molecular
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