A Strategy for Bioremediation of Marine Shorelines by Using Several Nutrient Release Points - Mathematical Modelling and Numerical Simulation of Oil Pollution Problems - page 24

2.1 Introduction

Crude oil is one of the most important organic pollutants in marine environments.
It has been estimated that worldwide approximately 1 10 6 tons of petroleum

impact marine waters and estuaries annually [ 27 ]. Massive releases from pipelines,
wells and tankers receive the most public attention, but in fact these account for only
a relatively small proportion of the total petroleum entering the environment. Al-
most 50% comes from natural seeps, and less than 9% emanates from catastrophic
releases. Consumption and urban run-off is responsible for almost 40% of the input
[ 27 ]. Independently of the source of pollution, a substantial number of smaller re-
leases of petroleum occur regularly in coastal waters [ 14 ], as a result, oil stranded in
shorelines has become a common problem which needs attention.
It is well known that oil is comprised of many different toxic compounds which
endanger the marine environment involved in a spill, however there are many natural,
native microorganisms which are not only capable, but thrive on the decomposition
of these toxic compounds. This process of using microorganisms for such cleanup
efforts in shorelines is known as bioremediation, and it has proven to be a successful
method for the cleanup of marine areas affected by oil spills [ 7 ]. There are two differ-
ent types of bioremediation used for oil spill cleanup: bioaugmentation and biostim-
ulation. Bioaugmentation is the addition of microorganisms capable of degrading the
toxic hydrocarbons, in order to achieve a reduction of the pollutants. Biostimulation
is the addition of nutrients needed by indigenous hydrocarbon degrading microor-
ganisms in order to achieve maximum degradation of toxic compounds present in the
oil. The degradation of hydrocarbons (biodegradation) begins by the conversion of
the alkane chain or polycyclic aromatic hydrocarbon (PAH) into alcohol. Oxidation
then converts the compound to an aldehyde and then into an acid and eventually into
water, carbon dioxide, and biomass. In the case of the PAH, fission occurs which
ultimately leads to mineralization [ 47 ]. More than 170 genera of microorganisms
have been identified in the environment which are able to degrade hydrocarbons, due
to such diversity and different conditions at the spill site, hydrocarbons do not all
biodegrade at similar rates, and not all hydrocarbons are degradable, but estimates for
the biodegradability of different crude oils range from 70 to 97%. What remain are
principally the asphaltenes and resin compounds, which are essentially biologically
inert [ 38 ].
Although biodegradation is a particularly important mechanism for removing the
non-volatile components of oil from the environment, this is a relatively slow natural
process and may require months to years for microorganisms to degrade a signifi-
cant fraction of an oil stranded in shorelines, within the sediments of marine and/or
freshwater environments [ 52 ]. The simplest way of stimulating biodegradation, and
the only one that has achieved experimental verification in the field, is to carefully
add nitrogen and phosphorus nutrients. This was first used on a large scale in Alaska,
following the 1989 spill from the Exxon Valdez [ 4 , 36 , 37 ]. Two fertilizers were
used in the large-scale applications: an oleophilic liquid product designed to adhere
to oil, named Inipol EAP22 [ 19 ]; and a slow-release granular agricultural product

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