Crude Oil is a naturally occurring liquid found in the Earth's crust, and is a source of numerous petrochemicals, lubricants and combustible fuels. Since it serves us in many ways in our daily lives, it is a necessity and there is an increasing demand of petroleum products all over the world. Unfortunately petroleum is not found in abundance in all parts of the world and so it is transported massively to other major oil consuming countries. Accidental oil spills occur as a result of this loading/unloading, transportation which immensely pollute the oceans and shorelines and prompt the development and refinement of techniques to degrade the contaminants to non-toxic form. Other causes of oil pollution are municipal and industrial wasters and runoffs, leaks in pipelines and underground storage tanks (USTs) and discharge of dirty ballast and bilge waters.
Bioremediation, is a rather new techniques, and one which is considered a good alternative to conventional clean-up methods. The, methodologies are not technically complex, but they require experience and expertise in order to implement the right bioremediation program to optimize conditions to achieve a beneficial result. In this paper I plan to explain the principles, factors, techniques, advantages and disadvantages of Bioremediation.
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Bioremediation is the process of restoring contaminated land, sludge, water or an air stream and making the environment safe by absorbing or destroying the harmless contaminants or decreasing their toxicity using microbes. Bioremediation of oil targets the decomposition of hydrogenous substances to their non-toxic or less toxic forms with the help of OEMs (Oil Eating Microbes) or Oleophilic bacteria which use oils in the environment as their food source.
Bioremediation of petroleum hydrocarbons (crude oil waste streams associated as a by-product of the drilling, production and refinery industry) is a conclusive and documented method of waste declassification. Compared to the conventional clean-up methods, it is relatively low cost, and has a high public acceptance. It is capable of completely destroying the pollutants using low technology techniques.
Many species of bacteria, fungi and yeasts metabolize petroleum hydrocarbons as food and energy source. The most prevalent hydrocarbon degraders belong to the genera Pseudomonas, Achromobacter, Flavobacterium, Rhodococcus, and Acinetobacter. Pencillium, Aspergillus, Fusarium and Cladosporium are most frequently isolated hydrocarbons degrading filamentous fungi. Among the yeasts Candida, Rhodotorula, Aureobasidium and Sporobolomyces are the hydrocarbons most often reported. (Van Hamme et al. 2003).
If the pollution is not treated and left alone, the crude oil spill will naturally be degraded by biological and non-biological processes, but it will pose a potential short term environmental damage. The oil kills sea life and will affect the surrounding beaches, seas and rocks and shoreline and plague the ecosystem indefinitely. (Edvo tec inc.)
OEMs break down the hydrocarbons into fatty acids or carboxylic acid, which are then further broken down for energy and carbon atoms, which are later used in the citric acid cycle to generate energy. Thus, oil broken down into basic, non-toxic elements: carbon, carbon dioxide and water.
Every year approximately 100 million US gallons of oil spill into the environment. There have been several oil spill incidents in which bioremediation products have been used in an attempt to enhance oil biodegradation. There was an increase in the bioremediation field trials associated with accidental spills in 1900s. The biggest spill incidence occurred in Persian Gulf War 1991, in which 240 million gallons spilled from oil tankers and terminals. The second biggest spill occurred over a ten month period (June 1979-1980) when 140 million gallons spilled at Ixtoc I well blowout in the Gulf of Mexico. Exxon Valdez accident at Bligh Reef in 1989, was the third biggest spill, where scientist and environmentalists worked at Prince William Sound, Alaska to clean 11 million gallons of spilled oil from the surrounding area. Bioremediation was used as a primary clean-up strategy. It was suggested that the natural rates of oil biodegradation on coastal shorelines can be stimulated two to sevenfold by bioremediation strategies. The process leads to the conversion of oil to biomass, water and gases which form part of the carbon cycle, whereas physical cleaning results only in the transfer of the oil from one compartment in the environment to another (e.g while some oil recovered physically from beaches may be recycled, in many cases it is stored in pits or landfills).. Furthermore in terms of biota, bioremediation is one of the few processes that will actually remove toxic components from the environment.
Composition of Crude Oil:
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Crude oil is a complex mixture of organic compounds with majority of compounds called hydrocarbons which can range in molecular weight from the gas methane to the high molecular weights like tars and bitumens. These hydrocarbons can also come in wide range of molecular structures. The 3 basic types of hydrocarbons are: straight chains, branched chains and 6-member rings; namely: saturates, olefins, aromatics and polar compounds.
The saturates consist of alkanes and cycloalkanes. Larger saturate compounds are called waxes. The olefins or unsaturated compounds have atleast one double carbon-to-carbon bonds. Significant amounts of olefins are found only in refined products (Fingas, 2002). The two major groups of aromatic hydrocarbons are monocyclic, such as benzene, toluene, ethylbenzene and xylene (BTEX), and the polycyclic hydrocarbons (PAHs) such as naphthalene, anthracene and phenanthrene. Polar compounds are those that have significant molecular charge as a result of interaction with compounds such as sulphur, nitrogen or oxygen. In the petroleum industry, the smallest polar compounds are called resins, which are largely responsible for oil adhesion. The larger polar compounds are called asphaltenes.
Spilled hydrocarbons mainly consist of crude, refined petroleum products such as get fuels, gasoline diesel, lubricating oils and waste oil. From an environmental perspective, the petroleum product, or a specific constituent may drive the program developed to address the concern. When a specific constituent drives the remedial response, this can present a challenge, since each organic or inorganic compound has specific physical, chemical and biological properties.
Factors of Bioremediation
Major basic factors required for the bioremediation of petroleum pollution are the presence of OEMs, nutrients, oxygen, phosphorus, moisture, pH, temperature, nutrient addition, salinity etc. In order for the OEMs to work at an optimum level a temperature range of -2 to 60 C and a pH ranging from 5.5 to 10 is necessary.
The amount of available oxygen will determine whether the system is aerobic or anaerobic. Hydrocarbons are readily degraded under aerobic conditions. The success also depends upon the type of contaminated beach, the penetration of the beach material by fertilizer etc. For example, Inipol EAP 22 does not appear to stimulate biodegradation on shorelines consisting of fine material such as sand but can be effective on the coarse cobble beaches of the Arctic (Lee K., and E.M. Levy 1992). In contrast, Rosenberg et al. 1986, have demonstrated that bioremediation involving an oleophilic fertilizer, seeding, regular tilling and watering stimulated oil degradation on a sandy beach in Israel.
In Nova Scotia, inorganic nutrients that were shown to work well on an oiled salt marsh environment (Lee K., and E. M. Levy 1991). Studies have also shown that "no bioremediation treatment" should be considered a recommended option but this will depend on the type and concentration of the oil and the type of contaminated sediment(Lee K., and E. M. Levy 1991). .