This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.
Wide-scale use of oil in industrialized world today has increased quantity of oil production and transportation, which in-turn has resulted in large amount of oil contaminating soil and marine environments due to daily minor spills and occasionally major ones. Oil spills are more common near petroleum production sites, pipelines, and shipping routes from municipal runoff and routine shipping. It is very important to take action to prevent oil spills and to remediate after spills, to ensure that minimal damage occurs to ecosystem. Bioremediation is the method of choice for elimination of oil from marshlands, because it is inexpensive and environmentally safe. Bioremediation is part of "tool kit" used by spill responders. In 1994, daily oil usage was estimated about 3.5 billion gallons/per day and spills over world oceans was about 150 million which is small fraction (<0.0035%) of usage (Etkin). Fortunately, even though the amount of oil transportation is increasing, the amounts of oil spills have been generally decreasing over the decades (Etkin). Even the amount of oil spills from shipwrecks was estimated to be less than the amount of oil entered the sea from natural seeps (National Research Council). Largest oil spill into marine environment to date was near Kuwait in 1991 of about 520 Million gallons (AlGhadban).
Safety of shipment and prevention of environmental spills has been improved significantly over the years. However, cost effective and environmentally friendly methods to deal with oil spills are always in demand. Bioremediation is one of the approaches that work with natural process to minimize the environmental impacts of oil spills. Bioremediation had already been used successfully in Alaska after Exxon Valdez, 1989 oil spill (Prince,1997). Bioremediation works by oil being degraded by many microorganisms that has evolved over the millions of years to utilize it.
Composition of crude oil and refined fraction that may be spilled at sea waters: Crude oil is fossil fuels also known as petroleum, which results from burial of ancient biomass and fossilized organic materials. Commercially useful Oil is as old as about 465 millions year old from source rocks to as recent as about 1000 years old, which does not seem to give raise to enough amount of oil (Tissot, 1984 159). Average crude oils used commercially are about 100 million years old (Tissot, 1984 159). Crude oil has been part of biosphere for millions of year, escaping from underground reservoirs through land and marine seeps. Although most tanker spills have severe local impact, their input is not less than that of natural seeps. Crude oil is very complex and varies in molecular structures. Mainly consist of hydrocarbons, molecules only composed of hydrogen and carbon. It also contains additional trace elements such as sulfur, oxygen, nitrogen, metals/heavy metals, and powder of diamonds. Crude oils are categorized by several types, mainly by specific unit known as API (American Petroleum Institute) gravity. API gravity of water is 10o, therefore oils with API gravity greater then 40o are said to be light oils and oils with API gravity less then 16o are said to be heavy oil. The sulfur content of crude oil which is inversely proportional to API gravity and viscosity of oil which is proportional to API is also important factor.
Hydrocarbon biodegradation: If nature, over millions of years had produced something like crude oil, it must have thought of solution for it. Hydrocarbons and refined products such as diesel and gasoline fuels are almost completely biodegradable under aerobic conditions. Some oil resins and polar molecules are sometimes resistant to biodegradation; therefore all molecules of oil are not expected to degrade by biodegradation method. Polycyclic aromatic hydrocarbons (PAHs) are small part of crude oil, however it has important toxic and hazardous properties that impacts environment and therefore is regulated by USEPA (Environmental Protection Agency).
PAHs have low solubility and in water as they are nonpolar and hydrophobic molecules which floats at water surface due it's less energetically favorable state in water. PAHs biodegradation must take place at the interface of hydrogen-carbon-water. This physical process results in formation of tar balls or pavements along the shorelines where oil and surface particle or organic matter become fully saturated excluding water. Separation of oil from oil-water interface leads to low bioavailability for microbial biomass as bacteria and algae grow in water. Population of natural oil-degrading microorganisms are usually low in wetlands, therefore there is possibilities for increasing bioremediation through process called bioaugmentation in conjunction with Nitrogen (N) and Phosphors (P) supplementation. Tar balls and pavements can be possibly biodegraded at significant rate by increasing surface area and enhancing microbial colonization by the bioagumentation process.
Many microorganisms once adhere with polycyclic aromatic hydrocarbons can start bioremediation process and transforms hydrocarbons into carbon dioxide, water, and biomass. In a complex interwork of organisms such as fungi, algae, and various hydrocarbon degrading bacteria are responsible for oil degradation process. Besides nutrients, nitrogen, and phosphate newly released hydrocarbons promotes the development of new and growing population. By this widespread nutrient in conjunction with crude oil a process in lunched which transforms crude oil into water, carbon dioxide, and biomass. This process accelerates the rapid growth of natural oil degrading bacteria. The intermediate products are degraded by secondary consumers and the released carbon dioxide is processed by photosynthesis into oxygen and carbohydrates which are observed by the natural environment. This process occurs only under aerobic environments, similar process occurs in anaerobic environment predominately such as deeper waters and marshes.
Diversity of organisms able to degrade oil components: Aerobic hydrocarbon-degrading microorganisms are commonly found in almost every ecosystem (Margesin, 2001 94). Organisms able to utilize hydrocarbons as the sole source of carbon and energy have been found in Bacteria, Archaea, alage, fungi. Most Eukaryotic organisms like fish and mammals that contain enzymes cytochrome P450 and peroxidase initiate and activates metabolism of PAHs but it leads to secretion rather than mineralization (124). The taxonomy of microorganisms is poorly distinguished, but many aerobic bacteria and some anaerobic bacteria, algae, and fungi have found to contain some hydrocarbon degrading species. Oil-degrading microorganisms somehow activate the hydrocarbons, either aerobically by inserting oxygen atoms or anaerobically by adding fumarate or carbon dioxide (Widdel, 2001169). Oil-degrading microorganisms are found in small amount at uncontaminated sites. At oil-spills sites where oil contaminations leverls are very high it is likely that catabolic strains will process solvent tolerance mechasnims.
Genes Pseudomonas is known to be able to metabolize about more than 90 different organic compounds as a sole source of carbon and energy (116). Multiple responses to solvent action are known in bacteria like cis-trans isomerizaation and efflux pumps. In genus Pseudomonas rapid respond to cis-trans modification after exposure to solvent is common (151). Solvent tolerance efflux pump in Pseudomonas Putida contains lux genes biosensor which responses to many different hydrocarbons. Plasmid Gpo1 on P. Putida contains all enzymes necessary for degradation of fatty acids and n-alkenes (132).
Plasmids are extrachromosomal structure which does not contain essential genetic information. Rather, they give the host bacteria a selective advantage under some conditions. Metabolic plasmids code for proteins involved in the catabolism of unusual substances. Pseudomonas has plasmids encoding genes for the degradation of octane and naphthalene. Bacterial metabolism of naphthalene proves that metabolism involved in the biodegradation of PAHs. The genes that encode naphthalene transformation are found on NAH 7 plasmids of P. Putida PpG7 (111). Light-emitting system such as lux system works by organism activating degradation of hydrocarbons by emitting light. Pseudomonas fluorescens is example of strain that is genetically engineered bioluminescent that helps biodegradation of naphthalene (137).
Pseudomonas putida possesses a plasmid called pWWO. It contains genes to enzymatically degrade toluene and xylene. Toluene is not manmade, and therefore must have always existed in nature at some level. Sigma factors do 2 things: They recognize promoters and help RNAP initiate transcription from them and they do nothing else. However, as RNAP cannot initiate transcription without them, they are vital to gene expression. All bacteria have a ÏƒA - the housekeeping sigma factor that controls ~75% of all gene transcription. Most bacteria also have additional sigma factors that are used for niche situations requiring unique regulatory control. Pseudomonas aeruginosa has 19 ECF Ïƒ factors
Strategies for encouraging the growth of biodegrading microorganisms: There are three principle approaches used by biodegrading organisms, natural attenuation known as intrinsic bioremediation which depends on natural biodegradation activities, biostimulation which is natural activities by environmental adjustments like addition of fertilizer to increase rates of biodegradation, and bioaugmentation is addition of exogenous microorganism in place of the natural degrading capacity.
Natural attenuation is completely depending on the natural biodegradation process to remove environmental pollutant which involves not alteration. Therefore, it is not fast enough process to remove toxic substance from nature. Secondly, biostimulation is used to increase on the site microorganism by environmental modifications. During oil spills hydrocarbon degrading are already present at the shorelines, addition of agricultural fertilizers enhances the microorganism growth. Biostimulation approach is not instantaneous and effective. Final approach, bioaugmentation involves the accumulation of live organisms and addition of enzymes to increase naturally occurring biota.
Majority of crude oil and refined product hydrocarbons are biodegradable under aerobic conditions and should eventually disappear from the environment thought the process of biodegradation. Most hydrocarbons are insoluble in water and biodegradation only occurs by surface area available for microbial colonization. Crude oil and refined products are great energy and carbon source for biodegrading organisms. Oil-degrading microorganisms are present almost everywhere and addition of bioaugmentation need to have additional properties to survive and compete.
Environmental harm that might be done if bioremediation were applied carelessly: It is important to be careful that fertilizer application can also have negative impacts on the environment and it should be used carefully. The total amount of nitrogen used in bioremediation process is should be minimum, as increased amount of nitrogen is eventually toxic to fishes and amphipods. Increase amount of nitrogen can also stimulate growth of algal and plankton. Sometimes ammonia runoffs from into coastal zones are held responsible for fish kills.
In conclusion, bioremediation is not the solution for clarifying and eliminating oil spills, but it is an important approach to reduce the ecological impact of some oil spills. Sometimes, bioremediation is the only method for treating coastal oil spills successfully. As evidence bioremediation approach is used during the Exxon Valdez oil spill, it can be very effective method for treating oil-contaminated marine sites and shorelines, in terms of both cost and efficiency.