Biodegradation of Petroleum Hydrocarbons - Literature review Example

Introduction to Biodegradation of Petroleum Hydrocarbons Introduction Over the years, large amounts of Petroleum hydrocarbons contaminants are spilled into the environments as a result of human activities. While some oil releases can be controlled just like industrial gas emissions. However, catastrophic oil spills from pipelines, tankers, oil wells are largely accidental and cannot be avoided and in some are their occurrence is frequent. Such oil spillages pose severe and sudden danger, with long-term environmental and ecological consequences, since too much hydrocarbons are lethal to both aquatic and terrestrial ecosystems. A number of physio-chemical methods of mitigating the effects of oil spillage contaminates have been developed (table 1). Figure 1: Physiochemical Methods of the decontamination of Hydrocarbon Oils (Salleh, Ghazali, Raja, & Basri, 2003) Majority of these methods are labor intensive and expensive thus often causing escalation of the pollution as the collected wastes ends up being deposited in other clean zones (Salleh, Ghazali, Raja, & Basri, 2003). (Guo-liang & Zhang, 2005) asserts that the traditional method for treating oil spill pollution was by using floating booms through absorption by either natural or synthetic materials etc., which however could not fully degrade the crude oil. A better method would be to adopt biodegradation. Biodegradation of hydrocarbons is however a very slow method of synthesizing the oil molecules under ambient conditions since it involves the hydrocarbons, environment and the composition of the microbial colony. The emphasis of research in the recent past is on the need to exploit the capabilities of the microbial population to degrade hydrocarbons to boost the rates of degradation found in nature. According to (Salleh, Ghazali, Raja, & Basri, 2003), bioremediation, which refers to the stabilization, or degradation of pollutants by microorganism is a safe, effective and more economical alternative means of carrying out environmental clean-up. Crude oil Crude oil refers to liquid petroleum in its unrefined state. Chemical, the principal constituents of crude oil are hydrogen and carbon (90% of the weight), which appear in form of a series of compounds known as hydrocarbons. Other constituents present in crude oil include sulphur, oxygen, and nitrogen compounds in small proportions (Salleh, Ghazali, Raja, & Basri, 2003). In crude oil, sulphur exists as thiopenes, mercaptans, thioethers, etc. Oxygen compounds mainly include naphthenic acids and asphaltenes while nitrogen compounds occur in form of alkaylated quinolones and pyridine. Also present in crude include traces of silicon, iron, nichrome and iron (Beal, 2000). Biodegradation and Bioremediation Biodegradation signifies complete microbial atomization of complex materials into simple inorganic products such as water, carbon dioxide and minerals and ultimate cell biomass. In terrestrial and aquatic environments, the biodegradation process of crude oil and other complex petroleum products mainly involves the actions of fungal and bacterial populations. According to (Salleh, Ghazali, Raja, & Basri, 2003), bioremediation is the site restoration which consist the elimination of organic compounds (contaminants) by microorganisms. The process exploits the natural metabolic flexibility of microorganisms to degrade the complex environmental contaminate compounds. Nowadays, bioremediation introduction of exogenous microbial populations called degraders or stimulating the indigenous microbial organisms to the contaminated substrate, in a process known as seeding. This bioremediation process provides a number of benefits such as destruction of the pollutants compounds, enhanced safety, reduced treatment costs as well as lower environmental disturbance. (Beal, 2000), notes that the introduction is not the only remedy to the organic contamination, the continued growth of the microorganisms is affected by environmental factors such as soil type, composition of the contaminant, nutrients available, soil type and temperature. The conditions stated above therefore, affect the process of bioremediation as a means of cleanup. (Salleh, Ghazali, Raja, & Basri, 2003), concludes that the effectiveness of the process differs considerably among the petroleum hydrocarbons; due susceptibility of the bacteria to metabolic breakdown; thus affecting the scope of success and effectiveness of the process. Microorganisms used in Biodegrading Crude oil and other petroleum Products In order for bacterial and fungal populations to occur in areas that are polluted with hydrocarbons shows that these organisms can favorably use hydrocarbons as their energy source. Due to the compound complexities of crude oil, the biodegradation process involves the interaction of a number of microorganism species. In aquatic environments, the biodegradation process is performed by diverse bacterial populations, which are universally distributed in the oceans. Some of this notable species are Acinetobacter, Vibrio, Achromobacter, pseudomonas. Petroleum hydrocarbons such as those released during oils spills into the marine ecosystems are natural products originates from aquatic algae that were buried down in over 100 million years ago. Crude oils consisting of aromatic hydrocarbons and diverse aliphatic hydrocarbons Literature Review Pertaining the oil biodegradation The use of dispersants have generated considerable bates after the incident at the Torrey Canyon. The motivations of using dispersants in oil biodegradation have remained relevant over the four decades; and which are; reduction of impact on shoreline, as well as reduction of the impacts of contamination of mammals and birds. In November 2005, Fringas, M, wrote a paper on the Stability and resurfacing of dispersed oil, on behalf of the PWSRCAC, Advisory Council. The paper reviews the stability of chemically-n dispersed oil after the initial dispersion. This tackles an abundance of experimental outcomes on the topic as well as theoretical approaches to the topic. The US National Academy of Sciences has carried out a number of field trials on oil biodegradation (Committee, 2006). The committee realized that the field tests offered opportunities for the team to verify the transport models and oil fate. However, it is apparent that those tests are very costly and there situation where legal issues may hinder their conduction. Also, the data obtained may be limited from any given test conducted. In their recommendation, the Committee proposes that future tests to be founded on coordinated and systematic bench- scale wave tank testing methods. According to (Fringas, 2004), many experimental tests have been carried out in the past, with the aim of assessing the effectiveness of oil dispersants. However, although a number of techniques have been assessed, there is no general consensus that parameters such as effectiveness can be measured in the field by using latest technology. All tests relied on the development of a mass balance between the water column and oil that remain on the surface showing that the energy regimes recorded in the lab are greater than those realized in the field trials. According to (Committee, 2006), the most recent results, which are reliable, show that dispersants extracted 10 to 40% to the sub- surface. The validity of most of the earlier tested is more questionable because of the analytical method used, and which has so far been disapproved also according to (Fingas, 2004) the data treatment method was also incorrect. In these early tests, the samples were analyzed in a lab using the colorimetric methods which are no longer in use due to their inaccuracy. Fluorometry is the latest method used, however it is still unreliable since it only measures a small portion of oil and does not distinguish between dispersed oil and dissolved components (Fingas, 2004). Biodegradation of Crude Oil in Marine Ecosystems According to (Colwell, R.R, & Walker, 1977), there are four classes of petroleum hydrocarbons in a typical oil spill i.e. resins, asphaltenes, aromatics, saturates. Majority of these hydrocarbons are biodegradable; and there are over 200 bacterial species that can readily degrade them (Prince, 2005) asserts that hydrocarbon microorganisms are omnipresent in the aquatic environment. These microorganisms utilize hydrocarbons as electron donors to produce energy for the cell growth and maintenance. The bioavailability of hydrocarbons starts when oil is dispersed in a water column creating oil-in-water emulsions. The most important preparatory step at this stage of biodegradation is the release of the biosurfactants (Singer, M.E, & Finnerty, 1984). This biosurfactants are basically extracellular substances possessing hydrophobic and hydrophilic component, which emulsify the hydrophilic (hydrocarbon) thus permitting the transportation of the hydrophilic (cell) for biodegradation. Temperature offers a critical chemical and physical role on oil, as well as the altering the rate under which the microbial metabolism and the subsequent decomposition by the microbial community (Atlas & R.M, 1981). In summary the degradation rates decrease with the reduction in temperature as a result of lowering rate of enzyme activity. In order for the microorganisms to start degrading the hydrocarbon, some transformation is necessary within the molecule. For instance, the double bonds within the molecule must be simplified into single bonds present in alkalines. The benzene, O- ring is inserted under aerobic conditions to create functional catechol form. The latter is then simplified to form aliphatic with the carboxyl group as shown in figure below (Atlas & Cerniglia, 1995). Figure 2: Schematic Flow of aromatic Ring Cleavage with Molecular Oxygen (BLANCHARD, 2006 ) Toxicity of the Oil Dispersants The latest results on the toxicity testing of dispersants are same as those found in previous years; that are toxicity among dispersants vary depending on the species, however always the dispersant toxicity is lower than toxicity of dispersed oil. In the recent studies on toxicity, concluded that chemically dispersed oil exhibited higher toxicity than physically dispersed oil. Majority of this concluded that the reason is as a result of increased Polynuclear Aromatic Hydrocarbons PAHs within the water column (Fingas, 2008). The reasons for such conclusions are because in the recent years there has been a better analytical technique being adopted as well as inclusion of newer tests. Conclusions (Fingas, 2008), discusses a number of areas regarding research on crude oil biodegradation that requires more research. This includes: Syntheses of literature regarding both chemical and physical properties on oil in order to ascertain the general effectiveness of the application of dispersant Offer data for decision makers for better prediction of the nature of the dispensability of the less studied oil through extrapolation of their properties in respect to the well studied standard oils Study of both operational and hydrodynamic parameters that impact of the overall effectiveness. References Atlas, & Cerniglia, R. m. (1995). Bioremediation of petroleum pollutant. Bioscience . Atlas, & R.M. (1981). Microbial degradation of petroleum hydrocarbons: an environmental perspective. Critical Review Microbiology . Beal, R. B. (2000). Constituent Analysis of Glycosaminoglycans. Journal of Applied. Microbiology . BLANCHARD, W. H. (2006 ). BIODEGRADATION POTENTIAL OF OIL IN ARCTIC FIRST-YEAR SEA ICE . University of New Hampshire, . Colwell, R.R, & Walker, J. (1977). Ecological espects of microbial degradation of petroleum in the marine environment. Critical Review of Microbiology . Fingas, M. (2008). A Review of Literature Related to Oil Spill Dispersants Especially Relevant to Alaska 2002-2008. Prince William Sound Regional Citizens’Advisory Council (PWSRCAC) Anchorage, Alaska . Guo-liang, Z., & Zhang, G.-l. (2005). Biodegradation of crude oil by Pseudomonas aeruginosain the presence of rhamnolipids. Journal of Zhejiang University SCIENCE . Khelifa, A. P. (2004). Prediction of Oil Droplet Size Distribution in Agitated Aquatic Environments. Proceedings of the Twenty-Seventh Arctic Marine Oilspill Program Technical Seminar. Environment Canada: Ottawa. Lee, K. Z. (2008). “Effects of Chemical Dispersants and Mineral Fines on Partitioning of Petroleum Hydrocarbons in Natural Seawater”. Proceedings of the 2008 International Oil Spill Conference . Washington, D.C.: American Petroleum Institute, . Lin, Q. (2005). Dispersants as Countermeasures in Nearshore Oil Spills for Coastal Habitat Protection”. Proceedings of the 2005 International Oil Spill Conference American Petroleum Institute. Washington, D.C: 447-451. Lumley, T. (2007). Evaluation of Methods For Assessing Toxicity of Oil Spill Treating Agents”,. in Proceedings of the Thirtieth Arctic Marine Oilspill Program Technical Seminar, Environment Canada, . Prince, R. (2005). Petroleum spill bioremediation in marine environments. Petroleum microbiology . Salleh, B. A., Ghazali, M., Raja, R. Z., & Basri, M. (2003, February 21). Bioremediation of Petroleum Hydrocarbon Pollution. Retrieved August 13, 2013, from Indian Journal of Biotechnology: http://nopr.niscair.res.in/bitstream/123456789/11330/1/IJBT%202(3)%20411-425.pdf Singer, M.E, & Finnerty, W. R. (1984). Microbial metabolism of straight-chain and branched alkanes. 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