Bioremediation of oil spills
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Introduction to oil spills
The spilling of petroleum into our natural waterways is a major issue, and petroleum causes both acute and long term issues. Oil is harvested and processed in so many ways, there is a lot of room for error. These spills can be caused by tankers, refineries, drilling operations, or even storage facilities. Regardless of how petroleum is released into nature, spills account for high percentages of marine death and complicate vegetative life. When oil leaks into an ecosystem, it alters the balance of both the habitat and the organisms that live there. These organisms experience altered growth and reproduction patterns, anatomical complications, and increased susceptibility to hypothermia. The water resistant properties of birds and mammals are compromised due to matting of fur and exposed skin.
Along with this, petroleum is toxic. Petroleum, or crude oil, is a complex mixture of many hydrocarbons and can be used as raw material or lubricant. It is known to contain upwards of 17,000 organic compounds and both volatile organic compounds (VOC's), and polycyclic aromatic hydrocarbons (PAH's). VOC's can be carcinogenic and evaporate into the air very easily, making them toxic when taken in. PAH's have some of the same effects, and can last much longer in the environment. In many expansive oil spills, such as the Exxon Valdez or BP Deepwater Horizon incidents, substantial effects were seen when petroleum was released into those marine ecosystems.
Bioremediation refers to the use of specific microorganisms to metabolize and remove harmful substances. In most cases, bioremediation works to either increase the numbers of naturally occurring microorganisms or add pollutant-specific microbes to the area. Bioremediation can involve using many varieties of microorganisms as well, either synergistically or independently of each other. Either way, bioremediation is commonly better for the environment and less expensive than other chemical methods. Different types of bacteria, archaea, algae, and some species of plants are all able to breakdown specific toxic waste products into safer constituents. However, specific bacteria mostly commonly are used in bioremediation of oil. These specific microorganisms are not hard to find, either. There are many types of bacteria and archaea that evolve to degrade all types of substances, including petroleum.
Bioremediation of petroleum
Oil degrading organisms have evolved to use the hydrocarbons and organic compounds in petroleum as energy, and utilize molecular transfer mechanisms to denature these toxins. The aerobic and anaerobic properties of these microbes allow them to respire and ferment compounds as well, and this tends to result in the transformation of toxins into innocuous compounds. These compounds have more stable pH levels, increased solubility in water, and are less aggressive molecularly. It is known that the composition of oil-degrading microorganisms in marine ecosystems is originally less than 1%. When these organisms are given the necessary substrate, they tend to thrive and grow to almost 10% of the complete microbiome. Dependent on physical and chemical properties, petroleum-degenerative microorganisms take longer to degrade high-molecular weighted compounds, such as polycyclic aromatic hydrocarbons (PAH's). These microbes require a wide array of enzymes for the breakdown of petroleum, and require very specific nutrient composition to work at an efficient rate.
Microbes work in a step-wise fashion to breakdown and metabolize the components of petroleum.
- Linear Alkanes
- Branched Alkanes
- Small aromatic compounds
- Cyclic Alkanes
Treatments that utilize these breakdown processes most commonly use heat and chemicals to extend the efficacy. Later, more biological systems are used for specific ecosystems that utilize specific mechanisms.
The efficiency and efficacy of each method of remediation has limitations. The goal of remediation is to eliminate the environmental pollutant as quickly as possible; only inefficient processes require human intervention. Environmental factors such as requirements of reaction, mobility of substances, and physiological needs of organisms will affect the rate and degree that contaminants are degraded. Over time, many of these requirements are overcome. This is when petroleum degrading bacteria and archaea are able to mediate oil spills most efficiently. Weathering and environmental factors play large roles in the success of bioremediation. Interacting soil and pollutant chemicals truly account for the work that can be completed by these microorganisms. These processes change the soil composition and layering, along with the biochemistry of the ecosystem. These chemical and biological changes require adaptation from soil microbes to bioremediate. The susceptibility of the pollutant is also important to consider. Properties such as solubility, temperature, and pH will affect bioremediation and affect the process. Pollutants that are more soluble will be easier for microbes to transform into the environment. Otherwise, pollutants with rigid molecular structures extend bioremediation as they are harder to convert into innocuous substances. Bioaccesability, the amount of pollutant available for absorption, and bioavailability of pollutant will affect efficiency as well. In many instances, needed nutrients are collected and allocated for petroleum degrading microorganisms in order to maximize the efficiency of the process. Providing microorganisms with the nutrients and conditions they need allow them to thrive.
- RED-OX reaction potential
- Oxygen and other molecules present
- Nutrient availability
- Soil composition
- Solubility of pollutant
|Aerobic Respiration||Petroleum substrate with molecular oxygen||Nitrogen Gas, Hydrogen Sulfide,
Methane, Metals, Carbon Dioxide, Water
|Inorganic Electron Donation||Ammonium, Nitrite, Iron, Manganese are oxidized.||Nitrate, Nitrite, Iron, Manganese, Sulfate|
|Fermentation||Toxic petroleum compounds of organic nature||Harmless Compounds, Fermentation Products|
|Demobilization||Iron, Sulfate, Mercury, Chromium, Uranium||Ferric Hydroxide, Sulfide, Pyrite, Reduced Chromium,
|Reductive Dehalogenation||Halogen compound with electron donor||Reduced contaminant|
Listed above, the chemicals required and products formed in petroleum degradation are shown. These microbes will reduce, oxidize, ferment, and demobilize the constituents of oil spills over time, and create innocuous compounds. Bioremediation techniques involve utilizing these mechanisms to reduce pollutant amounts and are dependent on pollutant aspects:
Ex situ bioremediation
Ex situ remediation refers to reactions performed outside the natural habitat of these organisms.
- Increased microbial activities through aeration, irrigation, and creation of bio-piles.
- Increased degradation activities via turning of polluted soils and addition of minerals and water.
- The use of bioreactors, to enhance and speed up the biological reactions of microorganisms to decrease bioremediation time.
- Farming techniques that call for addition of nutrients in soil to stimulate microbial mechanisms
In situ bioremediation
In situ remediation refers to reactions performed inside a reaction mixture.
- Bio-venting, using moisture and nutrients to enhance the transformation of pollutants to more innocent substances.
- Bio-slurping, using pumping to apply oxygen and water, thus separating and compiling soils to increase remediation of microbes.
- Bio-sparging, where air is pushed into soil to stimulate microbial bioremediation.
- Phytoremediation, utilizes the mechanisms of plants to decrease efficacy of pollutants.
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