Bioremediation, by definition, is the use of microorganisms, such as bacteria, plants, or fungi to remove pollutants, usually hydrocarbons, from a contaminated environment. In relation to mechanical and chemical oil spill cleanup processes, either bioaugmentation or biostimulation methods are used. In bioaugmentation, additional microorganisms are added to the polluted environment in order to reinforce natural biological processes. In biostimulation, however, optimum nutrients are added to the polluted area in order that the microbial population already present and indigenous to the area will multiply rapidly and thrive, and thus commence degradation of the pollutant.
Other physical, mechanical methods such as sorbent booms and skimmers to control any the spread of the oil slick on the water, and chemical dispersants are also used in conjunction with bioremediation in order to achieve the highest possible clearance of hydrocarbons from the affected area.
The degradation and break down of hydrocarbons begins by the conversion of the alkane chain or polycyclic aromatic hydrocarbon (PAH) into an alcohol. The next step in the process is oxidation, which then converts the compound to an aldehyde and thereafter, into an acid and eventually into water, carbon dioxide, and biomass. In the case of the PAH, fission occurs which leads to mineralisation.
Factors affecting Bioremediation
The conditions of the affected area are a major consideration when deciding whether bioremediation is the most affective method when decontaminating a polluted environment. Physical and chemical conditions must be considered prior to implementing the decision to utilise bioremediation as a cleanup method. Physical conditions, such as temperature, surface area of the contamination and the water forces within that area, such as strength of water currents and wave size, must be carefully considered. Chemical factors such as oxygen and nutrient content, pH and the viscosity of the oil must also be taken into consideration.
Temperature affects bioremediation by changing the properties and viscosity of the oil and also by influencing the oil degrading microorganisms. When the temperature is lowered, the viscosity of the oil is increased, causing the oil to thicken, which changes the toxicity and solubility of the oil, depending upon its chemical content. Temperature also has a direct affect on the log growth rate of the microorganisms, in addition to the degradation rate of the hydrocarbons, depending upon their specific characteristics.
The surface area of the oil is also a significant factor in the success of bioremediation. The growth of oil degrading microorganisms occurs at the interface of the water and oil. The larger the surface area of the oil results in a larger area for growth and hence a larger microbial population.
The force of the water is significant since rough and choppy waters will disperse and dilute even further the essential nutrients required for the microorganisms to multiply and thrive and also physically spread the oil further, thus polluting an even larger area.
Appropriate and optimum levels of oxygen, nutrients, and pH are factors which will directly control whether or not the microorganisms are able to survive within the environment. Oxygen is required for the survival of many microorganisms and also drives the reactions for the degradation of the hydrocarbons. Nutrients, particularly nitrogen and phosphorus are also crucial for the growth of the microorganisms and also for the conversion of the excess carbon present in the oil.
The chemical composition of the oil is another factor which affects whether bioremediation is a viable proposition. In contrast to many of the other requirements needed for successful bioremediation, the chemical composition of the oil is a factor which cannot be altered. If the oil is a heavy crude oil, containing resins and asphaltene compounds, it is very difficult for microorganisms to degrade in comparison to lighter crude oils.
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