Bioremediation - Case Study Example

Bioremediation INTRODUCTION Bioremediation is the process of work by biological agents; mainly micro-organisms are used to restore the environment in its original state after its alteration by contaminants. There are several substances that may interfere with the environment, both on land and in the sea, ranging from oil spills, wastes from industries, chemicals used in agricultural processes, and many others. These micro-organisms derive their nutrients from the breakdown of the contaminants. Bioremediation is carried out specifically to target known contaminants. However, there are other contaminants that may not be eliminated by bioremediation, for instance, the contamination resulting from heavy metals. Micro-organisms cannot break down metal particles. There are several bioremediation approaches that may be undertaken depending on the nature of the contaminant and the extent of contamination. QUESTION ONE There are several bioremediation methods that the company can adopt to avoid the disastrous effects of the oil spill accidents (Elweis 38). Bioremediation is necessary as it will reduce the effects of the oil spill in both environments – land and water. In the first accident, the oil spill will spread in the soil of the bed as well as in water. The methods that are to be used for the tanker that runs aground should be able to take care of the oil that gets absorbed by the bed while as the for the second ship, the method should focus on the elimination of oil that is found on top. The method of biodegradation that can be used to degrade petroleum in the second oil spill accident is nutrient enrichment. The research indicates that the major factor that hinders the biodegradation of petroleum that results from oil spills due to tanker accidents is the lack of an adequate nutrient supply to the marine micro-organisms that decompose oil. The process involves the addition of a carefully formulated fertilizer to the water contaminated by oil. This fertilizer contains specific nutrients that promote the growth of indigenous marine micro-organisms that are responsible for degrading petroleum. The fertilizers must be carefully selected to ensure only nutrients that are vital to the growth of the specific bacteria are present. The major nutrients that are required for optimum growth of the marine micro-organisms that degrade petroleum are nitrogen and phosphorus. The fertilizer selected should be that which provides the slow release of nutrients. This is very important as it ensures that the nutrients are available to the micro-organisms throughout the biodegradation period. The fertilizers used are usually present in two forms, either as granules or in a liquid form. The fertilizer in a liquid form is applied to the surface of water by the use of sprinklers. The use of nutrient enrichment method to combat the effects of oil spill has advantages as well as shortcomings as indicated in the table 1 below. Table 1 Advantages and Disadvantages of the Nutrient Enrichment Method Disadvantages Advantages Addition of nutrients could cause eutrophication leading to depletion of oxygen. No formation of algal blooms occurs. Some components of the fertilizer may be harmful to other marine organisms. Cases of adverse ecological effects are rare. Some of the products of bioremediation using nutrient enrichment may be harmful. The method is safer in comparison to other methods of conventional degradation. The increased growth and multiplication of the micro-organisms may cause an ecological imbalance in the marine environment. The other method that can be used by the company to reduce the effects of the oil spill is the slurry phase bioremediation that is suitable for contaminated soil (Elweis 292). It involves the excavation of the contaminated material and its transfer to the slurry where the contaminating agent is removed. The contaminated material is suspended in an aqueous solution, and the treatment process is conducted under saturated conditions. In this case, the contaminated material is the soil excavated from the ocean bed. The contaminated soil is mixed with water which also contains the petroleum to form the slurry. During the mixing of the slurry, there is a contact between the micro-organisms and the contaminating oil. This mixing increases the rate of reaction. The biodegradation process is usually maximized by incorporating into the slurry the necessary nutrients that promote the growth of the micro-organisms as well as the altering of the PH. The continuous mixing of the slurry coupled with the supply of oxygen is done so that the soil particles are broken down and further dissolve the oil spill products. The slurry phase biodegradation can be done at the site where the contamination occurred, or the contaminated materials can be carried, and biodegradation process conducted elsewhere. This method of biodegradation is particularly very suitable for the biodegradation of oil at the Straits of Juan De Fuca. In this accident, the oil spill is present both in the water and the soil at the bottom. The contaminated water is mixed with the soil to form the slurry. To ensure the complete biodegradation of the petroleum, it is advisable for the treatment to be done away from the site of an accident. Though it is mainly advantageous for the company to use this method for the biodegradation of the spilt petroleum, there are some disadvantages associated with this method as summarized in the table 2 below. Table 2 Advantages and Disadvantages of the Slurry Phase Method Advantages Disadvantages The slurry phase process is generally faster and requires less space of land to carry out. Not suitable for soils contaminated with volatile substances. In case the petroleum contained some volatile components, the method may not be effective. The conditions under which bioremediation process is conducted can be easily controlled making it very effective. Due to the many stages involved in the process, it is capital intensive. It also involves high operational costs. QUESTION TWO In order to combat the effects of the PCBs, bioremediation is recommended to restore the rivers in their original state (Singh and Ward 1-2). Being a natural process, bioremediation is more effective in comparison with other conventional processes that may be used as a remedy for the PCB and oil spill contamination. When conducting the remedial processes aimed at restoring an environment in its natural original state, a lot of factors must be taken into consideration. One of such factors is the effect of the process or results of the process influencing the organisms inhabiting the area in question. It is, therefore, very necessary that the method adopted should have minimal effects on the organisms. Being a natural process, a bioremediation method, for instance, the slurry phase method, does not give rise to other toxic products. It is, therefore, the most viable method to be used for elimination of the PCBs from the river sediments. The second reason why bioremediation is recommended is that it is less expensive in comparison with other methods that may be used to solve the problem. Bioremediation uses natural substances like microorganisms which are naturally available, and in most cases it does not require a lot of capital to acquire the necessary equipment to carry out. Given that the results at the end of both processes are the same, it is advisable to take the less expensive method so that the surplus capital can be used somewhere else. Bioremediation does not just ensure the separation of the dangerous PCBs from the bottom of the river, but guarantees their complete degradation. This makes bioremediation particularly advantageous over other methods that may leave residues of the contaminant in the soil found at the river bed. The complete removal of the chemical ensures prosperity of aquatic organisms as it restores the water back to its initially safe state. Another factor that makes bioremediation a good process to get rid of the PCBs and oil in the river is that it requires less energy to carry out in comparison with other conventional methods. In situations where bacteria are used to eradicate the PCBs, the only thing required is the nutrient supply to the bacteria. This is not expensive as the nutrients are locally available, and it does not require much processing. Bioremediation is also advantageous over other methods as it requires less supervision. It can be set and left to run to completion without further intervention. During the bioremediation process, some factors may become limited. These may include the equipment required to access the river beds to ensure that only the contaminated soil from the river bed is targeted to combat the effects of the PCB. Biodegradation also has limitations that make it not fully effective as a method of restoring the environment in its original state. The major limitation is the slow nature of the biodegradation process. The time period for the process usually lasts from days to months. This makes it very unsuitable in cases where the contaminants interfere with the environment at very fast rates. This often calls for the conventional degradation processes which act faster. The second shortcoming of biodegradation is its inability to get rid of the heavy metals. It cannot, therefore, be used to combat contaminants that are composed of heavy metals. Also when used in some instances, bioremediation may not get rid of all the contaminants. This is usually the case when specific conditions are not met. Some methods of biodegradation, for instance, the use of genetically engineered micro-organisms require a strong scientific base to carry out. If the proper knowledge is not available, the produced micro-organisms may cause adverse effects on the ecological balance in an environment. QUESTION THREE The use of electron donors and alternate electron acceptors in bioremediation are very important. They have been applied in several systems (Leeson and Alleman 93). One of the systems where alternate electron acceptors have been utilized is that of denitrifying systems used in bioremediation. This has been applied in several systems, for instance, the degradation of toluene in which nitrate is reduced completely to nitrogen gas while the toluene is reduced to carbon (iv) oxide. In cases where benzene, ethylbenzene, and xylenes are to be degraded together, degradation occurs in the following order from the first to the last: toluene, xylene, and ethylbenzene. Where an enrichment culture is used with ethyl benzene, it has been shown that single aromatic compounds are degraded at much faster rates. The sulphate reducing system also utilizes the electron donors and alternate electron acceptors. In this system of bioremediation, sulphate is used as the electron acceptor. It involves the biodegradation of aromatic hydrocarbons by sulfidogenic organisms with the reduction of the sulfate to hydrogen sulfide gas. Being an aromatic compound, toluene can be adequately reduced to carbon (iv) oxide given that there is no cell growth within the system. The degradation in the system also takes place sequentially, like the nitrate reducing system with toluene as the preferred substrate. Under this system, benzene is degraded only in the absence of other substrates like the toluene. The degradation of benzene also lasts during a relatively longer period of time in comparison with the cases when other substrates are used. The third example of a system in which the electron acceptors are used is the iron (iii) reducing systems. This system is used to reduce toluene, cresol, and phenol. These are used as substrates while iron (iii) is used as the electron acceptor. A lot of iron (iii) molecules are required to reduce a single molecule of the substrate, for instance, toluene. The iron (iii) molecules are reduced to iron (ii) molecules while toluene is degraded to carbon (iv) oxide which is less toxic than the toluene. For this system to be an effective bioremediation tool, occurrence, nutritional requirements, and growth conditions of the bacteria responsible must be properly modified. Another system that makes use of electron donors and alternate electron acceptors is the fermentative system, however referred to as a carbon dioxide reducing system. This is done under methanogenic conditions in which various aromatic hydrocarbon compounds including toluene and benzene are degraded to carbon dioxide and methane gases. The carbon source for this system is the ferulic acid while the bacterial culture is that obtained from sewage seeds. The biotransformation using toluene or benzene as the carbon source lasts for about sixty days after incubation. Other aromatic hydrocarbons that are degraded using the system include styrene, naphthalene, and acenaphthalene. Benzothiophene, sulfur containing heterocyclic hydrocarbon is also degradable under the system. Fermentative degradation is present in areas that have geochemical conditions as a passive process. It occurs without the intervention of human beings. This helps a great deal as it reduces the effect of hydrocarbons to a larger extent; compounds that may impact the environment negatively. The likely indication of this passive degradation process is the presence of the methane gas, though in diffuse amounts or at times as a mixture of other gases coming from the geochemical areas. Mixed electron acceptor system also helps in the biodegradation process to eliminate some aromatic compounds that impact the environment negatively making it unconducive for the inhabitation by organisms including human beings. This system is used mainly in aquifer segments. Biodegradation occurs either in the same system or in spatially separated compartments. In sites where denitrification activities are occurring, the data show the presence of oxygen in the feed water. There are biological and chemical reactions between the electron acceptors and the products of the biodegradation according to the observations over the years. For instance, there is a link between sulfate reductions to sulfide and iron (iii) reduction to iron (ii) by the sulfate reducing enrichment media. The various acceptor systems are very useful in the biodegradation processes for various aromatic hydrocarbon compounds. If left in the environment, the effects of these compounds can be very disastrous and cause massive effects on the living systems. Works Cited Alleman, Bruce C. and Andrea Leeson. In Situ and On-site Bioremediation: Alternative Electron Acceptors, Bioreactors, Bioslurry Reactors, Vapor-Phase Bioreactors, Biological Treatment of Wastewater, Biological Treatment of Landfill Leachate and Molecular Monitoring of Bioremediation Potential. Columbus: Battelle press, 1997. Print. Eweis, Juana B. Bioremediation Principles. New York, NY: McGraw-Hill, 1998. Print. Ward, Owen P. and Ajay Singh. Biodegradation and Bioremediation. London: Springer, 2004. Print. Read More