Bio-remediation of oil spills A Review on Challenges

Transcription

1 Bio-remediation of oil spills A Review on Challenges Abhishek Nandan S.M.Tauseefand N.A. Siddiqui University of Petroleum & Energy Studies, Dehradun, India Abstract Nature has its own way to maintain environmental balance. One of the tools, for maintaining environmental balance is bioremediation. Bioremediation is the use of phytoremediation, bioventing, bioleaching, land farming, bioreactor, composting, bio augmentation, rhizofiltration, bio stimulation, etc. to reclaim environment contaminated by anthropogenic activities. One of the anthropogenic activities that sometimes results in accidental release of large quantity of oil into water bodies is transportation of fossil fuel via sea route. The increasing demand for petroleum products has resulted in increased number of oil spills throughout the world. One of the examples of the extent of damage that an oil spill is capable ofdoing is the British Petroleum, Gulf of Mexico spill in It is estimated that the environmental cost of the spill is more than 14 billion US dollars. Therefore it is urgently required to identify a bioremediation technique, capable of clearing large oil spills, to protect and sustain marine and terrestrial life forms. Current bio remediation techniques are facing a number of challenges which includes nonbiodegradability of asphalthenes, retardation of bulky polycyclic aromatic hydrocarbon (PAH) biodegradation, biostimulation resulting in eutrophication, incompetency of biodegradation in anoxic environments and failure of successful bioremediation laboratory studies in the field. The objective of thisstudy is to find solutionof the problems encountered during application of bio-remediation processes. Few endorsements has been proposed to overcome this challenges temporarily which includes instigating asphalthene biodegradation with combination of heat (80 C), biosurfactant (thermophilic emulsifier) and bioagumentation (using aconsortium containing Bacillus lentus and Pleurotustuberregium). Keywords:Biological treatment, Bio stimulation, Crude oil bioremediation, Oil spill remediation etc. ISBN no Page 767

2 1. Introduction: Today s major environmental problems are hydrocarbon contamination resulting from the activities related to petrochemical industry. Petroleum products that are accidentally releases in to the environment are of serious concern. As we know that hydrocarbon components belongs to the family of carcinogens and neurotoxic organic pollutants. Mechanical and chemical methods that were generally used to remove hydrocarbons from contaminated sites have limited effectiveness and can be expensive. Bioremediation is the promising technology for the treatment of these contaminated sites since it is cost-effective and will lead to complete mineralization. Concept behind Bioremediation is basically biodegradation, which refers to complete mineralization of organic contaminants into carbon dioxide, water, inorganic compounds, and cell protein or transformation of complex organic contaminants to other simpler organic compounds by biological agents like microorganisms. Many microorganisms present in water and soil have the efficiency of degrading hydrocarbon contaminants. (Das, Chandran,2010) Crude oils composed of diverse aliphatic and aromatic hydrocarbons, regularly comes into contact with the environment from underground reservoirs. Because petroleum hydrocarbons occur naturally in all marine environments, there has been time for numerous diverse microorganisms to evolve the capability of utilizing hydrocarbons as sources of carbon and energy for growth. Oil-degrading microorganisms are ubiquitous, but may only be a small proportion of the prespill microbial community. There are hundreds of species of bacteria, archae, and fungi that can degrade petroleum. Most petroleum hydrocarbons are biodegradable under aerobic conditions; though a few compounds found in crude oils, for example, resins, hopanes, polar molecules, and asphaltenes, have practically imperceptible biodegradation rates. The polycyclic aromatic hydrocarbons (PAHs) are a minor constituent of crude oils; however, they are among the most toxic to plants and animals. Bacteria can convert PAHs completely to biomass, CO 2, and H 2 O, but they usually require the initial insertion of O 2 via dioxygenase enzymes. Anaerobic degradation of petroleum hydrocarbons can also occur at a much slower rates. Petroleum hydrocarbons can be biodegraded at temperatures below 0 C to more than 80 C. Microorganisms require elements other than carbon for growth. The concentrations of these ISBN no Page 768

3 elements in marine environments primarily nitrates (NO - 3 ), phosphates (PO 3-4 ), and iron (Fe) can limit rates of oil biodegradation. Having an adequate supply rate limiting nutrients when large quantities of hydrocarbons are released into the marine environment is critical for controlling the rates of biodegradation and hence the persistence of potentially harmful environmental impacts. Bioremediation, which was used extensively in the Exxon Valdez spill, involved adding fertilizers containing nitrogen (N) nutrients to speed up the rates of oil biodegradation. Most petroleum hydrocarbons are highly insoluble in water. Hydrocarbon biodegradation takes place at the hydrocarbon water interface. Thus the surface area to volume ratio of the oil can significantly impact the biodegradation rate. Dispersants, such as Corexit 9500, which was used during the BP Deep water Horizon spill, increase the available surface area and thus, potentially increase the rates of biodegradation. (Atlas, Hazen, 2015) These bacteria presumably utilize hydrocarbons that are naturally occurred by plants, algae and other living organisms. The hydrocarbon-degrading bacteria also utilize other substrates, such as carbohydrates and proteins (obligate hydrocarbonoclastic bacteria are only very rarely found). In many cases the genes for hydrocarbon degradation occur on plasmids within these bacteria.when an environment is contaminated with petroleum, the proportion of hydrocarbon-degrading microorganisms increases rapidly. (Atlas,1995) 2. Scientific factors affecting bioremediation: Energy sources are critical factor for bioremediation. Bioavailability increased microbial conversion capacities do not lead to higher biotransformation rates when mass transfer is a limiting factor (Boopathy and Manning, 1998). Treatments involving rigorous mixing of the soil and breaking up of the larger soil particles stimulated biodegradation drastically (Manning et al., 1995). Bioactivity and biochemistry: Improving bioactivity implies that system conditions are adjusted to optimize biodegradation (Blackburn and Hafker, 1993). Various factors affect biodegradation of oil under cold conditions which include temperature, bioavailability, metabolic limitations, nutrients, etc. The cold environment will exert selective pressures on both exotic and indigenous species once the microbes are released. Biological communities in the cold regions are more sensitive than those in temperate areas because of the complexity and variability of climate, population, ISBN no Page 769

4 permafrost, and environmental sensitivity in the cold regions. Non-technical criteria include regulatory factors, research and technical factors, human resource factors, economic and liability factor. The microbial population did not restore the biodiversity characteristics found initially during the interaction with the hydrocarbons. The reasons probably lie in the closed structure of used system andalso after degradation the microbial community is not able to reconstitute itself due to limited sources of nutrients 3. Regulation can have an impact on bioremediation in different ways: Creating markets: Federal environmental programs require treatment of recurring wastes and remediation of existing wastes contaminating soils and groundwater. (Day, 1993) Controlling the product: Environmental laws and regulation may specify health and safety criteria for products before they can be marketed in USA. Toxic substances control act (TSCA) inventory: All new chemicals marketed in US must be listed in this inventory. Naturally-occurring microbes are already considered on the TSCA inventory. Other regulatory programs: The Food and Drug Administration and the US Department of Agriculture control the introduction of human-food and soil pathogens. The EPA regulates the use of microbes as pesticides under the Federal Insecticide, Fungicide, and Rodenticide Act. (Day, 1993) Controlling the process: Environmental Laws and regulations may specify how a product or equipment can be used to accomplish waste-management objectives. 4. Effects of dispersants on biodegradation The various study reviewed the effects of dispersants and surfactants on biodegradation of oil components. Some studies showed biodegradation to be stimulated, many others pointed to inhibition, and yet others observed no effects with the addition of dispersants or surfactants. The effect of surfactants and dispersants depends on the chemical characteristics of the dispersants, the hydrocarbons, and the microbial community. It is clear that surfactants can interfere with the attachment of hydrophobic bacteria to oil droplets, making the process very complex to ISBN no Page 770

5 understand. The study reported that biodegradation of PAH, one of the toxic component of oil; is not simulated by dispersants (Khul et al.2013). The study concludes that only PAH mineralization can be equated with toxicity reduction; stimulation of alkane biodegradation would not be meaningful in the overall toxicity of oil spills. Nayman et al.2006, measured effects of chemical additives on hydrocarbon fates and concluded that use of these additives must generate benefits that outweigh the lack of effect on biodegradation demonstrated in this report. 5.Application of bio remediation: Bioemulsificants are one of the effective tools which could be applicable for enhancing oil recovery and also in bioremediation of hydrocarbon in aquatic environments. The interaction between molecules reduces the surface and interfacial tensions in both aqueous solutions and hydrocarbon mixture and have low (lg/ml) critical micelle concentrations (CMC) which increases solubility and availability of the oil to the microbial attack. This class of biomolecules presents a series of advantages such as low toxicity, biodegradability and effectiveness in a wide range of ph and temperature in comparison to synthetic surfactants. (Simone Cappello, Maria Genoveseet al., 2012). As we know that maximum amount of oil from oil spills gets in contact with the coastal ecosystems, microorganisms are directly involved in biogeochemical cycle they are key driver for the degradation of many carbon sources. If we properly manage and understand them they can provide very huge range of ecosystem services like bio degradation. (Santos et al.,2010) Use of bio remediation proved to be supplemental to the cleanup technology in the oil spills. Practical studies conducted by the scientist of US Environmental Agency demonstrated that oil degradation by indigenous micro flora on the beaches was accelerated by adding fertilizer directly on surface of oil contaminated beaches. (Pritchardet al.,1992). In past, Bioremediation along with other processes have been used to remediate petroleum hydrocarbon contaminants present in soil.different organisms are used by using various technique of bioremediation depending upon the hydrocarbon present in the contaminated soil. It is simpler, less labor intensive and public attitude toward bioremediation are generally favorable, the lack of knowledge about microorganisms and their natural role in the environment could ISBN no Page 771

6 affect the acceptability of their use. However, bioremediation can be considered one of the best technologies to deal with petroleum product contaminated soil. (Thapaet al.,2011). 6. Challenges of bioremediation in oil spills: Contamination of soils, groundwater, sediments, surface water, and air with hazardous and toxic chemicals is one of the major problems facing the industrialized world today. The need to remediate these sites has led to the development of new technologies that emphasize the destruction of the pollutants rather than the conventional approach of disposal. Bioremediation, the use of microorganisms or microbial processes to degrade environmental contaminants, is among these new technologies. Bioremediation has numerous applications, including clean-up of ground water, soils, lagoons, sludges, and process-waste streams. Bioremediation frequently must address multiphasic, heterogeneous environments, such as soils in which the contaminant is present in association with the soil particles, dissolved in soil liquids, and in the soil atmosphere. Because of these complexities, successful bioremediation is dependent on an interdisciplinary approach involving such disciplines as microbiology, engineering, ecology, geology and chemistry. (Si-Zhonget al.,2009) Bioremediation has some limitations also. Some chemicals are not amenable to biodegradation, for instance, heavy metals, radionuclides and some chlorinated compounds. In some cases, microbial metabolism of contaminants may produce toxic metabolites. There are many aspects that need to be looked upon prior to application of bioremediation techniques. This includes testing and assessing the area for natural biodegradability, environmental conditions suitable for biodegradability. Disposal of waste is not completely biodegraded. 7. Conclusion: Various applications and challenges of bio remediation of oil spills have been discussed here together with various limitations in terms of scientific factors and regulations in this review paper. Few endorsements has been proposed to overcome the aforesaid challenges temporarily which includes instigating asphalthene biodegradation with combination of heat (80 C), bio surfactant (thermophilic emulsifier) and bio agumentation (using aconsortium containing Bacillus lentus and Pleurotustuberregium). However,much of the research work still needs to be ISBN no Page 772

7 undertaken for developing a cost effective and efficient technology for better utilization of oil spills for a cleaner environment. References: 1. Pritchard, P.H., et al., Oil spill bioremediation: experiences, lessons and results from the Exxon Valdez oil spill in Alaska. Biodegradation, (2-3): p Yang, S.-Z., et al., Bioremediation of Oil Spills in Cold Environments: A Review. Pedosphere, (3): p Boopathy, R., Factors limiting bioremediation technologies. Bioresource Technology, (1): p Ron, E.Z. and E. Rosenberg, Biosurfactants and oil bioremediation. Current Opinion in Biotechnology, (3): p Atlas, R.M. and T.C. Hazen, Oil biodegradation and bioremediation: a tale of the two worst spills in US history. Environmental science & technology, (16): p Das, N. and P. Chandran, Microbial degradation of petroleum hydrocarbon contaminants: an overview. Biotechnology research international, Pritchard, P., et al., Oil spill bioremediation: experiences, lessons and results from the Exxon Valdez oil spill in Alaska. Biodegradation, (2-3): p Santos, H.F., et al., Bioremediation of mangroves impacted by petroleum. Water, Air, & Soil Pollution, (1-4): p Thapa, B., A.K. Kc, and A. Ghimire, A review on bioremediation of petroleum hydrocarbon contaminants in soil. Kathmandu university journal of science, engineering and technology, (1): p Bailey, A.A. and D. Khul, The externalisation of the hierarchy. 1957: Lucis Publishing Companies. ISBN no Page 773

8 11. Nyman, J.A., P.L. Klerks, and S. Bhattacharyya, Effects of chemical additives on hydrocarbon disappearance and biodegradation in freshwater marsh microcosms. Environmental Pollution, (2): p ISBN no Page 774