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Bioremediation: An Alternative to Conventional Remedial Technologies
Utkarsh Singh1* and Naveen Kumar Arora2
Department of microbiology, CSJM University, Kanpur 2
Department of environmental microbiology, BBA University, Lucknow
Received 22 December 2015; Accepted 28 December 2015; Available online 31 December 2015
Advances in technology and industrialization, bring with them, their unpleasant partners, pollution and degradation of the environment. The effects on the environment connected with industrial activities are mainly related to the production of industrial wastes. Management of these wastes is evolving with time and complexity of the problem. The conventional techniques used for remediation have been to dig up contaminated soil and remove it to a landfill, or to cap and contain the contaminated areas of a site. The methods have some drawbacks. A better approach than these traditional methods is to completely destroy the pollutants if possible, or at least to transfer them to innocuous substances. Bioremediation, or the use of organisms for the removal of contamination or pollutants has become a popular option. Bioremediation is an option that offers the possibility to destroy or render harmless various contaminants using natural biological activity. As such, it uses relatively low-cost, low-technology techniques, which generally have a high public acceptance and can often be carried out on site.
Keywords: Bioremediation; Environment; Microorganisms; Pollution
The quality of life on earth is linked inextricably to the overall quality of the environment. In early times, we believed that we had an unlimited abundance of land and resources; today, however, the resources in the world show, in greater or lesser degree, our carelessness and negligence in using them. The problems associated with contaminated sites now assume increasing prominence in many countries. Contaminated lands generally result from past industrial activities when awareness of the health and environmental effects connected with the production, use, and disposal of hazardous substances were less well recognized than today. The problem is worldwide, and the estimated number of
contaminated sites is significant (Cairney 1993). It is now widely recognized that contaminated land is a potential threat to human health, and its continual discovery over recent years has lead to international efforts to remedy many of these sites, either as a response to the risk of adverse health or environmental effects caused by contamination or to enable the site to be redeveloped for use.
60 Management of these wastes is evolving
with time and complexity of the problem.
The conventional techniques used for remediation have been to dig up contaminated soil and remove it to a landfill, or to cap and contain the contaminated areas of a site. The methods have some drawbacks. The first method simply moves the contamination elsewhere and may create significant risks in the excavation, handling, and transport of hazardous material. The cap and contain method is only an interim solution since the contamination remains on site, requiring monitoring and maintenance of the isolation barriers long into the future, with all the associated costs and potential liability (Kumar et al. 2011).
A better approach than these traditional methods is to completely destroy the pollutants if possible, or at least to transfer them to innocuous substances. Some technologies that have been used are high-temperature incineration and various types of chemical decomposition (e.g., base-catalyzed dechlorination, UV oxidation). They can be very effective at reducing levels of a range of contaminants, but have several drawbacks, principally their technological complexity, the cost for small scale-application, and the lack of public acceptance, especially for incineration that may increase the exposure to contaminants for both the workers at site and nearby residents (Mary 2011).
Because of the problems associated with pollutant treatment by conventional methods, an alternative approach, bioremediation, or the use of organisms for the removal of contamination or pollutants has become a popular option (Jorgensen 2007).
Bioremediation is an option that offers the possibility to destroy or render harmless various contaminants using natural biological activity. As such, it uses relatively
low-cost, low-technology techniques, which generally have a high public acceptance and can often be carried out on site.
Principles of Bioremediation
Bioremediation is defined as a process whereby organic wastes are biologically degraded under controlled conditions to an innocuous state, or to levels below concentration limits established by regulatory authorities (Mueller et al. 1996).
By definition, bioremediation is the use of living organisms, primarily microorganisms, to degrade the environmental contaminants into less toxic forms. It uses naturally occurring bacteria and fungi or plants to degrade or detoxify substances hazardous to human health and/or the environment. The microorganisms may be indigenous to a contaminated area or they may be isolated from elsewhere and brought to the contaminated site. Contaminant compounds are transferred by living organisms through reactions that take place as a part of their metabolic processes.
Microorganisms can be isolated from almost any environmental conditions. The main requirements are an energy source and a carbon source. Because of the adaptability of microbes and other biological systems, these can be used to degrade or remediate environmental hazards (Vidali 2001).
Aerobic bacteria, recognized for degrading pesticides and hydrocarbons, are Pseudomonas, Alkaligenes, Sphingomonas, Rhodococcus and Mycobacterium.
Anaerobic bacteria are not as frequently used as aerobic bacteria. There is an increasing interest in anaerobic bacteria used for bioremediation of polychlorinated biphenyls (PCBs) in river sediments, dechlorination of the solvent trichloroethylene (TCE), and Chloroform.
Methylotrophs, the aerobic bacteria that grow utilizing methane for carbon and energy, are active against a wide range of compounds, including the chlorinated aliphatic trichloroethylene and 1, 2-dichloroethane.
Fungi such as white rot fungus
Phanaerochaete chrysosporium have the
ability to degrade an extremely diverse range of persistent or toxic environmental pollutants.
The microorganisms are present in contaminated soil, but they cannot necessarily be there in the numbers required for bioremediation of site. Therefore, their growth and activity must be stimulated.
Biostimulation involves the addition of nutrients and oxygen to help indigenous microorganisms. These nutrients are the basic building blocks of life and allow microbes to create the necessary enzymes to break down the contaminants. In addition to hydrogen, oxygen, and nitrogen, carbon constitutes about 95% of the weight of cells (Zeyaullah et al. 2009).
Microbial growth and activity are readily affected by the environmental conditions like pH, temperature and moisture. It is important to achieve optimal conditions as most of the microorganisms grow optimally over a narrow range. Temperature affects biochemical reaction rates. Available water is essential for all the living organisms (Thapa et al. 2012).
A variety of different technologies and procedures are currently being used, and a number of new and promising approaches have been suggested or have reached advanced stages of development.
In situ bioremediation
These techniques are generally the most desirable options due to lower cost and fewer disturbances, in which soil is not removed from the field, materials from beaches contaminated with oil are not removed from the site, or groundwater is not pumped for aboveground treatment. The most important land treatments are:
62 to contaminated soil to stimulate the
In situ biodegradation, used for soil
and groundwater, involves supplying oxygen and nutrients by circulating aqueous solutions through contaminated soils to stimulate naturally occurring bacteria to degrade organic contaminants.
Biosparging, involves the injection of air under pressure below the water table to increase groundwater oxygen concentrations and enhance the rate of biological degradation of contaminants by naturally occurring bacteria.
Bioaugmentation, frequently involves
the addition of microorganisms indigenous or exogenous to the contaminated sites containing the target contaminant, where the population has acquired the catabolic activity, has had success (Andreoni and Gianfreda 2007).
Ex situ bioremediation
A variety of bioremediation technologies have been developed to treat toxic chemicals not at the place where they exist but rather after their removal or transfer from that location. Some of these techniques are used for waste disposal sites, and because the contaminated material is removed from its location in soil, sediment or aquifer, these procedures are considered as ex situ techniques.
Land farming is a simple technique in which contaminated soil is excavated and spread over a prepared bed and periodically tilled until pollutants are degraded. It has the potential to reduce
monitoring and maintenance costs, as well as clean-up liabilities; it has received much attention as a disposal alternative.
Composting involves mixing of polluted
material together in a pile with a solid nonhazardous, organic substance that is itself reasonably readily degraded such as manure or agricultural wastes. The presence of these organic materials supports the development of a rich microbial population and elevated temperature characteristic of composing.
Bioreactors- slurry reactors or aqueous reactors are used for ex situ bioremediation. Inoculation of bioreactors with individual bacteria, known mixtures of species, or a mixed culture is commonly practiced. Bioremediation in reactors involves the processing of contaminated soil material (soil, sediment, sludge) or water through an engineered containment system. In general, the rate and extent of biodegradation are greater in a bioreactor system than in situ or in solid-phase systems because the contained environment is more manageable and hence more controllable and predictable (USEPA).
Certain criteria must be met for bioremediation to be seriously considered as a practical mode for
treatment- Presence of microorganisms having the needed catabolic activity.
63 concentration to levels that meet
Products that are toxic at the concentrations likely to be achieved during remediation must not be produced.
The site must be free from the chemicals, markedly inhibitory to the biodegrading species.
The target compound(s) must be bioavailable.
Conditions at the site must be made appropriate to sustain microbial growth or activity.
The cost of the technology must be less or, at worst, no more expensive than other alternative technologies.
None of these criteria is negligible. The failure to meet any one could result in a rejection of a biodegradative approach or the inability to achieve the established cleanup goals (Quagraine et al. 2005).
Growing awareness of the harmful effects of the environmental pollution has lead to a marked increase in research into various strategies that might be used to clean up the contaminated environment. Bioremediation is a natural process and is therefore perceived by the public as an acceptable waste treatment process for contaminated material. Once a bioremediation program has been designed, its feasibility can be evaluated by considering the applicability; the treatability studies; the possible limitations and drawbacks, and the advantages. Only when all these conditions are met, a successful, productive, not-deleterious of soil quality, and costly convenient bioremediation process will occur.
Conflicts of interest
All contributing authors declare no conflicts of interest.
The authors would like to thank the Professors of the Department of microbiology, CSJM University, Kanpur and Department of environmental microbiology, BBA University, Lucknow for providing necessary assistance and guidance.
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