Bioremediation: Use of Microorganisms to Solve Some Environmental Problems

Environmental exposure of toxic chemicals such as PCBs, pesticides, oil, and heavy metals poses significant health risk for humans and other animals. These toxic chemicals not only cause many chronic abnormalities in human beings but may also degrade biodiversity. Bioremediation is one innovative technology that has the potential to alleviate toxic chemical contamination in environment.  These processes are basically an application of energetics and material flow.



Source: http://www.lexic.us/definition-of/bioremediation



Hussain al al., 2009 mentioned  several advantages of bioremediation that have made this technique a preferred technology over other physicochemical methods to remediate contaminated sites. Bioremediation is a natural process that uses microorganisms to utilize a wide range of organic compounds such as carbon and energy source and metabolize them to harmless products, or into carbon dioxide and water in case of complete mineralization. This complete removal of organic pollutants eliminates any future liability associated with treatment and disposal of contaminated material. Bioremediation is often employed on site by enhancing the natural processes of degradation and transformation without causing a major disruption. This eliminates the excavations and transportation of wastes offsite and the potential threats to human health and the environment that can arise during transportation. Onsite treatment of contaminants (bioremediation) with natural attenuation and fewer inputs proves to be less expensive than other technologies that are used for cleanup of hazardous wastes. Although bioremediation appears to be a promising alternative for the remediation of pesticide-contaminated sites, it is still in the developmental phase. It is a research-intensive technology because a large number of microorganisms and toxic compounds are involved in this process. Not all compounds present in the environment are substrates for microbial metabolism; hence, bioremediation is limited to those compounds that are biodegradable. In some cases, partial degradation of a compound may produce metabolites that are more persistent and toxic as compared to the parent compound, which can aggravate the pollution problem. A number of factors also come into play when bioremediation is envisaged to detoxify contaminants at field scale. As such it is necessary to expand the use and successful application of bioremediation , more research is needed to better understand the capability of microorganisms under different environmental conditions. This would help in better designing the engineered systems for remediation of contaminated sites.

Spillage of petroleum hydrocarbons causes significant environmental pollution. Bioremediation is an effective process to remediate petroleum oil contaminant from the ecosystem. In a recent study conducted in 2010 by Mukherjee and Bordoloi,  2011 found out that bacterial consortium consisting of Bacillus subtilis DM-04 and Pseudomonas aeruginosa M and NM strains were seeded to 20% (v/w) petroleum oil-contaminated soil, and bioremediation experiment was carried out for 180 days under laboratory condition. Bacterial consortium showed a significant reduction in total petroleum hydrocarbon level in contaminated soil (76% degradation) as compared to the control soil (3.6% degradation) 180 days post-inoculation. The Gas Chromotography analysis confirmed that bacterial consortium was more effective in degrading the alkane fraction compared to aromatic fraction of crude petroleum oil hydrocarbons in soil. The nitrogen, sulfur, and oxygen compounds fraction was least degraded. The reclaimed soil supported the germination and growth of crop plants (C. aretinum and P. mungo). In contrast, seeds could not be germinated in petroleum oil-contaminated soil.

In 2002, Barker and Bryson conducted a study on bioremediation of heavy metals and organic toxicants by composting. The study highlighted that high microbial diversity and activity during composting, due to the abundance of substrates in feedstocks, promotes degradation of xenobiotic organic compounds, such as pesticides, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs). For composting of contaminated soils, noncontaminated organic matter should be cocomposted with the soils. Metallic pollutants are not degraded during composting but may be converted into organic combinations that have less bioavailability than mineral combinations of the metals. Degradation of organic contaminants in soils is facilitated by addition of composted or raw organic matter, thereby increasing the substrate levels for cometabolism of the contaminants. Similar to the composting of soils in vessels or piles, the on-site addition of organic matter to soils (sheet composting) accelerates degradation of organic pollutants and binds metallic pollutants.

The accumulation of pesticides in the soil environment adversely affects soil health and productivity. Bacterial species (Staphylococcus sp. and Bacillus circulans) isolated from contaminated soil collected from the premises of a pesticide manufacturing industry were able to degrade 72 to 76% of endosulfan (initial endosulfan concentration: 50 mg L - 1 ) in aerobic and facultative anaerobic conditions in four weeks of incubation (Kumar and  Philip, 2006). Siddique et al. (2003) also isolated some bacterial and fungal species from soil that degraded 84—91% of isomers of endosulfan (initial concentration: 100 mg L _ 1 in 100 mL solution).

To achieve the full potential of bioremediation, efforts should be focused to expand research regarding soil-microbe-contaminant interactions vis-a vis with biotechnological advancement to translate effectively the bench- and pilot-scale findings to field scale.

Genome-derived model for physiological differences in Geobacter during growth on soluble electron acceptors or insoluble Fe(III) oxide. Source: http://www.nature.com/nrmicro/journal/v1/n1/fig_tab/nrmicro731_F4.html

References:

Barker, A.V. and Gretchen M. B.(2002). Bioremediation of Heavy Metals and Organic Toxicants by Composting. The Scientific World Journal, 2, 407-420. Retrieved from http://www.umass.edu/umext/soilsandplant/PDF%20Files/Barker%20PDF/MiniReview.pdf

Hussain, S., Siddique, T., Arsad, M.and Saleem, M. (2009). Bioremediation and Phytoremediation of Pesticides: Recent Advances. Critical Reviews in Environmental Science and Technology, 39, 843-907.

Kumar, M., and Philip, L. (2006). Bioremediation of endosulfan contaminated soil and water-optimization of operating conditions in laboratory scale reactors. Journal Hazardous Materials, 136, 354-364.

Mukherjee, A., and Bordoloi, N.. (2011). Bioremediation and reclamation of soil contaminated with petroleum oil hydrocarbons by exogenously seeded bacterial consortium: a pilot-scale study. Environmental Science and Pollution Research International, 18(3), 471-478.  Retrieved February 22, 2011, from ABI/INFORM Global. (Document ID: 2269257671).

Siddique, T., Okeke, B.C., Arshad, M., and Frankenberger, W.T. (2003). Enrichment and isolation of endosulfan-degrading microorganisms. Journal of Environmental Quality, 32, 47-54.