In Situ Groundwater Bioremediation

Bioremediation usually requires a procedure for stimulation of and maintaining the activity of microorganisms. For biodegradation to be successful, it is necessary to provide a continuous supply of a suitable electron acceptor (such as oxygen or nitrate), nutrients (nitrogen, phosphorus), and a carbon source for energy and cell material. The most commonly deficient components in the subsurface are eiectron acceptors and nutrients. 

Aerobic degradation has been shown to be most effective in reducing the concentration of aliphatic and aromatic hydrocarbon fuel compounds. Anaerobic reactions are more effective in degrading chlorinated hydrocarbons and long-chain animal fats and oils. Detailed study is necessary to determine the most-effective procedure for a specific site. 

Aerobic treatment of aquifer oxygen is usually supphed by one of three methods direct air sparging of air or oxygen into wells screened below the contaminated zone, saturation of water with air or oxygen prior to reinjection, or addition of an oxidant (typically a peroxide compound) directly into an injection well or injection water. Regardless of the mechanism of introduction, the important factor is that the oxidant is distributed throughout the contaminated zone at a concentration and rate such that it can be utilized by the microorganisms. 

The key factors that determine the effectiveness of bioremediation in aquifers are  

The location, distribution, and disposition of chemical contaminants in the aquifer can strongly influence the likelihood of success for bioremediation. This technology generally works well for dissolved contaminants and contaminants adsorbed onto higher-permeability sediments. However, if the majority of the contamination is trapped in lower-permeability sediments or outside the flow path, where it is in contact with nutrients and electrons acceptors, this technology will have reduced impact, or none at all. 

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Hopkins GD, J Munakata, L Semprini, PL McCarty (1993a) Trichloroethylene concentration effects on pilot-scale in-situ groundwater bioremediation by phenol-oxidizing microorganisms. Environ Sci Technol 27 2542-2547. 

After the feasibility of in situ groundwater bioremediation has been established, the engineering design can proceed. Detailed design documents should be based on ... 

Aerobic bacteria complete most of the petroleum bioremediation applications, particularly those above the groundwater table. Aerobes are those bacteria that require an oxygen source as their TEA. Conversely, anaerobic species require the absence of oxygen (anoxic conditions) for their respiration. In situ anaerobic bioremediation is typically only conducted in the saturated zone because of the difficulty in maintaining a strict anaerobic environment. In some instances, facultative anaerobes are utilized because they can alter the respiration to be metabolically active under both anaerobic and aerobic conditions. As such, the type of TEA available will dictate the metabolism and subsequent degradation mode. The most common TEAs used for bioremediation are listed in Table 2. Careful selection of microbe-TEA combinations can enable a specific degradation pathway to facilitate cometabolism and prevent undesired degradation by-products. 

Ortiz-Bernad I, RT Anderson, HA Vrionis, DR Lovley (2004a) Resistance of solid-phase U(VI) to microbial reduction during in situ bioremediation of uranium-contaminated groundwater. Appl Environ Microbiol 70 7558-7560. 

For practitioners of in situ technologies, note that U.S. EPA has issued a policy statement that reinjection of contaminated groundwater is allowed under Resource Conservation and Recovery Act (RCRA)35 36 as long as certain conditions are met. This policy is intended to apply to remedies involving in situ bioremediation and other forms of in situ treatment. Under this policy, groundwater may be reinjected if it is treated aboveground prior to reinjection. Treatment may be by a pump-and-treat system or by the addition of amendments meant to facilitate subsurface treatment. Also, the treatment must be intended to substantially reduce hazardous constituents in the groundwater (either before or after reinjection) the cleanup must be protective of human health and the environment and the injection must be part of a response action intended to clean up the environment.37... 

In situ bioremediation In situ from soil and free product/ groundwater and treatment using aboveground processes Addition of oxygen or other... 

Tables 24.13 and 24.14 summarize performance data for the 35 completed and 38 ongoing in situ bioremediation projects. The concentration of MTBE in groundwater prior to treatment was as high as 870,000 pg/L and as low as 10 pg/L. The data show that bioremediation (either alone or in combination with other technologies) has been employed to remediate MTBE in groundwater and soil to concentrations <50 pg/L and has achieved MTBE concentration reductions >99%. The median project duration for the 20 completed sites ranged from 6 months to 1 year.

A full-scale cleanup was performed using in situ bioremediation to treat MTBE and BTEX at a service station in Massachusetts. Soil at the site consists of a layer of sand and gravel underlain by peat, silt, and clay. The in situ bioremediation system consisted of 12 injection wells and two butane injection panels used to stimulate cometabolic aerobic biodegradation of the contaminants in groundwater. The system was operated between October 2000 and January 2001. MTBE concentrations were reduced from 370 to 12 pg/L and BTEX contamination in groundwater was reduced by approximately two orders of magnitude during the 4-month period.74... 

Environmental Security Technology Certification Program (ESTCP), Cost and Performance Report— In-Situ Bioremediation of MTBE in Groundwater, CU0013, September 2003. 

Mysona, E. S. and Hughes, W. D., 1999, Remediation of BTEX in Groundwater with LNAPL Using Oxygen Releasing Materials (ORM) In In Situ Bioremediation of Petroleum Hydrocarbons and Other Organic Compounds (edited by B. C. Alleman and A. Leeson), Battelle Press, Columbus, OH, Vol. 5, No. 3, pp. 283-288. 

Brubaker, G. R., 1993, In-Situ Bioremediation of Groundwater In Geotechnical Practice for Waste Disposal (edited by D. E. Daniel), Chapman Hall, New York. 

Kinsella, J. V. and Nelson, M. J. K., 1993, In Situ Bioremediation Site Characterization, System Design, and Full Scale Field Remediation of Petroleum Hydrocarbon and Trichloroethylene Contaminated Groundwater In Bioremediation Field Experience (edited by P. E. Flathman and D. E. Jerger), CRC Press, Boca Raton, FL. 

Norris, R. D., 1994, In-Situ Bioremediation of Soils and Groundwater Contaminated with Petroleum Hydrocarbons In Handbook of Bioremediation (edited by R. D. Norris, R. E. Hinchee, et al.), CRC Press, Boca Raton, FL. 

Without appropriate cleanup measures, BTEX often persist in subsurface environments, endangering groundwater resources and public health. Bioremediation, in conjunction with free product recovery, is one of the most cost-effective approaches to clean up BTEX-contaminated sites [326]. However, while all BTEX compounds are biodegradable, there are several factors that can limit the success of BTEX bioremediation, such as pollutant concentration, active biomass concentration, temperature, pH, presence of other substrates or toxicants, availability of nutrients and electron acceptors, mass transfer limitations, and microbial adaptation. These factors have been recognized in various attempts to optimize clean-up operations. Yet, limited attention has been given to the exploitation of favorable substrate interactions to enhance in situ BTEX biodegradation. 

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