Bioremediation in situ

In Situ Bioremediation. In situ bioremediation can be an aerobic or anaerobic process, or a combination of the two. In designing an in situ bioremediation system, one should consider the types of microorganisms available (naturally in place or added), the stmctural and chemical makeup of the soil matrix, types of contaminants, oxygen and nutrient addition and distribution, and temperature. These factors are discussed prior to introducing the individual techniques for in situ bioremediation. 

Environmental issues are driving several aspects of biotechnology. Sites contaminated by toxic wastes can be cleaned by several alternative methods, but all are expensive. The most certain way to remove toxic materials from soil is to excavate it for incineration, but this requires much labor, energy, and money. Bioremediation in situ tends to be much less expensive on one hand but is slow and uncer-... 

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

Bioremediation in situ is much more complicated than the system used in the laboratory controlled condition. Microorganisms in natural community interact with each other and also with other organisms and plants such interactions are more complicated than the scientific technique can delineate simply. Because of this, more systematic approaches are needed to reveal the connectivity between these biological factors and non-biological factors to understand the underlying processes. 

Ex sitn bioremediation is generally nsed in landfarming. This involves placing the contaminated media in a treatment cell. Dnring treatment, the soil is periodically tilled and the water content is monitored to assnre complete bioremediation, in situ is much the same, only there is no treatment cell. 

Can be used to enhance the performance of several in situ technologies, including bioremediation, in situ chemical oxidation, in situ thermal treatments, and in situ solidification. 

National Research Council, In situ Bioremediation. When Does it WorJC National Academy Press, Washiagton, D.C., 1993. 

Microbial-enhanced oil recovery involves injection of carefully chosen microbes. Subsequent injection of a nutrient is sometimes employed to promote bacterial growth. Molasses is the nutrient of choice owing to its low (ca 100/t) cost. The main nutrient source for the microbes is often the cmde oil in the reservoir. A rapidly growing microbe population can reduce the permeabiHty of thief zones improving volumetric sweep efficiency. Microbes, particularly species of Clostridium and Bacillus, have also been used to produce surfactants, alcohols, solvents, and gases in situ (270). These chemicals improve waterflood oil displacement efficiency (see also Bioremediation (Supplement)). 

Ex situ bioremediation may use various biological wastewater treatment processes, soil piles, or land appHcation. With in situ bioremediation, the basic process is the same microbes, soil, and water working together as a bioreactor. Where the in situ techniques differ are in how contaminants and microbes are brought in contact and how oxygen, nutrients, and other chemical supplements ate distributed in the soil—water—air matrix. Typical in situ bioremediation techniques include natural or intrinsic attenuation, air sparging, and bioventing. 

Aerobic, Anaerobic, and Combined Systems. The vast majority of in situ bioremediations ate conducted under aerobic conditions because most organics can be degraded aerobically and more rapidly than under anaerobic conditions. Some synthetic chemicals are highly resistant to aerobic biodegradation, such as highly oxidized, chlorinated hydrocarbons and polynuclear aromatic hydrocarbons (PAHs). Examples of such compounds are tetrachloroethylene, TCE, benzo(a)pyrene [50-32-8] PCBs, and pesticides. 

Design Considerations. The effectiveness of in situ bioremediation is influenced by many factors, including microorganisms, soils, oxygen, pH, temperature, type and quantity of contaminants, and nutrients. 

Contaminants. The type and concentration of contaminants in an aquifer dictate what type of in situ bioremediation system, aerobic, anaerobic, or combination, ate the most effective. 

J. L. Sims and co-workers. In Situ Bioremediation of Contaminated Ground Water, U.S. Environmental Protection Agency, EPA/540/S-92/003, Washington, D.C., 1992. 

Istok JD, JM Senko, LR Krumholz, D Watson, MA Bogle, A Peacock, Y-J Chang, DC White (2004) In situ bioremediation of technetium and uranium in a nitrate-contaminated aquifer. Environ Sci Technol 38 468-475. 

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. 

Seller HR, W-S Ding, M Reinhard (1995) Byproducts of anaerobic alkylbenzene metabolism useful as indicators of in situ bioremediation. Environ Sci Technol 29 2864-2870. 

Enrichment factors during the anaerobic degradation of o-xylene, m-xylene, m-cresol, and p-cresol by pure cultures of sulfate-reducing bacteria that use the fumarate pathway ranged from -1.5 to -3.9 ppm (Morasch et al. 2004). It was therefore proposed that this could be applied to evaluating in situ bioremediation of contaminants that use this pathway for biodegradation. 

A comparison had been made of fractionation during the dechlorination of tetrachlo-roethene by Sulfurospirillum multivorans and Desulfitobacterium sp. strain PCE-S in laboratory experiments (Nijenhuis et al. 2005). Isotope fractionation in growing cultures was 1.0052 for Desulfitobacterium sp. and only 1.00042 for Sulfurospirillum multivorans, whereas fractionation was greater in crude cell extracts from both strains. It was concluded that caution should therefore be exercised in applying fractionation factors to the evaluation of in situ bioremediation. 

Dott W, D Eeidieker, M Steiof, PM Beckerm, P Kampfer (1995) Comparison of ex situ and in situ techniques for bioremediation of hydrocarbon-polluted soils. Int Biodet Biodeg 35 301-316. 

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