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Bioremediation - 4 - 10 Septemher 1993 <br /> C. Fixed film bioreactor <br /> 2. land farming and composting <br /> 3. In-situ bioremediation <br /> a. Biostimulation or bioenhancement <br /> b. Bioaugmentation <br /> In-situ bioremediation is most effective when large volumes of soil and/or ground water have been <br /> impacted in highly permeable soil, the zone of soil contamination is within 20 - 30 feet below grade, <br /> and ground water is C 30 feet below grade. Bioremediation has resulted in significant degradation <br /> in as little as 2.5 months. However, typical degradation is normally noted in 6 to 18 months with a <br /> total time of 12 to 24 months. It has been used most often in degradation of gasoline. In soil, the <br /> remedial target level is the Iow mg/kg TPH range. In ground water the remedial target level is <br /> < 100 1Ag11 TPH range (maybe as low as 10 gg/l). It is possible to achieve 5 ppb benzene and <br /> 0.44 mg/1 xylene with a system that is appropriately designed and optimally operated_ <br /> Bioenhancement involves stimulation of indigenous microorganisms to degrade contaminants. This <br /> method requires that nutrients he added to enhance the microbial population and it is assumed that <br /> every organism to accomplish the desired treatment results are present. Therefore, the goal is to <br /> provide the proper environment or enhance the existing environment. It may be necessary to add <br /> oxygen, nitrogen, phosphorus, trace minerals, and adjust the pH. Microbial counts in excess of 105 <br /> cells per gram are required. Sites typically contain 101 - 10' cells per gram. <br /> Bioenhancement has shortcomings - How can we be certain the microbes present are the must <br /> suitable to degrade all the materials present? What if the only organisms stimulated are those that <br /> eliminate the primary substrate but do not cometabolize specifically targeted substrates? Many <br /> problem substrates may not be biodegraded directly and if they are the only food available microbes <br /> may not be able to use them. This method also has the potential to curate large populations of <br /> pathogenic or other undesirable microbes. A feasibility/treatability study must he conducted. <br /> Bioaugmentation involves the addition of preselected organisms to degrade contamination. This <br /> process usually consists of the controlled addition of specifically formulated biocultures in <br /> conjunction with development and monitoring of a growth environment in which the selected <br /> bacteria can survive and wmpete. The targeted contaminants either serve as the food source or are <br /> cometabolized. As with bioenhancement, it may be necessary to add essential nutrients to provide <br /> the proper environment. Bioaugmentation ensures that the proper microorganisms are present in <br /> sufficient number, type, and compatibility to attack contamination and break it down. It also allows <br /> selection of organisms that are not harmful to humans and will not produce phytotoxins or nuisance <br /> odors, such as hydrogen sulfide. <br /> Bioaugmentation has shortcomings - Mere addition of bacteria is not enough. Selected microbes <br /> must be carefully matched to the contamination and metabolites formed. The microbes must be able <br /> to favorably compete with the ubiquitous organisms. The nature of the subsurface must be studied <br /> and manipulated to support the introduced organisms_ <br /> 50 ' d 800' oN ££:5 26' 91 dag ON I31 <br />