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I
<br /> Engineered Approaches to In Situ Bioremediation of Chlorinated Solvents
<br /> ^1 For direct aerobic oxidation, primary reactants include oxygen and CAH and possible additives include
<br /> air, oxygen, hydrogen peroxide (HZOZ) and magnesium peroxide. For cometabolic aerobic oxidation,
<br /> additional primary reactants include organic or anthropogenic carbon and additional additives include
<br /> methane, propane, butane, and ammonia. For anaerobic reductive dechlorination, primary reactants
<br /> include hydrogen, organic carbon, carbon from a contaminant source (anthropogenic), and CAH while
<br /> possible additives include lactate, methanol, hydrogen, and molasses. The additives listed in Exhibit 4-5
<br /> could be used in any of the configurations described in Section 3, as determined by the specific
<br /> requirements of the site.
<br /> Exhibit 4-5: Primary Reactants and Additives Typically Employed for Engineered
<br /> In Situ Bioremediation of CAHs
<br /> Engineered Typical Primary Reactants and Additives in Engineered Systems
<br /> Bioremediation Targeted
<br /> Mechanism CAHs Typical Additives (primary reactant
<br /> Primary Reactants supplemented)
<br /> Aerobic oxidation DCH, VC Oxygen, CAH Air, oxygen, hydrogen peroxide, magnesium
<br /> (direct) DCA, CA, peroxide (oxygen)
<br /> MC CM
<br /> Aerobic oxidation TCE, DCE, OxygenAir, oxygen, hydrogen peroxide, magnesium
<br /> (cometabolic) VC, TCA,. peroxide (oxygen)
<br /> CF, MC Organic carbon or Methane, propane, butane, ammonia (organic
<br /> carbon from a carbon)
<br /> contaminant source
<br /> (anthropogenic)
<br /> Anaerobic PCE, TCE, Hydrogen, organic Lactate, methanol, hydrogen, molasses
<br /> -_ reductive DCE, VC, carbon, or carbon from (electron donor)
<br /> dechlorination TCA, DCA, a contaminant source
<br /> CT, CF, MC (anthropogenic) 11
<br /> Sources: Anderson and Lovley 1997; McCarty 1994; McCarty and others 1998; USAF 1998; EPA 1998; Yager and others 1997
<br /> 4.1 .4 Treatability (Bench-Scale) Testing
<br /> Treatability (bench- or laboratory-scale) testing is generally conducted after site characteristics,
<br /> degradation mechanisms, and potential enhancements have been identified. Treatability testing is used to
<br /> evaluate the effectiveness of degradation mechanisms and enhancements that are being considered for the
<br /> site. For example, results of treatability testing can be used to determine the conditions under which
<br /> degradation products are produced, the rates of degradation, and the paths of degradation in order to
<br /> identify the specific formulation that supports the most complete and rapid biodegradation of the targeted
<br /> CAHs. Examples of treatability tests for in situ bioremediation of CAHs include microcosm bottle
<br /> studies and soil column studies. Typically, samples of the media to be treated at the site (groundwater,
<br /> sediment, or soils) are used in the treatability tests. Because microbial populations usually are
<br /> heterogeneous in the subsurface and the type of plume may vary across the site, treatability tests are often
<br /> conducted using samples from several areas of a site.
<br /> In addition, data from treatability testing can help identify the parameters to be used for field-scale
<br /> testing and implementation. It should be noted that rates of biodegradation observed during bench-scale
<br /> microcosm studies typically will be higher than those observed in the field and that in situ residence
<br /> times will require adjustment accordingly (U.S. Air Force 1998).
<br /> 4-7
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