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1 <br />' 7.0) AEROBIC AND ANAEROBIC BIODEGRADATION tN GROiTN <br /> DWATER <br /> Durinio g aerobic respiration, oxygen is reduced to r■rater, and dissolved oxygen concentrations <br /> decrease Under anaerobic conditions (hiruted oxy gen), ,Ltrate concentrations decrease as itis <br /> reduced to N2(denitrification), sulfate concentrations decrease as it is reduced to HSS, and iron <br /> (M) concentrations decrease as !i is reduced to iron (11), These processes are kilo-*i as terminal <br /> electron-accepting processes (TE-APs) The dominant TEAP process will be determined throug <br /> the monitonrg of the above mentioned intrinsic b`oremediation indicators which vary both <br /> spatially and temporally <br />' 7.1) Aerobic Biodegradation <br /> Testing for aerobic biodegradation is performed using the Expressed Assimilative Capacity (EAC) <br /> for dissolved oxygen, the dominant TEAP of aerobic biodegradation The EAC for a given TEAP <br /> is the amount of petroleum hydrocarbon contamination, such as BTEX (benzene, toluene, <br /> ethylbenzene, and Xylene), that a body of ground-%-ater has shown it has degraded using the <br /> stoichiometry of the oxidation reaction The EAC for aerobic biodegradation. of dissolved <br /> benzene is derived from the following reaction <br /> 7502 + C6H6 =* 6CO2 + 3 H2O <br /> From the stoichiometry of aerobic benzene biodegradation, 3 08 mg of oxygen are required to <br /> r co—pletely metabolize t m'�' cif ben gene and I tog of dissolved oxygen is Capable ol"facilriating the <br /> destruction of 0 32 mg of benzene Similar calculations can be made rasing the stoichiometry for <br /> I toluene, ethylbenzene, and xylene aerobic biodegradation reactions Using, the average mass ratio <br /> m <br /> of dissolved oxygen to total BTEX from, the individual compound biodegradation stoichiometry, <br /> 1 mg of dissolved oxygen is required !o metabolize 0 32 mb of total BTEX The FAC of <br /> groundwater for aerobic respiration is determined as follo`vs <br /> E.A,CDO = 0 32 (OB-OM) <br /> Where E ACllo �Expressed AssinulatiIre Capacity, aerobic respiration <br /> 0 32 = mg/L BTFX degraded per dissolved oxygen consumed ratio <br /> Qa = background dissolved oxygen concentration (mo-1 <br /> n„r = dissolved oxygen concentration rn plume (mg/L) <br /> A reduction in dissolved Oxygen and BTEX co -tran-o-O `;';thin 4n exrMting RTEX Yluiiie is a <br /> strong indication that indigenous microbes are established and actively biodegrading petroleumhydrocarbon, `ria aerobic res;iral0011 <br /> 1J <br />