1. © Pilot-Scale In Situ Bioremediation Of Gasoline-Contaminated Groundwater: Impact Of Process Parameters Nakhla, G; Niaz, M AMER INST CHEMICAL ENGINEERS, ENVIRONMENTAL PROGRESS; pp: 37-46; Vol: 21 King Fahd University of Petroleum & Minerals http://www.kfupm.edu.sa Summary This study evaluated the impact of groundwater velocity and dissolved oxygen (DO), added as hydrogen peroxide to overcome oxygen solubility limitations, and contaminant concentrations, on the efficiency of an engineered in situ bioremediation (ISB) strategy to treat groundwater contaminated with benzene, toluene, and xylene (BTX). BTX served as model compounds of gasoline contamination. Groundwater velocities of 1, 2, and 4 m/d were studied. At each velocity, two concentrations of BTX were employed - 10 and 50 mg/l of each of the contaminants to reflect 'hot spot' conditions following a spill or major leak. Similarly DO:BTX mass rations of 1:5:1 and 3:2:1 were employed. The results of the study indicated that BTX removal efficiencies of 96.7 to 99.7% were achievable at a groundwater velocity of 1 m/d with final concentrations reaching as low as 30 mug/l. BTX removal efficiencies decreased to 70 to 85 percent at a velocity of 2 m/d, and to 37 to 53% at a velocity of 4 m/d. At any given groundwater velocity, BTX removal efficiencies generally increased with increasing DO and BTX concentrations. Mathematical equations for the first-order biodegradation rate coefficients as a function of the three parameters were derived. Statistical analysis of the data revealed that groundwater velocity was the most significant parameter impacting biodegradation efficiency, accounting for approximately 80% of the variability. Hydraulic conductivity of the aquifer decreased by approximately 80% over the course of the seven-month study, with 90% of the decline occurring within the first six weeks. Plate counts also impacted hydraulic conductivity. However, it was not possible to model hydraulic conductivity by plate Copyright: King Fahd University of Petroleum & Minerals; http://www.kfupm.edu.sa

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