Effects of environmental conditions on MTBE degradation in model column aquifers: II. Kinetics

Convincing proof for in situ biodegradation of MTBE is difficult to obtain from field data alone due to a number of distinctive properties of MTBE. An alternative approach to study MTBE degradation is to use controlled model systems designed to simulate typical field conditions. Two sets of experiments were designed to study the nature of the aerobic degradation observed in a previous study, in which MTBE degraded to tert-butyl alcohol (TBA) after 35 days but only under aerobic conditions and in the absence of BTEX. The first set of studies investigated whether the rate of MTBE degradation might be improved by the addition of a cometabolic substrate, while the second set examined the kinetics of degradation. The average half-lives for MTBE conversion to TBA were 2.7, 1.7, and 1.9 yr for Base Borden, Lake Erie, and New Jersey sediments, respectively. The similarity among these values suggested that slow biodegradation of MTBE to TBA (with half-lives ca. 2 yr) may occur in a broad range of aerobic aquifers. This estimate was consistent with available approximations of MTBE biodegradation rates in the field. Degradation was observed when the column aquifers were operated under aerobic conditions and in the absence of more favorable substrates, e.g., BTEX. Under typical groundwater conditions in and around plumes from many gasoline spill sites, the column results indicated that biodegradation will generally be negligible.