Impact of Ethanol on the Natural Attenuation of MTBE in a Normally Sulfate-Reducing Aquifer

Abstract

Side-by-side experiments were conducted in an aquifer contaminated with methyl-tert-butyl ether (MTBE) at a former fuel station to evaluate the effect of ethanol release on the fate of pre-existing MTBE contamination. On one side, for approximately 9 months we injected groundwater amended with 1-3 mg/L benzene, toluene, and o-xylene (BToX). On the other side, we injected the same, adding approximately 500 mg/L ethanol. The fates of BToX in both sides ("lanes") were addressed in a prior publication. No MTBE transformation was observed in the "No Ethanol Lane." In the "With Ethanol Lane", MTBE was transformed to tert-butyl alcohol (TBA) underthe methanogenic and/or acetogenic conditions induced by the in situ biodegradation of the ethanol downgradient of the injection wells. The lag time before onset of this transformation was less than 2 months and the pseudo-first-order reaction rate estimated after 7-8 months was 0.046 d(-1). Our results imply that rapid subsurface transformation of MTBE to TBA may be expected in situations where strongly anaerobic conditions are sustained and fluxes of requisite nutrients and electron donors allow development of an active acetogenic/methanogenic zone beyond the reach of inhibitory effects such as those caused by high concentrations of ethanol.

Enthalpies of Formation and Bond Dissociation Energies of Lower Alkyl Hydroperoxides and Related Hydroperoxy and Alkoxy Radicals

“…Hence, as part of an ongoing study of the combustion chemistry of oxygenates in general and biobutanol, CH 3 (CH 2 ) 2 -CH 2 OH, in particular, we have re-examined the thermochemistry of organic hydroperoxides, ROOH, for methyl, ethyl, n-propyl and n-butyl for which little data exist. Previous studies have largely focused on changing the alkyl group along the sequence R ) methyl, ethyl, isopropyl and tert-butyl to determine the effect of increased substitution on bond energies.…”

Effect of Ethanol on Microbial Community Structure and Function During Natural Attenuation of Benzene, Toluene, and o-Xylene in a Sulfate-reducing Aquifer

“…For example, in locations with existing MTBE contamination, a likely characteristic of sites with potential for unintended subsurface gasoline release, active methanogenic conditions may result in increased rates of conversion of MTBE to tert-butyl alcohol (TBA). 10,25 Based on our work, additional studies examining the influence of ethanol release on other subsurface contaminants (e.g., 1,2-dichloroethane dichloride or ethylene dibromide, both previously used in gasolines) 26 may be warranted.…”

Comparative Transcriptome Analysis of Methylibium petroleiphilum PM1 Exposed to the Fuel Oxygenates Methyl tert -Butyl Ether and Ethanol

“…MTBE and its primary metabolite tert-butyl alcohol (TBA) are suspected and known carcinogens, respectively (1, 7, 31, 57). Recently, alternative oxygenates, such as ethanol, have been substituted for MTBE, but because of the very slow depletion of contaminant mass from spill areas under anoxic conditions, the impacts of MTBE on the subsurface will be felt for many years and likely decades to come (8,29).Methylibium petroleiphilum PM1 is one of the best-characterized aerobic MTBE degraders known to date, and PM1-like bacteria have been shown to be present in several MTBEcontaminated aquifers in California (19,20,25) and Europe (12,33,42). M. petroleiphilum PM1 uses MTBE as a sole carbon source, oxidizing it completely to CO 2 without accumulation of TBA (16).…”

“…MTBE and its primary metabolite tert-butyl alcohol (TBA) are suspected and known carcinogens, respectively (1, 7, 31, 57). Recently, alternative oxygenates, such as ethanol, have been substituted for MTBE, but because of the very slow depletion of contaminant mass from spill areas under anoxic conditions, the impacts of MTBE on the subsurface will be felt for many years and likely decades to come (8,29).…”