Simulation of aerobic and anaerobic biodegradation processes at a crude oil spill site

Abstract

A two-dimensional, multispecies reactive solute transport model with sequential aerobic and anaerobic degradation processes was developed and tested. The model was used to study the field-scale solute transport and degradation processes at the Bemidji, Minnesota, crude oil spill site. The simulations included the biodegradation of volatile and nonvolatile fractions of dissolved organic carbon by aerobic processes, manganese and iron reduction, and methanogenesis. Model parameter estimates were constrained by published Monod kinetic parameters, theoretical yield estimates, and field biomass measurements. Despite the considerable uncertainty in the model parameter estimates, results of simulations reproduced the general features of the observed groundwater plume and the measured bacterial concentrations. In the simulation, 46% of the total dissolved organic carbon (TDOC) introduced into the aquifer was degraded. Aerobic degradation accounted for 40% of the TDOC degraded. Anaerobic processes accounted for the remaining 60% of degradation of TDOC: 5% by Mn reduction, 19% by Fe reduction, and 36% by methanogenesis. Thus anaerobic processes account for more than half of the removal of DOC at this site. Introduction Experience obtained from remediation efforts at contaminated groundwater sites has demonstrated the limitations of pump-and-treat technology, especially at sites contaminated with nonaqueous phase liquids (NAPLs). Increasing effort isbeing devoted to the development and testing of alternative technologies [MacdonaM and Kavanaugh, 1994]. A promising alternative to traditional pump-and-treat methods is intrinsic bioremediation, a method that relies on the naturally occurring biodegradation processes at a site [Lee et al., 1988; Madsen, 1991; Bouwer and Zehnder, 1993; Salanitro, 1993]. Both aerobic and anaerobic biodegradation processes can be effective at removing hydrocarbons from the environment [Grbi&Gali•, 1991; Barker et al., 1987; Wilson et al., 1987; Chiang et al., 1989; Cozzarelli et al., 1990; Wilson et al., 1990; Acton and Barker, 1992; Lyngkilde and Christensen, 1992b; Thieftin et al., 1993; Baedecker et al., 1993; Eganhouse et al., 1993]. Long-term, detailed monitoring of the groundwater plume caused by a crude oil spill near Bemidji, Minnesota, has documented the importance of both aerobic and anaerobic biodegradation at this site [Baedecker et al., 1993]. The availability of electron acceptors determines the sequence of biodegradation processes. Based on the thermodynamics of reactions and redox potential, the theoretical sequence is aerobic degradation, followed by denitrification, manganese and iron reduction, sulfate reduction, and then methanogenesis. This sequence may cause zonation of a contaminant plume with different biodegradation processes dominating in each redox zone [Baedecker and Back, 1979; Chapelle This paper is not subject to U.S. copyright. Published in 1995 by the American Geophysical Union. Paper number 95WR02567. and Lovley, 1992; Lyngkilde and Christensen, 1992a; Vroblesky a...

Inverse modeling of BTEX dissolution and biodegradation at the Bemidji, MN crude-oil spill site

“…In a previous modeling effort (Essaid et al, 1995), a numerical model incorporating sequential use of terminal electron acceptors was used to analyze the evolution of the ground-water contaminant plume at the Bemidji site. The model was based on field observations that provided substantial evidence for the sequential use of electron acceptors Cozzarelli et al, 2001.…”

“…Many studies of hydrocarbon attenuation at field sites have involved numerical modeling (Borden et al, 1986;Rifai et al, 1988;Chiang et al, 1989;MacQuarrie et al, 1990;Thierrin et al, 1993;Essaid et al, 1995;Landmeyer et al, 1996;Lu et al, 1999;Schirmer et al, 2000). In general, these models have had limited data sets, have not included dissolution processes, and have relied on trial and error calibration.…”

Influence of Petroleum Deposit Geometry on Local Gradient of Electron Acceptors and Microbial Catabolic Potential

“…In case of NAPLs in groundwater, substantial field evidence exists in support of presence of multiple electron acceptors within one contaminated site [72,74,75]. In presence of multiple TEAs microbes tend to utilize them sequentially, in increasing order of their Gibbs free energy (Table 2.2).…”

“…In presence of multiple TEAs microbes tend to utilize them sequentially, in increasing order of their Gibbs free energy (Table 2.2). In an aquifer, recharge replenishes nutrients and TEAs in the upper boundary of the contaminant plume and results in higher biodegradation in the upper boundary [72] Sequential utilization of TEAs might result in zonation of a contaminant plume with different biodegradation processes dominating in each redox zone [75]. Most of the current models take in account the sequential use of TEAs and transport and uptake of nutrients necessary for microbial growth [75].…”

“…In an aquifer, recharge replenishes nutrients and TEAs in the upper boundary of the contaminant plume and results in higher biodegradation in the upper boundary [72] Sequential utilization of TEAs might result in zonation of a contaminant plume with different biodegradation processes dominating in each redox zone [75]. Most of the current models take in account the sequential use of TEAs and transport and uptake of nutrients necessary for microbial growth [75]. As explained in Essaid et al (2003), these models are of varying complexity depending on the extent to which they represent: 1) physical, chemical, and biological processes;…”