Hydrogeochemical modeling of enhanced benzene, toluene, ethylbenzene, xylene (BTEX) remediation with nitrate

Abstract

[1] During a 5-month field test, active remediation of a benzene, toluene, ethylbenzene, xylene (BTEX)-contaminated aquifer was initiated by injecting water with varying amounts of KNO 3 . The experiment was performed prior to selecting bioremediation for full-scale cleanup, particularly to evaluate the competing reaction of nitrate with hydrocarbons and reduced sulfur components. The nitrate oxidized sulfides that had precipitated earlier as a result of the natural degradation of BTEX with SO 4 2À from groundwater. When the sulfides were exhausted, BTEX degradation was enhanced by nitrate. A hydrogeochemical model with kinetic oxidation reactions for Fe(II), FeS and BTEX by nitrate was developed to calculate the observed concentration patterns along a flow line in the aquifer. The rates for the kinetic model were based on published kinetic reaction equations for oxidation with oxygen. Nitrate was introduced in the equations in the same form as oxygen, with a premultiplier added to fit the observed concentration changes in the aquifer. The oxidation of Fe(II) with nitrate in the aquifer was 4 times slower than the abiological oxidation reaction with oxygen in water. Similar rates were found for oxidation of FeS with nitrate as for FeS 2 with oxygen, but the specific surface area of FeS in the aquifer was larger. The reaction rate for degradation of BTEX compounds was about 10 7 times faster than for natural organic matter. BTEX release from pools in the aquifer was modeled with a linear driving force equation in which the pollutant/water interfacial area was linked to the mass of BTEX. The release rate and the denitrification rate were used to calculate the initial amounts of BTEX at the start of the KNO 3 injection. This study shows that an assessment of the efficiency of nitrate addition for stimulating bioremediation has to consider possible reactions of nitrate with reduced sulfur components and ferrous iron.

Surface micro‐topography causes hot spots of biogeochemical activity in wetland systems: A virtual modeling experiment

“…C k [ML −3 ] is the corresponding concentration of the electron acceptor (for k = 1: oxygen, k = 2: nitrate, k = 3: iron(III); k = 4: sulfate). Monod kinetic coefficients ( μ max, k and K s,k ) for all reduction processes are based on values reported for biodegradation of organic chemicals in aquifers [ Appelo and Postma , 2005; Bekins et al , 1998; Schirmer et al , 1999; MacQuarrie et al , 1990; Eckert and Appelo , 2002; Kelly et al , 1996; Goldsmith and Balderson , 1988] and were later modified and adjusted as part of the calibration process. Simulated depth profiles for redox sensitive compounds (nitrate, sulfate and iron(II)) were calibrated by systematic variation of the Monod coefficients to best fit observed data taken at the study site [ Knorr and Blodau , 2009; Knorr et al , 2009].…”

Development of a Fully Coupled Biogeochemical Reactive Transport Model to Simulate Microbial Oxidation of Organic Carbon and Pyrite Under Nitrate‐Reducing Conditions

“…An empirical equation for the oxidation rate of pyrite due to reduction of oxygen and nitrate was published by Eckert and Appelo () and Prommer and Stuyfzand (), who based their research on the previous work of Williamson and Rimstidt () and Appelo et al (). Oxygen was not present in our experiment and the calculation of the pyrite oxidation rate is therefore reduced to where r pyr is the rate of pyrite oxidation (mol·L −1 ·day −1 ); c NO3 − ,H + are the concentrations of nitrate and hydrogen (mol/L); k pyr is the specific rate constant (dm·mol·L −1 ·day −1 ), which was originally determined by Williamson and Rimstidt () with 5.58 × 10 −6 (dm·mol·L −1 ·day −1 ); c pyr is the current pyrite concentration (mol/L); c pyr,0 is the initial pyrite concentration (mol/L); and p 2,3 are the exponent parameters.…”

In situ biostimulation of petroleum hydrocarbon degradation by nitrate and phosphate injection using a dipole well configuration

“…Eckert and Appelo (2002) showed that oxidation of Fe(II) and FeS occurred prior to BTEX degradation in a BTEX-contaminated aquifer when nitrate was injected for enhanced bioremediation. Since concentrations in organic compounds decreased without a lag phase, both reactions probably occurred simultaneously.…”