title: Nitrate addition to groundwater impacted by ethanol-blended fuel accelerates ethanol removal and mitigates the associated metabolic flux dilution and inhibition of BTEX biodegradation.
abstract: A comparison of two controlled ethanol-blended fuel releases under monitored natural attenuation (MNA) versus nitrate biostimulation (NB) illustrates the potential benefits of augmenting the electron acceptor pool with nitrate to accelerate ethanol removal and thus mitigate its inhibitory effects on BTEX biodegradation. Groundwater concentrations of ethanol and BTEX were measured 2 m downgradient of the source zones. In both field experiments, initial source-zone BTEX concentrations represented less than 5% of the dissolved total organic carbon (TOC) associated with the release, and measurable BTEX degradation occurred only after the ethanol fraction in the multicomponent substrate mixture decreased sharply. However, ethanol removal was faster in the nitrate amended plot (1.4 years) than under natural attenuation conditions (3.0 years), which led to faster BTEX degradation. This reflects, in part, that an abundant substrate (ethanol) can dilute the metabolic flux of target pollutants (BTEX) whose biodegradation rate eventually increases with its relative abundance after ethanol is preferentially consumed. The fate and transport of ethanol and benzene were accurately simulated in both releases using RT3D with our general substrate interaction module (GSIM) that considers metabolic flux dilution. Since source zone benzene concentrations are relatively low compared to those of ethanol (or its degradation byproduct, acetate), our simulations imply that the initial focus of cleanup efforts (after free-product recovery) should be to stimulate the degradation of ethanol (e.g., by nitrate addition) to decrease its fraction in the mixture and speed up BTEX biodegradation.
authors.affiliation: Federal University of Santa Catarina, Department of Sanitary and Environmental Engineering, Florianópolis, Santa Catarina, Brazil. Electronic address: henry.corseuil@ufsc.br.
authors.forename: Henry Xavier
authors.initials: HX
authors.lastname: Corseuil
authors.affiliation: University of Exeter, Centre for Water Systems, Exeter, Devon EX4 4QF, United Kingdom.
authors.forename: Diego E
authors.initials: DE
authors.lastname: Gomez
authors.affiliation: Federal University of Santa Catarina, Department of Sanitary and Environmental Engineering, Florianópolis, Santa Catarina, Brazil.
authors.forename: Cássio Moraes
authors.initials: CM
authors.lastname: Schambeck
authors.affiliation: Federal University of Santa Catarina, Department of Sanitary and Environmental Engineering, Florianópolis, Santa Catarina, Brazil.
authors.forename: Débora Toledo
authors.initials: DT
authors.lastname: Ramos
authors.affiliation: Department of Civil and Environmental Engineering, Rice University, MS-317, 6100 Main St., Houston, TX 77005, USA.
authors.forename: Pedro J J
authors.initials: PJ
authors.lastname: Alvarez
mesh_terms: D001554:Benzene / Q000737:chemistry; D001555:Benzene Derivatives / Q000737:chemistry*; D001673:Biodegradation, Environmental; D000431:Ethanol / Q000737:chemistry*; D060587:Groundwater / Q000032:analysis / Q000737:chemistry*; D064688:Metabolic Flux Analysis / Q000379:methods; D009566:Nitrates / Q000737:chemistry*; D014050:Toluene / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000009:adverse effects / Q000737:chemistry*; D014992:Xylenes / Q000737:chemistry
chemical_list: D001555:Benzene Derivatives; D009566:Nitrates; D014874:Water Pollutants, Chemical; D014992:Xylenes; D014050:Toluene; D000431:Ethanol; D001554:Benzene; C004912:ethylbenzene
keywords: BTEX; Fuel ethanol; GSIM; Metabolic flux; Mixed substrates; Natural attenuation