title: In situ lifetimes and kinetics of a reductive whey barrier and an oxidative ORC barrier in the subsurface.
abstract: Permeable reactive barriers (PRB) are being used to engineer favorable field conditions for in-situ remediation efforts. Two redox adjustment barriers were installed to facilitate a 10-month research effort on the fate and transport of MTBE (methyl tert-butyl ether) at a site called the Michigan Integrated Remediation Technology Laboratory (MIRTL). Thirty kilograms of whey were injected as a slurry into an unconfined aquifer to establish an upgradient reductive zone to reduce O2 concentration in the vicinity of a contaminant injection source. To minimize the impact of contaminant release, 363 kg of oxygen release compound (ORC) were placed in the aquifer as a downgradient oxidative barrier. Dissolved oxygen and other chemical species were monitored in the field to evaluate the effectiveness of this technology. A transient one-dimensional advective-dispersive-reaction (ADR) model was proposed to simulate the dissolved oxygen transport. The equations were solved with commonly encountered PRB initial and constant/variable boundary conditions. No similar previous solution was found in the literature. The in-situ lifetimes, based on variable source loading, were estimated to be 1,661 and 514 days for the whey barrier and ORC barrier, respectively. Estimates based on either maximum O2 consumption/production or measured O2 curves were found to under- or overestimate the lifetime of the barriers. The pseudo-first-order rate constant of whey depletion was estimated to be 0.303/d with a dissolution rate of 0.04/d. The oxygen release rate constant in the ORC barrier was estimated to be 0.03/d. This paper provides a means to design and predict the performance of reactive redox barriers, especially when only limited field data are available.
authors.affiliation: Department of Civil and Environmental Engineering, The University of Michigan, Ann Arbor 48109-2099, USA. mikebar@engin.umich.edu
authors.forename: M J
authors.initials: MJ
authors.lastname: Barcelona
authors.forename: G
authors.initials: G
authors.lastname: Xie
mesh_terms: D001673:Biodegradation, Environmental; D002273:Carcinogens / Q000032:analysis* / Q000378:metabolism; D004738:Engineering; D007700:Kinetics; D008567:Membranes, Artificial; D008738:Methyl Ethers / Q000032:analysis* / Q000378:metabolism; D008894:Milk Proteins; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D010539:Permeability; D012037:Refuse Disposal; D000067816:Whey Proteins
chemical_list: D002273:Carcinogens; D008567:Membranes, Artificial; D008738:Methyl Ethers; D008894:Milk Proteins; D000067816:Whey Proteins; C043243:methyl tert-butyl ether; D010100:Oxygen