title: Nitrate reduction and its effects on trichloroethylene degradation by granular iron.
abstract: Laboratory column experiments and reactive transport modeling were performed to evaluate the reduction of nitrate and its effects on trichloroethylene (TCE) degradation by granular iron. In addition to determining degradation kinetics of TCE in the presence of nitrate, the columns used in this study were equipped with electrodes which allowed for in situ measurements of corrosion potentials of the iron material. Together with Raman spectroscopic measurements the mechanisms of decline in iron reactivity were examined. The experimental results showed that the presence of nitrate resulted in an increase in corrosion potential and the formation of thermodynamically stable passive films on the iron surface which impaired iron reactivity. The extent of the decline in iron reactivity was proportional to the nitrate concentration. Consequently, significant decreases in TCE and nitrate degradation rates and migration of degradation profiles for both compounds occurred. Furthermore, the TCE degradation kinetics deviated from the pseudo-first-order model. The results of reactive transport modeling, which related the amount of a passivating iron oxide, hematite (α-Fe2O3), to the reactivity of iron, were generally consistent with the patterns of migration of TCE and nitrate profiles observed in the column experiments. More encouragingly, the simulations successfully demonstrated the differences in performances of three columns without changing model parameters other than concentrations of nitrate in the influent. This study could be valuable in the design of iron permeable reactive barriers (PRBs) or in the development of effective maintenance procedures for PRBs treating TCE-contaminated groundwater with elevated nitrate concentrations.
authors.affiliation: Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada.
authors.forename: Qiong
authors.initials: Q
authors.lastname: Lu
authors.affiliation: Department of Earth and Environmental Sciences & The Earth and Environmental Science System Research Center, Chonbuk National University, Jeonju-si, Jeollabuk-do, 561-756, Republic of Korea. Electronic address: sjeen@jbnu.ac.kr.
authors.forename: Sung-Wook
authors.initials: SW
authors.lastname: Jeen
authors.affiliation: Pest Management Regulatory Agency, Health Canada, Ottawa, Ontario, K1A 0K9, Canada.
authors.forename: Lai
authors.initials: L
authors.lastname: Gui
authors.affiliation: Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Gillham
mesh_terms: D005290:Ferric Compounds; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D009566:Nitrates; D014241:Trichloroethylene / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry
chemical_list: D005290:Ferric Compounds; D009566:Nitrates; D014874:Water Pollutants, Chemical; D014241:Trichloroethylene; D007501:Iron
keywords: Granular iron; Nitrate; Permeable reactive barrier; Reactive transport modeling; Trichloroethylene