HR: 1340h
AN: H33A-1379    [Abstracts]
TI: Micromodel Study of Transport Issues during TCE Dechlorination by ZVI Colloids
AU: * Baumann, T
EM: thomas.baumann@ch.tum.de
AF: Institute of Hydrochemistry, TUM, Marchioninistr. 17, Muenchen, D-82131 Germany
AU: Keller, A A
EM: keller@bren.ucsb.edu
AF: Bren School of Environ. Sci. & Mgmt, 3420 Bren Hall, Univ of California, Santa Barbara, CA 93106 United States
AU: Auset-Vallejo, M
EM: mauset@bren.ucsb.edu
AF: Bren School of Environ. Sci. & Mgmt, 3420 Bren Hall, Univ of California, Santa Barbara, CA 93106 United States
AU: Lowry, G V
EM: glowry@cmu.edu
AF: Dept. of Civil & Env. Engr., Carnegie Mellon University, 119 Porter Hall, Pittsburgh, PA 15213-3890 United States
AB: Zero valent iron (ZVI) is known to effectively dechlorinate TCE, PCE and other highly chlorinated compounds. Applications at contaminated sites include reactive walls and funnel-and-gate systems. In cases where groundwater treatment by these near-surface setups are not feasible, ZVI nano-particles injected into the TCE plume or source area might be an alternative. In this micromodel study the mobility, stability, and possible interface reactions of ZVI nano-particles were evaluated in both, TCE wet and water wet micromodels. The pore structure consisted of a network of coarse channels with smaller pore spaces in between. The average flow velocity was on the order of cm/day to m/day, which are the flow velocities typically observed in shallow aquifers. TCE NAPL was trapped in the micromodel as discrete blobs. The ZVI nano-particles were partially coated with novel triblock co-polymers designed to bind to the iron particle surface, reduce aggregation, and to provide an affinity for the NAPL/water interface. In all cases the nano-particles proved to be colloidally stable and were not found to aggregate, indicating that the surface modifications were successful at mitigating particle-particle interactions. Bare ZVI particles rapidly aggregate at the dispersion concentration used. At the flow velocities and NAPL distribution evaluated, the particles showed only very little tendency to attach to interfaces (air-water, TCE-water, or liquid-solid). Instead they moved around the TCE blobs without significant interaction. This is contrary to the TCE-water partitioning behavior previously demonstrated ex situ for these particles. The absence of targeting at TCE-water interface is likely because the residence time of the nano particles in the vicinity of the TCE blobs is on the order of a second or less so particles do not have sufficient time to diffuse across flow lines and attach to the TCE-water interface. Targeted in situ delivery of nanoiron directly to the TCE-water interface will therefore require favorable hydrodynamics. Based on the reaction stoichiometry, the concentration of the ZVI-colloids has to be fairly high, in which case clogging of pore spaces needs to be considered.
DE: 1831 Groundwater quality
DE: 1875 Vadose zone
DE: 1894 Instruments and techniques: modeling
DE: 5112 Microstructure
SC: Hydrology [H]
MN: Fall Meeting 2005