HR: 0800h
AN: H11A-0290    [Abstracts]
TI: Flow Characteristics in Permeable Reactive Barrier Affected by Biological Clogging
AU: * Seki, K
EM: seki@soil.en.a.u-tokyo.ac.jp
AF: University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-8657 Japan
AU: Hanada, J
EM: junya_hanada@nm.maff.go.jp
AF: University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-8657 Japan
AU: Miyazaki, T
EM: amiyat@soil.en.a.u-tokyo.ac.jp
AF: University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-8657 Japan
AB: Permeable reactive barriers (PRB) are becoming popular for the in situ remediation of contaminated groundwater. The efficiency of the PRB is affected by permeability of the reactive zone, because when permeability decreases contaminants can bypass the reactive zone without degraded. One of the factors affecting permeability of the permeable reactive zone is biological clogging of soil pore, i.e., biomass buildup and resultant decrease in hydraulic conductivity. So far biological clogging in laboratory was mostly observed in one-dimensional flow field, but the actual flow field in PRB is better simulated in two-dimensional flow field. The objective of this study is to observe the flow characteristics in PRB by using simulated flow cells in laboratory, by comparing one-dimensional and two-dimensional flow field. One-dimensional flow field was simulated by 20 cm length and 1 cm width flow cell, and two-dimensional flow field was simulated by 20 cm length and 10 cm width flow cell. Each flow cell was operated under water-saturated conditions, in horizontal position, and at a constant temperature of 20 degree centigrade. Glass beads of 0.1 mm mean diameter was packed uniformly in the flow cells and inoculum was injected into the nutrient injection ports at the middle of the flow cells. After 24 h incubation time continuous flow was started. Background flow of de-ionized water was supplied to the inlet ports, and the mineral medium was supplied from the nutrient injection ports. The flux was measured every day and local hydraulic head distribution was measured by water manometer, and hydraulic conductivity was calculated. The flow cell experiments were continued for 9 days. In one-dimensional flow cell, hydraulic conductivity of the nutrient supplied part decreased to about half of the initial value in 9 days flow period, where the hydraulic conductivity of the part where nutrient was not supplied remained constant. Bacterial and fungal number in the moderately clogged zone, where nutrient was supplied, increased in two orders of magnitude and the decrease in the hydraulic conductivity was associated with biomass buildup. In two-dimensional flow cell, biomass buildup of the nutrient supplied zone was also observed and moderately clogged biobarrier was formed. Unlike one-dimensional flow cell, where flux was kept uniform throughout the flow cell, the flux decreased at the biobarrier and the preferential flow between biobarriers was invoked. Flux at the preferential flow path was higher than average flux in the whole cell. This result suggests that biological clogging of PRB wells can cause changes in flow field pattern of contaminant plume, even if the extent of clogging is moderate.
DE: 1800 HYDROLOGY
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting