HR: 1340h
AN: H33B-0467    [Abstracts]
TI: Intermittent Filtration of Bacteria and Colloids at Pore and Column Scales
AU: * Auset, M
EM: mauset@bren.ucsb.edu
AF: Bren School of Environmental Science & Management , University of California , Santa Barbara, CA 93106 United States
AU: Keller, A A
EM: keller@bren.ucsb.edu
AF: Bren School of Environmental Science & Management , University of California , Santa Barbara, CA 93106 United States
AU: Brissaud, F
EM: brissaud@msem.univ-montp2.fr
AF: Maison des Sciences de l'Eau, University of Montpellier, 300, avenue du Professeur Emile Jeanbrau, Montpellier, 34095 France
AU: Lazarova, V
EM: valentina.lazarova@ondeo.com
AF: Ondeo CIRSEE, 38 rue du President Wilson, Le Pecq-sur-Seine, 78230 France
AB: Intermittent sand filters used for water and wastewater treatment can achieve high disinfection performance if properly designed and operated. Soil filtration can also play a significant role in pathogen removal. In order to help predict removal of pathogenic bacteria in sand filters and natural porous media, the effects of cyclic infiltration and draining events (transient unsaturated flow) on microorganism fate were investigated. We visualized bacterial transport in unsaturated porous media at the pore scale using micromodels. Column experiments provided quantitative measurements of the phenomena observed at the pore scale. Escherichia coli and a conservative tracer (NaI) were applied once in a pulse to a 1.5 m sand column. Outflow concentrations during subsequent tracer-free pulses were monitored for 4 days. The reproducibility of the breakthrough curve was established in five repeated experiments. We observed earlier breakthrough of bacteria compared to the dissolved tracer, as predicted from pore scale studies. Transport of bacteria and tracer was influenced by the temporal variations in pore water velocity and moisture content. Advancement of the wetting front remobilized bacteria either attached to the air-water interface (AWI) or entrapped in stagnant pore water between gas bubbles. Remobilization leads to successive concentration peaks of bacteria and tracer in the effluent. Overall microbial retention rate was high, 99.972 %. Observations at the pore-scale showed that bacteria retention was due to reversible bacteria entrapment in stagnant regions and sorption onto the AWI and essentially irreversible attachment onto solid-water interface (SWI). Bacterial detachment from the AWI was only observed during complete gas bubble dissolution or if bubble interface stress occurred during the dissolution process.
DE: 5104 Fracture and flow
DE: 5139 Transport properties
DE: 3210 Modeling
DE: 3260 Inverse theory
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting