HR: 1340h
AN: H53F-1482    [Abstracts]
TI: Transport and Straining of Colloid-Sized Materials in Saturated Sand
AU: * Chamindu, D K
EM: chamindu78@yahoo.com
AF: Department of Civil and Environmental Engineering,Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama, 338-8570, Japan
AU: Kawamoto, K
EM: kawamoto@post.saitama-u.ac.jp
AF: Department of Civil and Environmental Engineering,Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama, 338-8570, Japan
AU: Saito, H
EM: hiros@cc.tuat.ac.jp
AF: Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology, 3-8-1 Harumi-cho, Fuchu, Tokyo, 183-8509, Japan
AU: Moldrup, P
EM: pm@bio.aau.dk
AF: Department of Biotechnology, Chemistry and Environmental Engineering Aalborg University, Sohngaardsholmsvej 57, Aalborg, DK-9000, Denmark
AU: Komatsu, T
EM: komatsu@post.saitama-u.ac.jp
AF: Department of Civil and Environmental Engineering,Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama, 338-8570, Japan
AB: The fact that colloids facilitate transport of contaminants such as heavy metals, pesticides, radionuclides etc. through porous media has gained widespread acceptance in the last few decades. Colloid attachment and straining have been identified as key mechanisms on colloid retention/filtration in porous media. Much research attention was focused on colloid straining during recent years since the attachment-based classical filtration theory could not accurately predict colloid deposition, especially under unfavorable attachment conditions. Recent studies further revealed that transport and filtration of colloids largely depend on initial colloid concentration and flow rate. Despite growing attention, however, the knowledge of colloid filtration, especially for natural soil colloids, is still limited. This study investigated attachment and straining of colloid-sized glass beads with the diameter of 1-10μm and soil colloids with the diameter of less than 1 μm extracted from a volcanic ash soil in saturated sand (Toyoura sand) by means of a series of column experiments at different colloid concentrations and flow rates (Darcian flux 0.16-1.0cm/min). The height and internal diameter of the sand column were 10cm and 4.91cm, respectively. Bromide was also added to colloidal solution as a conservative tracer. In each column experiment, 3 pore volumes of artificial rainwater was initially applied downward at a steady flow rate, then shifted to 10 pore volumes of colloidal solution, followed by another 5 pore volumes of artificial rainwater. By measuring the colloid concentration of effluents, colloid breakthrough and breakdown curves were observed. Glass bead colloids exhibited essentially no breakthrough on both high and low flow rates, suggesting all colloids deposited in the soil column. Since colloid attachment is unlikely due to mutual repulsion of negatively charged colloids and sand grains, we presume all colloids were physically strained in porous media interstices. Soil colloids, on the other hand, exhibited complete deposition at low flow rate, but only 31 percent deposition at high flow rate. Particle size distribution measurements of effluent colloids of the latter revealed that both smaller and larger size regions of input colloids preferentially deposited in sand column. Deposition of large soil colloids can be attributed to straining while smaller colloids are presumably attached to sand grains. Following completion of each column experiment, sand columns were disjointed in order to examine the colloid retention profile. Colloid retention profile of glass bead colloids was non monotonic with multiple deposition peaks. The highest peak occurred near the column inlet while two relatively smaller secondary peaks occurred at dimensional depths of 0.35 and 0.75 respectively. Particle size distribution measurements of deposited colloids revealed that larger size colloids were retained near the column inlet while relatively smaller size colloids were captured by deeper layers. Furthermore, HYDRUS-1D code will be used to estimate the straining parameters of colloids.
DE: 1829 Groundwater hydrology
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: 2007 Fall Meeting