Impact of flow rate, water content, and capillary forces on in situ colloid mobilization during infiltration in unsaturated sediments

Abstract

[1] We studied in situ colloid mobilization under transient flow conditions using columns repacked with Hanford sediments. Rainfall infiltration was experimentally simulated using different flow rates and initial moisture conditions. Five series of column experiments were performed with initial infiltration rates of 0.018, 0.036, 0.072, 0.144, and 0.288 cm/min, and the columns reached water saturations in the range of 53 to 81%. The infiltration of water into the columns provided unfavorable conditions for colloid attachment to the sediments. Colloids were eluted by the infiltrating water with the peak colloid concentrations in the outflow coinciding with the arrival of the infiltration front. A larger flow rate led to a greater amount of colloids released from the column. The cumulative amount of colloids released was proportional to the column water content established after steady state flow rates were achieved. We used the advection-dispersion equation with a first-order colloid release reaction to analyze the experimental data. The colloid release rate coefficient increased with the increase of water content. We calculated forces exerted on colloids, and found that electrostatic and van der Waals interactions, calculated based on the DLVO (Derjaguin-Landau-Verwey-Overbeek) theory, and hydrodynamic forces, were all less important than capillary forces in controlling colloid release. In one experiment, the ionic strength of the infiltration solution was increased, such that colloid attachment was favorable. Nonetheless, colloids were mobilized and eluted with the infiltration front, implying that non-DLVO forces, such as capillary forces, played a prominent role in colloid mobilization.Citation: Shang, J., M. Flury, G. Chen, and J. Zhuang (2008), Impact of flow rate, water content, and capillary forces on in situ colloid mobilization during infiltration in unsaturated sediments, Water Resour. Res., 44, W06411,

Processes in Pathogenic Biocolloidal Contaminants Transport in Saturated and Unsaturated Porous Media: A Review

“…In the unsaturated porous media, the additional mechanisms (compared with saturated system) for colloid/biocolloid transport are: colloid/biocolloid captured at the liquid-gas interface (Chen et al 2008;Lazouskaya and Jin 2006;Lazouskaya and Jin 2008;Oettel and Dietrich 2008;Shang et al 2008;Sharma et al 2008;Sirivithayapakorn and Keller 2003;Wan and Wilson 1994;Williams and Berg 1992), colloid captured due to straining (Bradford et al 2006;Torkzaban et al 2008;Wan and Tokunaga 1997), the colloid/biocolloid captured at solid-liquid-gas interface (Crist et al 2004;2005;Zevi et al 2005Zevi et al , 2006Gao et al 2008;Morales et al 2009), and colloid storage in immobile zone (Gamerdinger and Kaplan 2001;Gao et al 2006;Saiers and Lenhart 2003). Biocolloids sorption at the air-water interface has been recognized as an important process in their transport (Keller and Auset 2007;Wan and Wilson 1994).…”

Intra-annual variation of the calcite deposition rate of drip water in Shihua Cave, Beijing, China and its implications for palaeoclimatic reconstructions

“…During the summer rainy season, the water content and the temperature of the soil enhance biogeochemical processes, in particular organic matter degradation, which increases PCO 2 (unpublished data) and mobilizes organic colloids in soil (Laedsmand et al 1999). When intense rain events occur, the intense leaching of the soil enhances the transport of organic colloids (Shang et al 2008), resulting in a low pH and high PCO 2 and DOC of soil water. This chemically aggressive water then enters the bedrock, leading to calcite dissolution in the bedrock.…”

Geological Disposal of Nuclear Waste: Fate and Transport of Radioactive Materials

“…A considerable amount of colloids were captured at the liquid-gas interfaces and moved with the infiltration front depending on flow velocity and the solution ionic strength [68]. This has been verified by numerical solution of the Young-Laplace equation that expanding water film can lift the subsurface colloids from the mineral surfaces [66]. The detachment of sub-micron sized particles from initially wet solid surfaces had been investigated by air-bubble experiments to understand the strength of moving liquid-gas interfaces [30-32, 45, 53].…”

“…The exchange of colloids between mobile and immobile zones were likely controlled by slow advection in addition to diffusion. The occurrence of larger quantity of colloids from unsaturated column studies were found in transient flow condition due to movement of colloids present in immobile zone [61,66,89]. All these studies indicated that the colloid can be attached in the immobile zone created by heterogeneity of the medium and by the presence of gaseous phase, which could be remobilized in the large rainfall and infiltration events.…”