ARS | Publication request: Single collector attachment efficiency of colloid capture by a cylindrical collector in laminar overland flow

Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 16, 2012
Publication Date: August 21, 2012
Citation: Wu, L., Gao, B., Munoz-Carpena, R., Pachepsky, Y.A. 2012. Single collector attachment efficiency of colloid capture by a cylindrical collector in laminar overland flow. Environmental Science and Technology. 46(16):8878-8886.

Interpretive Summary: There is a need for management practices that control the transport of colloidal particles suspended in overland water flow. Colloidal-size particles may consist of protozoan parasites, bacteria or viruses, or organic/inorganic particles with adsorbed harmful contaminants. Vegetated buffer strips are routinely recommended as an effective management practice. However, opinions differ widely on the relative importance of different factors and their impact on the efficiency of colloidal particle retention by buffer strips. One of the reasons is that the mechanism of colloid retention by dense vegetation has not been adequately quantified. The purpose of this work was to elucidate the contribution of simulated plant stems on colloid retention efficiency. We found that classic colloid filtration theory did not explain colloidal retention dependence on solution properties and flow velocity. However, we were able to identify a modification that accurately described our results, as well as independent data from the scientific literature. Results of this work will be useful for environmental engineers in that they show the effect of physical parameters on suspended colloidal particle retention by vegetated buffer strips, and may assist in improved efficacy.

Technical Abstract: Little research has been conducted to investigate fate and transport of colloids in surface vegetation in overland flow under unfavorable chemical conditions. In this work, single collector attachment efficiency (a) of colloid capture by a simulated plant stem (i.e. cylindrical collector) in laminar overland flow was measured directly in laboratory flow chamber experiments. Florescent microspheres of two sizes were used as experimental colloids. The colloid suspensions flowed towards a glass cylindrical rod installed in a small size flow channel a different laminar flow rates. Different solution ionic strengths (IS) were used in the experiment to simulate unfavorable attachment conditions. Our results showed that a increased with IS and decreased with flow velocity. Existing theoretical and empirical models of colloid attachment efficiency for porous media were used to simulate the experimental measurements of a and found to fall short in matching the experimental data. A new regression equation was proposed that predicts the a of colloid capture by a cylindrical collector in laminar overland flow with reasonable accuracy. In addition, the equation was also effective in predicting the attachment efficiency of colloid deposition in porous media.