Experimental Analysis of Colloid Capture by a Cylindrical Collector In Laminar Overland Flow.

Although colloid and colloid-facilitated transport in water flow is a well-recognized contamination process, little research effort has been dedicated to investigate the fate and transport of colloidal particles in emergent dense vegetation. In this study, a series of laboratory experiments were conducted to measure the single-collector contact efficiency (η₀) of colloid capture by a cylindrical collector in laminar overland flow. Florescent microspheres of various sizes were used as experimental colloids. The colloid suspensions were applied to a glass cylinder installed in a small size flow chamber at different flow rates. Two cylinder (collector) sizes were tested in the experiment and silicone grease was applied to the cylinder surface to make it favorable for colloid deposition. Our results showed that increases in flow rate and collector size reduced the value of η₀ and a minimum value of η₀ might exist at a critical colloid size.  The experimental data were compared to theoretical predictions of various single-collector contact efficiency models. The results indicated that existing single-collector contact efficiency models underestimated the η₀ of colloid capture by the cylinders in laminar overland flow. A correlation equation of η₀ as a function of collector Reynolds number (Re_c) and Peclet number (N_Pe) was developed and matched the experimental data very well. This correlation equation can be used to inform the construction and refinement of mathematical models of colloid transport and filtration in laminar overland flow on vegetated surfaces.