Speaker
Description
Traditional colloid filtration theory predicts exponential colloid retention profiles (RPs) based on a constant fractional removal per grain passed. However, under unfavorable conditions, where repulsive barriers inhibit colloid attachment, observed transport exhibits non-exponential RPs. These anomalies are observed across diverse colloid types, including pathogens, engineered nanomaterials, and micro- and nanoplastics, and arise even without variations in colloid size, surface properties, or density, or the presence of straining and detachment.
A new theoretical model and experimental observations motivate a paradigm shift: instead of fractional removal per grain passed, it occurs with each interception, defined as when a colloid trajectory enters the near-surface zone where interaction forces are significant. With this perspective we can upscale transport from the grain to the Darcy scale, accounting for a fraction of colloids being removed at each encountered interception. If the fraction remains constant, RPs are exponential but shallower than under favorable conditions. If it varies with interceptions, multi-exponential and non-monotonic RPs emerge.
Experimental evidence supports this new perspective, demonstrating that under favorable conditions, attachment primarily occurs after a single interception, leading to exponential RPs. Conversely, under unfavorable conditions, a significant or dominant fraction of colloids attaches after multiple interceptions, resulting in non-exponential RPs. Specifically, RPs for multiple-interception attachers follow gamma distributions, resulting from the convolution of exponentials, with maxima that shift further down-gradient with increasing interception order. The superposition of RPs for single and multiple-interception attachers can explain the observed multi-exponential and non-monotonic RPs. This "interception history" paradigm offers a simpler, more predictive framework for colloid transport.
| Country | USA |
|---|---|
| Acceptance of the Terms & Conditions | Click here to agree |
