The Effect of Pore Water Evaporation on Transport of Caffeine, Propranolol, and Ciprofloxacin: A Sand Column Study and Model Simulation

Abstract

The purpose of this study was to explore the transport of selected pharmaceuticals under saturated and unsaturated conditions, simulating environmental processes of evaporation and flooding. Caffeine (a stimulant), propranolol (a beta blocker), and ciprofloxacin (an antibiotic), were used in multiple sand column experiments that examined sorption behavior under two conditions: 1) standard, completely saturated sand column experiments, and 2) saturated sand column experiments where intermediate steps of partial drainage and complete pore water evaporation were introduced before the final flushing stage. The experimental flushing-out breakthrough curves, or elution curves, were compared to simulated elution curves. The model employed in this study was developed using a one-dimensional transport equation accounting for advection, adsorption, and dispersion. Differences between the experimental and simulated curves were attributed to the effects of rate-limited dissolution. Results suggest that dissolution hinders the removal of each pharmaceutical during flushing. The effect of dissolution is explored as it relates to the retention of mass in the column. Findings suggest that dissolution affects the transport of a compound based on the relationship between the concentration and solubility values: a ratio of C_O/S close to 1 shows little dissolution effect, whereas C_O/S ratios much less than 1 show greater dissolution effect.