INVESTIGATING POTENTIAL COMPETITIVE ADSORPTION AND FACILITATED TRANSPORT OF CAFFEINE ON MOBILE CLAY MINERALS

Organic chemicals can enter groundwater flow systems through wastewater. The contaminants may experience sorption and/or degradation depending on the nature of the chemical and the aquifer material. Caffeine is commonly used as an anthropogenic tracer, making it important to better understand its mobility in groundwater. Our research has shown the transport of caffeine is particularly impacted by the presence of montmorillonite clay, with adsorption coefficients as high as 18.7±0.1 L/kg in soil containing just 1% montmorillonite (compared to 0.8±0.8 L/kg in pure quartz sand). However, caffeine adsorption was decreased (K_d = 5.3±0.2 L/kg) when other compounds were in solution--indicating the possibility of competitive adsorption--while an initial flux of caffeine through the saturated columns indicated the possibility of facilitated transport. These results show caffeine may be an inconsistent tracer in the presence of clay minerals and other wastewater contaminants.

This study explored the potential for caffeine to travel through groundwater while adsorbed to mobile montmorillonite clay using paired laboratory soil column experiments. The experimental columns were pumped with solutions of caffeine, or caffeine and competing chemicals, adsorbed to suspended montmorillonite clay and compared to identical control columns. Montmorillonite clay particles with adsorbed caffeine were imaged using a scanning electron microscope to better understand the action of caffeine adsorption to montmorillonite.