LABORATORY EXPERIMENTS WITH HETEROGENEOUS REACTIONS IN MIXED POROUS-MEDIA

The limited success and high cost of traditional ''active'' ground-wat er-contaminant plume management efforts (i.e., pump-and-treat systems) has stimulated a search for less expensive ''passive'' plume intercep tion and in-situ treatment technologies. The ''funnel/gate system,'' w hich uses heterogeneous (surface-mediated) reactions on porous media t o degrade dissolved contaminants, is one passive technology under cons ideration. Research on a heterogeneous reaction is presented in this p aper, which can be extended to facilitate the design of engineered por ous media systems (i.e., funnel/gates). Results are examined from batc h and flow-through column experiments involving nitrobenzene degradati on in a surface-mediated reaction with granular metallic iron. A noneq uilibrium transport model that incorporates solute mass-transfer resis tance near reactive iron surfaces is shown to simulate breakthrough cu rves (BTCs) from column systems, using model parameters estimated from batch systems. The investigation shows pseudo first-order degradation -rate coefficients increasing with higher solid:liquid ratios and with greater iron concentrations. In addition, nitrobenzene degradation is found to be faster in batch systems than in comparable column systems , indicating the presence of mass-transfer limitations in the how-thro ugh systems. Finally, the present study provides insights on condition s pertinent to the design of engineered in-situ treatment zones, such as how mass-transfer, hydraulic, and reaction kinetic conditions affec t ground-water-contaminant fate and transport through reactive porous media.