Ozone Consumption by Soils: A Critical Factor in In Situ Ozonation Processes

In situ chemical ozonation (ISCO3), in which gaseous ozone is being injected into the subsurface, is a common method for remediating contaminated groundwater that is largely affected by the inevitable consumption of ozone by soil itself (rather than the target contaminants). In this study, ozone consumption by two main soil types of Israeli coastline aquifer was examined. Iron-rich soil showed considerably higher reactivity than did calcareous soil. We further investigated the effect of both physical and chemical soil characteristics on finite and catalytic ozone decay, hydroxyl-radical formation, and ozone transport behavior. Ozone consumption increased by >90% in the presence of fine soil particles (<100 mu m), resulting from the large number of reactive sites and the higher content of ozone consumers compared to coarse soil particles. Soil organic matter consumed ozone twice as fast as iron components, promoted radical formation at higher rates, and mainly acted as a finite ozone consumer. In continuously fed column experiments, the reactions with iron components dominate catalytic ozone consumption during transport in porous media. Overall, this study demonstrates that the characterization of ozone reactions in soil can be helpful in evaluating the feasibility and efficiency of ISCO3 and inform the design of ISCO3 treatment, e.g., the need to inject additional radical promoters.