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Abstract
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 μm), 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.
Highlights
Chronic contamination of groundwater by anthropogenic pollutants originating from industrial, municipal, and agricultural activities is a growing environmental challenge
The kinetics of ozone decay in soil suspensions can be divided into two stages, including a rapid decay stage in the first 15 s and a subsequent slower decay stage
Ozone decay rates for each soil are determined from linearization of the data in logarithmic scale (Figure 1A, inset), ranging from 8.6 × 10−4 s−1 to 5.7 × 10−3 s−1 (Hamra)
Summary
Chronic contamination of groundwater by anthropogenic pollutants originating from industrial, municipal, and agricultural activities is a growing environmental challenge. The Israeli coastal aquifer is contaminated with a number of persistent organic pollutants (POPs) such as explosives, volatile solvents, pesticides, and petroleum products.[1,2] As aquifers are often considered as a vital water supply reservoir with multiyear storage capacity, the release of POPs into groundwater requires remedial actions. Air sparging is typically limited to volatile compounds, and its efficiency depends on the physicochemical properties of both the aquifer matrix and the treated contaminants.[3] Bioremediation processes are most efficient for natural organic compounds but may not be efficient for the removal of anthropogenic POPs. Air sparging is typically limited to volatile compounds, and its efficiency depends on the physicochemical properties of both the aquifer matrix and the treated contaminants.[3] Bioremediation processes are most efficient for natural organic compounds but may not be efficient for the removal of anthropogenic POPs For such chemicals, oxidation processes are often considered as promising alternatives.[4,5]
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