Kinetics of soil ozonation: an experimental and numerical investigation

https://doi.org/10.1016/j.jconhyd.2003.11.003Get rights and content

Abstract

This study investigates the use of ozone for soil remediation. Batch experiments, in which ozone-containing gas was continuously recycled through a soil bed, were conducted to quantify the rate of ozone self-decomposition and the rates of ozone interaction with soil organic and inorganic matter. Column experiments were conducted to measure ozone breakthrough from a soil column. Parameters such as ozone flow rate, soil mass, and ozonation time were varied in these experiments. After ozone concentration had reached steady state, the total organic carbon concentration was measured for all soil samples. The ozonation efficiency, represented by the ratio of soil organic matter consumed to the total ozone input, was quantified for each experiment. Numerical simulations were conducted to simulate experimentally obtained column breakthrough curves. Experimentally obtained kinetic rate constants were used in these simulations, and the results were in good agreement with experimental data. In contrast to previous studies in which soil inorganic matter was completely ignored, our experiments indicate that soil inorganic matter may also promote depletion of ozone, thus reducing the overall ozonation efficiency. Three-dimensional numerical simulations were conducted to predict the efficacy of ozonation for soil remediation in the field. These simulations indicate that such ozonation can be very effective, provided that effective circulation of ozone is achieved through appropriately placed wells.

Introduction

Soil contamination is a challenging problem because of its extent and the difficulty involved in remediation. Several decontamination technologies, including soil vapor extraction (SVE), in situ aeration (air sparging/venting), chemical oxidation, bioremediation, soil heating, and surfactant-aided flushing are currently being used for soil cleanup. Organic pollutants are a major source of soil contamination and commonly occur as a result of disposal of industrial wastes, leaky underground storage tanks, and accidental spills (Hutzler et al., 1991). Organic compounds exist in the subsurface in several forms based on their chemical properties. They may be sorbed onto the soil matrix, be dissolved in groundwater, exist in vapor phase, or exist as a nonaqueous phase liquid (NAPL) (Volkering et al., 1997).

Chemical oxidation is an attractive alternative for remediating organic-contaminated soils because the byproducts are usually harmless and the removal efficiency is usually high if the chemicals can be delivered properly. Potassium permanganate and ozone are two commonly used chemical oxidants. Because it is delivered in the aqueous phase, potassium permanganate is more effective for groundwater cleanup than for soil cleanup. Ozone, which can be delivered as a gas mixture, is effective for both unsaturated and partially or fully saturated soils. The high aqueous solubility of ozone makes it effective in saturated soils as well. The use of gaseous ozone as the oxidizing agent in soil remediation has a relatively short history. Chemical oxidation with ozone-containing gas has been identified as a promising treatment method for soils contaminated with toxic or persistent wastes Siedel et al., 1993, Voigtländer, 1993. Siedel et al. reported that polycyclic aromatic hydrocarbons (PAHs) in soil could be reduced by as much as 99% by ozonation (with an ozone consumption rate of 45 g/kg) in a rotating reactor. Hsu (1995) reported that when ozone was used in a polishing step, the removal efficiency of trichloroethylene (TCE) was significantly improved over that achieved when only air stripping was employed. Cole et al. (1996) demonstrated that removal efficiencies of greater than 90% were achieved for PAHs when ozone was used. More recently, extensive modeling studies supported by column experiments have been conducted for PAH remediation using ozone Hsu and Masten, 2001, Kim and Choi, 2002, Sung and Huang, 2002. Despite the success of ozonation in soil remediation, only a limited amount of studies have been published. The complex and inhomogeneous nature of soil and the relatively short half-life of ozone demand more research efforts (Hsu, 1995).

The present study systematically investigates the behavior of ozone in soil. The objectives are (1) to evaluate the reaction kinetics of ozone and soil, including ozone self-decomposition, catalytic decomposition by soil, and interaction with soil organic matter (SOM) and soil inorganic matter (SIM); (2) to conduct bench-scale soil column experiments to evaluate the behavior of ozone in soil; (3) to numerically simulate ozone breakthrough via soil columns using experimentally obtained rate constants; and (4) to perform three-dimensional numerical simulations to investigate the efficacy of ozonation for field remediation.

Section snippets

Materials and methods

Experiments were conducted using the type of bench-scale soil column reactor shown in Fig. 1. Ozone was produced by a corona discharge ozone generator (Model CD-06, Aqua-Flo). The air-ozone mixture was then passed through a gas-washing bottle to saturate the mixture with moisture. The moisture-saturated air–ozone mixture was intended to mimic both vadose- and saturated-zone ozonation. The flow rate of the system was monitored by a volumetric flowmeter and manually controlled. After passing

Batch experiments

Ozone in soil can be consumed in several ways, including empty-column self-decomposition in the gas phase and at the surfaces of the system; catalytic decomposition through interaction with soil particles; and reactions with moisture, SOM, and SIM. Interactions of ozone with soil are complex and thus difficult to understand completely. However, to a certain extent, it is possible to identify experimentally the effects of soil on ozone consumption. These effects are expressed by the kinetic rate

Conclusions

This study investigated soil–ozone interactions in a sandy soil mixture from the Savannah River Site in South Carolina. The interactions of ozone with soil were expressed by linear and nonlinear reaction kinetics. Cycling batch experiments were conducted to quantify the appropriate rate constants for ozone self-decomposition, catalytic decomposition in the presence of soil, and ozone-SOM and ozone–SIM interactions.

Column experiments were also conducted to measure ozone breakthrough from a soil

Acknowledgements

This research was supported by Lynntech. Partial support was provided by NSF (BES-9702356) and DOE under contract DE-AC05-00OR22725 with UT-Battelle, LLC. The authors are grateful to Dr. David DePaoli for his comments during the course of the work and to Ms. Marsha Savage for editing the manuscript. The authors also appreciate the constructive criticisms provided by Dr. Hoigne and other reviewers in improving this manuscript.

References (22)

  • U Jans et al.

    Activated carbon and carbon black catalyzed transformation of aqueous ozone into OH-radicals

    Ozone: Sci. Eng.

    (1998)
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    The submitted manuscript has been co-authored by a contractor of the U.S. Government under contract DE-AC05-00OR22725. Accordingly, the U.S. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes.

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