In the agricultural industry, weeds, insects, nematodes, bacteria and other single celled or multi-celled living organisms in the top soil of a field, are killed immediately prior to growing crops, for example by application of methyl bromide. Methyl bromide destroys living cells once transported across the cell walls. However, methyl bromide is being phased out of agricultural use due to deleterious effect on the ozone layer of earth and due to a hazard to human health.
Ozone dissolved in aqueous solutions (also called "aqueous ozone") is used for inhibition or reduction of biological life forms such as molds, fungi, bacteria, algae, in numerous applications including swimming pools, potable water, bottled water, aquaria, fish hatcheries, and cooling towers. However, application of aqueous ozone to soil is not expected to be effective to kill living organisms because aqueous ozone has the drawback of slow dispersion of water into and through the soil of a field. Also, aqueous ozone suffers from rapid breakdown of ozone, so that maintaining sufficiently high concentrations of ozone in the water in soil can be difficult. Aqueous ozone has a half life on the order of minutes in ambient conditions.
Moreover, according to traditional thinking, if gaseous ozone were used for soil treatment, ozone would quickly dissolve in the entrapped soil moisture and rapidly break down. Furthermore, conventional thinking suggests that dispersion of gaseous ozone would be inhibited by the compacted, compressed nature of soil in a field or that untoward emissions of ozone gas would escape from a field into the atmosphere and so minimize ozone's effectiveness. Traditional thinking also indicated that the sometimes high concentration of naturally occurring organic compounds in soil close to the surface of a field can consume large amounts of ozone and so result in insufficient exposure of living organisms to ozone.
To "increase the stability of the ozone in the soil environment," prior art teaches that an "ozone containing gas is treated with acid" (see abstract of U.S. Pat. No. 5,269,943 to Wickramanayake). Regarding untreated ozone, Wickramanayake states that "long-term treatment of soils to remove contaminants with untreated ozone is not feasible since ozone decomposes too rapidly" (column 6, lines 31-33), and that "ozone that was not acidified was not expected to be useful especially for the treatment of larger quantities of soils" (column 8, lines 25-27).
Wickramanayake also states that his "treatment results in degradation of the organic compounds to less hazardous compound or compounds that are more readily biodegradable than the parent compound" (column 1, lines 14-17). Wickramanayake further states that "[a]fter the decontamination process, if the soil is found to be too acidic, the pH may be increased to the required level by applying unacidified gas ozone mixture for some time" (column 9, lines 65-68).
However, for "field applications," Wickramanayake requires "injecting of a stabilized gas-ozone mixture . . . into one or more injection wells in the contaminated areas. The distribution of the well bank is to be determined by the effective ozonation zone in the subsurface" (column 9, lines 45-50). In contrast, U.S. Pat. No. 5,566,627 describes the "agricultural use of ozone (O.sub.3) to sanitize, i.e. kill or weaken living organisms in top soil suitable for plant growth purposes" (column 2, lines 31-34). See also U.S. Pat. No. 5,624,635.