Aqueous reaction of ozone and alachlor: Kinetics and product identification

Ozone has been used for water treatment since the early 1900\u27s. It is utilized for many different reasons; its biocidal effect, its ability to oxidize iron (II) and manganese (II) to solid precipitates, and its ability to oxidize organic contaminants present in water. Irrespective of the reason for using ozone in water treatment, organic contaminants which are known to be present should be considered and the effect of ozone on them elucidated. The city of Lincoln, Nebraska, has recently constructed a new treatment plant in which the main oxidant is ozone. The main reason for utilizing ozone is for iron and manganese removal, but organic contaminants do exist in the water. A contaminant class which must be considered in east-central Nebraska is agricultural pesticides, alachlor, an acetanalide herbicide, being one of those found in waters there. The kinetics of the decomposition of alachlor by ozone and also the products formed from the reaction were both investigated. The kinetics of any reaction involving ozone is necessarily complicated by the decomposition of ozone itself. The decomposition of ozone has been studied since the early 1900\u27s and up to present no consensus has been reached on the fundamental kinetic characteristics of this reaction. Rate laws advancing first, second and a mixed first, three halves-order dependence on ozone have all been given in the research. There is also great disagreement on the reaction\u27s dependence on hydroxide ion concentration. The reaction of ozone with the hydroxide ion is widely thought to be one of the main first steps in the reaction of ozone, but the overall dependence on the hydroxide ion varies greatly in the literature. This work advanced a model to elucidate the kinetics of alachlor decomposition by ozone, which has embedded in it, the decomposition of ozone itself. The ozone dependence was determined along with any effects that pH and carbonate (a radical scavenger) may have. The products of the reaction were determined using GC-MS, ion exclusion chromatography and anion exchange chromatography