Modeling Advanced Oxidation Processes for Water Treatment

Abstract

The Advanced Oxidation Processes (AOPs) are water treatment techniques which generate free-radicals in sufficient quantity that they are the primary active species responsible for the degradation of organic contaminants. Although water treatment units based on AOPs have been commercially available since the early seventies, the complex chemistry of such processes has only recently been well enough understood to allow modeling with any generality. A stoichiometric model for the AOPs such as ozone/UV, ozone/peroxide, etc., has been developed, and we are in the process of verifying its utility for understanding the application of these processes. An eventual goal is the use of the model for prediction of optimum process configurations and parameters, ozone and UV dose requirements, by-products, etc. The model is based on the fact that organic radicals, created by hydroxyl radical attack on organic contaminants, react quickly with oxygen to form peroxyl radicals. These peroxyl radicals can either 1) eliminate superoxide to become stable by-products, or 2) undergo more complicated bimolecular decay to yield hydrogen peroxide and other by-products. The usefulness of the model has already been verified for the methanol/formaldehyde/formic acid system, where superoxide production predominates, and is currently being extended to molecules which do not produce superoxide directly from their peroxyl radicals.