¹Department of Civil Engineering, University of Utah, Salt Lake City, UT, 84112, 801-581-7232; ²USACE Waterways Experiment Station, Environmental Engineering Division, Vicksburg, MS, 39180; and ³Department of Chemical Engineering, Mississippi State University, Starkville, MS, 39705
The United States Department of Defense (DoD) has literally thousands of sites that have been contaminated from past military activities. The cost of remediating these sites using existing technologies, such as activated carbon, will be astronomical. Advanced oxidation processes (AOPs) have promise because they effect on-site destruction of the contaminants. However, AOPs must be optimized for treatment, because without increased process optimization AOPs could result in costs similar to that of activated carbon. AOPs are by definition those oxidation processes that utilize the hydroxyl radical (·OH) as one of the (or the) primary contaminant oxidation mechanisms. Since the hydroxyl radical is an unstable chemical species, AOPs must be designed to produce the radical on-site through a variety of photolytic (illuminated) and/or chemical reactions (dark).
To optimize AOPs and reduce remediation costs, the mechanistic workings of various AOPs must be understood. The kinetics of AOP systems are complex. The rates of contaminant removal and reaction orders often change according to the water matrix and oxidant concentrations. Maximum rates of treatment have occasionally been observed for certain oxidant concentrations and ratios. We have developed a kinetic model and used the model to derive a rate expression that describes the ·OH radical concentration given a set of operating conditions. The model explains well some of the observed complex dependence behaviors of AOPs
This model and derived expression is useful for process optimization. In its final form, this paper will present experimental results of process optimization for hazardous waste treatment. Kinetic constants of contaminant degradation will be presented as a function of test parameters such as pH, O3 and H2O2 concentrations and ratios, contaminant concentration, water characteristics including hardness, carbonate content, alkalinity, and radical scavenger concentration. A major emphasis of this paper will be to test the mechanism proposed for AOPs. The kinetic results will be used to validate or modify the proposed AOP kinetic model. Limitations of the model will be identified. Optimal operating conditions and recommendations for hazardous waste treatment will be made according to the experimentally validated kinetic model.
advanced oxidation processes, contaminants degradation, remediation, optimization
This paper is from the Proceedings of the 10th Annual Conference on Hazardous Waste Research 1995, published in hard copy and on the Web by the Great Plains/Rocky Mountain Hazardous Substance Research Center.