ABSTRACT
Ozone has been used for almost 100 years in water treatment in Europe, where it is largely used for disinfection, the control of taste and odor, and the removal of color. The role of ozone in the treatment of potable water supplies and waste water is as a disinfectant and a powerful oxidant. As a disinfectant, ozone successfully inactivates enteric bacteria, viruses, amoebic
cysts, and spores. As an oxidant, ozone oxidizes many inorganic materials completely and rapidly, for example, sulfides to sulphates, nitrites to nitrates, etc. Ozone also oxidizes organic materials such as unsaturated and aromatic compounds, which are oxidized and cleaved at the double bonds; humates and fulvates, which are commonly found in potable water supplies are effectively bleached; and foul-tasting phenol materials are readily destroyed. In addition to the direct reactions of molecular ozone described earlier, ozone can also react
CONTENTS
16.1 Introduction ................................................................................................................................................................... 339 16.1.1Brief Review of Ozone Generation Methods .............................................................................................. 339 16.1.2Overview of Concepts and Challenges for Production of Ozone by Electrolysis ................................. 341
16.2Description of the Process: Electrochemical Ozone Generation ............................................................................ 342 16.2.1Reaction Mechanisms .................................................................................................................................... 342 16.2.2Role of the PEM ............................................................................................................................................... 343 16.2.3Role of Anode and Cathode Electrocatalysts .............................................................................................. 344 16.2.4 PEM Electrolyzer Designs for Ozone Generation: Example..................................................................... 345
16.3 Preparation and Characterization Methods for Catalyst Layers ........................................................................... 345 16.3.1 Anode Materials and Preparations: PbO2 Anodes for Ozone Generation ............................................. 345 16.3.2 Cathode Catalyst Layer .................................................................................................................................. 346 16.3.3Counter-Diffusion Deposition (Takenaka-Torikai Method) .................................................................... 347 16.3.4Impregnation-Reduction Deposition (Fedkiw and Her Method) ........................................................... 347 16.3.5Pretreatment of a Membrane ........................................................................................................................ 347 16.3.6 Cathode CCM: Experimental Example ........................................................................................................ 348 16.3.7 Chemical Modification of Membrane Surface ............................................................................................ 348 16.3.8Role of Chemical Reducing Agents .............................................................................................................. 349 16.3.9Effect of External Activation ......................................................................................................................... 351 16.3.10Characterization Methods............................................................................................................................. 351
16.4 Performance Testing ..................................................................................................................................................... 352 16.4.1 Cathode Water Feed Test ............................................................................................................................... 352 16.4.2 Durability Challenges.................................................................................................................................... 353
16.5Examples of Applications of Electrochemical Ozone Systems .............................................................................. 354 16.5.1Laboratory Evaluation of Phenol Removal by Means of Direct Anodic Oxidation
and Low-Concentration Ozone Generated Electrochemically................................................................. 354 16.5.2Anodic Oxidation of Phenol on PbO2 Anodes ........................................................................................... 354
16.6 Detailed HPLC Analysis of Products of Phenol Oxidation by Means of Ozone Generated Electrochemically on PbO2 Anodes ........................................................................................................................... 357
16.7 Conclusions .................................................................................................................................................................... 358 References ................................................................................................................................................................................ 358
indirectly via the radical species formed when ozone decomposes in water. The production of hydroxyl radicals (•OH) can be enhanced by an increase in pH, addition of hydrogen peroxide, or irradiation with ultraviolet (UV) light. Ozone competes with chlorinebased technologies on the water treatment market. The safety of ozone treatment plants is an advantage over chlorine plants.
