Investigation of Photocatalytic Oxidation for Wastewater Cleanup and Reuse

摘要

This program investigated a new treatment process for removal of low concentrations of organic compounds from wastewaters. The treatment process uses light energy as the driving force for the photocatalytic oxidation of dissolved organic species on suspended semiconductor powders. Based on the results of a previous study, TiO2 was the semiconductor used in this program, which was designed to further characterize the process with respect to operating parameters and scope of applicability. Detailed kinetic analyses for the removal of a variety of organic compounds are presented. Factors such as light intensity, amount of semiconductor added, irradiated surface to volume ratio, light intensity, and amount of ionic constituents in the water were also investigated. Actual wastewater samples were obtained from several sources and used for process testing. The degree of effectiveness of the process was found to depend in part on the type of organic molecule being treated. Polar substances and compounds containing nitrogen or sulfur groups were much more susceptible to treatment than unsubstituted aromatics, mineral oils, or saturated hydrocarbons. The relative removal rates were not in direct relationship to the corresponding reaction rates with hydroxyl radicals, indicating that more is involved than hydroxyl radical production at the semiconductor powder surface. The main limiting rate factor for the systems studied was the low quantum efficiency found, coupled with the wide band gap of TiO2 which allows use of only a small fraction of the solar spectrum.