Abstract
Studies to decompose persistent organic pollutants in wastewater from chemical factories by using Advanced Oxidation Processes (AOPs) have recently been performed. Oxidation reactions involving ozone and •OH radicals and cleavage caused by UV are the main decomposition reactions that occur in AOPs using ozone and UV. The mechanisms through which organic compounds are decomposed in AOPs are complicated and difficult to understand because various decomposition reactions occur simultaneously. The Total Organic Carbon (TOC) removal efficiencies achieved in several different AOPs were evaluated in this study. The TOC removal efficiencies were different for organic compounds with different chemical structures. The TOC was more effectively removed when aromatic compounds were treated using the O3-UV-TiO2 process than when using the other AOPs, and the TOC was removed more effectively by the O3-UV process than by the UV-TiO2 process. However, the TOC was removed more effectively when open-chain compounds were treated using the UV-TiO2 process than using the O3-UV process, and the UV-TiO2 and O3-UV-TiO2 processes resulted in similar TOC removal efficiencies. Therefore, it is necessary to use the O3-UV-TiO2 process to decompose aromatic compounds as quickly as possible. On the other hand, the UV-TiO2 process degraded the open-chain compounds most effectively, and the O3-UV-TiO2 process did not need to decompose open-chain compounds. Moreover, the TOC of aromatic compounds was removed more slowly than that of open-chain compounds. The TOC removal efficiency increased with decreasing the number of carbon atoms in the molecule. The TOC removal efficiencies increased in order of the organic compounds containing methyl groups, aldehyde groups and carboxyl groups. The removal of the TOC when organic compounds were treated using the O3-UV-TiO2 process followed pseudo-zero-order kinetics.
Highlights
Persistent organic pollutants in industrial wastewater cause serious pollution problems in the aquatic environment [1]
The Total Organic Carbon (TOC) removal efficiencies achieved in the catechol and p-benzoquinone tests were clearly higher when the O3-ultraviolet light (UV) process was used than when UV alone was used
The TOC removal efficiencies achieved in the catechol and p-benzoquinone tests were higher when the O3-UV-TiO2 process was used than when the UV-TiO2 process was used
Summary
Persistent organic pollutants in industrial wastewater cause serious pollution problems in the aquatic environment [1]. Persistent organic pollutants are poorly biodegradable, meaning that natural processes cause very little decomposition of these compounds to occur, so these compounds can pollute the environment for a long time. It is thought that the efficiencies with which organic compounds are decomposed in an AOP depends on the chemical structures of the organic compounds and the AOP conditions. We confirmed that the decomposition efficiencies achieved in an AOP are influenced by the AOP conditions and the chemical structures of the organic compounds being decomposed. We examined the influence of the AOP conditions on the decomposition efficiency achieved by performing tests using different AOPs (using ozone, UV, and TiO2 to generate OH radicals) but the same organic compounds. We examined the influence of the chemical structure on the decomposition efficiency achieved by performing tests using an O3UV-TiO2 process and different organic compounds
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