Formation of the intermediates and by-products during the degradation of diclofenac by ozonation
Date Issued
2011
Date
2011
Author(s)
Hu, Nai-Hsin
Abstract
Diclofenac (DFC) is a widely used anti-inflammatory drug and thus enters the aquatic environment. The realistic environmental concentration levels at harmful effects to different organisms have been demonstrated by many previous studies. Many investigations have revealed that diclofenac can not be completely removed by conventional sewage treatment plants (STP) and was detected in STP effluents at trace levels. Therefore, the presence of diclofenac in the aquatic environment should be assessed critically.
The objective of this study was to evaluate the removal of diclofenac using ozonation process. The effect of various operating parameters including ozone dose, pH, and the presence of phosphate buffer on the removal of diclofenac and TOC in ozonation process was investigated. In addition, the formation of ozonation by-products, including chloride, ammonia ions, intermediates and aldehyde, was also studied. Meanwhile, a simplified mass balance based on intermediates containing carbon, chlorine, and nitrogen was developed to determine the formation rate constants of CO2, chloride, and ammonia. Furthermore, kinetic studies based on the degradation of diclofenac and formation of chloride and ammonia were also developed to determine the selectivity of reaction pathway and rate constants of diclofenac. Finally, the constants obtained in this study were used to propose the possible pathway and evaluate the optimum operational parameters.
The results show that ozonation was efficient in degrading diclofenac. In absence of phosphate buffer, the removal of diclofenac and TOC, and formation rate of chloride basically increased as the ozone doses increased. In presence of phosphate buffer, the maximal diclofenac removal and CO2 formation rate constant is at pH 7.4 at two levels of ozone dose. The reaction rate constants of DFC can be determined in a second order reaction. The diclofenac degradation models can predict the selectivity of pathway. In addition, the aldehyde concentration increased with increasing pH in the ozonation process, which indicated the involvement of hydroxyl radical in aldehyde formation.
Subjects
Diclofenac
Ozonation
Ozonation by-product
Kinetic constants
Intermediates
Pathway
Optimum operational condition
Type
thesis
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