| Summary: | 博士 === 淡江大學 === 水資源及環境工程學系博士班 === 98 === The goal of this study is to understand the decomposition of Reactive Blue C.I. 19 (RB 19) in oxidation processes, to acquire a kinetic model for reactor and process design, and to develop the process as a viable alternative to advanced oxidation processes (AOPs) for industrial waste effluent decolorization.. The study was divided into chemical oxidation, electrochemical oxidation and membrane enhanced electrochemical processes.
For chemical oxidation process, the reaction kinetics of RB 19 and sodium hypochlorite (NaOCl) was investigated. The decline of RB 19 was monitored continuously by an ultraviolet-visible range (UV-Vis) spectrophotometer to avoid sampling errors. The objective of this study is to develop a kinetic model for reactor and process design.
For electrochemical oxidation, direct and indirect electrochemical oxidation methods were explored for their effectiveness on color removal and COD reduction. In the indirect electrochemical process oxidizing agent was produced and mixed with RB19-containing solutions to determine its efficiency on color removal and dye decomposition. For direct method, dye-containing solutions were treated in the electrochemical reactor. A thorough comparison was done among direct and indirect electrochemical processes, and chemical method.
For membrane enhanced electrochemical oxidation, a borosilicate glass membrane (4.0 ~ 5.5 μm) was inserted into the electrochemical reactor, and divided the reactor into anode and cathode chambers. The reactor was test in both direct and indirect modes. For indirect operation, anolyte was used to treat RB19 in the synthetic dye bath. As for direct method, the synthetic dyebath was injected into the anode chamber for treatment. The results were compared with the previous study.
The chemical oxidation results were in agreement with 0.5-order reaction kinetics with respect to the RB 19 concentration. The lumped rate constant of the pseudo-0.5-order reaction is proportional to the NaOCl concentration. The Arrhenius activation energy obtained from the slope of the best-fit line is 76.6 kJ/mol, with a corresponding preexponential factor of 1.3884 × 1010. The reaction rate is strongly affected by the pH of the solution. During the oxidation decomposition process, color was rapidly removed by the NaOCl but chemical oxygen demand (COD) resisted the treatment. A molar ratio of more than 44 is essential for OCl- to completely decompose the dye molecules thus remove COD from the solution. A system of liquid chromatography mass spectrometry (LC/MS) was used to determine the intermediates in the initial steps of the decomposition process.
The results from electrochemical oxidation indicated that indirect method generates oxidation agent (OCl-) efficiently, and the OCl- effectively decomposes RB-19 in the solution. The key parameters of the process are applied voltage and operating time. A maximum concentration (6.5 mM OCl-) of oxidation agent was generated when 2 g/L NaCl solution was treated in the reactor at 20 volts DC for 30 minutes. It indicates that the amount of electrolyte determines the amount of oxidation agent that can be produced in the reactor. Color and COD reduction were 100% when the synthetic dyebath was treated with anolyte that was produced at 15 volts for 20 minutes. When directly treated in the anode chamber, color was completely removed in 5 minutes at 15 volts. Under the condition the decolorization efficiency was 100% while COD reduction was only 83%.
The test result from the membrane enhanced electrochemical oxidation indicates that insert borosilicate glass membrane in the reactor significantly increased the oxidation potential of the anolyte. The oxidizing agent produced is believe to be the mixture of Cl2 and HOCl. The pH of anode solution was strongly acid (pH = 2) when operated under higher voltage for a long time. Decolorization efficiency of the membrane enhanced electrochemical oxidation was similar to that of the electrochemical oxidation. When treated the dyebath directly in the anode chamber color was completely remove in three minutes. However, under the same condition only 70% of the COD was removed.
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