| Summary: | 碩士 === 國立屏東科技大學 === 環境工程與科學系所 === 98 === Recently, TMAH (tetramethylammonium hydroxide) is extensively used as the reagent of PCB (printed circuit board) manufacturing. It has resulted the wastewater containing high concentrations of organic matter, nitrogen, and phosphorus which are highly contaminated materials. Hydrogen peroxide (H2O2) are commonly used as the oxidant in photo-Fenton process. However, its disadvantage includes short half-life and only useful under the acidic conditions. In this study, we used persulfate as the oxidant to investigate the effect of the degradation of TMAH. TiO2 (titanium dioxide) photocatalyst and persulfate were combined in the photoreaction of batch and circulation systems. Further more, the optimum operating conditions for the degradation of TMAH can be tested in a short period of time. For the analysis of the concentration of TMAH, we not only used the traditional method of IC (Ion Chromatography) but also self-developed method of GC-NPD (Gas Chromatograph - Nitrogen Phosphorus Detector).
This study compared the decomposition of TMAH using the photo / persulfate procedure and UV/TiO2 photocatalysis in the batch and circulation systems. The best results for higher concentration of TMAH was using photo/persulfate process and then UV/TiO2 photocatalysis in the batch reaction system. This is due to a high redox potential of sulfate radicals (SO4-．) generated from photo/persulfate in the reaction. These results (the removal rate was 99% TMAH in 12 hours) indicated that the best reagent concentration of 0.05 M for [Fe2+/S2O82-]. In this treatment, the toxicity of TMA+ (tetramethylammonium cation) could be reduced by sulfate radicals through demethylation (the toxicity reduced by 94.2% in 12 hours). When the reagent concentration was equal to or less than 0.05 M, the pH of the solution was decreased using photo / persulfate procedures and the photocatalytsis of TiO2. The concentration of ammonia-nitrogen is the highest when 0.075 M reagent was used. In the process of TMAH degradation, there are various intermediates generated including sulfate radical and hydroxyl radical that may increase the release of ammonia-nitrogen. Scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS) results showed that titanium dioxide particles have smooth surface through the initial preparation of crystallization. After the adsorption, the surface changed from smooth to rough with many small holes on it. The carbon and sodium were found on the surface of titanium dioxide (reagent concentration of 0.05 M) which is due to the reaction of persulfate and ferrous sulfate. However, the EDS test doesn’t show the iron on the surface of titanium dioxide. It was suggested that the concentrations of iron ions in the reaction process were below the instrument detection limit.
|
|---|
