The preparation and oxidation of catalyst for heterogeneous catalytic ozonation using metal-coagulated sludge

• Main Authors: Ssu-Yi Li, 李思儀
• Other Authors: Jiunn-Jei Wu
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/26398556377707205284

碩士 === 逢甲大學 === 環境工程與科學所 === 97 === In this research, wasted chemical sludge generated from Ping-Ding drinking water plant was employed as novel catalyst materials. By modifying the surface characterization of sludge using calcination and alkaline activation, ozone molecule in water would be decomposed and produced more free radicals with high oxidation potential on the degradation of organic substances. Two pahses have been involved in this thesis including catalyst preparation and heterogeneous ozonation for oxalic acids and methyl benzoic acids. According to the research results, a new, efficient, and stable sludge catalyst has been successfully prepared and applied in oxalic acid (OA) decomposition by combining with heterogeneous ozonation at acidic pH, where the self-decomposition of ozone can be substantially neglected. The catalyst was characterized using various analytical techniques. X-ray diffraction (XRD) and inductively coupled plasma optima optical emission spectrometer (ICP-OES) analysis showed that sludge catalyst as prepared contains SiO2 as the major constituent and Al2O3, Fe2O3, MgO, K2O, CaO, NaO as minor ones. Scanning electron microscope (SEM) analysis revealed that non-crystal infrastructure was formed on the catalyst surface. Since sludge was prepared by chemical activation with NaOH and high-temperature calcination, it displays uniform and granulized surface. By raising concentration of NaOH, which is used as modified and etched reagent, the surface structure of sludge would be enhanced by the formation of more hydroxyl functional groups, indicating activation zone is substantially intensified. However, the surface area of sludge cayalyst decreases gradually. When ozonation system was operated by loading 0.25 g of sludge catalyst, 29% (P800), 53% (P8002.5 N), 84% (P8005.0 N), and 87%(P80010.0 N) of oxalic acid were decomposed respectively. Adsorption or ozonation processes alone is not effective for the removal of oxalic acid. In addition, the pH value in solution is also another influential factor for the removal of oxalic acid. The optimum pH was closely related to pHpzc of catalyst itself. It is found that acidic pH would result in more degradation of oxalic acid by comparing to neutral and alkaline pH due to the affinity of oxalic acid and ozone molecules towards the surface of sludge catalyst at pHpzc of sludge catalyst equal to 3.7. Althlough it is found that benzoic acid could be degraded by directly ozonation, heterogeneous ozonation by adding sludge catalysts, which were activated by NaOH (5 N), could effectively promote its decomposition from 58% to 83% and TOC removal from 15% to 52% in 30 minutes. An oxidation model considering side reations between ozone and OH radicals towords with other byproducts or impurities has been established. The reaction coefficients for oxalic acid are 10, 10, 15, 11 1/sec at catalytic ozonation. The larger reaction coefficient found in catalytic ozonation indicates that competition mechanisms for hydroxyl radicals are involved.