The study on the yield of hydroxyl radical and characteristics alteration of municipal wastewater by TiO2 catalytical electrode

• Main Authors: Cheng-Hung Tung, 唐政宏
• Other Authors: Jih-Hsing Chang
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/81312550470862395566

碩士 === 朝陽科技大學 === 環境工程與管理系碩士班 === 95 === Hydroxyl radicals can be produced by water molecule interacting with the catalytic materials in the aquatic system. Hydroxyl radicals are effectively able to oxidize the organic pollutants into harmless water and carbon dioxide, therefore, they have been applied to wastewater and air pollution treatment extensively. This study has been composed by three parts such as manufacture method and characteristic analysis of different catalytic electrodes, the yield of hydroxyl radicals by the catalytic electrode of titanium dioxide, and the COD removal efficiency of municipal wastewater decomposed by the electrocatalytical technique , respectively. In the aspect of manufacturing different catalytic electrodes, three types of electrodes were used. One is the electrode plate of cuprous oxide that was made by the electroplating process. The other is a titanium-dioxide electrode with nano scale net-shaped which is supplied from the surface treatment laboratory of professor Tsong-Jen Yang at department of materials science and engineering in Feng Chia University. Another is the commercially available titanium dioxide electrode which manufactured by the sputtering process. The surface features and element composition of all electrodes were observed by field-emission scanning electron microscope (FE-SEM) and X-ray energy dispersive spectrometer (EDS), individually. According to the FE-SEM image of Cu2O electrode under pH=9 manufacturing condition, it can be seen that the cuprous oxide crystals pile on the substrate, the stainless steel plate, and the diameter of surface particles smaller than 50 nm. For the FE-SEM images of nano scale electrode of titanium dioxide, it can be observed that the titanium dioxide is columnar on the substrate. This type of electrode will be corrosive after used several times. For the commercially available TiO2 electrode, the texture of the TiO2 electrode is quite tight and includes a small number of pores. However, there is no nano-scale particles found on the electrode surface. The surface of TiO2 electrode remains even after used several times. This type of electrode possesses high reactive and stable characteristics based on the EDS images of all electrodes. Aiming to the yield of hydroxyl radicals produced by TiO2 electrode under direct current, the main operational parameter is the voltage magnitude. The hydroxyl radicals trapped in the known concentration of propionaldehyde and measured by HPLC. According to experimental results, the yield of hydroxyl radical maintains steady after 40-second operation under certain of voltage applicaiton. Under the voltage gradient of 5.0 and 7.0 V cm-1, the yield is 0.496 10-3 M/sec and 0.93 10-3 M/sec, respectively. The yield of hydroxyl radicals presents positive linear correlation with voltage gradient, and the electrocatalytic process produces more hydroxyl radicals than Fenton technology (about 1.39 10-9 M min-1). For the experiments of degrading organic pollutants in municipal wastewater, the commercially available TiO2 electrode, nano scale titanium dioxide electrode, and self-manufactured cuprous oxide electrode plate were used. By conducting experiments, the degradation phenomenon of municipal wastewater by the above electrocatalytic electrodes was investigated. Through analysis of chemical oxygen demand (COD), pH, conductivity, and dissolved oxygen (DO), the degradation efficiency was evaluated. According to experimental results, the proper treatment parameters include: the voltage gradient of 7.0 V cm-1 and the electrode of commercially available TiO2 (punctured). After 60-minute treatment under such conditions, the COD of wastewater can be roughly degraded from 400 ppm to 40 ppm, the conductivity degraded efficiency roughly is 30%, the pH of wastewater can maintain at neutral range, and the DO of wastewater can be enriched to 6 mg L-1.