The study on the yield of hydroxyl radical and characteristics alteration of raw wastewater by the electrocatalytical technique

• Main Authors: Cheng-Hung Tung, 唐政宏
• Other Authors: Yung-Hsu Hsieh
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/50678028526513849219

博士 === 國立中興大學 === 環境工程學系所 === 102 === 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 the yield of hydroxyl radicals, treatment of real municipal and printing wastewater with an electrocatalytic process, respectively. The 4-hydroxybenzoic acid (4-HBA) was served as a trapping reagent to determine the concentration the concentration hydroxyl radicals. The 4-HBA reacts with hydroxyl radicals to from 3,4-dihydroxybenzoic acid (3,4-DHBA), which can be used as an indicatiors of hydroxyl radicals concentration. Results showed that the equilibrium concentration of derivatives (3,4-DHBA) could be reached after 30-second reaction in electrocatalyst system. The electrolyte of NaNO3 was relatively appropriate for producing hydroxyl radicals. In addition, production rate of hydroxyl radicals possessed linear correlation with energy application. High pH conditions were beneficial to the production of hydroxyl radicals in comparison with pH neutrality and acidity. The highest hydroxyl radicals concentration of 1.57×10-2 M could be obtained by using the TiO2 electrode. The yield rate of hydroxyl radicals in the electrocatalyst system was about 4.5×10-5 M W-1cm-2, based on the electrode area and energy application. For the experiments of degrading organic pollutants in municipal wastewater, the commercially available and nano scale titanium dioxide electrode plate were used. By conducting experiments, the degradation phenomenon of municipal wastewater by the above electrocatalytic electrodes was investigated. Through analysis of 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. As for the remediation of printing wastewater, wastewater with lower conductivity could lead to greater electrical voltage thus contributing to the higher removal efficiency of TOC and chroma. With current density at 50 mA cm-2 by one pair of electrodes (IrO2 + stainless steel), the TOC and chroma removal efficiencies was 53.0% and 71.0% after 60-min treatment. Based on the same operation conditions but two pairs of electrodes, the removal efficiency of TOC and chroma was enhanced to 75.41% and 82.0%; TOC and chroma removal efficiencies was improved to 90.0% and 92% by integrated with the activated carbon absorption.