| Summary: | 碩士 === 嘉南藥理科技大學 === 環境工程與科學系 === 101 === Taiwan has one of the major high-technology industry clusters in the world. Manufacturing industries such as, photonics and semiconductors are flourishing in the region. However, various chemicals used in these industries may cause significant pollution when discharged into the environment. In 2006, the output values of TFT-LCD (thin-film transistor liquid-crystal displayer) are 66% and 53% of the total photonics and semiconductor industries, respectively. On the other hand, the corresponding wastewater discharge flow rates from the same industries are 85% and 66%. It is evident that the amount of pollutants produced during TFT-LCD manufacturing substantially increased in the recent years. The volume of these pollutants comes from etching process wastewater. Therefore, finding an effective and economical way to treat etching wastewater is an essential work for the Taiwanese TFT-LCD industry.
Advanced oxidation processes (AOPs) are efficient methods to degrade organic compounds. Fenton process is one of these advanced oxidation processes. A new approach to increase ferric reduction efficiency using electro-Fenton procedures has been developed to degrade organic contaminants. In the electrolytic cell, the organic compound is ionized or oxidized by direct electrolysis on the anode. This method uses hydrogen peroxide (H2O2) and ferrous ion to produce hydroxyl radicals to oxidize the contaminants. Ferrous ion is regenerated via the reduction of ferric ion on the cathode.
The chemical oxygen demand (COD) in the TFT-LCD etching wastewater exceeds the effluent standards. This study used Fenton process and Electro-Fenton procedures to remove COD from the etching wastewater. The COD removal efficiencies of the electro-Fenton and Fenton method is discussed through the oxidation efficiencies of the process. .
The operating conditions used for the Fenton process are: initial pH (2, 2.5, 3, 3.5, 4); ferrous ion concentration (3 mM, 3.5 mM, 4mM); H2O2 concentration (259 mM, 285 mM, 311 mM); and current density (1 A/m2, 1.5 A/m2). Increasing the ferrous ion concentration from 2 to 4 mM increased the hydroxyl radicals and consequently increased the degradation efficiency of COD. Results showed that the COD removal efficiency is optimum using the following operating conditions, Fe2+ = 3.5 mM, H2O2 = 285 M, initial pH＝4.0, current density＝1.5A. Using two (2) hours of continuous electrolysis, the COD removal efficiency increased to 30% compared to that of the Fenton treatment.
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