Electrocoagulation and electrochemical-fenton processes for removal of heavy metals and organic contaminants from electroplating wastewater

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Title:	Electrocoagulation and electrochemical-fenton processes for removal of heavy metals and organic contaminants from electroplating wastewater
Other Titles:	電混凝及電 Fenton 程序去除電鍍廢水中重金屬及有機污染物研究
Authors:	維恩亞;Ya, Vinh
Contributors:	淡江大學水資源及環境工程學系碩士班李奇旺;Li, Chi-Wang
Keywords:	電鍍廢水;電混凝法;電Fenton法;化學污泥;Electroplating wastewater;Electrocoagulation;Electrochemical-Fenton;Chemical sludge
Date:	2017
Issue Date:	2018-08-03 15:05:25 (UTC+8)
Abstract:	本實驗使用鐵作為電解的電極板，藉由電混凝(EC)及電Fenton法(ECF)程序處裡電鍍廢水。由於電鍍廢水具有高導電度(> 11 mS/cm)及低pH值(< 2)的特性，適合使用EC及ECF程序來去除水中重金屬及有機污染物。在此實驗中探討了不同的實驗參數對重金屬和有機物的去除效果，包括反應時間，初始pH和電流密度。在反應時間為四分鐘、電流密度為24.15 mA / cm2的條件下，可以完全去除金屬污染物，但化學需氧量(COD)只有40％能被去除。而在固定理論的鐵添加劑量下，增加電流密度並不會影響金屬及COD的去除效率，反而需要更多的能量消耗。例如:比較電流密度4.83mA / cm 2、反應時間20分鐘及電流密度77.29mA / cm 2、反應時間1.25分鐘，兩種條件下，前者所消耗的能量為1.69kWh / m3、後者為13.4kWh / m3，高電流密度下能量消耗明顯更多。在污泥方面，低電流條件下，產生褐色的氫氧化鐵污泥(Fe (OH)3)，而在高電流條件下產生的污泥為綠色的氫氧化亞鐵(Fe(OH)2)。氫氧化亞鐵具有對水較高的溶解度，會嚴重影響處理後的水質。 EC程序在對COD的處理上較為不足，進而採用ECF程序來補足。在H2O2/Fe（II）莫耳比為5的情況下，ECF對COD的去除率達到67％以上，符合台灣EPA的排放標準(COD < 100 mg/L)。此時若增加電流密度， COD的去除率會略為下降。 Electrocoagulation (EC) and Electrochemical Fenton (ECF) processes using iron electrodes were employed to treat electroplating wastewater. The wastewater is suitable for the EC and ECF treatment due to high in conductivity (>11 mS/cm) and low in pH (~2). Different experiment parameters were investigated including electrolytic time, initial pH, and current density on the removal of heavy metals and organic. A completed removal of metal contaminants was achieved, whereas only 40% of chemical oxygen demand was removed with the electric current density of 24.15 mA/cm2 and electrolytic time of 4 min. At the fixed theoretical iron dose, the increase of current density had no improvement in removal efficiency but increased energy usage. The energy consumption was approximate 1.69 kWh/m3 at a current density of 4.83 mA/cm2 and a reaction time of 20 min but it dramatically increased to 13.4 kWh/m3 at a current density of 77.29 mA/cm2 and a reaction time of 1.25 min. Under the low current condition, a brown color sludge was produced, which is associated with ferric hydroxide. On the contrary, a greenish color sludge was created under the high current condition, suggesting the formation of ferrous hydroxide. Ferrous hydroxide with a relatively high solubility profoundly impacted the treated water quality. The ECF process was employed to overcome the low COD removal of the EC process. At the H2O2:Fe(II) molar ratio of 5, the ECF achieved > 67% of COD removal and met the regulatory COD level of 100 mg/L. At the fixed H2O2:Fe(II) molar ratio of 5, increasing current density resulted in the slight decrease of COD removal.
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