以 Fenton 程序處理 4-硝基酚廢水

Abstract

本研究以 Fenton 作為 4-硝基酚廢水之前處理程序，實驗藉由控制不同過氧化氫及亞鐵離子添加量 (H2O2 1 - 10 mM; Fe2+ 0 - 10 mg/L)，探討其對前處理效果之影響，並求得最佳之加藥量；此外，實驗更控制不同初始 pH 值，探討於不同 pH 值環境下對前處理效果之影響。藉由分析實驗過程中 4-硝基酚的降解、溶液中硝酸根及亞硝酸根離子之濃度、DOC 的去除率以及生物可分解度 (BOD5/COD) 的變化，探討處理效果之優劣。當控制初始反應條件於：pH 3、過氧化氫及亞鐵離子添加量為 5 mM 及 5 mg/L 以及溫度控制於 20oC，經過 120 分鐘 Fenton 程序前處理後，4-硝基酚之去除率可達 99.9% 以上、硝酸根及亞硝酸根離子之釋出比例可達 88% 以上、礦化效率達 24% 以及生物可分解度更可由處理前之 0.03 顯著提升至 0.55。由上述結果顯示以 Fenton 作為 4-硝基酚廢水之前處理程序，可以有效去除廢水中之 4-硝基酚，並使有機氮順利礦化，而形成硝酸根及亞硝酸根離子釋出於水溶液中，此外，更可順利降低廢水對生物之抑制性，而提升處理後廢水之生物可分解度，以期能達到後續以生物程序處理此廢水之目標。本研究於反應過程中更分析出 p-benzoquinone 及 oxalic acid 兩種中間產物，顯示 4-硝基酚經氧化後，會釋出亞硝酸根離子形成 p-benzoquinone，進一步再被氧化形成 oxalic acid，最終被礦化形成二氧化碳及水。此外本實驗更針對此含氮有機物的氧化，探討氮之平衡，於反應過程中分析有機氮、氨氮、硝酸根及亞硝酸根離子，並探討其變化趨勢。由結果顯示，處理後有機氮明顯減少，同時溶液中亦伴隨硝酸根及亞硝酸根離子之釋出，顯示此含氮有機物被氧化，此外，於溶液中亦分析出少量之氨氮，顯示於此系統中亦有還原反應，然而於整個反應過程中，此四種含氮化合物之總和維持於 0.96 - 0.98 mM，顯示於反應過程中含氮化合物主要以此四種物質為主。

In the present work 4-nitrophenol (4-NP) was decomposed in aqueous solution using Fenton process, which was a pretreatment method. The effect of initial concentration of hydrogen peroxide and ferrous ion on the decomposition of 4-NP by Fenton process was investigated. The effect of the initial pH on the decomposition of 4-NP was also examined. The efficiency of Fenton process was measured by the decomposition of 4-NP, removal of dissolved organic carbon, release of nitrite and nitrate ions and variation in biodegradation. After 120 minutes Fenton process pretreatment, the decomposition of 4-NP was above 99.9% and the release of nitrite and nitrate ion was more than 88% for the initial condition of 4-NP 1 mM, H2O2 5 mM, Fe2+ 5 mg/L concentrations, pH 3 and temperature 20oC. The mineralization of wastewater was above 24% and the biodegradation of wastewater increased form 0.03 to 0.55. It was found that Fenton process decomposed 4-NP completely and mineralized the organic nitrogen compound by release of nitrite and nitrate ions in aqueous solution. In addition to the detoxification of wastewater, the biodegradation of wastewater increased and it becomes suitable for conventional biological treatment after the pretreatment. p-benzoquinone and oxalic acid were the intermediates during the 4-NP decomposition that were detected by GCD and HPLC analysis. It was shown that after decomposition of 4-NP, nitrite ion was released and p-benzoquinone was formed. Oxalic acid was produced by the oxidation of p-benzoquinone. Finally, carbon dioxide and water was produced by mineralization of oxalic acid. In this work, the nitrogen mass balance was also investigated by analyzing the organic nitrogen, ammonia nitrogen, nitrite and nitrate ions. The nitrite and nitrate ions were released form organic nitrogen compound with the decrease of organic nitrogen. This shows that the organic nitrogen compound was mineralized and ammonia nitrogen was formed. It was shown that, nitrite can be reduced in the system. Total nitrogen that include organic nitrogen, ammonia nitrogen, nitrite and nitrate ions maintained in between 0.96 - 0.98 mM.