以芬頓反應探討苯酚之降解與礦化－溫度變化以及腐植酸共存之影響

Abstract

在現代工業日益發展之下，工業產出之污染物處理成為亟需重視的一項議題。苯酚雖然具有腐蝕性以及生殖毒性，卻是被廣泛使用之工業原料的芳香族有機化合物之一，並且除了苯酚本身之毒性以外，它的不完全降解所產生的中間產物如鄰苯二酚、對苯二酚，皆會對環境造成更甚的毒性污染。因此，苯酚的完全降解以及礦化，在處理排放污水之中則變得極為重要。芬頓反應（Fenton process）乃是一項屬於高級氧化處理(Advanced oxidation process，AOP)的污水處理技術，因其應用之簡單性以及低成本之特色被多方研究。然而在實際應用芬頓反應處理水污染時，應考慮水環境中存在之腐植酸（huimic acid, HA），又，台灣本身之水體條件受到四季溫度之變化和工廠排水之影響而可能有不定的水體溫度。因此綜述以上，有關溫度和腐植酸存在對於芬頓水處理之影響仍為需要加以討論之議題。 本研究之目標是能夠得知在模擬台灣水體之溫度變化影響以及腐植酸存在下，芬頓水處理運用在低濃度苯酚之降解以及礦化之效益為何。本實驗將芬頓反應在不同的溫度條件和腐植酸濃度下進行，除了剩餘苯酚濃度以外，也進行了總酚濃度、總有機碳分析（TOC）、氧化還原電位（ORP）、氫氧自由基（‧OH）濃度和化學需氧量（COD）等因子的測量以監測或比較各個條件下的降解效率。 以實驗結果而言，本研究發現溫度的強化效應或腐植酸的存在對於低濃度苯酚在芬頓反應（芬頓試劑Fe2+/H2O2=0.1mM:0.5mM，亞化學劑量）中之降解並無太明顯的差異影響，但對於苯酚整體礦化之影響卻較為顯著。由於高溫條件下（>50℃）芬頓反應的不穩定性和腐植酸可能造成的抑制效應，腐植酸對於苯酚礦化率之強化在較低的室溫（20℃）時可將礦化率提升至40.3%，優於其他較高溫的條件之下所得到小於30%之礦化結果。反應速率常數k在芬頓60℃、有腐植酸的條件下是9.73×10^-4 M^-1min^-1並低於在沒有腐植酸情況的5.41×10^-3 M^-1min^-1，反之，在20℃有腐植酸的條件下k是2.11×10^-3 M^-1min^-1並大於沒有腐植酸的1.60×10^-3 M^-1min^-1。由於腐植酸的存在會提供電子促使亞鐵離子的再生、與腐植酸錯合或是對污染物進行吸附反應，以致芬頓反應內部機制變得更加複雜，並且高溫作用下這些反應會更加加劇，因此高溫條件下的苯酚降解即受到影響而降低降解效率。由本實驗所得到之結果，認為當處理真實低濃度苯酚污水時，有效益之芬頓處理應運用於低室溫20℃而非其他較高溫之條件。

Degradation of pollutants in the environment has become an issue through the development of industry nowadays. Phenol, a widely used aromatic organic compound, is a hazardous substance due to its corrosiveness and reproductive toxicity. The incomplete degradation of phenol results in the formation of toxic phenolic intermediates such as catechol and hydroquinone. For the reason, the degradation and mineralization of phenol containing phenolic compounds is a critical concern when disposal with sewage discharge. Fenton process is one of the mostly-used AOP (advanced oxidation processes) when it comes to wastewater treatment due to its simplicity and low cost. However, the effects of the existence of humic acid (HA) in the treatment should be considered when wastewater treatment is conducted in real aquatic water environment. Furthermore, seasons in Taiwan causes the variation in temperature of the water body, which ranges from 20℃ to 30℃, and even reaches a higher level if containing the discharge of industrial wastewater. Therefore, discussion of temperature impact and HA coexistent on wastewater treatment of phenol by Fenton process should be an essential issue. The objective of this study is to obtain the degradation and mineralization efficiency in Fenton wastewater treatment of low concentration phenol. This study applies Fenton process to the degradation of phenol and its phenolic intermediates at different conditions of temperature and humic acid concentrations. Beside the residual phenol and phenolic compounds concentration, TOC, ORP, hydroxyl radicals and COD were measured to compare the degradation efficiency under different experimental conditions. In regard with the results, the impact caused by temperature variation or humic acid coexistence on low concentration phenol with sub-stoichiometric Fenton reagent (Fe2+: H2O2=0.1 mM: 0.5 mM) is not as apparent, but more TOC mineralization was observed. The enhancement of the mineralization rate by the coexistence of humic acid could reach 40.3% removal at room temperature of 20℃ rather than at higher temperature as the rate <30% due to the hinder effect produced by the humic acid and instability of the processes over 50℃. The constant value k of TOC mineralization at 60℃ with humic acid is 9.73×10^-4 M^-1min^-1 and is slower than that without humic acid as 5.41×10^-3 M^-1min^-1. The k of 20℃ with humic acid process is 2.11×10^-3 M^-1min^-1 and is 1.60×10^-3 M^-1min^-1 in the process without humic acid. The presence of humic acid in Fenton process resulted in more complicated mechanisms such as providing electrons, competing for oxidants and sorption. Therefore, the hinder effect on the mineralization of phenol by Fenton process at higher temperature is enhanced. According to the results in this study, an effective Fenton treatment with sub-stoichiometric Fenton reagent for low concentration phenol degradation should be applied at ambient temperature as 20℃ rather than higher temperature in the real water body.