偶氮性染料臭氧化處理之化學降解研究

Abstract

本研究探討臭氧以半批次反應的方式，與水中偶氮性染料(酸性橘色6號，AO6)之反應，以不同的控制參數，包括：溫度、酸鹼度及臭氧劑量做為研究的起點，逐一探討其對AO6之去色與礦化之影響，並分別提出相關之反應速率常數做為探討較佳處理參數之依據；此外，以連續的逆流式氣泡塔探討氣體液體流量比率及管柱高度對水中偶氮性染料(反應性黑色5號，RB6)之去色與礦化之影響，以瞭解上述因子之影響程度，並經由對生物降解性及毒性的量測，確認較佳之操作參數，相關研究成果可做為後續研究之基礎。 在半批次反應方面，當臭氧與AO6的反應主要發生在液相範圍，在pH小於7時，以直接反應為主，當pH大於7時，以間接反應為主，此一結果亦在pH因子影響量測中獲得證實，在pH大於7時的總有機碳去除速率常數較pH小於7時大。在臭氧化開始後約30分鐘內，AO6的色度快速降低，在40分鐘之內，達到無色階段，其顯示臭氧的選擇性攻擊主要針對偶氮鍵(N=N)，因其氧化潛能低於芳香族的不飽和鍵，而此時的總有機碳去除比率則小於0.9，其證實臭氧處理於色度存在之時，臭氧多消耗於偶氮鍵的破壞，然因，臭氧消耗速度較快之故，固此時於水中並未發現溶臭氧的存在。 臭氧劑量的高低與去色速率呈現正相關，其影響幅度較溫度的影響為明顯，而礦化速率則明顯受溫度的影響，在35oC的狀況下，礦化速率常數為0.029 min-1，而在15 oC的狀況下，礦化速率常數為0.016 min-1，其受影響的幅度稍大於去色反應(由0.14增加至0.17 min-1)。如以臭氧劑量為探討因子，當臭氧劑量由9.7增加至33.3mg/L-min時，去色反應速率常數由0.14增加至0.26 min-1，而礦化速率常數的增幅則僅33%。臭氧處理無法將水中有機物質完全礦化，因此，必須借助輔助氧化系統，而本研究中亦以紫外線(254nm波長)為範例，探討臭氧與臭氧/紫外線對含有AO6染料水樣中總有機碳去除與毒性降解之影響。 當以臭氧為唯一的處理單元時，在4小時的處理時間下，溶解性總有機碳的去除率為82%，而增加紫外線為輔助時，在120分鐘內即可達到100%的去除效果，在處理過程中，無法達成氮質量平衡，其原因在於部份氮元素轉化為一氧化氮、二氧化氮與氮氣而跟隨排氣排除，對於毒性降解方面，臭氧/紫外線處理對水樣中毒性的降低效果比僅以臭氧為處理方式者為快且明顯。如以一多步驟動力模式為基礎，探討並預測去色、礦化及硫酸鹽之生成，以反應速率及決斷係數做為判定是否提高反應步驟之依據。 在連續逆流式氣泡塔研究中，約在1HRT的時間內，出口處的色度與總有機碳濃度即達穩定，當提高氣體進流量時，管柱內無色之高度逐漸向上升，反之提高液體進流量時，管柱內無色之高度逐漸向下降，可知氣體/液體進流量比率可改變去色與礦化的效果，而管柱高度亦影響其效果，在固定液體流量的情況下，當1<氣體/液體進流量比率<2時，礦化的效果較佳；在生物降解方面，固定液體流量的情況下，BOD5/COD值由0.1增加至1.0，反之，固定氣體流量的情況下，BOD5/COD值由0.1增加至0.5，顯示增加氣體流量對生物降解性的提升具明顯效果。在毒性降解方面，氣體/液體進流量比率增加的情況下，毒性快速下降，因此，控制氣體/液體進流量比率即可做為控制放流水毒性的參考依據。

The ozonation of azo dyes both in semibatch reactor and continuous bubble column reactor are investigated in this study. The reaction rate for decolorization is faster than that of total organic carbon (TOC) reduction, and, as TOC removal ratio > 0.9 in semibatch system, the dissolved ozone concentration is nearly not detectable, suggesting that most ozone transfer from gas phase to liquid phase is consumed rapidly in oxidizing the azo dye by breaking the azo bond (N=N). As monitoring the selected parameters during the semibatch experiments, decolorization, and TOC removal were affected by pH, temperature, and ozone dose. Decolorization and AO 6 reduction were completed within 40 minutes of ozonation time for all examined cases. When the ozone dose increased from 9.7 to 33.3 mg/l-min, the decolorization rate constant increased from 0.14 to 0.27 min-1. The increases of k values suggest that decolorization and AO6 removal were affected by ozone dose. For the TOC removal, its reaction rate constants were temperature dependent and the effects of ozone dose and pH were not significant. Sulfate yield was accelerated upon the completion of decolorization. The sulfate yield may be due to the destruction of azo bonds and surplus ozone or OH– turns to attack aromatic rings. Significant increment of sulfate yield was observed during the TOC removal process. Due to the ability to oxidize organics in water, both ozone alone and O3/UV254 are used to investigate the effectiveness of deolorization and mineralization of AO 6, the target compound. The results show that O3/UV254 system may reach the level of total mineralization of AO6 within 120 min, also revealing that the O3/UV254 system is a powerful treatment to breakdown all organic carbon in solution. During the ozonation, the nitrogen mass balance can be achieved that is due to the nitrogenous compounds are formed, such as N2, NO, and NO2. In the countercurrent flow bubble column system, TOC, sulfate, and nitrate, but the variations of pH, A597 nm, and color all reach steady constants at 1 HRT. It suggests that color and N=N are easily to be removed comparing to TOC; the sulfate formation is consistent with TOC reduction. To control liquid or gas flow can affect the order of reaction, a pseudo-first order reaction is suggested in the fixed liquid flow rate experiments and a second order reaction may well explain for the fixed gas flow rate conditions. Not only flow patterns affect the RB5 removal and the mineralization of derivatives but also the column height may have influence on the ozone consumption. The extent of decolorization and mineralization decrease as the sampling port height increasing, indicating that the column height may reflect the retention time of ozone gas and the contacting time between ozone and RB 5 in BCR system. The biodegradability is enhanced via ozone treatment that is not proportional to the amount of ozone consumption but all results exhibit the similar increment trends.