超音波程序應用於鄰氯酚以及腐植酸處理之研究

Abstract

近年來將超音波氧化程序應用於水及廢水處理的研究相當的廣泛，主要的原理即係利用超音波程序所產生之高溫及氫氧自由基對於有機物進行熱解及氧化之反應，但由於有機物的性質愈趨複雜，若僅以單一氧化程序對有機物進行處理，一般需要較長的反應時間，因此目前多將複合式的氧化程序應用於水及廢水的處理，希望能夠藉此提高有機物的分解率，同時縮短反應所需之時間。此外反應條件的改變對於處理效率高低的影響性亦受到廣泛的注視，一般而言，氧化劑的添加量、pH 值的高低以及氧化程序所提供之能量等三項為最常被討論的因子。本研究即利用超音波程序分別針對實驗室配置之鄰氯酚廢水以及腐植酸溶液進行處理，並探討不同因子以及處理程序對於目標污染物處理之效果。 為了能夠瞭解不同反應因子的改變對於超音波程序處理有機污染物之影響性，本研究分別針對過氧化氫的添加量、溶液之初始 pH 值、離子強度、陽離子的添加以及有機物的初始濃度等因子進行探討；此外，為了縮短反應所需之時間，本研究亦將超音波程序與 Fenton 程序加以合併對鄰氯酚廢水進行處理，並探討不同過氧化氫與亞鐵離子加入量時，鄰氯酚廢水的分解與礦化率。實驗結果顯示，當反應的溫度以恆溫控制器控制於 25oC，單純以超音波程序對鄰氯酚廢水 (濃度為 100 mg/L) 進行處理時，經過六個小時的反應，僅有 10% 的鄰氯酚可被分解，若於反應中添加 200 mg/L 的過氧化氫，則分解率可提高至 50%，此一結果顯示，氧化劑的添加確實能有效的提升有機物的處理效果；此外，若將處理時之 pH 值以及離子強度分別調整於 3 及 0.1 N，經過六個小時的處理後，鄰氯酚的分解率可高達 99% 以上，礦化率則達 65% 以上。此一結果顯示，若能將反應的因子控制於合適的條件下，確實可以將有機物進行有效的分解及處理。 雖然利用超音波程序並配合過氧化氫的添加能夠將有機物污染物的去除率提升至 99% 以上，但六個小時的處理時間仍屬較長，因此本研究於反應過程中添加亞鐵離子做為催化劑，以期能使處理所需之時間縮短。根據實驗之結果顯示，亞鐵離子的添加，確實有助於處理效率的提升以及處理時間的縮短。當反應的條件控制於 pH 3 及離子強度 0.1 N，過氧化氫及亞鐵離子的添加量僅各需 50 及 10 mg/L，即可在 20 分鐘內將鄰氯酚的去除率提升至 99% 以上，若與前述之結果比較即可發現，亞鐵離子的添加不但能使處理的時間縮短為原本的 1/18，同時過氧化氫的添加量亦可減少為原本的 25%。除此之外，在此一條件下過氧化氫的利用率最高 (約為 92%)，顯示以超音波配合 Fenton 之程序處理鄰氯酚廢水，確實能達到提高分解率與縮短反應時間之功效。 以超音波序列程序處理鄰氯酚廢水時可分析出 15 種中間產物的生成，同時在不同反應條件下有不同種類之中間產物生成，其中以 2-chloro-p-benzoquinone 為主要產物。過氧化氫之濃度較高時 (100、200 及 500 mg/L)，中間產物的種類較少，多為 2-chloro-p-benzoquinone、 bis(2-ethylhexyl) phthalate、2-chloro-hydroquinone 等，過氧化氫濃度較低時 (10 及 50 mg/L)，主要之中間產物為 2-chloro-p-benzoquinone、bis(2-ethylhexyl) phthalate、2-chloro-hydroquinone、4-chloro-3-methylphenol、2-chloro-6-methylphenol 等。不含過氧化氫之條件時，主要產物為 2,6-dichloro-p-benzoquinone、bis(2-ethylhexyl) phthalate、2-chloro-6-methylphenol 等。由上述結果可以推斷，過氧化氫的濃度較高時，氧化能力較強，因此主要產物為 chlorinated benzoquinone，過氧化氫的濃度較低時，主要產物除 chlorinated benzoquinone 外，亦包含 chlorinated methylphenol。此外根據中間產物的生成量亦可發現，氫氧自由基與鄰氯酚的反應主要發生位置應為對位 (para-position)。 實驗數據亦顯示，鄰氯酚的分解與過氧化氫的消耗多依循一階之反應動力模式，且其反應常數隨過氧化氫以及亞鐵離子濃度的增加而增加。以 Arrhenius model 探討不同過氧化氫以及亞鐵離子濃度對鄰氯酚分解之關係時發現，其影響因子為 0.57，較氫離子濃度 (0.51)、離子強度 (0.19) 以及有機物初始濃度 (-0.05) 為高，僅較超音波振幅與過氧化氫的添加量略低 (0.6)，顯示過氧化氫與亞鐵離子的濃度對有機物之分解具有相當之影響，此一結果的獲得將可做為未來處理廢水時反應因子調整之指標，而以氧化還原電位的變化做為有機物分解率之判定依據，亦可有效的縮短分析有機物所需之時間。 除了鄰氯酚廢水以外，本研究亦將超音波程序應用於腐植酸溶液之處理，反應之設計包括探討不同反應條件對於腐植酸加氯試驗之影響、以超音波程序對腐植酸溶液前處理後加氯副產物的生成變化以及利用超音波程序處理腐植酸溶液加氯反應後之有機物等三項進行討論。本研究所使用的前驅物質為商業用的腐植酸，主要的變化因子為反應的初始 pH 值以及離子強度。在反應過程中主要分析的項目包括水樣之溶解性有機碳濃度變化、餘氯的消耗量以及加氯副產物的生成；反應槽的體積為 3 L，外層並具有體積同樣為 3 L 之夾層，並連接恆溫控制器加以控制溫度，此外並將水樣以迴流幫浦迴流至超音波反應裝置，以固定之功率加以處理。為探討反應過程中之產物對於生物之影響性，本研究亦利用稀釋法對生化需氧量進行分析，同時建立一種程序做為處理前後毒性是否改變的指標。 實驗結果顯示，由於 pH 值以及離子強度均會對腐植酸分子的結構以及組成造成影響，因此 pH 值的高低以及離子強度的大小均會影響加氯試驗中溶解性有機碳的濃度變化、餘氯的消耗量以及加氯副產物的生成量及其種類。在較低之 pH 值條件下，加氯程序以及超音波程序不但能對於腐植酸溶液進行有效的分解，降低水樣之溶解性有機碳濃度，同時對於生物抑制性的降低亦有較為明顯的效果；此外，在好氧條件下，以超音波程序對腐植酸溶液進行前處理所獲得之效果為最佳。在生物抑制性的評估上，以較低之 pH 值以及較高之離子強度進行加氯試驗時，生物抑制性降低的幅度較大；而以超音波程序進行前處理時，若於前處理過程中同時曝氧，可得到最佳之生物抑制性降低率。加氯過程中所生成之主要副產物為三氯丙酮以及五氯丙酮，以超音波序列程序對腐植酸進行前處理時，無法有效降低副產物的生成量，但作為後段的處理程序時，則可將氯化副產物進行有效的分解處理。

Ultrasonic oxidation has been proven to be an effective process for the removal of hazardous organic compounds from water and wastewater; there are two different reaction mechanisms such as thermal cleavage and hydroxy radical oxidation are observed during the removal of hazardous organic compounds by sonication. However, the application of combining several advanced oxidation processes in the decomposition of organic pollutants is growing up for achieving short reaction period and high decomposition efficiency. Also, the effect of reaction parameters such as addition of oxidants, pH value and strength of oxidation method on the decomposition of organic pollutants is often investigated. Therefore, in this research, we prepared the humic acids and ortho-chlorophenol solutions in lab and used the ultrasonic process to treat them. When the ultrasonic process was applied in the decomposition of ortho-chlorophenol, the effect of oxidant addition, pH value, ionic strength, catalyst addition and initial concentration of ortho-chlorophenol was discussed in this research. In addition, to reduce the treatment period and increase the decomposition efficiency of ortho-chlorophenol, a combination of ultrasonic process and Fenton process was developed. Experimental result indicated that the decomposition of ortho-chlorophenol by sonication at 25oC was only 10% for the reaction period of 6 hours; it could be increased to 50% when 200 mg/L of H2O2 was added into the solution. This fact reveals that the addition of oxidant is useful to increase the decomposition of organic pollutants. If the pH value and ionic strength was adjusted at 3 and 0.1 N, the decomposition of ortho-chlorophenol achieved more than 99% for the reaction period of 6 hours; mineralization of ortho-chlorophenol was greater than 65%. Based on this result, it is understood that a well decomposition efficiency of organic pollutants can be achieved if an optimal condition is conducted. Laboratory result also indicates that the extent of ortho-chlorophenol decomposition increases with increasing concentration of H2O2 and Fe2+. When the ultrasound/Fenton process was conducted at pH 3 and ionic strength 0.1 N with 50 mg/L of H2O2 and 10 mg/L of Fe2+, more than 99% of ortho-chlorophenol was decomposed for the reaction period of 20 min. Comparing the result of ortho-chlorophenol decomposition by ultrasound/H2O2 and ultrasound/Fenton process, it is found that the addition of H2O2 in the ultrasound/Fenton system is reduced to 25% of the ultrasound/H2O2 system; the reaction period is significantly reduced in the ultrasound/Fenton system. Also, the utilization proportion of H2O2 is higher than 92 %. Therefore, it is understood that the decomposition of ortho-chlorophenol by ultrasound/Fenton process is much better than ultrasound/H2O2 process. There are fifteen types of intermediate were observed during the decomposition of ortho-chlorophenol by ultrasonic process. 2-chloro-p-benzoqninone was the major one. When the reaction was conducted at higher concentrations of H2O2, the types of intermediates observed in the reaction were less than the reaction conducted at lower concentrations of H2O2. Experimental result also shows that higher the concentration of H2O2 higher the oxidation potential; and hence the chlorinated benzoquinone is observed as the major intermediate. When the reaction was conducted at lower H2O2 concentrations, both chlorinated benzoquinone and chlorinated methylphenols were observed. Based on the formation of intermediates, it is understood that the oxidation of ortho-chlorophenol by OH radicals was taken place in the para-position. To understand the effect of reaction parameters deeply, it is necessary to study the reaction kinetics of ortho-chlorophenol decomposition by ultrasonic process. Experimental results indicate that the decomposition of ortho-chlorophenol and utilization of H2O2 fit well with the first-order kinetic equation. The rate constant of ortho-chlorophenol decomposition increases with increasing concentrations of H2O2 and Fe2+. In this research, we used the Arrhenius model to study the relationship between the decomposition of ortho-chlorophenol and change of reaction conditions. It is found that the magnitude of effect of reaction parameter is in an order of ultrasonic amplitude (0.6) = H2O2 concentration > concentration of Fenton reagents (0.57) > [H+] concentration (0.51) > ionic strength (0.19) > initial concentration of ortho-chlorophenol (-0.05). This information is very useful to estimate which reaction parameter should be adjusted for achieving the ideal decomposition efficiency of target compound. In this research, an oxidation-reduction potential (ORP) monitoring technique was developed as a surrogate index to determine the treatment efficiency. Experimental results reveal that the variations of the monitored ORP values were dependent on the oxidation of ortho-chlorophenol. Hence, it has been proven that the ORP monitoring technique can be used to determine the treatment efficiency of organic pollutants by the ultrasound and ultrasonic/Fenton processes. In this research, we also investigated the treatment of humic acids solution by ultrasonic process. Three experimental sets were established to 1) study the effect of reaction parameters such as pH value and ionic strength on the formation of chlorinated by-products; 2) study the performance of ultrasonic pretreatment on the formation of chlorinated by-products; 3) study the performance of ultrasonic posttreatment on the formation of chlorinated by-products. The precursor used in this research is the commercial humic acids. The extent of dissolved organic carbon (DOC) removal, chlorine consumption and by-products formation during the reactions was investigated. A 3-L lab-scale Pyrex reactor equipped with the temperature controller and water jacket was carried out. And, the sample was introducing into the sonication cell conducted with a constant power output sonicator. To study the inhibition of chlorinated by-products for organisms, we applied the dilution method in biochemical oxygen demands (BOD5) measurement as a surrogate method. Experimental results reveal that both initial pH value and ionic strength affect the removal of DOC, consumption of chlorine and formation of by-products due to the structure and composition of humic acids is changed by these two parameters. Furthermore, initial pH value and ionic strength affected the types of chlorinated by-products formation. When the chlorination reaction was conducted at acidic condition, it was found that the reduction of DOC was higher than basic condition. Also, the type of chlorinated by-products formation was affected by pH value. By means of the ultrasound/O2 method to pretreat 50 mg/L of humic acid solution, experimental result gives an effective increase of DOC removal and decrease of inhibition, and this method decreases the consumption of chlorine. Depending on this, it is estimated that the inhibition caused by the chlorination in humic acids solution could be reduced when the ultrasound/O2 pretreatment process is performed. However, experimental results also reveal that the ultrasonic process is effective to reduce the amount of chlorinated by-products and inhibition. When the ultrasonic process was controlled at the frequency of 20 kHz and amplitude of 120 mm, almost 100% of the chlorinated by-products were removed; the decrease of inhibition was 53.3%. In addition, there was a remarkable reduction in the concentration of DOC. The above results suggest that ultrasonic process can be designed as a final treatment process in the treatment of humic acids solution and ortho-chlorophenol wastewater.