以液相非熱電漿技術降解高濃度酚類廢水之研究

Degradation of High Concentration Phenolic Wastewater by Non-thermal Plasma Technology

吳欲齊(Yu-Chi Wu)

指導教授 ： 陳孝行

國立臺北科技大學/工程學院/環境工程與管理研究所/碩士(2008年)

摘要

本研究採用「非對稱性電極」之放電方式，自製研發不鏽鋼針-板放電系統，藉由氣電混合放電分別處理酚(phenol)、鄰苯二酚(catechol)及鄰-甲酚(o-cresol)三種酚類廢水。本研究之放電系統藉由中空不鏽鋼注射針頭通氣並進行放電，以減少放電時能量之損耗為其主要優點。本研究之實驗參數如下，利用外接高壓電源供應器提供電流2mA、4mA及6mA；放電系統之電極間距固定為1cm及3cm；曝氣源氣體分別為空氣、氬氣與含氧量10%及30% 之氣體並以150ml/min通入系統，於系統內分別置入濃度100 mg/L酚、鄰苯二酚及鄰-甲酚之水樣50ml進行放電試驗。
本實驗結果顯示當系統通入電流6mA對酚之去除效果最佳，反應60分鐘後酚可完全去除，然而系統通入2mA及4mA酚仍有53%與30%殘存於水樣中，此外污染物之反應速率隨著電流提升而增加，當電流為2mA時，酚之反應速率常數為0.0087 min-1，當電流為6mA時，酚之反應速率常數提升為0.0732 min-1，主要原因系統通入較高電流，會使放電系統於高電壓下進行放電，於此情況下較容易誘發出具強大能量的電場，高能電子更易與空氣及液體分子產生碰撞，故有解離、激發或離子化等現象產生，而使污染物去除率較佳。此外，調整系統電極間距會影響系統所產生的電場強度，而間接影響實驗處理效率。當電極間距1公分時，放電通道較易形成，因此導致故較多電場能量蓄積於水中，故放電60分鐘後三種酚類污染物皆能完全去除；電極間距3cm放電60分鐘，除鄰苯二酚能完全去除，酚與鄰-甲酚分別仍有14%及9%殘存於水樣中。此外，系統通入含氧量較高之氣體進行放電有助於H2O2之產生，藉由空白試驗當系統以含氧量30%之氣體進行曝氣，水樣經放電60分鐘後有41.29 mg/L H2O2存在，因此酚之降解效率及反應速率較佳；然而放電系統曝以含氧量0%之氣體，放電後之水樣中僅有13.05 mg/L H2O2，故三種酚類污染物去除效果及反應速率較差，因此驗證酚類污染物降解過程中活性物種多寡為主要關鍵之一。
綜合上述之實驗結果，當系統通以電流6mA、系統間距1cm及以空氣為曝氣源進行放電，為本研究之放電系統最佳放電參數，三種100 mg/L酚類污染物於放電反應時間60分鐘內均可達到100%去除。降解過程中，酚類污染物因活性物種之強氧化能力，最終部份可氧化成為有機酸物質及其他中間產物存在於水樣中，如：苯醌類物質，甲酸，乙酸，故可證實液相非熱電漿技術不但可降解水中有機污染物之濃度與毒性，亦不會造成二次污染等問題，即符合綠色化學之潮流。

關鍵字

非熱電漿 ； 過氧化氫 ； 酚 ； 鄰苯二酚 ； 鄰-甲酚

並列摘要

In this research, a newly designed stainless-steel hollow needle in the anode to achieve gas-electricity mixture in a liquid-phase non-thermal plasma system was utilized to simulate the treatment of industrial phenolic wastewater with a concentration of 100mg/L. The main advantage of this system is to purge gas through the needle in order to provide oxygen into the system and form active species like hydroxyl radical, and H2O2 easily. Phenol, catechol and o-cresol were selected as the target pollutants to be oxidized by active species with high oxidizing potential, such as hydroxyl radical, H2O2 and ozone. The current, electrode gap and gas type were the experimental parameters in this research.
The removal efficiency and reaction rate of phenolic compounds were highest when the current was 6 mA in this study due to stronger electric field and more energize electrons with higher voltage. Phenol was degraded completely and the pseudo-first-order rate constant kobs was 0.0732 min-1 after 60 minutes. The experimental results also indicated the removal efficiency was enhanced with a shorter electrode distance that increased the intensity of the electric field. When the electrode gap was 1cm, 100% of phenolic compounds were degraded at the corona discharge of 60 minutes, results from the formation of plasma channel to deposit more energy into the solution to make high phenolic removal in such a short electrode gap. However, when electrodes were placed at a longer distance in the discharge system, catechol was completely removed, but there were only 86% of phenol and 91% of o-cresol removed in the solution after 60mins. The efficiency of phenolic compounds removal was furthermore affected by gas type. Higher concentration hydroxyl peroxide was measured when air was bubbled into discharge system. After discharging, 34.19 mg/L hydroxyl peroxide was produced with air bubbles in 60 minutes; however, only 13.05 mg/L hydroxyl peroxide was produced in 60 minutes with argon bubbles. The degradation efficiency of phenolic compounds and reaction rate were higher with the addition of air than with the addition of argon, indicating hydroxyl peroxide played a crucial role in the removal of phenolic compound.
To summarize the above experimental results, 6mA input current, 1cm electrode gap and air bubbling were the optimum experimental parameters in this research with complete phenolic compound degradation in 60 minutes. The rate constant of phenol, catechol and o-cresol were 0.0665, 0.2382, and 0.1131 min-1, respectively. Phenolic compound was oxidized to organic acids or other intermediates such as formic acid, acetic acid, and quinine during the degradation process.

並列關鍵字

Non-thermal plasma ； hydroxyl peroxide ； phenol ； catechol ； o-cresol

參考文獻

[41] 鄭立群，以非熱電漿處理CF4 及SF6 之效率探討，碩士論文，國立中央大學，桃園，2006。

[84] 張榕峻，應用還原性氣體於零價鐵填充床處理NOx之研究，碩士論文，國立台北科技大學環境規劃與管理研究所，台北，2006。

[1] K.-C. Loh, T.-S. Chung, and W.-F. Ang, "Immobilized-cell membrane bioreactor for high-strength phenol wastewater," Journal of Environmental Engineering. vol. 126, no. 1, 1999, pp. 75-79.

[3] G.J. Mileski, J.A. Bumpus, M.A. Jurek, and S.D. Aust, "Biodegradation of pentachlorophenol by the white rot fungus Phanerochaete chrysosporium.," Applied and Environmental Microbiology. vol. 54, no. 12, 1988, pp. 2885-2889.

[6] J.K. Jokela, M. Laine, M. Ek, and M. Salkinoja-Salonen, "Effect of biological treatment on halogenated organics in bleached kraft pulp mill effluents studied by molecular weight distribution analysis," Environmental Science and Technology. vol. 27, no. 3, 1993, pp. 547-557.