預臭氧對加氯程序含鹵消毒副產物生成影響之研究

Effects of Pre-ozonation on the Halogenated Disinfection By-products Formation during Chlorination

莊朝欽(Chao-Chin Chuang)

指導教授 ： 蔣本基

共同指導教授 ： 張怡怡(E-E Chang)

國立臺灣大學/工學院/環境工程學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.00311

摘要

三鹵甲烷 (Trihalomethanes, THMs) 及含鹵乙酸 (Haloacetic acids, HAAs) 為一般加氯程序中常見、濃度高且廣為討論之含氯消毒副產物，因此過去數十年，許多學者均將研究焦點放在此二類消毒副產物之生成及控制。然而，近年諸多研究指出其它在加氯程序中亦會出現之消毒副產物如含鹵乙腈 (Haloacetonitriles, HANs)、三氯硝基甲烷 (Trichloronitromethane, TCNM) 及含鹵丙酮 (Haloketones, HKs)，儘管其出現濃度較低但其所具有之毒性及對人體之健康風險衝擊亦需被重視。為削減加氯消毒副產物之生成潛勢，臭氧程序為發展較完全且廣為利用之前處理。因此，本研究之主要目的係探討臭氧程序對HANs、HKs 及 TCNM生成之影響。
本研究係以金門太湖原水作為實驗之水源，其水中有機物含量較高 (約 8 mg L-1)，且一般而言，有機物於傳統淨水程序中較不易被除，因此在加氯程序中勢必具有消毒副產物生成潛勢之風險。本研究初步以長時間 (long-term) 加氯反應對 HANs、HKs及 TCNM 生成趨勢作初步討論 (pH = 7; 加氯量 40 mg L-1 as Cl2)，結果顯示 HANs 及 HKs於生成時會伴隨著水解之反應，因此當生成濃度達最高值，持續水解作用會降低其濃度。而原水加氯生成之 TCNM 濃度均低於5 µg L-1。
以臭氧程序作為前處理對於水中 THMs生成潛勢具顯著削減成效，但對於 HANs、HKs及 TCNM 之生成則產生了不同之效應。比較加氯時間 24 小時，臭氧劑量 8.0及 10.0 mg O3 min-1可減少 40-50% 之 HANs生成，但於加氯反應結束 (168 小時)，卻仍有較原水加氯所生成之 HANs 高之現象 (原水加氯約 2.1 µg L-1，而臭氧結合加氯之濃度則約為 7 µg L-1)，主要係由於臭氧化水進行加氯反應時，於後續水解速率較慢所造成。而於高臭氧劑量 (25.0 mg O3 min-1) 時，HANs之生成潛勢則有顯著之下降，同樣比較加氯時間 24 小時，HANs之生成約減少80%，而168 小時反應後，HANs之殘餘濃度約 1 µg L-1 (小於原水之濃度 2 µg L-1)。
有別於原水加氯 HKs之生成，臭氧結合加氯程序中，加氯反應初期有大量之 HKs 生成，可能係由於如丙酮等小分子前質於臭氧程序中大量生成，HKs生成之尖峰值發生於加氯反應 2-6 小時，生成濃度約介於 40-50 µg L-1，惟隨著加氯時間之增長，水解效應使得 HKs 濃度逐步降低，於 168 小時反應後，可見臭氧結合加氯所生成之 HKs 濃度略低於原水加氯者。
此外，臭氧結合加氯反應對於 TCNM生成有顯著之增加，推測可能係由於臭氧化程序中含硝基之前質大量生成。 加氯反應 168 小時後，生成濃度約30-50 µg L-1 (原水濃度 < 5 µg L-1)，且其生成濃度與臭氧劑量呈正相關。
由本研究結果顯示，評估臭氧程序對於加氯消毒副產物生成潛勢之影響，建議以長時間加氯反應評估 HANs、HKs及TCNM之生成趨勢，使臭氧對此些加氯消毒副產物削減效益評估能作更多面之考量。 此外，臭氧結合加氯程序所造成大量之 HKs 及 TCNM 生成亦可能造成飲用水之衝擊。

關鍵字

臭氧程序 ； 加氯程序 ； 含鹵乙腈含鹵丙酮 ； 三氯硝基甲烷

並列摘要

The effect of ozonation on the formation of haloacetonitriles (HANs), trichloronitromethane (TCNM), and haloketones (HKs) was evaluated. HANs such as dichloroacetonitrile (DCAN) and bromochloroacetonitrile (BCAN) and HKs such as 1, 1-dichloropropanone (1, 1-DCP) and 1, 1, 1-trichloropropanone (1, 1, 1-TCP) were studied. Factors (i.e., chlorine dose and pH) affecting HANs, TCNM and HKs formation were also evaluated. Ozone doses used in this study were 8.0, 10.0 and 25.0 mg O3 min-1. Results show high UV254 reduction (> 80%) and relatively low dissolved organic carbon reduction (40-70%) after ozonation, indicating that ozone may change significantly the chemical properties of natural organic matters presented in the raw water. However, undesired ozonation by-products such as aldehydes and ketones were also formed during ozonation process. Although the formation of DCAN and BCAN in ozonated water (at low ozone dose of 8.0 and 10.0 mg O3 min-1) were reduced; the residual DCAN and BCAN concentration were still higher than that of the raw water without ozonation. Unlikely, at high ozone dose of 25.0 mg O3 min-1, the formation of DCAN and BCAN formation can be reduced significantly. Moreover, the formation trends of HKs and TCNM changed in the ozonated water by chlorination. High HKs formations by chlorination of ozonated water were observed (Maximum 1, 1-DCP and 1, 1, 1-TCP concentrations were 8-10 and 31-48 µg L-1, respectively); however, continuous hydrolysis at longer reaction time decreased the formation of HKs rapidly. Ozonation prior to chlorination increased the TCNM formation significantly (e.g., 30-50 µg L-1 after 168 h); there was a good correlation between TCNM formation and ozone dosage, indicating that TCNM formation increased with increasing ozone dosage. The result implied that the formation of TCNM and HKs in the combined ozonation and chlorination processes should be of great concern.

並列關鍵字

Pre-ozonation ； Chlorination ； Haloacetonitriles (HANs) ； Haloketones (HKs) ； Trichloronitromethane (TCNM)

參考文獻

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