高級氧化處理程序對於游泳池中消毒副產物生成之影響

Abstract

游泳池普遍會透過加氯消毒程序以維持水質安全並避免水媒疾病的傳播。不過在加氯消毒的過程當中，游泳池中的天然有機物以及泳客在游泳過程中所產生的有機物 (例如汗液及尿液) 會與氯進行反應，進而產生對人體健康造成危害的消毒副產物，包括三鹵甲烷 (Trihalomethanes, THMs)、含鹵乙酸 (Haloacetic acids, HAAs)以及含鹵乙腈 (Haloacetonitriles, HANs) 等。然而游泳池基於維護以及管理成本的考量，大多會使用水循環系統且鮮少更換池水，也因此增加有機前質與氯的反應機會及時間，進而導致游泳池水中消毒副產物的持續生成並且不斷地累積在泳池當中，也使得泳客有較高的消毒副產物暴露量。因此，為了減少游泳池水中的消毒副產物，除了透過定期換水之外，也能利用高級氧化處理程序 (例如UV/chlorine及UV/H2O2) 當中所生成的自由基，利用其高氧化力將有機前質降解成中間副產物甚至是無機物。以UV/H2O2為例，過程中所產生的氫氧自由基，能夠有效地將大分子有機物降解成小分子，同時也能夠有效地減少消毒副產物的生成潛能。 本研究首先針對游泳池進行環境採樣，監測並了解水質變化以及消毒副產物濃度。採樣地點為國立台灣大學綜合體育館溫水游泳池，採樣時間分別為2016年八月、十月以及2017年二月。其後對於不同高級氧化處理條件進行批次模擬實驗，比較不同紫外光強度以及氧化處理程序對於水中非氣提性溶解性有機碳 (non-purgeable dissolved organic carbon, NPDOC)的降解趨勢、消毒副產物的減少及其有機前質的降解效率之影響。 環境採樣結果顯示此游泳池的水質特性、NPDOC以及消毒副產物濃度趨勢變化並不明顯。由於游泳池是使用先臭氧後加氯的消毒程序，因此消毒副產物濃度略不同於加氯消毒的泳池，尤其是以含鹵乙酸的減少較為明顯，此情形也與過去文獻的觀察相符。 關於高級氧化處理條件改變的影響，首先紫外光強度對於高級氧化處理效率有很顯著的影響，不論是NPDOC的減少、消毒副產物以及其前質的變化和降解都隨著紫外光劑量上升以及氫氧自由基生成量增加而有所提升。然而當紫外光強度不足時，即使給予足夠的氧化時間對於氧化初期所增加的含鹵乙酸前質仍然無法有效地降解。 至於不同氧化處理方法的影響，結果顯示單獨使用UV以及UV/chlorine處理對於有機物的礦化作用影響較不顯著；反觀UV/H2O2氧化過程中，隨著氫氧自由基的增加，有機碳濃度也隨之下降。消毒副產物的部分，在三種不同處理方法之下三鹵甲烷均較含鹵乙酸難以降解，因其含有立體結構所以不易被光解。此外，氫氧自由基對於具有立體結構之化合物有較小的反應速率常數，因此需要較長的反應時間才能有效地降解。在UV/chlorine反應過程當中，消毒副產物濃度隨反應快速地增加，包括三鹵甲烷、含鹵乙腈等，即便反應一段時間後能夠減少其含量，但相較於未反應前之濃度仍有明顯地增加。另外，單獨UV處理會增加含溴之三鹵甲烷之生成比例，此現象可歸因於含溴大分子有機物經由光解後，會促使溴離子的生成，並於後續加氯過程中形成次溴酸，促使含溴消毒副產物生成。 有機前質經過三種不同處理方法之後，其變化趨勢均略有不同。單獨UV處理之後會使黃酸類物質增加，而此與三鹵甲烷之生成潛能上升之結果相符。有機物經過UV/chlorine處理過後，可以看到明顯的減少趨勢，推測可能與有機物於處理過程中與氯進行反應產生消毒副產物有關；而經過UV/H2O2處理後可觀察到芳香族蛋白質類的化合物於反應初期產生，此情形也與消毒副產物的生成潛能於反應初期上升有關。

Chlorine-based disinfectants are widely used in swimming pools to maintain water quality and inhibit the spreads of waterborne diseases. During chlorination, natural organic matter (NOM) and swimmers-derived organic matter (such as perspiration and urine) will react with chlorine to generate disinfection by-products (DBPs) such as trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs) and which are harmful to human health. However, owing to the cost of maintenance and management, most of swimming pools use recirculation system and seldom replace the whole pool water with fresh water, result in the accumulation of DBPs in water thus swimmers will have higher exposure of DBPs. In addition to replace pools water frequently, DBPs can also be minimized by the free radicals generated from advanced oxidation processes (AOPs), including UV/chlorine and UV/H2O2. The high oxidation power of free radicals can degrade organic precursors into intermediate by-products or inorganic matters. Taking UV/H2O2 for example, the formation of hydroxyl radials can efficiently degrade higher molecular weight organic matters into smaller species and reduce the DBPs formation potentials (DBPFPs). The first part of this study was field sampling for monitoring of water quality and the occurrences of DBPs. The sampling location was National Taiwan University (NTU) Sports Center indoor swimming pool and the samples were taken in August, October of 2016 and February of 2017. Secondly, bench scale simulations were conducted with different operation conditions of AOPs to compare their effects on non-purgeable dissolved organic carbon (NPDOC) degradation, DBPs formation and DBPs precursors’ reductions. The results of field sampling showed that the variations of water quality including NPDOC and DBPs were not apparent. Owing to the type of disinfectant in the swimming pool was ozone combined with chlorine, the concentrations of DBPs were slightly differ from those observed in chlorinated swimming pools; especially the HAAs reduction which was consistent with previous studies. As for the change of operation conditions during AOPs, the results showed that increases of UV intensities had significant effects on NPDOC reduction, DBPs and their precursors’ alterations and degradation; and the efficiencies increased with the increasing UV intensities. However, when the UV intensities were insufficient, the HAAs precursors were be increased and a longer oxidation time could not efficiently degrade the HAAs precursors. As for the effects on organic matter among various oxidation processes, single UV and UV/chlorine treatments had slightly effects on organic matter mineralization; however, the NPDOC concentrations decreased gradually with the generation of hydroxyl radicals during the UV/H¬2O2 processes. The degradation efficiencies of HAAs were better than those of THMs among different oxidation treatments because THMs had steric hindrance itself therefore they were hard to be oxidized by free radicals or UV irradiation. In the reaction of UV/chlorine, concentrations of THMs, HANs and other DBPs would increase rapidly. Although DBPs concentrations decreased after a longer oxidation time with UV/chlorine treatments, they were still higher than the initial DBPs concentrations. Additionally, the reactions of single UV would increase the portion of Br-THMs which could be attributed to the release of bromide ion from large molecular compound and promoted the formation of hypobromous acid (HOBr). The tendencies of organic precursors among various oxidation processes were different. Through the UV treatments, the fulvic acid-like organic matters would increase and which were coincided with the elevated THMFPs. In the UV/chlorine treatments, it could be observed that organic matters had apparent degradation which could be associated with organic matters reacted with chlorine for the formation of DBPs; while during UV/H2O2 treatments, the portion of aromatic protein compounds increased initially, thus this was slightly consistent with the increasing DBPFPs.