- 學位論文
UV/H2O2高級氧化程序處理藻類和活性污泥對其消毒副產物生成影響之研究
Effects of UV/H2O2 Oxidation Process on Disinfection By-products Formation for Algae and Activated Sludge
摘要
自來水廠淨水流程中普遍透過加氯消毒程序以避免微生物生長並控制水媒傳染疾病發生。但在加氯消毒過程中氯會和有機物質反應生成各種消毒副產物(Disinfection By-Products, DBPs)，例如三鹵甲烷(Trihalomethanes, THMs)、含鹵乙酸(Haloacetic acids, HAAs)及含鹵乙腈(Haloacetonitriles, HANs)等。這些消毒副產物可能會使人類產生致癌或其他不良健康效應。為了避免消毒副產物的產生，部分自來水廠會使用高級氧化程序以提升飲用水的水質安全。UV/H2O2是一種很有效的高級氧化方式，透過氫氧自由基將有機物質降解成二氧化碳、水及其他小分子有機酸，減少消毒副產物的前質以降低後端加氯消毒所生成之消毒副產物的濃度。除了淨水流程之外，部分污水處理流程也會使用高級氧化程序使處理過後的汙水更具可利用性。 過去的文獻大多著重於UV/H2O2對於天然有機物質或常見污染物質的氧化效果，鮮少有研究討論UV/H2O2處理含微生物水體後對水質的影響。本研究觀察以UV/H2O2氧化程序處理過的藻類與活性污泥所釋放出有機前質的變化，量測氧化後之水體中非氣提性溶解性有機碳(non-purgeable dissolved organic carbon, NPDOC)和溶解性有機氮(dissolved organic nitrogen, DON)濃度的改變，並探討對消毒副產物生成之影響。評估因子包括不同初始H2O2濃度、不同初始pH值、不同粒徑之有機質、不同消毒劑及溴離子與氯離子的競爭效應等對於UV/H2O2氧化效能或對消毒副產物生成潛能的影響。最後比較生物性樣本與非生物性樣本包括污水(代表人為有機質)及生態池水(代表天然有機質)之消毒副產物生成潛能的差異。 實驗結果顯示活性污泥及藻類在經過UV/H2O2氧化後，有機物質會被釋出但隨後再被降解，因此NPDOC濃度會隨著反應時間呈現先升後降的趨勢。含氮有機物質較不易被降解，因此DON濃度的下降趨勢較不明顯。消毒副產物之生成趨勢與NPDOC一致，但可以看到不論是活性污泥還是藻類樣本，THMs生成均較HAAs生成先達到最高濃度，這表示THMs前質較易被鹵化生成消毒副產物，但也易因UV/H2O2的氧化而降解；而HAAs之前質則需要較充足的氧化才易進行鹵化作用。 添加0.1% H2O2可氧化出較高濃度之NPDOC，亦可持續降解這些有機物質，而0.05%及0.01%之H2O2由於氧化力不足，較不易降解污泥釋出之有機物質。鹼性環境下H2O2的鹼性水解作用會導致氧化效能降低而使有機物質的降解率下降，因此不論藻類或是污泥在鹼性環境下均有最高之NPDOC濃度生成；然而酸性環境下的變化較不一致。經0.22、0.45和1.0 μm三個粒徑濾膜過濾的有機質經消毒副產物生成潛能試驗結果顯示不同粒徑有機質並未偏好產生特定的消毒副產物。此外添加溴離子之後，由於HOBr具有較強的鹵素取代能力，因此總含溴消毒副產物的比例及總消毒副產物的濃度會隨著所添加之溴離子的濃度而上升。總THMs濃度隨著所添加溴離子濃度而上升的趨勢較明顯，然而總HAAs之濃度上升的幅度較小甚至下降。HKs及其他含氮消毒副產物的濃度會隨著所添加溴離子的增加而下降。 在各有機物種比較方面，污水樣本每一單位NPDOC具有最高濃度之消毒副產物生成潛能，其次為活性污泥和生態池水，藻類之消毒副產物生成潛能最低。活性污泥及藻類等生物性樣本主要生成之消毒副產物會隨著氧化時間由THMs轉變成HAAs；汙水樣本較易生成HAAs；而生態池水樣本則較易產生THMs。添加溴離子之後，各樣本之含溴THMs及HAAs的濃度均會增加並導致總含溴消毒副產物比例的上升。在各物種生成潛能方面，藻類及生態池水樣本在添加溴離子之後消毒副產物生成潛能增加量較高，而污水樣本因為需要較高之氧化力以進行鹵化作用，因此低氧化力的HOBr反而降低其消毒副產物生成潛能。以氯氨進行消毒副產物生成潛能試驗可發現各有機物種生成之消毒副產物均大幅下降，HAAs在各物種中均成為優勢產物，此外含溴之HAAs濃度並未明顯改變因此提高了含溴消毒副產物所佔之比例。
並列摘要
Chlorination has been widely used in drinking water supply systems for control of the growth of microorganisms; however, the formation of various disinfection by-products (DBPs) such as trihalomethanes (THMs), haloacetic acids (HAAs) and haloacetonitriles (HANs) in chlorination has been concerned due to their potential carcinogenicity and other adverse health effects. To avoid the generation of DBPs, advanced oxidation processes (AOPs) such as UV/H2O2 process have been applied as a substitute for pre-chlorination. Most studies focused on the effects of UV/H2O2 on specific chemical pollutants; however, the influences on water quality after treating microorganisms by UV/H2O2 are still unclear. This study focuses on the changes of DBPs precursors and DBPs formation potential (DBPFP) after the treatment of activated sludge and algae by UV/H2O2 oxidation. Non-purgeable dissolved organic carbon (NPDOC) and dissolved organic nitrogen (DON) were measured; subsequently, DBPs including THMs, HAAs, HKs and HANs were analyzed after DBPFPs tests. Moreover, the effects of different initial H2O2 concentrations, initial pH disinfectants and the role of Br− were discussed. The characteristics of biological organic matter were also compared with which of anthropogenic organic matter (domestic sewage samples) and natural organic matter (ecological pond water samples). After the UV/H2O2 oxidation, the experimental results showed that the organic matter was released from the samples of activated sludge and algae and soon was degraded, which caused that the NPDOC and DON of the tested samples could increase in the beginning and then decrease. The trends of DBPs were similar to that of NPDOC; however, the occurrence of highest THMs concentration was earlier to that of HAAs. Comparing to using 0.05% and 0.01% initial concentrations of H2O2, using 0.1% H2O2 produced more NPDOC but could also keep on degrading the organic matter released from the microorganism samples. Higher NPDOC concentrations also could be produced when oxidation were conducted under the basic conditions. Moreover, there was no specific DBPs speciation from organic particulates with different sizes (0.22, 0.45 and 1.0 μm) after disinfection. Due to the stronger halogenation ability of bromine, the proportions of Br-DBPs and the concentrations of total DBPs could increase with the amounts of Br−. Comparing the four different sources of organic matter, the highest DBPFP/NPDOC occurred in the domestic sewage samples; and then was in the activated sludge samples and the ecological pond water samples; the algae samples had the lowest DBPFP. Moreover, the dominant species shifted to HAAs form THMs in the samples of activated sludge and algae with the oxidation time. More HAAs could be generated in the domestic sewage while the ecological pond water samples could produce more THMs. The brominated species of THMs and HAAs could increase in all the samples after the addition of Br−; moreover, the increased amount of DBPFP was much higher in the algae and the ecological pond water samples while the lower oxidizing capacity of HOBr reduced the DBPFP of the domestic sewage due to the higher demand of the domestic sewage for oxidation before halogen substitution. The DBPFP generated from the chloramination was much lower than which from the chlorination. HAAs became the dominant species in all the samples. However, the unchanged Br-HAAs concentrations caused the increased proportion of brominated species in HAAs.
參考文獻
延伸閱讀
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