台灣的公共給水約有70 %來自於水庫，根據環保署對主要水庫水質之監測資料顯示，台灣主要水庫普遍都有優養化問題。而優養化問題之一為造成水中天然有機物(Natural Organic Matter, NOM)濃度增加，導致消毒副產物(Disinfection by-product, DBPs)生成之疑慮。由於DBPs對人體健康的危害性，所以日益受到重視，而控制DBPs之有效方法，為減少NOM這類前驅物質(Precursor)與氯接觸之機會，包括混凝或薄膜處理以去除前驅物質等。
本研究主要探討水中各類有機物去除及DBPs生成之關聯，並採集路竹原水及太湖慢砂濾出水以做為研究標的。其中對路竹原水進行高錳酸鉀前氧化搭配混凝試驗，而對太湖慢砂濾出水進行混凝處理及UF過濾試驗。水質分析方面除了pH值、濁度、UV254、NPDOC、THMFP及HAA9FP等參數外，更利用高效能粒徑排除層析儀(HPSEC)連接線上OC 偵測器及UV/Vis偵測器分析水中有機物之分子量分布及特性，並搭配Peak-fit軟體模擬量化HPSEC之OC圖譜中各個有機物族群面積。
混凝試驗結果顯示，路竹原水HPSEC之OC圖譜中的Peak a (Biopolymers)及Peak b (Humics substances)，為主要去除的有機物族群，其中明礬對此兩個Peaks之去除明顯優於氯化鐵。而在太湖慢砂濾出水方面，結果亦顯示Peak a及Peak b能有效的被去除。另外混凝對於消毒副產物生成之減少，與對Peak a及Peak b去除之趨勢相同，因此推斷兩者所含有機物為重要的THMFP及HAA9FP物質。
高錳酸鉀氧化試驗結果顯示，高錳酸鉀主要將路竹水中有機物由大分子轉變為小分子但無去除現象，對消毒副產物之降低不明顯，推測由大分子轉變的小分子部分仍可與氯生成消毒副產物。在高錳酸鉀前氧化搭配混凝試驗部分，雖然前氧化造成路竹水中Peak a因轉變成小分子而減少，同時導致Peak c (Building Blocks)及Peak d (LMW Acid and Humics)增加，然而搭配混凝處理可使Peak c及Peak d之去除率與單純混凝相近，代表由Peak a轉變的小分子仍可被混凝去除。而此試驗所選擇的前氧化劑量對路竹消毒副產物生成影響甚微，但搭配混凝處理對THMFP降低較單純混凝來得佳，根據有機物去除結果推測是因Peak a所轉變的小分子仍可被去除，而這些小分子仍具有消毒副產物潛勢，尤其THMFP。最後UF過濾試驗顯示，太湖水中Peak a為主要被去除的有機物族群，而Peak a之減少對THMFP及HAA9FP降低有不錯的效果，證實Peak a為消毒副產物重要之前驅物質。

The relationship between NOM removal and DBPs formation
Yung-Chen Chou
Hsuan-Hsien Yeh
Department of Environmental Engineering, NCKU.
SUMMARY
Due to its adverse effect on human health, disinfection by-products (DBPs) problem, especially trihalomethane (THM) and haloacetic acid (HAA), has received considerable attention recently. The effective way to control the DBPs formation is avoiding the contact between natural organic matter (NOM) and chlorine. The main purpose of this study is to understand the relationship between the removal of NOM species and DBPs formation. Two water samples, Luju raw water (LJ) and Taihu slow sand filtration effluent (TH), were chosen as the targets. Coagulation tests combined with permanganate (KMnO4) preoxidation were conducted for LJ, while coagulation and UF filtration were conducted for TH. Water quality analysis included pH, turbidity, UV254, NPDOC, THMFP (FP, formation potential) and HAA9FP. Moreover, high performance size exclusion chromatography (HPSEC) with UV/Vis and OC detectors was used for characterize NOM, based on molecular size distribution. The coagulation results of both LJ and TH waters indicated that organics in the Peak a (Biopolymers) and Peak b (Humic substances) of HPSEC-OCD chromatograms were important DBPs precursors. The results from coagulation combined with KMnO4 preoxidation with LJ water indicated that the treated water had lower THMFP than that from sole coagulation. The reason might be that the LMW organics, produced by KMnO4 preoxidation, were still DBPs precursors, and which could be removed by coagulation. The result from UF filtration of TH water shows that Peak a was the major organic fraction removed by UF membrane. The corresponding reduction in THMFP and HAA9FP also indicates that Peak a was important DBPs precursors.
Key words: Coagulation, DBPs, KMnO4, NOM, HPSEC
INTRODUCTION
In Taiwan, about 70 % of the source water for public water supply come from reservoirs. However, based on the water quality monitoring program conducted by the Environmental Protection Administration, many major reservoirs have eutrophication problem, which may cause the increase in NOM concentration and further DBPs problem. Due to its adverse effect on human health, DBPs problem has drawn much attention recently. The effective way to control DBPs formation is avoiding the contact between NOM and chlorine. Therefore, if we could decrease the NOM concentration before chlorination by pretreatment processes, such as coagulation, membrane filtration; and understand which NOM species could be important DBPs precursors, it would be a benefit for controlling DBPs formation.
In this study, two water samples, Luju raw water (LJ) and Taihu slow sand filtration effluent (TH), were chosen as the targets. Coagulation test combined with permanganate (KMnO4) preoxidation were conducted for LJ, while coagulation followed by UF filtration were for TH. Water quality analysis included pH, turbidity, UV254, NPDOC, THMFP and HAA9FP. Moreover, HPSEC connected with OC and UV detector was used to characterize the NOM based on molecular size distribution. Also the peak-fit method was applied to model the NOM species area in HPSEC chromatogram. The main purpose of this study is to understand the relationship between NOM removal and DBPs formation in different processes.
MATERIALS AND METHODS
Coagulation test: The samples were coagulated by alum (Al2(SO4)3．18H2O, Merck, Germany) and FeCl3 (Katayama, Japan) with the conventional jar test apparatus (Jar tester, Phillips & Bird, Richmond, Virginia). Six 1.0 Liter jars were used and each was filled with the pre-filtered source water.
KMnO4 oxidation test: KMnO4 stock solution was prepared by dissolving 10.0 g KMnO4 (Merck, Germany) in 1 liter deionized water (MilliQ water, Millipore). Then KMnO4 oxidation test was carried out with the conventional jar test apparatus (same procedure as coagulation test). The KMnO4 residual concentration measurement was based on Standard Methods for the Examination of Water and Wastewater (20th ed., APHA, AWWA, & WEF. 1998).
UF membrane filtration: Membrane filtration was conducted with bench-scale dead-end membrane testing system under room temperature (23 ± 2 oC). The membrane materials included PVC (Polyvinyl Chloride), CA (Cellulose Acetate), PVDF (Polyvinylidene Fluorides) and PS (Polysulfone).
Water quality analysis: The analysis items included nonpurgeable dissolved organic carbon (NPDOC), ultraviolet absorbance at 254 nm (UV254) and turbidity. Also the samples were analyzed for DBPFP (THMFP and HAA9FP). All analysis procedures were based on Standard Methods. Turbidity measurement was carried out by a turbidity meter (Model 2100N, Hach, USA). NPDOC was measured by using a total organic carbon analyzer (Model TOC-500, Shimadzu, Kyoto, Japan). UV254 was measured by a UV/Vis spectrophotometer (Model U-2001, Hitachi, Japan). THMFP and HAA9FP were analyzed by gas chromatograph with electron capture detector (GC-ECD, Agilent - 6890 series, USA) Samples for NPDOC, UV254 and DBPFP measurement were filtered through 0.45 μm membrane (Advantec, Japan) before analysis.
The composition of dissolved organic matter: High performance liquid chromatography (HPLC, LC-20 ATV, Shimadzu, Japan)- size exclusion chromatography (SEC) was conducted with sequential on-line detectors consisting of UVD (254 nm, SPD-20A, UV-VIS detector, Shimadzu) and OCD (modified Sievers Total Organic Carbon Analyzer 900 Turbo, GE Water & Process Technologies). Chromatograms were analyzed using PeakFit software (Version 4.12, Systat Software Inc., USA, CA) to resolve the overlapped peaks and to determine the area under each peak.

RESULTS AND DISCUSSION
The coagulation result of LJ indicates that the Peak a (Biopolymers) and Peak b (Humic substances) in HPSEC-OCD were the main organic fractions removed, and alum had much better removal on these two NOM fractions than FeCl3. The coagulation result of TH also confirms that Peak a and Peak b could be removed more effectively than other peaks. Furthermore, the decrease of DBPs is similar to the trend of NOM removal in coagulation. Therefore, Peak a and Peak b were assumed to be the important precursors for THMFP and HAA9FP.
In permanganate preoxidation test for LJ, the result shows that KMnO4 could oxidize high molecular NOM into lower molecular ones, but no removal was observed. KMnO4 preoxidation could slightly lower DBPs formation, and it was also noticed that the low molecular NOM, generated by oxidizing high molecular NOM, could still form DBPs. In the part of coagulation combined with KMnO4 preoxidation (1 mg/L), the results shows that preoxidation caused the decrease in the area of Peak a, and the increase in the Peak c (Building blocks) and Peak d (LMW acid and humics), probably through the oxidation and breakdown of large MW organics into lower ones. Further, the results also show that these lower MW organics could be removed in the following coagulation step under higher coagulant dosages. In DBPs test, the preoxidation dosage used did not change the DBPs formation, but the following coagulation could lower THMFP better than sole coagulation. It is conjectured that low MW organic species, which were formed by preoxidation of high MW species (Peak a), still could be the precursors of THM. However, these also could be removed by coagulation.
Further, the result from UF filtration of TH water shows the Peak a was the major organic fraction removed by UF membrane. The corresponding reduction in THMFP and HAA9FP also supports the previous statement that Peak a was important DBPs precursors.
CONCLUSION
In this study, there are several important findings: (1) Peak a (Biopolymers) and Peak b (Humic substances) in HPSEC-OCD could be important DBPs precursors, (2) Coagulation with KMnO4 preoxidation could lower THMFP than sole coagulation, (3) In UF filtration, it confirmed that Peak a (Biopolymers) could be important DBPs precursors.

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