藻類有機物之含碳消毒副產物的生成與預測

Formation and prediction of carbonaceous disinfection byproducts from algogenic organic matter

許立強(Lap-Cuong Hua)

指導教授 ： 黃志彬

國立交通大學/工學院/環境工程系所/博士(2018年)

摘要

藻類優養化造成大量水中藻類有機物(algogenic organic matter, AOM)如藻體與藻類代謝物的生成，一直是影響淨水場的操作效能的關鍵因素。這些藻類有機物在淨水程序中通常無法藉由混沉及過濾的程序去除，進而在消毒的過程中形成消毒副產物(disinfection by-products, DBPs)而影響用水安全。因此，藻類有機物的去除是飲用水處理的重要議題。現今，研究大都探討藻類有機物的特性和消毒副產物的生成潛勢，對於藻類有機物生成之消毒副產物的原理和預測研究之極為有限。因此，本研究目的為 (1)探討不同藻種生成的消毒副產物生成潛勢(disinfection by-product formation potential , DBPFP)；(2, 3)以不同生長期的藻類之光學特性與分子量預測消毒副產物的生成量；(4)評估不同分子量之藻類有機物在預測消毒副產物時所扮演的角色；(5)溴對不同生長期的藻類之消毒副產物生成的影響。其中，含碳的消毒副產物(carbonaceous DBPs, C-DBPs)以三鹵甲烷(trihalomethanes, THMs)和鹵乙酸(haloacetic acids, HAAs)最為常見。藻類有機物可以細分為胞內有機物(intracellular organic matter, IOM)、胞外有機物(extracellular organic matter, EOM)和細胞有機物質(cell-bound organic matter, COM)，其光學特性可透過吸光值(UV254和UV280)、三維螢光光譜(excitation-emission matrix, EEM)分析有機物結構組成和高效能分子篩層析儀(high-performance size exclusion chromatography, HPSEC)進行分子量量測，並藉此特性來預測消毒副產物生成。
相較於EOM和COM，IOM擁有較多的芳香族和脂肪族蛋白且可產生最多的三鹵甲烷和鹵乙酸前驅物。雖然COM跟IOM有相似的化學結構但由於其成分含量比較低，使得C-DBPs生成較少。而EOM則因含較多不利於氯的取代基，故C-DBPs的生成量也較低。
藻類生長過程中，其UV254和UV280皆很低。IOM主要的成分為類芳香族蛋白質和類溶解性微生物質，平均螢光強度(average fluorescent intensity, AFI)為80%；EOM則是主要由類腐植酸與類黃酸(60% AFI)組成。由消毒副產物生成潛勢試驗結果顯示不同生長階段的藻類會有不同的THMFP和HAAFP；相關性分析結果顯示吸光值與THMFP和HAAFP呈現低度相關。反之，各組成之AFI值與HAAFP (R2 = 0.879, p < 0.01)和C-DBPFP (R2 = 0.846, p < 0.01)則具有關聯性。相較於吸光值，EEM的分析結果可作為一有效預測含藻原水之消毒副產物生成的依據。
HPSEC的分析結果顯示AOM的peaks A和B (生物聚合物)和peak C (腐植質)對C-DBPs的生成具有顯著相關性，主要係因其結構中含有較多的芳香族和碳-碳雙鍵。故將HPSEC結合EEM分析可有效提升對含藻原水的消毒副產物生成潛勢的預測能力(R2 > 0.7, p < 0.05)，特別是THMs的生成。
AOM的分子量大小為影響消毒副產物生成多寡的重要因子。大分子物質(> 30 kDa)因其富含可作為電子提供者之官能基和含碳的類芳香蛋白質和類溶解性微生物質，因此相較於低分子量物質(< 30 kDa)，能產生較多的C-DBP。其中大分子量物質會產生較多的HAAs，小分子量物質生成的消毒副產物則以THMs為主。
藻類的DBPs生成的種類和含量也會受到溴存在的影響，其會取代氯和消毒副產物的前驅物質之作用，進而降低三氯甲烷(chloroform, TCM) ，一氯乙酸(monochloroacetic acid, MCAA) ， 二氯乙酸(dichloroacetic acid, DCAA) 和三氯乙酸(trichloroacetic acid, TCAA)的生成量，但同時會顯著增加含溴副產物的含量。透過溴含量和螢光物質的量測能提供一有效預測消毒副產物生成和控制的方法。

關鍵字

消毒副產物 ； 藻類有機物 ； 螢光物質 ； 分子篩層析 ； 加氯消毒

並列摘要

Algal eutrophication in fresh water frequently challenges the effective performance of water treatment plants (WTPs) because of its exponential rise in the algogenic organic matter (AOM), including OM from the cell and algal metabolism. As AOM is not amendable to remove by traditional coagulation/sedimentation/filtration processes, it is a critical issue for sustainable treatment of drinking water. Importantly, AOM has a strong tendency to remain and react with downstream disinfectants. AOM is thus well-known as a major organic precursor of disinfection by-products (DBPs). Its occurrence in water undesirably worsens the safety of drinking water.
To date AOM characterization and its associated DBP formation potential have been subjected elsewhere, however, limited work has paid attention to in-depth studies on the principle and prediction of AOM-derived DBP formation. The aims of this study were (1) to investigate the formation potential of AOM-derived DBP formation from different AOM origins, (2, 3) to characterize AOM optical and molecular weight (MW) properties within algal growth for the prediction of AOM-DBP formation; (4) to examine the role of MW properties of AOM on the formation of AOM-DBP; (5) to reveal the effects of bromide on AOM-DBP formation within algal growth. Two major classes of carbonaceous DBPs (C-DBPs) were subjected in this study, which was trihalomethanes (THMs) and haloacetic acids (HAAs) because they are mostly-generated DBPs after the chlorination and are regulated worldwide. AOM from different origins, including intra- (IOM), extra- (EOM), and cell-bound organic matter (COM), were fully investigated. Optical properties including chromophores (UV254 and UV280 absorbance) and fluorophores (excitation-emission matrix – EEM) were used for AOM characterization and its DBP formation prediction. Characterizing MW profile of AOM was carried out by high-performance size exclusion chromatography (HPSEC) coupled with a peak-fitting technique to comprehensively extract the overlapping MW information in SEC chromatograms. The principle of AOM-derived DBP formation was explored by nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS).
Of the AOM origins, IOM was the highest-yielding precursor of both THMs and HAAs because its chemical structure was richest in aromatic and aliphatic protein moistures compared to EOM and COM. Although COM precursor had similar chemical structures to IOM, its quantitative contents were much lower, resulting in the lower C-DBP formation. In contrast, as the abundance of unfavorable substitution sites for chlorine incorporation, EOM also had low tendency to produce C-DBPs.
Optical properties of AOM showed relatively low UV254 and UV280 absorbance during the entire algal growth phase. Within algal growth, while IOM chiefly comprised of aromatic proteins and soluble microbial products-like substances (80% of average fluorescent intensity–AFI), EOM was rich in humic- and fulvic-like substances (60% AFI). Results from DBP tests showed insignificant variations of EOM-derived THMFP and HAAFP during the algal growth phase, whereas the algal growth status strongly influenced the yields of IOM-derived THMFP and HAAFP. From correlation analysis, our results showed no correlation between UV absorbance with THMFP and HAAFP. Conversely, the regional AFI well correlated with HAAFP and C-DBPFP. As a result, predicting models of HAAs and C-DBPs comprised great predictabilities for laboratory AOM-containing water samples, with a coefficient of determination R2 = 0.879, p <0.01 and R2 = 0.846, p <0.01, respectively. This study indicates a promising application of fluorescent spectra for predicting DBPs derived from algae-rich water. In contrast, the conventional UV absorbance is an insufficient surrogate of the prediction of AOM-DBP formation due to the poor respond of AOM to UV.
The overlapping MW information in the SEC chromatograms of all AOM samples was successfully resolved into six major peaks with R2 >0.996. The results explored significant insights into the HPSEC profiles of AOM, in which resolved peaks A and B (biopolymers) and peak C (humic substances) showed a strong correlation with the formation of AOM-C-DBPs. This likely resulted from the abundance of aromatic structures and conjugated C=C double bonds in their chemical nature. The combination of the extracted information from HPSEC profiles and EEM fluorescent components showed great improvements in the predictions of most AOM-C-DBP formation (R2 >0.7 and p <0.05), especially of THM formation.
AOM-derived C-DBPs strongly depends on the MW properties of AOM. Large molecules of AOM >30 kDa had the highest-yielding tendency to the C-DBP formation over the lower molecules (<30 kDa) because they were abundant in AP- and SMP-like components with more available carbon content and electron-donating functional groups. While the abundance of AP- and SMP-like components in large MW precursors results in the higher yields of HAAs, small MW with HA- and FA-like favorably produces THMs during chlorination. Although small MW of AOM have a lower potential to C-DBPs formation, it still contributes relatively a considerable amount in the overall C-DBPFP.
Bromide has significant effects on the formation quantity and speciation of AOM-derived C-DBPs. The presence of bromide in the chlorination of AOM-containing water resulted in a shift of DBP formation from chlorinated to brominated. Bromide simultaneously caused the rapid reduction of TCM, MCAA, DCAA, and TCAA formation. However, the increase of bromide content initiated the sudden increase in producing brominated THMs and HAAs. As the increase in THMFP and HAAFP with bromide, the total C-DBPs correspondingly elevate with the rise of bromide content. Monitoring of bromide content and fluorescence of OM in a brominated eutrophic water would give a better prediction and control of AOM-DBP formation in practice.

並列關鍵字

disinfection by-products ； algogenic organic matter ； fluorescence ； size exclusion chromatography ； chlorination

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