加氯氧化對小球藻細胞有機物釋出及衍生消毒副產物之影響

Effect of chlorination on the released cellular organic matter of Chlorella sp. and the corresponding disinfection by-product formation

黃奕維(Yi-Wei Huang)

指導教授 ： 林志麟

中原大學/工學院/環境工程學系/碩士(2021年)

https://doi.org/10.6840/cycu202100049

摘要

當水庫優養化或藻華發生，此時淨水場取用水庫原水，傳統混凝沉澱無法有效去除藻類有機物(algogenic organic matter, AOM)，以至於AOM殘留在水中，會加重淨水處理單元操作負擔。AOM經加氯氧化程序，於清水中形成大量的鹵化消毒副產物(halogenated disinfection by-products, DBPs)如三鹵甲烷(trihalomethanes, THMs)和鹵化乙酸(haloacetic acids, HAAs)，升高飲用水水質安全風險。水庫微藻生長需要營養鹽如氮及磷，其中氮源(硝酸鹽)濃度改變對微藻的生長行為、細胞大小及內質成分特性有顯著影響，進而改變其藻細胞及AOM與氯反應之消毒副產物生成潛能(DBP formation potential, DBPFP)。因此，本研究旨在利用不同硝酸鹽進料濃度改變小球藻(Chlorella sp., CH)細胞生長大小及內質成分，並以此探討加氯氧化對小球藻細胞有機物釋出及衍生消毒副產物之影響。氧化實驗前後，分析藻細胞尺寸、葉綠素a濃度、溶解性有機碳(dissolved organic carbon, DOC)及AOM螢光與分子量特性，以評估NaOCl對小球藻(CH)細胞之氧化行為，並分析氧化過程之即時生成DBP與DBPFP，探討氧化後細胞有機物釋出對DBP之影響。

研究結果顯示，在小球藻生長過程中，藻細胞與衍生之AOM特性隨培養時間發生改變，且也會受不同硝酸鹽濃度進料影響，其中胞外有機物(extracellular algogenic organic matter, EOM)的主要成分為類腐植酸物質(humic acid-like substances, HAL)和類磺酸物質(fulvic acid-like substances, FAL)，胞內有機物(intracellular algogenic organic matter, IOM)則以類芳香族蛋白質(aromaticprotein-like substances, APL)和類微生物副產物(soluble microbial by-product-likesubstances, SMPL)為主。此外，各生長期的EOM與IOM具有相似的DBPFP，除了指數期的EOM的DBPFP以THM為主外，穩定期與死亡期的EOM及全生長階段的IOM皆以HAA佔多數。相比低硝酸鹽進料濃度(NO3--N:0.2471 g/L)，在高硝酸鹽進料濃度下(NO3--N:2.471 g/L)，小球藻(CH)細胞的AOM之SMPL比例上升尤其是IOM的SMPL增加最為明顯，而AOM的DOC/DON比例則降低。EOM之DBPFP無明顯改變但HAAFP占比增加，IOM之DBPFP增加則是因為HAAFP的上升，但AOM的鹵乙腈(Haloacetonitrile, HANs)之單位生成量反而降低。

在加氯氧化程序中，螢光物質中HAL和SMPL的消減量較其他物質高，而即時生成之HAA的產量較THM高，但氧化後水樣的DBPFP結果則是顯示出THMFP高於HAAFP。此外，相較低硝酸鹽進料濃度(NO3--N:0.247 g/L)，高硝酸鹽進料濃度(NO3--N:2.471 g/L)養成之CH細胞及AOM成分特性造成與氯反應時產生較少即時生成DBP，且氧化後藻細胞釋出溶解性有機物之DBPFP也較少。關聯性分析結果得知小球藻CH細胞的AOM中HAL與SMPL是C-DBP與N-DBP的重要前驅物，但此相關性會在高硝酸鹽進料濃度中降低。加氯氧化不會造成水中AOM的性質改變進而影響其DBP生成之種類，生成DBP的種類及特性仍需視水體氧化前的有機物成分特性而定。

關鍵字

藻類有機物 ； 小球藻 ； 硝酸鹽 ； 加氯氧化 ； 消毒副產物

並列摘要

When the reservoir occurs algae bloom and water treatment plant take the raw water from the reservoir, the algogenic organic matter (AOM) would not be effectively removed by coagulation-sedimentation process, so that increases residual AOM in water, which burdens the operation unit in water clarification process. In chlorination process, AOM frequently results in the occurrence of voluminous halogenated disinfection by-products (DBPs) such as Trihalomethanes (THMs) and Haloacetic acids (HAAs) in finished water, which increases the safety risk of drinking water quality. Algae growth needs nutrient salts such as nitrogen and phosphate, the change in nitrogen source (NO3-) concentration would significantly affect algae growth behaviors, cell size and AOM characteristics, which would vary the DBP formation potential (DBPFP) after chlorine react with algal cells and AOM. Therefore, this study aims to feed different concentration of NO3- to change the characteristics of Chlorella sp.(CH) cell and the corresponding AOM, and then to investigate the effect of chlorination on the released cellular organic matter and the in-situ formed disinfection by-products. The cell size, chlorophyll a, DOC and optical properties , molecular weight of AOM as indicators were determined to evaluate the behaviors of NaOCl oxidation on cells. The in-situ formed DBP and DBPFP were analyzed to evaluate the effect of liberation from cellular organic matter by the oxidation on DBP.

The results showed that the characteristics of CH cells and the derived AOM change with culture time, and they are also siganificantly varied with nitrate concentrations during algal growth. Humic acid-like substances (HAL) and fulvic acid-like substances (FAL) are determined to contribute most of extra cellular organic matter (EOM), and intra cellular organic matter (IOM) are mostly compsed of aromatic protein-likesubstances (APL) and soluble microbial by-product-like substances (SMPL). In addition, EOM-and IOM-derived DBPFP are similar with mostly formed HAA at each growth phase, while the EOM at exponatial phase mostly contributes THM.

Compared to the low feeding concentration of NO3- (0.247 g/L), the SMPL ratio of AOM increased at higher concentration of NO3- (2.471 g/L) especially in IOM, which results in the decreased DOC/DON ratio. The EOM-derived DBPFP is insensitive to feeding NO3- concentration but high NO3- concentration causes the increased HAAFP. The IOM-derived DBPFP becomes higher due to the increased HAAFP, but the specific Haloacetonitriles (HANs) decrease.

In the chlorination process, the consumption of HAL and SMPL is higher, and the yield of in-situ formed HAA is higher than that of THM. However, the HAAFP of suspension after chlorination is lower than THMFP. In addition, it behaves less in-situ formed DBP yield and lower DBPFP in chlorination process at higher concentration of NO3- compared to low concentration of NO3- due to the characteristics of CH cells and AOM components. The correlation analysis has shown that HAL and SMPL are determined to be the main precursors of C-DBP and N-DBP, but this correlation would be reduced at high nitrate feeding concentration. Chlorination would not significantly change the properties of AOM and the class of in-situ formed DBPs, which is depending on the orginal composition of AOM before chlorination.

並列關鍵字

algogenic organic matter ； Chlorella sp. ； NO3- ； chlorination ； disinfection by-product

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