小球藻生長階段之胞內外有機物特性及其消毒副產物生成潛能

Abstract

當水庫呈現優養化時，藻類不僅大量繁殖且常伴隨藻類有機物(algogenic organic matter, AOM)濃度增加，AOM又為淨水處理中主要生成消毒副產物(disinfection by-products, DBPs)之前驅物。因此，了解AOM之物化特性與其加氯後生成DBPs之關係是當前於淨水程序中重要的議題。本研究目的為取自馬祖勝利水庫水並培養分離後之優養化常見綠藻(小球藻，Chlorella sp.)，在藻類生長過程中取樣並分離胞外有機物(extracellular organic matter, EOM)、胞內有機物(intracellular organic matter, IOM)及細胞有機物(cell-wall organic matter, COM)，分析胞內外有機物之物化特性及組成成份，並進一步分析其消毒副產物生成潛能(DBPs formation potential, DBPFP)，其中包含三鹵甲烷(trihalomethanes, THMs)及鹵化乙酸(haloacetic acids, HAAs)。研究中將於6 L之光生物反應器中培養Chlorella sp.，培養基為modified Chlorella medium並混合90% Air及10% CO2為曝氣氣體，流量為500 mL/min、溫度恆為30°C、光度為35 μmol/m2/s，並在小球藻培養過程中，以葉綠素a (chlorophyll a)、藻類乾重(dry mass)及溶解性有機碳(dissolved organic carbon, DOC)指標建立小球藻之生長曲線。根據3D螢光光譜顯示，不同生長階段下EOM組成成份均以類黃酸(fulvic acid-like)物質為主，而IOM及COM成份以芳香族類蛋白質(aromatic protein-like)物質為主。Chlorella sp.生長過程中，當藻類處於指數生長期(exponential phase)時，EOM之螢光物質會逐漸增加，直到生長穩定期(stationary phase)時則逐漸下降，而IOM之螢光物質會隨生長過程逐漸減少，直至生長穩定期才上升，COM之螢光物質變化則較不顯著。此外，亦發現EOM、IOM及COM之鹵化乙酸生成潛能(haloacetic acids formation potential, HAAFP)皆大於三鹵甲烷生成潛能(trihalomethanes formation potential, THMFP)，IOM之C-DBPFP也較EOM及COM高。然而，小球藻中aromatic protein-like含量與其氯化後生成之C-DBPs之皮爾森相關係數(r)可達到0.956。本研究結果證實小球藻生長階段會影響胞內外有機物之C-DBPFP。

Algal eutrophication often occurs in reservoirs associating with the increase of algogenic organic matter (AOM). Because AOM is one of the major precursors to disinfection by-products (DBPs) in drinking water treatment, it is crucial in investigating the physiochemical properties of AOM and its impact on DBPs formation potential (DBPFP). The goal of this study was to separate extracellular (EOM), intracellular organic matter (IOM) and cell-wall organic matter (COM) in each algae growth phase and to characterize their physico-chemical properties and composition and thier corresponding DBPFP, including trihalomethanes (THMs) and haloacetic acids (HAAs). Raw water was collected from the reservoirs in Matsu to isolate the common green alga, Chlorella sp.. Chlorella sp. cultured in a 6 L photo-bioreactor in modified Chlorella medium with 90% Air and 10% CO2 (Illumination：35 μmol/m2/s, Temperature：30°C). The algae growth phases were determined by chlorophyll a, dry mass and DOC. The water samples of EOM, IOM and COM were collected by a serial filtration-gridding protocol at each growth phase. The results during different growth phases in 3D EEM showed that EOM mainly comprised of fulvic acid-like substances, while IOM and COM dominantly comprised of aromatic protein-like substances. The average fluorescence intensity (AFI) of EOM increased gradually in exponential phase, then decreased during stationary phase. The AFI of IOM decreased slowly and increased at stationary phase, but there was no apparent change in the AFI of COM. The yield of haloacetic acid formation potential (HAAFP) from EOM, IOM and COM were higher than trihalomethane formation potential (THMFP). C-DBPFP of IOM was also higher than that of EOM and COM. In addition, the intensity of aromatic protein-like in 3D EEM had a great Pearson correlation coefficient with the yield of C-DBPFP which can reach to 0.956. The results confirm that algal growth phases remarkably affect the yield of C-DBPFP.