碩士 / 國立成功大學 / 環境工程學系碩博士班 / 97 / Membrane processes have high removal efficiency for algal cells that contained in the eutrophic source water. However, the fouling problem caused by both algal cells and the extracellular polymeric substances (EPS) that interact with the background materials in water is the major obstruct to the further development of membrane processes. Preoxidations, such as adding chlorine, are used to control the biofouling of membrane. However, it may also stimulate algae to secret more EPS and cause organic fouling.
In this study, two algal species, namely Microcystis aeruginosa and Chodatella sp., were chosen as the target species. The algal cells, harvested from axenic cultures in the lab, were used to prepare synthetic algae suspensions. Different amount of calcium ion were also added to simulate the hardness in various eutrophic source waters. The major objective of this research is to study the effect of preoxidation by either potassium permanganate or ozone on the fouling phenomena of the subsequent UF membrane (regenerated cellulose, MWCO 10 kDa) filtration of the synthetic algae suspensions. In order to avoid damaging algal cells and releasing intracellular substances, the flow cytometry technique with FDA and SYTOX fluorescent dye were used to determine the appropriate preoxidants dosage. Then the original and the preoxidized synthetic algal suspensions were filtered through UF membrane separately. In order to estimate the critical flux, stepwise increase in the transmembrane pressure (TMP) was conducted, maintaining each TMP for 30 min, and the corresponding permeate flux were recorded. The same UF membrane filtrations were also conducted for the solution containing only soluble EPS.
The results from flow cytometry show that ozone caused cell damage at much lower dosage than that of potassium permanganate. However, M. aeruginosa has more resistance to ozone than Chodatella sp., probably due to the thicker extracellular mucilage layer of the former. The results from UF membrane filtration experiments show that the solution, contained only soluble EPS, caused almost no flux decline. When algae cell suspensions were filtered through UF membrane, the flux decline was mainly caused by the cake layer which consisted of algae cells deposited on membrane surface. The original M. aeruginosa suspension caused much serious fouling than that of Chodatella sp. After preoxidation by potassium permanganate, the flux decline of M. aeruginosa suspension though UF membrane was minor than that without preoxidation, as permanganate oxidation caused some algal cell aggregation. However, permanganate preoxidation caused more serious flux decline for Chodatella sp. suspension compared to that without preoxidation. This probably was due to the release of gelatinous EPS by the Chodatella sp. after permanganate oxidation. With the addition of calcium ion into the algae suspension, the floc formation after permanganate preoxidation for both algae species was further promoted, and flux decline rate reduced. This is speculated to be due to the bridging effect of Ca2+ ion between negatively charged algal cell surface and MnO2 (s), the reduced product of potassium permanganate. For preozonation, as it did not alter the floc size distribution, its effect on flux decline was also insignificant.
As far as the functional groups of algae cell surface are concerned, the ATR-FTIR spectrums reveal that these two algae have components of protein, polysaccharides, and carboxyl group … etc. With preoxidation with either permanganate or ozone, there were some alternations of the cell surface, such as the formation of C-N bound peak of amino acid. This may indicate the change or release of protein components after preoxidation, and may be related to the release of gelatinous EPS after Chodatella sp. was preoxidized by permanganate.
| Identifer | oai:union.ndltd.org:TW/097NCKU5515027 |
| Date | January 2009 |
| Creators | Woan-chi Wang, 王婉綺 |
| Contributors | Hsuan-Hsien Yeh, 葉宣顯 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 113 |
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