博士 / 國立臺灣科技大學 / 化學工程系 / 95 / Microfiltration of difficult-handle suspensions such as algae-containing water and high turbidity backwash water was examined in this study. The deformable algae used in this work was Chlorella sp.. The commercial PMMA particles were taken to mimic rigid particulates in nature raw waters. The concentration of algae was controlled to be 10 mg/L (i.e. approximately equals to 400,000 cells/ml) for all experiments with the additional PMMA whose concentration was 0, 10, 20, 40 mg/L, respectively. The transmembrane pressure (TMP) was adjusted at 20, 40, and 60 kPa, respectively. The cross-flow velocity was increased all the way from 0.43 to 1.11m/s to evaluate the effect of Reynolds number on flux behavior. The characteristics of algal suspension subjected to preozonation were assessed by FTIR spectrum and optical density measurement. The effect of preozonation on fouling resistance of microfiltration mounted with hydrophobic and hydrophilic membrane was also examined. Cake properties like specific cake resistance and compressibility as affected by different mass ratio of algae to PMMA was measured. FESEM photographs of cake surface and structure were taken to compare with experimental results. The results show that the microfiltration of algal suspension was operated with many difficulties, like a low permeate flux and a very insignificant improvement of flux by changing operating conditions when under both dead-end and cross-flow operations because of serious cake compression. Preozonation increased the dissolved organic carbon, decreased algal viability and made the size of algal cells smaller. It also increased dissolved polysaccharide that derived from extracellular organic matter (EOM). Different effects of preozonation on flux behavior of MF were observed when utilizing hydrophobic and hydrophilic membrane. Generally speaking, preozonation improved performance of microfiltration by reducing cake compressibility and the biomass loading when both membranes were used. However, dissolved polysaccharide released during preozonation was adsorbed onto the hydrophobic membrane. Consequently, fouling resistance of the hydrophobic membrane became higher. The presence of PMMA particles leaded to a dramatic change in cake properties such as porosity and cake compressibility, which were confirmed by FESEM photographs in this study. For cross-flow microfiltration, the effect of cross-flow velocity on flux enhancement became more obvious as more PMMA particles were involved. Since the rigid particles turned the distribution of local specific cake resistance along cake thickness more uniform, thus the reduction in cake thickness became effective in lowering cake resistance. Furthermore, the cake growth became more containable by rising cross flow velocity when more PMMA particles were added. As a result, the steady state flux was more readily attained when under turbulent flow condition.
For cross-flow microfiltration (MF) for reclaiming backwash water from two water treatment plants, both transmembrane pressure (TMP) and cross flow velocity affected the permeability significantly. Cake resistance (Rc) contributed to the majority of total filtration resistance among all MF experiments. It was found that higher solid loading of backwash water did not lead to lower permeability. On the contrary, size distribution and fractal dimension of particulate matters in backwash water were more important in determining specific cake resistance and permeability. Packing of particulate matters with higher fractal dimension induced more compact structure of cake layer, which resulted in higher specific cake resistance. It was found that the effect of fractal dimension on cake compressibility was insignificant, probably because of the decrease in cake deposition during turbulent cross flow MF. Theoretical analysis on the size distribution of deposited particulate matters indicated that the proportion of submicron to micron particulate matters deposited became higher when cross flow velocity was increased. As a result, cake porosity became lower when under turbulent cross flow. Permeate quality was satisfactory in meeting drinking water standards.
| Identifer | oai:union.ndltd.org:TW/095NTUS5063057 |
| Date | January 2007 |
| Creators | Ming-tsung Hung, 洪銘聰 |
| Contributors | Jhy-chern Liu, 劉志成 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | en_US |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 142 |
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