碩士 / 中原大學 / 化學工程研究所 / 100 / Global warming and energy crisis are currently major problems of the world, and in recent years the use of algae to absorb carbon dioxide and convert it into biodiesel has attracted many attentions. However, due to the algal cells have a quite small size and its bulk density is close to water, how to effective recovery of algae cell from fermentation suspension is very important on the practical applications. Although direct membrane filtration method for treatment of microalgae solution can remove more than 98% algae, but the small size of cells, the cellular metabolism of macromolecules and cell debris are likely to cause serious membrane fouling. To give a better understanding of the effect of operation conditions on the filtration rate and fouling resistance of this bio-suspension is important for algae harvesting by membrane separation.
In this study, 0.22 μm MCE, 0.20 μm PC and 0.20 μm PTFE three different membranes were used for cross-flow filtration experiments of Nannochloropsis oculata suspension. The effect of applied pressure, cross flow velocity and interactions between algae cell and membrane on the filtration rate and fouling resistance are analyzed. In addition, experiments with an electric field imposed on the filter chamber will also carried out to investigate the electrokinetic effect on the filtration performance.
Experimental results of 4000 ppm algae suspension with cross flow velocity ranging from 0.004 to 0.052 m/s and pressure drop of 0.4 bar showed that among the three membranes MCE membrane has a larger filtration rate and also has an obvious rise in filtration rate as the increase of cross flow velocity. After 1 hr of filtration, the PTFE membrane will exhibit significant increase in membrane resistance, even up to 8.6 times the virgin membrane. Transmembrane pressure applied in the range of 0.2~0.6 bar showed that the pressure variation will not cause obvious impact on the filtration rate, but the pressure increasing will make a raise in cake resistance and a decrease of fouled membrane resistance. All the experimental results of the study showed that the overall filtration resistance is mainly contributed by cake resistance.
Comparison of the filtration results between the feed with the original microalgae suspension and the feeds with pretreatments of the original suspension by centrifugation or gravity sedimentation showed that the centrifuged microalgae suspension has the highest filtration rate . Due to the original culture medium contains more impurities and EOM, the average specific cake filtration resistance exhibits a very high value as 1.93 x1014 m/kg which is about six times that with centrifugation pretreatment.
An external electric field imposed on the filtration system can effectively improve the initial flux. But, due to the high conductance of the solution will cause a large amount of bubbles generated by water electrolysis and therefore reduce the effective electric field strength, it appeared that after 50 min operation the influence of applying electric field on flux enhancement becomes less obvious. If the microalgae suspension was pretreated with centrifugation, the solution conductivity decreases and the zeta potential of algae cells increases to -39.5 mV. Therefore, there is a significant effect by applying electric field to enhance filtration rate for the pretreated suspension.
| Identifer | oai:union.ndltd.org:TW/100CYCU5063091 |
| Date | January 2012 |
| Creators | Pei-Hua Wu, 巫佩樺 |
| Contributors | Ching-Jung Chuang, 莊清榮 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 107 |
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