Harvesting of oil-rich microalgae and converting the microalgal oil into biodiesel

• Main Authors: Bich HanhLe, 李世民
• Other Authors: Jo-Shu Chang
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/98502344125617256478

碩士 === 國立成功大學 === 化學工程學系碩博士班 === 101 === Microalgae has been considering as a potential feedstock for renewable energy production, especially for biodiesel, due to their high oil content, fast growth rate, low land and freshwater requirements. However, industrial application of microalgal biodiesel has been hindered due to the high production costs and the uncertainties during biomass harvesting. In this study, three microalgal strains namely Chlorella vulgaris ESP-31 (fresh water), Chlorella sp. (sea water) and Chlamydomonas orbicularis Tai-04 (sea water) were harvested by coagulation method using chitosan and polyaluminium chloride (PACl) as coagulant agents. The effect of parameters influencing harvesting efficiency, such as coagulant dose, pH, mixing rate, mixing time, biomass concentration, and lipid content, were examined. The results show that under the optimal conditions, the amount of chitosan and PACl needed for harvesting 1 g of dry microalgal biomass C. vulgaris ESP-31 were 0.013 g and 0.101 g, respectively. For Chlorella sp., 0.044 g chitosan/g micoalgae biomass was required. For C. orbicularis Tai-04 grown under different nitrogen source concentration (1N, 2N, and 3N), the required PACl dose was 0.491, 0.175 and 0.491 g PACl per gram of Tai-04. The harvested C. vulgaris ESP-31 was directly employed as the oil source for biodiesel production via enzymatic-transesterification catalyzed by immobilized lipase (Burkholderia sp.), and chemical transesterification catalyzed by synthesized solid catalyst (SrO/SiO2). Both enzymatic- and chemical-transesterification were significantly inhibited in the presence of PACl, while the immobilized lipase worked well with wet chitosan-coagulated ESP-31. The conversion of biodiesel by immobilized lipase from chitosan-coagulated ESP-31 reached 97.6 w/w (oil), which is at a level comparable to that of biodiesel conversion from centrifugation-harvested microalgae (97.1% w/w oil). The solid catalyst SrO/SiO2 worked well with water-removed centrifuged ESP-31, and biodiesel conversion reached around 80% w/w (oil). However, water-removed chitosan-flocculated ESP-31 only slightly induced SrO/SiO2 in transesterification with methanol, and thus the biodiesel conversion only reached 55.7–61.4% w/w (oil). The biocatalyst seems to have higher potential than solid catalyst SrO/SiO2, since the former can be applied with wet microalgae, thus eliminating the need to dry the microalgae biomass before the transesterification reaction. Moreover, the biocatalyst can be easily separated and re-used for up to three cycles in repeated-batch reactor without significantly decreasing its activity.