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Harvesting and Lipid Extraction of Microalgae

Liu, Shihong
http://orcid.org/0000-0003-3387-8330
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou153745894209388

Abstract Details

2018, Doctor of Philosophy (PhD), Ohio University, Chemical Engineering (Engineering and Technology).
Microalgae are one of the most promising feedstocks for energy production due to its high lipid content and easy farming. However, the energy production process from microalgae is energy intensive and costly, mainly due to the microalgae harvesting step and the lipid extraction step. This research focused on investigating these two steps in order to establish effective and cost competitive methods, which could reduce the overall cost in the energy production process, and make biofuels more competitive in todays market. For the microalgae harvesting step, electrolytic flocculation using non-sacrificial graphite electrodes with flocculants added was studied on harvesting Scenedesmus sp. Aluminum electrodes were first used in the electrolytic flocculation process to optimize the operating conditions. It was found that under optimal conditions, the microalgae removal efficiency using aluminum electrodes could reach 98.5%. To determine the type of flocculants added, different metal electrodes were studied, and high microalgae removal efficiency was witnessed only using aluminum electrodes, indicating the influence of the aluminum ion in flocculation. After testing via ICP-OES, it was found that 34.2 mg/L of aluminum ions were released during the electrolytic flocculation process. When non-sacrificial graphite electrodes were used in the electrolytic flocculation process, the corresponding amount of aluminum sulfate was added so that the aluminum ion concentration in water was also equal to 34.2 mg/L. The result showed that the microalgae removal efficiency of graphite electrodes reached above 90% after aluminum sulfate was added. On the contrary, using graphite electrodes alone and using the metal salt alone only yielded 22% and 7% of microalgae removal efficiency, respectively. These results indicated the presence of metal ions was necessary in the electrolytic flocculation process. The energy consumption of the process was found to be 0.3 kWh/m3 or 0.88 kWh/kg, which was considerably lower than centrifugation (8 kWh/m3). The total cost of the process, including energy and chemicals, was found to be $ 0.19/m3, proving a cost-competitive method in microalgae harvesting. For the lipid extraction step, an industrial scale lipid extraction technology using SCCO2 was studied on two microalgae species; Spirulina sp. and Schizochytrium sp. For each species, SCCO2 extraction was conducted on 200 g of biomass for 6 h. Methanol was added as a co-solvent in the extraction process in a volume ratio of 4%. The results showed that adding methanol in SCCO2 increased the lipid extraction yield significantly for both species. Under the operating pressure of 4000 psi, the lipid extraction yields for Spirulina sp. and Schizochytrium sp. were increased by 80% and 72%, respectively. It was also found that a stepwise addition of methanol was more effective than a one-time addition. In comparison with a Soxhlet extraction using methylene chloride/methanol (2:1, v/v), the methanol-SCCO2 extraction demonstrated its high effectiveness of lipid extraction. In addition, the methanol-SCCO2 mixture showed a high lipid extraction yield after the loading amount of biomass increased fivefold, indicating the scaling up potential of this method. Finally, a kinetic study of the SCCO2 extraction was conducted, and the results showed that methanol concentration in SCCO2 had the strongest influence on the lipid extraction yield.
Guy Riefler (Advisor)
Valerie Young (Committee Member)
Marc Singer (Committee Member)
Benjamin Sperry (Committee Member)
Robert Brannan (Committee Member)
154 p.
Alternative Energy; Biochemistry; Chemical Engineering
microalgae; lipid extraction; supercritical fluid; harvesting; electrolytic flocculation; biodiesel production

Recommended Citations

Citations

  • Liu, S. (2018). Harvesting and Lipid Extraction of Microalgae [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou153745894209388

    APA Style (7th edition)

  • Liu, Shihong. Harvesting and Lipid Extraction of Microalgae. 2018. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou153745894209388.

    MLA Style (8th edition)

  • Liu, Shihong. "Harvesting and Lipid Extraction of Microalgae." Doctoral dissertation, Ohio University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou153745894209388

    Chicago Manual of Style (17th edition)

ohiou153745894209388
542
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This open access ETD is published by Ohio University and OhioLINK.