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Research Papers: Energy From Biomass

Investigation of the Effect of Growth From Low to High Biomass Concentration Inside a Photobioreactor on Hydrodynamic Properties of Scenedesmus obliquus

[+] Author and Article Information
Evan Le

Department of Mechanical Engineering,  University of Nevada, Reno, NV 89557-0312

Chanwoo Park1

Department of Mechanical Engineering,  University of Nevada, Reno, NV 89557-0312chanwoo@unr.edu

Sage Hiibel

Department of Biochemistry and Molecular Biology,  University of Nevada, Reno, NV 89557-0330

1

Corresponding author.

J. Energy Resour. Technol 134(1), 011801 (Dec 23, 2011) (6 pages) doi:10.1115/1.4005245 History: Received September 11, 2010; Revised August 16, 2011; Published December 23, 2011; Online December 23, 2011

Most of the current production cost in algae biodiesel plants utilizing photobioreactors comes from the high energy required for pumping, CO2 transfer, mixing, and harvesting. Since pumping affects the mixing and CO2 transfer, which are the main factors in algae productivities, solutions to reduce the required energy for pumps can significantly make algae biodiesel production more economically feasible. An investigation on the effect of Scenedesmus obliquus’s growth from low to high biomass concentration inside a horizontal tubular photobioreactor to determine the impact that it has on hydrodynamic performances, which will affect cost and production efficiency, was performed. As the biomass concentration increased, the algal culture was found to remain Newtonian. Additionally, the biomass concentration (expressed in cell density) was found to have lower viscosity even at the highest concentrations evaluated at 2.48 × 108 cell/ml (1.372 × 10−3  ± 1.32 × 10−4 Pa s) compared to the Modified Bold’s 3N medium (1.408 × 10−3  ± 9.41 × 10−5 Pa s). Furthermore, the total energy consumption does not appear to depend on the S. obliquus biomass concentrations, but rather on the medium the algae grows in. The rheological properties of autotrophic algae will not have significant impact on energy requirements until technology improves so that the concentrations reach those of heterotrophic algae.

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Figures

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Figure 1

Behavior of non-Newtonian fluids

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Figure 2

Schematic presentation of the experimental setup showing a centrifugal pump, a differential pressure transducer, and a culture reservoir: The inner diameter (Dt) of the acrylic tube used for the pressure drop measurement is 1.25 cm, and the length (Lt) between the two pressure taps is 38.1 cm. The total volume of the system is about 600 ml.

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Figure 3

The conversion curve of the absorbance measurement at 600 nm (OD600 ) of samples of S. obliquus grown in Modified Bold’s 3N medium

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Figure 4

The growth of S. obliquus over time in Modified Bold’s 3N medium

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Figure 5

Bulk liquid densities and viscosities (at 23 °C) of S. obliquus grown in Modified Bold’s 3N medium at various cell densities compared with pure water and Modified Bold’s 3N medium

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Figure 6

Hydraulic pumping power consumed by the algae culture flow through the acrylic tube at different Reynolds numbers and various cell densities

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Figure 7

Friction factors of the algae culture flow for different Reynolds numbers and various cell densities compared with the friction factors of laminar and turbulent flows of a Newtonian fluid in a circular tube

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