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# Design and Performance of a Solar Photobioreactor Utilizing Spatial Light Dilution

[+] Author and Article Information
Dan Dye

Department of Biological Engineering, Utah State University, Logan, UT 84322dan.dye@usu.edu

Jeff Muhs

USTAR Biofuels, Utah State University, Logan, UT 84322

Byard Wood

Department of Mechanical Engineering, Utah State University, Logan, UT 84322

Ron Sims

Department of Biological Engineering, Utah State University, Logan, UT 84322

J. Sol. Energy Eng 133(1), 015001 (Feb 14, 2011) (7 pages) doi:10.1115/1.4003419 History: Received August 03, 2010; Revised December 10, 2010; Published February 14, 2011; Online February 14, 2011

## Abstract

A photobioreactor with an optical system that spatially dilutes solar photosynthetic active radiation has been designed, built, and tested at the Utah State University Biofuels Center. This photobioreactor could be used to produce microalgal biomass for a number of purposes, such as feedstock for an energy conversion process, or high-value products, such as pharmaceuticals and nutraceuticals. In addition, the reactor could be used to perform services such as removing nitrates, phosphates, and other contaminants from waste water, as well as scrubbing toxic gases and carbon dioxide from flue gas. Preliminary tests were performed that compared growth and productivity kinetics of this reactor with that of a control reactor without spatial light-dilution. Tests indicated higher specific growth rates and higher areal and volumetric yields compared with the control reactor. The maximum specific growth rate, volumetric yield, and areal yield were $0.21 day−1$, $0.059 gm l−1 day−1$, and $15 gm m−2 day−1$, respectively. Over 10 days of sequential-batch operation, the prototype photobioreactor converted direct-normal solar energy to energy stored in biomass at an average efficiency of 1%. The areal productivity, as mass per aperture per time, was three times higher than that of the control reactor, indicating the photobioreactor design investigated holds promise.

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## Figures

Figure 1

Strength of the correlation between dry weight and optical density between the wavelengths 300–900 nm

Figure 2

Comparison between DW and OD750 for N. oleoabundans from several different reactors and growth curves

Figure 3

End-view of sdPBR, showing multiple culture chambers between planar waveguides

Figure 4

Picture of prototype sdPBR

Figure 5

Side-view of reactor chamber, showing location of ports for supporting systems

Figure 6

Batch growth curves, which show that the sdPBR is more affected by cloudy weather than the control reactor

Figure 7

Accumulative energy from direct-normal irradiance as measured by the NIP, and total hemispherical irradiance as measured by the PSP

Figure 8

Culture density before and after each harvest during the sequential-batch test for both reactors

Figure 9

Daily accumulative energy input during the sequential-batch test as measured by the NIP and PSP

Figure 10

Nutrient concentration relative to the original media concentration over the course of the test

Figure 11

Areal biomass yield from the sdPBR and control reactors over 10 days of sequential-batch operation

Figure 12

Energy efficiency of the sdPBR operated in sequential-batch mode. Data corresponds to efficiency over the full solar spectrum (left vertical axis) and efficiency over the PAR portion of the solar spectrum (right vertical axis)

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