Design and Performance of a Solar Photobioreactor Utilizing Spatial Light Dilution

Abstract

A photobioreactor with an optical system that spatially dilutes solar photo synthetic 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 sen>ices such as removing nitrates, phosphates, and other contaminants from waste water, as well as scrubbing toxic gases and carbon dioxide from fiue 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 area! and volumetric yields compared with the control reactor. The maximum specific growth rate, volumetric yield, and areal yield were 0.21 day~', 0.059 gm /"' day~', and 15 gm m~-day^', 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.

Light dilution via wavelength management for efficient high‐density photobioreactors

“…High productivity requires high intensity light, and this typically has a negative impact on photosynthetic efficiency owing to energy losses that occur when the light intensity nears or exceeds the saturation limit of the organism (Goldman, 1979;Simionato et al, 2013). Large-scale photobioreactor design requires optimizing the combination of culture depth, optical density, and mixing rate in order to maintain an optimal light environment inside the photobioreactor (Cuaresma et al, 2009;Dye et al, 2011;Pierobon et al, 2014;Posten, 2009). Large-scale photobioreactor design requires optimizing the combination of culture depth, optical density, and mixing rate in order to maintain an optimal light environment inside the photobioreactor (Cuaresma et al, 2009;Dye et al, 2011;Pierobon et al, 2014;Posten, 2009).…”

“…Full sunlight can be many times greater than this saturation limit, necessitating strategies to reduce photoinhibition and increase photosynthetic efficiency without compromising productivity (Ooms et al, 2016). Large-scale photobioreactor design requires optimizing the combination of culture depth, optical density, and mixing rate in order to maintain an optimal light environment inside the photobioreactor (Cuaresma et al, 2009;Dye et al, 2011;Pierobon et al, 2014;Posten, 2009). Genetic engineering of microalgae to reduce the light harvesting antenna size has also been explored as a means of reducing the cell's absorption and allowing it to tolerate higher light intensities (de Mooij et al, 2015;Kirst et al, 2014;Kwon et al, 2013;Ort and Melis, 2011).…”

Geometric Design of Scalable Forward Scatterers for Optimally Efficient Solar Transformers

“…Photobioreactors, or closed, engineered systems for growing lipid‐rich algae, use solar energy to create biofuel via photosynthesis, with no requirement for additional reagents such as sugar or lipids . Despite many attempts to engineer photobioreactors, one of the major hurdles of this technology in practice is the poor efficiency of utilizing direct incoming solar flux: algae at the surface of the system must have small absorption cross sections and utilize non‐photochemical mechanisms to quench light to avoid photodamage, while the growth of cells deeper in the system is light‐limited . The greater the potential solar resource present in a given location, the more severe this fundamental obstacle to efficient resource utilization in these systems becomes.…”

Antenna size reduction in microalgae mass culture

“…Technical solutions to improve the light intensity distribution in the photobioreactor are at hand, but this principle of light dilution (Tredici et al 1998, Dye et al 2011, Zemke et al 2013) often leads to high material costs while in the end, the surplus of light absorption should be regarded as a problem of biological origin. …”

“…In addition, microalgae have a high pigment content to be able to survive under low light conditions. Technical solutions to minimize light absorption per cell and provide a better light distribution in the photobioreactor are at hand, but this principle of light dilution (Tredici et al 1998, Dye et al 2011, Zemke et al 2013 often results in high photobioreactor material costs. Photosystem oversaturation is a biological problem and the most effective solution would therefore be to prevent that oversaturation occurs by means of genetic engineering (Chisti 2007).…”