Fluorescent Microbeads for Tuning the Local Light Availability in High Density Algae Photobioreactors

Minimizing mass and volume of algal cultivation systems for space requires ultra-efficient photobioreactors. Light is the most difficult input to efficiently deliver to individual cells. The magnitude of light intensity decreases exponentially within algal cultures, leading to photoinhibition near the light facing surface and photolimitation in the deeper regions. Only a small region of the culture is optimally illuminated. Photosynthetic pigments also selectively absorb red and blue photons, allowing green photons to penetrate deeper into the culture. Thus, the quality, in addition to the quantity, of locally available light degrades with increasing depth. This project will use fluorescent dyes and microbeads to enable deeper penetration of photosynthetically active photons into high density algal cultures (Figure 1). Fluorescent dyes will be selected that absorb ultraviolet (UV) light, which causes DNA damage, and green light, which is inefficiently utilized and re-emit as blue and red light, respectively. In this way, the microbeads will "upgrade" the solar spectrum in situ and with no energy requirement, bypassing the need to convert solar energy to electricity to power LEDs to illuminate algae, an inherently energy-negative process. Long duration manned space missions will require closed loop technologies for food production, generation of oxygen and waste recycling. On Earth, biology provides a closed mass balance to perform all necessary functions for keeping humans alive. Specifically, since its evolution 2.7 billion years ago, oxygenic photosynthesis has been solely responsible for oxygenating the atmosphere, and converting solar energy into biomass, directly or indirectly producing all food consumed by humans. Photosynthetic organisms are therefore natural candidates as symbiotic companions for sustaining human life for deep space exploration; both plant and algal photosynthetic organisms are proposed but present technical challenges. Minimizing mass and volume of algal cultivation systems for space requires ultra-efficient photobioreactors. Light is the most difficult input to efficiently deliver to individual cells. The magnitude of light intensity decreases exponentially within algal cultures, leading to photoinhibition near the light facing surface and photolimitation in the deeper regions. Only a small region of the culture is optimally illuminated. Photosynthetic pigments also selectively absorb red and blue photons, allowing green photons to penetrate deeper into the culture. Thus, the quality, in addition to the quantity, of locally available light degrades with increasing depth. This project will use fluorescent microbeads to enable deeper penetration of photosynthetically active photons into high density algal cultures (Figure 1). Fluorescent dyes will be selected that absorb ultraviolet (UV) light, which causes DNA damage, and green light, which is inefficiently utilized and re-emit as blue and red light, respectively. In this way, the microbeads will "upgrade" the solar spectrum in situ and with no energy requirement, bypassing the need to convert solar energy to electricity to power LEDs to illuminate algae, an inherently energy-negative process.

NASA OCT: TA06 Human Health Life Support and Habitation Systems; Cross cutting with TA11 Modeling, Simulation Information Technology and Processing and TA03 Solar Energy and Harvesting & cross cutting Green energy and alternative fuels Impact. The photosynthetic efficiency of algae cultures for life support and bioproduct generation is severely limited by the difficulty in delivering large quantities of high quality photons to cells deep within large cultures. Suspension of fluorescent microbeads within high density liquid cultures and biofilms will serve to enhance light delivery and significantly enhance culture productivity. Enhanced capability for algal food, and bioproduct production at lower energy, water and volumetric costs. Enhanced capability for CO2 scrubbing and O2 production. Dept. of Energy: Biomass Program: Increased Efficiency of Solar Energy conversion to biomass and system monitoring. Quantitative metrics: Increase photosynthetic efficiency of bioreactors by ~30% Reduce harmful UV exposure by ~90%

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