Abstract
Photoautotrophic microbes present vast opportunities for sustainable lipid production, CO2 storage and green chemistry, for example, using microalgae beds to generate biofuels. A major challenge of microalgae cultivation and other photochemical reactors is the efficiency of light delivery. In order to break even on large scale, dedicated photon management will be required across all levels of reactor hierarchy – from the harvesting of light and its efficient injection and distribution inside of the reactor to the design of optical antenna and pathways of energy transfer on molecular scale. Here, we discuss a biomimetic approach for light dilution which enables homogeneous illumination of large reactor volumes with high optical density. We show that the immersion of side-emitting optical fiber within the reactor can enhance the fraction of illuminated volume by more than two orders of magnitude already at cell densities as low as ~5 104 ml−1. Using the green algae Haematococcus pluvialis as a model system, we demonstrate an increase in the rate of reproduction by up to 93%. Beyond micoralgae, the versatile properties of side-emitting fiber enable the injection and dilution of light with tailored spectral and temporal characteristics into virtually any reactor containment.
Highlights
The aquatic biosphere accounts for about half of the global carbon fixation[1], using photosynthesis to store solar energy and CO2 in complex chemical compounds
A major challenge in aquatic photosynthesis and, all photochemical reaction beds is the efficient delivery of light to the photochemical machinery
Realistic estimates of the theoretical productivity of microalgae reactors predict an annual output of unrefined oil of ~35 L.m−2 14
Summary
The aquatic biosphere accounts for about half of the global carbon fixation[1], using photosynthesis to store solar energy and CO2 in complex chemical compounds. A major challenge in aquatic photosynthesis and, all photochemical reaction beds is the efficient delivery of light to the photochemical machinery This starts with the light source (and, in case of solar illumination, the choice of location12) and encompasses all subsequent optical interfaces down to intracellular antenna designs (e.g.13). Interlayers or containments[16], and photon utilization loss results from quenching effects such as photo inhibition, heat generation, or a mismatch between photon energy and dye band-gap[14,17] On this line, reactor layout and implementation remain the most important factors for economic success[18]: enhancing the productivity of microalgae cultivation systems will require dedicated optical engineering and photon management on reactor level[19,20,21,22]. It was suggested that the productivity of microalgae reactors could be enhanced about fourfold by ideal, volumetric light dilution[30]
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