Mass Cultivation of Microalgae: II. A Large Species Pulsing Blue Light Concept

Abstract

If mass cultivation of photoautotrophic microalgae is to gain momentum and find its place in the new “green future”, exceptional optimizations to reduce production costs must be implemented. Issues related to illumination should therefore constitute the main focus, since it is the availability of photons in time and space that drives synthesis of biomass. Further, artificial illumination (e.g., LEDs) is needed to transport enough photons into dense algae cultures contained in large photobioreactors. In the present research project, we employed short-term O2 production and 7-day batch cultivation experiments to evaluate the potential to reduce illumination light energy by applying blue flashing light to cultures of large and small diatoms. Our results show that large diatom cells allow more light penetration for growth compared to smaller cells. PAR (400–700 nm) scans yielded twice as much biovolume-specific absorbance for small biovolume (avg. 7070 μm3) than for large biovolume (avg. 18,703 μm3) cells. The dry weight (DW) to biovolume ratio was 17% lower for large than small cells, resulting in a DW specific absorbance that was 1.75 times higher for small cells compared to large cells. Blue 100 Hz square flashing light yielded the same biovolume production as blue linear light in both the O2 production and batch experiments at the same maximum light intensities. We therefore suggest that, in the future, more focus should be placed on researching optical issues in photobioreactors, and that cell size and flashing blue light should be central in this.

Mass Cultivation of Microalgae III: A Philosophical and Economic Exploration of Carbon Capture and Utilization

“…The UiT-Finnfjord AS project has, as mentioned earlier, been described in detail in Eilertsen et al [36,40,48]. The main Finnfjord product, ferrosilicon, is a necessary ingredient in steel production, and Finnfjord is committed to sustainable production and is working to reduce its environmental impact.…”

“…Main material requirements for mass producing diatom biomass at Finnfjord AS. Thorough description is in Eilertsen et al [36,48]. The filtered seawater used as cultivation medium is cooling water from the energy recovery system at the factory.…”

“…The UiT-Finnfjord project uses large cells that allows for longer light depths and thereby larger reactors that can serve larger volumes of biomass. When this is combined with blue pulsing light, this can lead to significant energy savings [48,51].…”

“…Most reactors applied today are complicated and expensive and operate small volumes at short light depths. This is due to the high self-shading of the small species applied, i.e., small cells have larger surface-to-volume ratios than large cells [48]. The UiT-Finnfjord project uses large cells that allows for longer light depths and thereby larger reactors that can serve larger volumes of biomass.…”

“…The main project partners are the ferrosilicon factory Finnfjord AS and UiT-The Arctic University of Norway, both situated in the southern part of northern Norway. Thorough descriptions of the project, processes, and data referred to are already published [36,40,48], i.e., this article only focuses on the most important project inventory and cultivation results. The main application of the diatom biomass was from the start fish/salmon feed, this with the alleviation of the lack of marine biomass in the feed as a result.…”