[P008] Poster

1:00 PM - 1:50 PM JST(4:00 AM - 4:50 AM UTC)

[P04-582] Development of growth-promoting technology for microalgae using calcium silicate hydrate

○Yui Nishiwaki¹, Yuka Yokoi¹, Akiko Hanada³, Toshihiro Kasuga³, Tsuyoshi Aketo³, Hiroaki Usui³, Kenta Sugiyama¹, Satoshi Murata¹, Kosuke Kataoka^1,2, Tsuyoshi Tanaka¹ (1. Graduate School of Engineering, Tokyo University of Agriculture and Technology (Japan), 2. Comprehensive Research Organization, Waseda University (Japan), 3. Taiheiyo Cement Corporation (Japan))

Keywords:

microalgae,Carbon capture and storage (CCS),Calcium Silicate Hydrate

[Purpose]
Carbon sequestration using microalgae has attracted attention because of their high CO₂ fixation capacity and potential for large scale biomass production. However, low solubility of CO₂ into aqueous solutions limits the CO₂ fixation of microalgae. To address this bottleneck, our laboratory has developed a carbonate enrichment approach using inorganic materials. Calcium silicate hydrate (CSH) can be produced from waste concrete and is suitable for low cost, large-scale production. In addition, CSH has been shown to promote the hydration of CO₂ in culture media, thereby increasing carbonate concentration. These findings suggest that CSH is a useful material for promoting microalgal growth. In this study, the effect of CSH on microalgal growth was evaluated using three species of marine microalgae: a coccolithophore (Emiliania huxleyi), a diatom (Fistulifera solaris) and a green alga (Pseudoneochloris sp.).

[Method]
E. huxleyi was cultured in ESM medium, F. solaris in f/2 medium and Pseudoneochloris sp. in IMK medium. CSH granules were added to each medium at a final concentration of 1 g/L, and cultures were maintained under aeration (0.8 vvm). Cell concentration and biomass were monitored throughout cultivation, and dissolved inorganic carbon (DIC) was measured using a CO₂ electrode.

[Results and Consideration]
CSH supplementation increased the final cell concentrations by 3.2-fold for E. huxleyi, 1.8-fold for F. solaris, and 2.0-fold for Pseudoneochloris sp., compared with no CSH conditions. There was also a similar increase in the DIC concentration of each medium. These results indicate that the addition of CSH promotes cell growth in these microalgae. On the other hand, the growth rates of E. huxleyi and F. solaris did not change between the two conditions, while the growth rate of Pseudoneochloris sp. was significantly improved by the addition of CSH. One possible reason for this difference could be a preferred inorganic carbon source of each microalga for photosynthesis, being species dependent.

[Conclusion]
This study demonstrates that CSH is a promising material that enhances CO₂ dissolution into culture media and improves microalgal growth, thereby contributing to enhanced carbon sequestration. The species-dependent responses further suggest that selecting appropriate cultivation conditions and target species will be critical for maximizing the benefits of CSH-based carbonate enrichment.