Microalgae are not an umbrella solution for power industry waste abatement but could play a role in their valorization.

Microalgae have long been regarded as a promising solution for biological carbon abatement from the power industry, offering renewable biomass without competing for land or water resources used for food crops. In this study, we extensively examined the application of photosynthetic microorganisms for closing carbon, nitrogen, and micronutrient loops in the power industry. Subsequently, we explored the bottom-up integration of algal biorefineries into power industry waste streams for increased economic benefits and reduced environmental impacts. Analysis of the available data indicated that microalgae integration with the power industry is primarily performed using flue-gas-assisted cultivation. This approach allows for carbon sequestration typically below one gram per liter per day, too low to significantly impact carbon abatement at achievable scales of microalgae cultivation. Alternative approaches are also being explored. For example, soluble bicarbonate platforms allow for higher biomass productivity and temporary carbon storage. Meanwhile, the use of ashes and waste heat and thermophilic strains can result in lower cultivation costs and better control of cultivation conditions. These approaches offer further incremental improvement to microalgae-based carbon abatement systems in the power industry but are unlikely to be an umbrella solution for carbon reduction. Consequently, in the near term, microalgae-based carbon valorization systems are likely to be limited to niche applications involving the synthesis of high-value products. For microalgae to truly transform carbon abatement processes radical improvements in both biology and engineering approaches are urgently needed.

Effect of light colour and photoperiod on biomass growth and phycocyanin production by Synechococcus PCC 6715.

The effect of light colour and light regime on growth and production of the thermostable C-phycocyanin (PC) by the thermophilic cyanobacterium Synechococcus 6715 in the tubular photobioreactor has been analysed. The highest specific growth rate (1.918 d-1) and biomass concentration (5.11 gVS ⋅L-1) were observed under constant illumination of the red light. However, the PC concentration in volatile solids (e.g blue light 30.68 ± 0.8 mgPC⋅gVS-1 PP and 21.7 ± 1 mgPC⋅gVS-1 CI) as well as per photobioreactor unit volume (e.g red light 122.66 ± 2.28 mgPC⋅L-1 PP and 74.71 ± 8.43 mgPC⋅L-1 PP) was higher in the 16L:8D photoperiod. The obtained PC purity was higher in the case of photoperiod (≈1.5). PCC6715 lacks genes encoding phycoerythrins what suggests T1 type of pigmentation. Although changes in biomass pigmentation were not significant, the strain was able to adapt its photosystem what can be used in the optimization of PC production by application of different light colours.