Evaluation of calcium alginate beads immobilization of Chlorella vulgaris for biomass production in space life support systems

As space missions extend in duration and distance, there is an increasing need for autonomous life-support systems capable of recycling resources and producing essential compounds in situ. In this context, alginate-entrapped microalgae were used to assess growth under reduced liquid conditions, testing two different beads-to-volume ratios (1:1 and 1:2). In batch cultures conducted in flasks without aeration, the immobilized microalgae using HEPES-Acetate-Phosphate (HAP) medium reached a maximum dry weight (DW) of 0.93 ± 0.03 g/L and 33.65 ± 1.19 x 10⁶ cells/mL in the 1:2 configuration, compared to 1.01 ± 0.02 g/L and 37.44 ± 1.56 x 10⁶ cells/mL in suspension. Biomass productivity peaked at 404 mg/(L·d) for suspension and 240 mg/(L·d) for 1:2 immobilized cultures. Biochemical analysis of immobilized biomass revealed high nutritional value, with up to 32.5 % DW lipids, 23.6 % DW proteins, and 12.5 % DW carbohydrates. In the pre-prototype column reactor with medium recirculation and air bubbling, microalgae showed lower productivity than in batch tests indicating the need for further optimization of process configuration. Immobilized Chlorella vulgaris offers a trade-off between reduced productivity and engineering advantages, such as ease of recovery, and suitability for automated, closed-loop bioregenerative in space life-support systems as well as for terrestrial application.