Life cycle assessment of microalgal cultivation medium: biomass, glycerol, and beta-carotene production by Dunaliella salina and Dunaliella tertiolecta.

Purpose: Dunaliella is a halophilic genus of microalgae with high potential in the global food market. The microalgal cultivation process contributes to not only economic impact but also environmental impact, especially regarding the artificial medium composition. In this context, a life cycle assessment was carried out to analyze the impacts associated with the components of the modified Johnson medium (MJM) and to predict the best scenarios to cultivate Dunaliella tertiolecta and Dunaliella salina for biomass, glycerol, and beta-carotene production.

Method: Two chains were analyzed separately: (1) Dunaliella salina (strain DF 15) cultivated in 8 scenarios combining different nitrogen (0.1 and 1.0 g L^-1 KNO₃) and magnesium (1.1-2.3 g L^-1 MgCl₂.6H₂O) concentrations to produce biomass, glycerol, and beta-carotene and (2) Dunaliella tertiolecta (strain CCAP 19/30) cultivated in 5 scenarios combining different nitrogen (0.1 and 1.0 g L^-1 KNO₃) and salt (116.9-175.4 g L^-1 sea salt) concentrations to produce biomass and glycerol. In addition, we evaluated the potential of cultivating these species to reduce the carbon footprint of the proposed scenarios.

Results and discussion: For D. salina, S₅ (1 g L^-1 KNO₃, 1.1 g L^-1 MgCl₂.6H₂O) had the lowest environmental damage for biomass (74.2 mPt) and glycerol production (0.95 Pt) and S₃ (0.1 g L^-1 KNO₃, 1.9 g L^-1 MgCl₂.6H₂O) for beta-carotene (3.88 Pt). T₄ (1 g L^-1 KNO₃, 116.9 g L^-1 sea salt) was the best for D. tertiolecta for biomass (74 mPt) and glycerol (0.49 Pt). "Respiratory inorganics," "Non-renewable energy," and "Global warming" were the most impacted categories. "Human health," "Climate change," and "Resources" had the highest share of all damage categories. All the scenarios presented negative carbon emission after proposing using brine as alternative salt source: S₅ was the best scenario (- 157.5 kg CO₂-eq) for D. salina and T₄ for D. tertiolecta (- 213.6 kg CO₂-eq).

Conclusion: The LCA proved its importance in accurately predicting the optimal scenarios for MJM composition in the analyzed bioproducts, as confirmed by the Monte Carlo simulation. Although the absolute values of impacts and productivity cannot be directly compared to large-scale cultivation, the validity of the LCA results at this scale remains intact. Productivity gains could outweigh the impacts of "surplus" MJM components. Our study showcased the potential of combining D. salina and D. tertiolecta cultivation with CO₂ capture, leading to a more environmentally friendly cultivation system with a reduced carbon footprint.

Supplementary information: The online version contains supplementary material available at 10.1007/s11367-023-02209-2.