Techno-economic analysis of microalgae cultivation strategies: batch and semi-continuous approaches

Algal biomass is a promising sustainable feedstock for low-carbon fuels, chemicals, and proteins, but large-scale deployment remains economically challenging due to high cultivation costs. This study evaluates the economic viability of algal biomass production using batch and semi-continuous cultivation in open raceway ponds. A modular engineering process model was developed to quantify mass and energy flows across key processes, including seed production, biomass cultivation, and dewatering. Two seed train configurations were evaluated: high-density systems using photobioreactors and low-density systems relying on covered and lined ponds. This process model informed a techno-economic analysis to determine the minimum biomass selling price (MBSP) across four cultivation and seed train scenarios. Results indicate that semi-continuous cultivation achieves a lower MBSP ($1130–$1200 per metric tonne) than batch cultivation ($1380–$2040 per metric tonne), primarily due to reduced seed train costs. Seed production costs ranged from $40 to $350 per metric tonne in low-density configurations and $105 to $940 per metric tonne in high-density configurations, making batch systems with high-density seed trains economically unviable. Economic viability in semi-continuous cultivation was found to be sensitive to culture stability, with cost-parity reached if mean-time-to-failure decreases to 26 days. Additionally, batch cultivation can match the cost levels of semi-continuous systems at productivities exceeding 28 g m⁻² d⁻¹. These findings provide key insights into optimizing algal biomass production costs by balancing seed train configuration, cultivation strategy, and productivity thresholds, offering a pathway to more cost-competitive algae-based bioproducts.