Productivity, carbon utilization, and energy content of mass in scalable microalgae systems

This study was designed to examine carbon utilization within scalable microalgae production systems. Neochloris oleoabundans was produced in replicated troughs containing BG11 nutrient formulation. Atmospheric CO2 was supplemented with ∼5% CO2 or with NaHCO3, and the pH of troughs receiving NaHCO3 was adjusted with HCl or H3PO4. Peak biomass concentrations reached 950, 1140, or 850 mg L−1 and biomass productivities of 109, 96, and 74 mg L−1 day−1 were achieved in the CO2, NaHCO3:HCl and NaHCO3:H3PO4 troughs, respectively. The highest productivity is expected in a scaled-up continuous batch process of the CO2 supplemented system, which was projected to yield 8948 L lipids ha−1 yr−1. Carbon utilization in the CO2, NaHCO3:HCl and NaHCO3:H3PO4 systems was ∼0.5, 15.5, and 12.9%, while the energy content of the combustible biomass was 26.7, 13.2, and 15.4 MJ kg−1, respectively. Techno-economic analyses of microalgal production systems should consider efficiencies and cost-benefit of various carbon sources.