High-Alkalinity Algal Cultivation with Direct Air Capture: An Economic Feasibility Analysis

Hunter Spitzer, Yash Vijay Amonkar , Nazanin Nowzari, David Quiroz, Sridhar Viamajala, Robin Gerlach, Gregory W Characklis

Weather variability and CO₂ supply costs remain key barriers to the commercial viability of algal biofuel production. Recent experimental work has demonstrated that the algae Chlorella sp. strain SLA-04 achieves high productivity in extreme alkaline growth media (pH greater than 10), where the solution chemistry enables direct capture of atmospheric CO₂, eliminating the need for costly CO₂ sparging. The extreme alkaline medium also provides resistance to microbial contamination and culture crashes. Despite these promising experimental results, the commercial-scale economic and environmental implications of this cultivation approach have not yet been assessed. Here we present the first integrated Techno Economic Analysis (TEA)/Life Cycle Analysis (LCA) of high pH-high alkalinity production, driven by 500 stochastic simulations of 20-year weather and market conditions. We compare four SLA-04 cultivation scenarios against a baseline strain cultivation scenario with Nannochloropsis oceanica and sparged CO₂. These scenarios also include the first incorporation of Trona, a naturally occurring carbonate mineral and the primary domestic source of bicarbonate in the United States, into our TEA/LCA framework as a low-cost alternative to commercial NaHCO₃ for establishing the high-alkalinity growth medium. Our results indicate that the SLA-04-Trona scenario reduces operating expenses by 60% per gallon relative to the baseline, and SLA-04 exhibits lower production variability across all seasons. The high pH-high alkalinity cultivation method also reduces the carbon intensity of algal biofuel by approximately 40%, achieving values below corn-based ethanol. These findings provide the first quantitative evidence that high pH-high alkalinity cultivation can substantially improve both the economics and environmental footprint of commercial-scale algal biofuel production.