Abstract
Studies on microalgal lipid production as a sustainable feedstock for biofuels and chemicals are scarce, particularly those on applying open thin-layer cascade (TLC) photobioreactors under dynamic diurnal conditions. Continuous lipid production with Microchloropsis salina was studied in scalable TLC photobioreactors at 50 m2 pilot scale, applying a physically simulated Mediterranean summer climate. A cascade of two serially connected TLC reactors was applied, promoting biomass growth under nutrient-replete conditions in the first reactor, while inducing the accumulation of lipids via nitrogen limitation in the second reactor. Up to 4.1 g L−1 of lipids were continuously produced at productivities of up to 0.27 g L−1 d−1 (1.8 g m2 d−1) at a mean hydraulic residence time of 2.5 d in the first reactor and 20 d in the second reactor. Coupling mass balances with the kinetics of microalgal growth and lipid formation enabled the simulation of phototrophic process performances of M. salina in TLC reactors in batch and continuous operation at the climate conditions studied. This study demonstrates the scalability of continuous microalgal lipid production in TLC reactors with M. salina and provides a TLC reactor model for the realistic simulation of microalgae lipid production processes after re-identification of the model parameters if other microalgae and/or varying climate conditions are applied.
Highlights
We report on the continuous production of lipid-rich M. salina biomass in a scalable 50 m2 thin-layer cascade (TLC) photobioreactor under a physically simulated Mediterranean summer climate
The second TLC reactor with a surface area of 50 m2 was continuously fed from the first reactor during the day
The accumulation of lipids was induced in M. salina by application of nitrogen-limited conditions due to almost complete consumption of urea used as the nitrogen source in the first TLC reactor
Summary
With the ability to harvest light energy while recirculating carbon dioxide from air or flue gases, as well as removing nitrogen and phosphorus from municipal or agricultural wastewater [1,2], the utilization of biomass from microalgae can contribute to several of the United Nation’s Sustainable Development Goals, e.g., affordable and clean energy, climate action, responsible consumption and production, and zero hunger [3]. Major advantages of microalgae over terrestrial crop plants are the approximate 10 times higher productivities with shorter growth cycles and less consumption of fresh water [4,5]. They can be cultivated on non-fertile ground, thereby avoiding the competition for agricultural land. To swiftly support CO2 emission reductions in these sectors, and needing a high energy density, the utilization of synthetic or biofuels might offer a drop-in solution [7]
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