Carbon Dioxide Absorption by Microalgae: Analysis of Technologies and Energy Costs

Reducing greenhouse gas emissions remains a topical issue in fundamental and applied scientific research, including in terms of analyzing developed and applied CO2 capture technologies. The main focus is on methods of carbon dioxide burial in stable geological formations, absorption, filtration, etc. The absorption of carbon dioxide during photosynthesis is usually associated with terrestrial biota, although aquatic organisms have a higher productivity of photosynthesis. The use of microalgae as photosynthetic agents is determined mainly by their value for obtaining high-quality food and feed additives, pharmaceutical products, and biofuels, but it is important to consider their effectiveness in the associated absorption of CO2. When producing products with a long carbon sequestration period, this method can be included in the list of effective carbon capture technologies. To estimate the specific energy costs for CO2 absorption, proven cultivation methods were considered: open-plane cultivators (microalgae Arthrospira platensis, growth rate from 20 to 40 g/m2 per day on dry matter) and cylindrical closed photobioreactors (microalgae Chlorella vulgaris, growth rate 0.7 g/dm3 per day in dry matter). Based on experimental results of microalgae cultivation under conditions of elevated CO2 concentrations, it is shown that specific energy consumption is in the range from 27 to 768 GJ/t when cultivating A. platensis microalgae and from 59 to 373 GJ/t in microalgae cultivation of C. vulgaris. The greatest energy costs are required for heating and lighting microalgae plantations as well as for separating biomass from the culture liquid for microalgae with small cell sizes. Specific energy consumption can be reduced by maximizing the use of natural light and waste heat from industrial facilities and optimizing biomass collection systems.