The photo is sourced from rscf.ru
One of the alternatives to classic hydrocarbons is biofuel produced from plant raw materials, including cultures of microscopic algae and cyanobacteria. These microorganisms are characterised not only by high growth rate and low requirements for culture media, but also by the ability to capture carbon dioxide during photosynthesis, which helps reduce CO2 concentration in the atmosphere.
The scientists from the Joint Institute for High Temperatures RAS, MSU and RUDN conducted experiments to obtain biofuel from cultures of Arthrospira platensis – free-floating filamentous cyanobacteria that can grow and develop under high temperatures and illumination, as a result of which they are found mainly in tropical and subtropical lakes. Earlier studies have shown that the growth rate of Arthrospira platensis depends on the concentration of carbon dioxide, in which the bacterium grows: the higher the concentration, the faster the growth. This is why the authors of the study placed the Arthrospira platensis culture in a 90-litre bioreactor connected to a chamber supplying carbon dioxide to the medium at a constant concentration of 8%.
The scientists grew cyanobacteria in the bioreactor, after which they drained the culture of all water and heated it to 330 degrees Celsius. These operations made it possible to obtain liquid biofuel and biochar from Arthrospira platensis. The yield of bio-oil – the share of the original biomass that was converted into the final product – was about 14%. After this, the authors changed the experimental conditions, reducing CO2 concentration to the atmospheric level (0.035%) and thereby increasing bio-oil yield to 37%. They found that large amounts of carbon dioxide not only accelerate bacterial growth, but also change the chemical composition of cells. As a result, the cyanobacterium synthesises 25% fewer lipids, which are the main contributor to bio-oil yield.
Chemical analysis of the obtained biofuel showed that the biofuel has a high concentration of heavy metals compared to fossil oil: the specific weight of iron exceeds the norm by 90 times while that of copper and molybdenum surpasses the norm by 3 and 10 times, respectively. For that reason, Arthrospira platensis-based bio-oil requires additional purification stages.
“In this study, we managed to go all the way from growing Arthrospira platensis at an increased concentration of carbon dioxide to obtaining bio-oil via hydrothermal liquefaction. Further on, we plan to consider the possibility of producing other types of biofuel from this type of biomass. In the future, the results obtained could be used to create testing grounds for the absorption of carbon dioxide and the production of valuable products, including biofuels,” Mikhail Vlaskin, candidate of technical sciences and head of the laboratory of the Joint Institute for High Temperatures RAS, is quoted as saying by the Russian Science Foundation.
