Microalgal biotechnology algae is one of the topics studied at our institute. This is a multidisciplinary field of applied research. One of the sub-topics is the issue of harvesting of microalgae, as this step is one of the most energy-intensive during the production of algal biomass for food purposes. Chlorella vulgaris, as a typical representative of microalgae widely used as a food and feed supplement, has cells with a diameter of approximately 10 μm. Due to this small size, the cells form a stable suspension, sediment very slowly and their filtration is very difficult to perform. Therefore, the most commonly used harvesting method in practice is centrifugation on plate centrifuges, which, however, has a high consumption of electricity. Research led by Dr. Brányiková, recently published in the prestigious biotechnology journal Bioresource Technology, focused on studying the use of electrocoagulation as an alternative way to harvest algae, which could lead to a significant reduction in the energy costs of the process.
Electrocoagulation is a phenomenon in which metal electrodes are inserted into an algal suspension, the anode slowly dissolves due to the applied electric current, while metal cations are released into the solution. Due to the fact that algal cells are negatively charged, there is an electrostatic interaction with positively charged ions, which leads to the aggregation of cells into clusters that sediment readily. The influence of a number of parameters on the efficiency of this process, its energy consumption and the degree of “contamination” of the harvested biomass with electrode material (in this case iron) was studied. A completely new and yet unpublished result is the finding that by applying optimized process conditions it is possible to keep the iron content in biomass at such a level that the obtained biomass meets the legislative requirements for food. It is also unique to note that to involve the electrocoagulation as a preconcentration step prior to centrifugation saves almost 90% of the energy costs of biomass separation.
Individual stages during the electrocoagulation of Chlorella vulgaris: (1) the original stable suspension, electrolysis in progress; (2) destabilized suspension, ongoing coagulation; (3) sedimentation of the formed aggregates.
Simona Lucakova, Irena Branyikova, Sara Kovacikova, Martin Pivokonsky, Monika Filipenska, Tomas Branyik, Marek C. Ruzicka: Electrocoagulation reduces harvesting costs for microalgae, Bioresource Technology, Volume 323, 2021, 124606, https://doi.org/10.1016/j.biortech.2020.124606.