Research Group of Algal and Microbial Biotechnology

This research focused on the issue of harvesting unicellular algae, 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 unicellular algae 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 are very difficult to filter. In practice, therefore, the most commonly used method of harvesting is centrifugation on plate centrifuges, which, however, has a high power consumption. Research led by Dr. Branyika and recently published in the prestigious biotechnology journal Bioresource Technology was aimed at studying the use of electrocoagulation as an alternative method of algae harvesting that could lead to a significant reduction in the energy cost of the process.

Electrocoagulation is the phenomenon where metal electrodes are inserted into the algal suspension, and the anode slowly dissolves due to the applied electric current, releasing metal cations into the solution. Since the algal cells are negatively charged, electrostatic interaction with the positively charged ions occurs, leading to the aggregation of the cells into clusters that already have good sedimentation properties. In this work, 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 by the electrode material (in this case iron) were studied. A completely new and previously unpublished result is the finding that by applying optimized process conditions, it is possible to maintain the iron content of biomass at a level such that the resulting biomass meets the legislative requirements for food. Also unique is the finding that the inclusion of electrocoagulation as a pre-concentration step prior to centrifugation saves almost 90% of the energy costs of biomass separation.

• Lucáková S., Brányiková S., Kováčiková S., Pivokonský M., Filipenská M., Brányik T., Růžička M., Electrocoagulation reduces harvesting costs for microalgae. Bioresour. Technol. 323, 124606, 2021. DOI

Chlorella is a genus of unicellular microscopic algae often used in the food and feed industry, nowadays it is commonly available in retail in the form of dried powder or tablets. Although the productivity of Chlorella is orders of magnitude higher than that of agricultural crops, its biomass is still significantly more expensive than food produced by traditional agriculture. One reason for this is the costly separation of biomass from the cultivation medium. Chlorella cells are coccal with a diameter of about 10 µm, so they form a stable colloidal suspension in the culture medium and low-cost separation methods such as sedimentation or filtration cannot be effectively used to separate them. The most commonly used method is energy-intensive centrifugation.

The recently published research follows on from the 2020 paper 'Electrocoagulation reduces harvesting costs for microalgae', in which it was shown that electrocoagulation can be used as a suitable pretreatment prior to actual centrifugation and its use leads to a significant reduction in centrifuged volume and thus energy costs. In the current follow-up paper, the design and testing of an innovative flow-through electrocoagulation unit with a working volume of 160 liters were described; the design of which was based on the knowledge gained during a previous parametric study of the process at a laboratory scale. The constructed flow-through reactor consists of three functional parts - (i), (ii) aggregation channel, (iii) lamellar settling tank - in which (i) electrolytic dissolution of the iron anode (coagulant dosing), (ii) formation of cell aggregates during flow of the cell suspension through an aerated channel with vertical perforated baffles, and (iii) sedimentation of the aggregates in the lamellar settling tank occur. It has been verified that high separation efficiency (>85%), low iron contamination of the harvested biomass (<4 mg/g dry biomass - thus the harvested biomass complies with the legislative requirements for food), and at the same time energy savings of more than 80% compared to harvesting by centrifugation alone can be achieved in this device.

• Lucáková S., Brányiková I., Kováčiková S., Masojídek J., Ranglová K., Brányik T., Růžička M.C., Continuous electrocoagulation of Chlorella vulgaris in a novel channel-flow reactor: A pilot-scale harvesting study. Bioresour. Technol. 351, 126996, 2022. DOI

• Lucáková S., Brányiková I., Hayes M., Microalgal proteins and bioactives for food, feed, and other applications, Appl. Sci. 12, 4402, 2022. DOI
• Lucáková S., Brányiková I., Brányik T., Matoulková D., Krausová G., Wastewater from demineralization of cheese whey for cost-efficient cultivation of spirulina, J. Appl. Phycol. 34, 89, 2021. DOI
• Brányiková I., Lucáková S., Kuncová G., Trögl J., Synek V., Rohovec J., Navrátil T., Estimation of Hg(II) in soil samples by bioluminescent bacterial bioreporter E. coli ARL1, and the effect of humic acids and metal ions on the biosensor performance, Sensors 20, 3138, 2020. DOI
• Potočár T., Pereira J. A. V., Brányiková I., Barešová I., Pivokonský M., Brányik T., Alkaline flocculation of Microcystis aeruginosa induced by calcium and magnesium precipitates, J. Appl. Phycol. 32, 1-4, 2020. DOI
• Brányiková I., Lucáková S., Technical and physiological aspects of microalgae cultivation and productivity—spirulina as a promising and feasible choice, Org. Agric. 11, 269–276, 2021. DOI
• De Souza L., Daniel L. A., Pivokonský M., Novotná K., Brányiková I., Brányik T., Interference of model wastewater components with flocculation of Chlorella sorokiniana induced by calcium phosphate precipitates, Bioresour. Technol. 286, 121352, 2019. DOI
• Brányiková I., Procházková G., Potočár T., Ježková Z., Brányik T., Harvesting of microalgae by flocculation. Fermentation 4, 93, 2018. DOI
• Brányiková I., Filipenská M., Urbanová K., Růžička M., Pivokonský M., Brányik T., Physicochemical approach to alkaline flocculation of Chlorella vulgaris induced by calcium phosphate precipitates. Colloids Surf. B 166, 54-60, 2018. DOI