Electrocoagulation reduces harvesting costs for microalgae

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 A completely new and previously unpublished result is the finding that by applying optimized process conditions, it is possible to maintain the iron content of biomass at a level such that the resulting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