Application of Extracellular Polymeric Substances during Cultivation of Microalgae Biomass

Featured Application The biomass of microalgae/cyanobacteria selected in this study had different characteristics and applications and included Chlorella sp. (bio-oil production), Tetraselmis subcordiformis (bio-hydrogen production), and Arthrospira platensis (phycocyanin production). A critical, well-diagnosed, and proven problem of microalgae/cyanobacteria cultivation on an industrial scale is the lack of a simple and effective technology for separating the obtained biomass from the culture medium. The study aimed to solve the problem of biomass harvesting using extracellular polymeric substances extracted from activated sludge.Abstract Extracellular polymeric substances (EPS) produced by microorganisms contain polymers that are used for the bioflocculation of microalgae; however, these polymers are also organic compounds that might be used as carbon sources. The study analyzed two strategies for the introduction of EPS for Tetraselmis subcordiformis, Chlorella sp., and Arthrospira platensis biomass harvesting. In the first variant, EPS in the dose of 100 mg TOC/g were added to the photobioreactor every other day from the beginning of the cultivation, while in the second variant, EPS in the two doses of 100 mg TOC/g and 300 mg TOC/g were only added at the end of cultivation. In the first variant, the results proved that microalgae/cyanobacteria can use the EPS as external carbon sources. The cultures were characterized by a faster increase in biomass concentration, which contained less chlorophyll. However, the EPS content did not change. In the second variant, the addition of EPS did not affect the EPS content and the sedimentation of the Chlorella sp. biomass. The biomass of T. subcordiformis was characterized by a much better sedimentation coefficient. The greatest differences were observed in the A. platensis culture: the biomass concentration increased from 1.2 +/- 0.2 g/L to 1.9 +/- 0.2 g/L, EPS content increased by 16%, and sedimentation efficiency increased to 72%.