Differences between attached and suspended microalgal cells in ssPBR from the perspective of physiological properties

Attached microalgae cultivation for the algae-based products is considered as a promising approach to simplify biomass recovery processes and reduce the cost. However, as an incipient research field, biomass accumulation is the mainly index for attached microalgal growth evaluation. To break through such limitations, physiological properties of attached microalgae (e.g. the oxygen evolving activity and the main organic composition of cells), which are important for microalgal growth evaluation but are still unclear in most studies, were studied using an attached microalgae culture system, i.e. suspended-solid phase photobioreactor (ssPBR) in this paper. As light, nutrients and other environmental conditions of attached microalgae were different from the suspended microalgae, physiological properties of attached microalgae also varied from the suspended ones. Besides the relatively lower biomass accumulation rate, attached microalgae also had a lower oxygen evolving activity (65% on average) comparing to suspended microalgae. The composition of microalgae changed towards accumulating more protein when suspended microalgae turned to attached status. The relative protein content of attached microalgae (50.1% +/- 10.1%) was approximately 30% higher than the suspended algae (36.0% +/- 16.1%) on average. The discovery of physiological properties of attached microalgae in this paper could help the production of high-protein microalgae-related products and explain some phenomenon during the production of microalgae-related products.