Tuning the Solid Retention Time to Boost Microalgal Productivity and Carbon Exploitation in an Industrial Pilot-Scale LED Photobioreactor

Abstract

Operating conditions strongly affect the productivity of photobioreactors (PBRs). Even though it is demonstrated that continuous systems allow higher biomass productivity, the use of the semicontinuous mode is more widespread for technological reasons. However, even on such a system, tuning the residence time can improve production, in particular if the solid retention time (SRT) is adjusted. Conversely, the hydraulic residence time (HRT) should be set to minimize nutrient loss. In this work, a previously implemented model was applied to a 3.4 m 3 , artificially illuminated pilot plant cultivating Arthrospira platensis, to define the best operating conditions in terms of SRT, which is often neglected in the common operating procedures. This new approach that combines modeling and management of operating conditions allowed obtaining a biomass productivity of 0.8 g L −1 day −1 , more than 3 times higher than that obtained in the same system operated with standard procedures (0.24 g L −1 day −1 ), even though the stability of the production is strongly related to the efficiency of the separation system. The SRT also influenced the protein content of the biomass, which was found to increase at lower residence times. Finally, by optimizing the culture medium in terms of the carbonate/bicarbonate ratio, a higher CO 2 exploitation was obtained.

From Nitrogen to Protein: Harnessing the Power of Nitrogen-Fixing Cyanobacteria for Protein-Rich Biomass Production

“…It is usually observed that the protein content in fast replicating stages is increased (i.e., with lower residence time), as a result of the increased need for protein pool and protein turnover to support the resource-intense cell replication process. Thus, it is consistent with previous observations ,, that the residence time should be shortened if the protein content is to be optimized.…”

Advances in Spirulina Cultivation: Techniques, Challenges, and Applications

“…Both the chemostat and turbidostat mode rationales can be applied with this perspective. The feasibility of spirulina cultivation under an optimized semicontinuous rationale was proved in the work of Pastore et al [24], where A. platensis growth performances were tested on a 3.4 m 3 pilot-scale PBR adjusting the harvesting frequency to optimize harvested biomass concentration as well as inner composition, with particular focus on protein accumulation. Thus, the investigation of the effect of operating variable at lab scale is still a powerful source of information that can be translated into good practices at larger scale, if coupled with modeling and process simulation approaches.…”