Development of a thin-film solar photobioreactor with high biomass volumetric productivity (AlgoFilm©) based on process intensification principles

Abstract

This work presents the rational development up to its final characterization and validation of an intensified solar photobioreactor (PBR) for microalgal production, AlgoFilm©. Our aim was to achieve very high volumetric performance for phototrophic conditions, in the range of that found in fermentation processes.The overall design procedure was underpinned by robust engineering rules derived from knowledge models developed for PBR in-depth modeling. This approach was used to pinpoint the main engineering parameters governing PBR kinetic performance. It introduces generic principles of PBR performance enhancement for the setting-up of culture systems combining high volumetric and areal productivities. These principles were then applied to the design of a solar culture system, integrating the attendant constraints. The result was the AlgoFilm© PBR, based on the falling-film principle, which enables very thin culture depth (around 1.5–2mm) and provides a high specific illuminated surface area (around 500m2·m−3, corresponding to 2.1L/m2 illuminated surface).A complete experimental characterization was then conducted to (i) determine operating conditions for the setting of optimal parameters governing AlgoFilm© PBR performance, such as depth of the falling film, and (ii) ensure that no limitation other than light occurred, a mandatory condition to control the system and ensure high biomass productivities.AlgoFilm© PBR performance was characterized by Chlorella vulgaris culture. Batch, continuous and semi-continuous cultures were run, and typical irradiation conditions of a year's operation in Nantes (France) were applied using a LED panel to simulate constant, and then fully-controlled day/night cycles. Our results demonstrate the high performance of the AlgoFilm© PBR, with volumetric productivities very close to those expected from the prior theoretical design. The best measured productivity was 5.7kg·m−3·day−1 (7.07kg·m−3·day−1 in constant light). This value was significantly higher than those reported in the literature, and similar to those generally found for microalgal production in heterotrophic processes.