Development of a novel user-friendly platform to couple light regime characterization with particle tracking - cells' light history determination during phototrophic cultivations

Abstract

Depending on the light regime inside the photobioreactor (PBR) and the flow pattern verified, cells experience different histories with respect to the light regimes they are exposed to, wavelengths of light absorbed and period of time spent under each specific condition. The high heterogeneity of the radiation field inside the PBR – due to absorption and scattering of radiation by microalgae/cyanobacteria cells - and the fluctuating cells' light history (CLH), greatly influence photosynthetic conversion and ultimately biomass productivity.This work presents a relatively low-cost, simple, experimental technique which combines light regime and flow pattern characterization, to determine the CLH inside PBRs. A fibre optic spectrometer and probes were employed for quantitative and qualitative light characterization/mapping inside the PBR – in this study a split cylinder airlift photobioreactor (SCAPBR) was used – while the flow pattern was determined by means of two perpendicular digital cameras which were used to follow fluorescent alginate particles.Temporal and spatial aspects of light patterns were obtained using a MATLAB algorithm that enables automatic merging and synchronization of the data obtained by those two approaches. This provided information about the average time during which cells are subjected to each light regime and how they alternate between them, thus characterizing their CLH.