Productivity correlated to photobiochemical performance of Chlorella mass cultures grown outdoors in thin-layer cascades

Abstract

This work aims to: (1) correlate photochemical activity and productivity, (2) characterize the flow pattern of culture layers and (3) determine a range of biomass densities for high productivity of the freshwater microalga Chlorella spp., grown outdoors in thin-layer cascade units. Biomass density, irradiance inside culture, pigment content and productivity were measured in the microalgae cultures. Chlorophyll-fluorescence quenching was monitored in situ (using saturation-pulse method) to estimate photochemical activities. Photobiochemical activities and growth parameters were studied in cultures of biomass density between 1 and 47 g L -1. Fluorescence measurements showed that diluted cultures (1-2 g DW L -1) experienced significant photostress due to inhibition of electron transport in the PSII complex. The highest photochemical activities were achieved in cultures of 6.5-12.5 g DW L -1, which gave a maximum daylight productivity of up to 55 g dry biomass m -2 day -1. A midday depression of maximum PSII photochemical yield (F v/F m) of 20-30% compared with morning values in these cultures proved to be compatible with well-performing cultures. Lower or higher depression of F v/F m indicated low-light acclimated or photoinhibited cultures, respectively. A hydrodynamic model of the culture demonstrated highly turbulent flow allowing rapid light/dark cycles (with frequency of 0.5 s -1) which possibly match the turnover of the photosynthetic apparatus. These results are important from a biotechnological point of view for optimisation of growth of outdoor microalgae mass cultures under various climatic conditions. © 2010 Society for Industrial Microbiology.