Chlorella fusca (Chlorophyta) grown in thin-layer cascades: Estimation of biomass productivity by in-vivo chlorophyll a fluorescence monitoring

Abstract

The microalga Chlorella fusca showed high biomass productivity in thin-layer cascades (TLCs) with large light-exposed surface (high exposed surface to total volume ratio; S/V). Two trials – E1 and E2 – were conducted in Málaga (Southern Spain) in July and October, respectively using a TLC with an S/V ratio of 27m−1. The third trial E3 was carried out in the Czech Republic in July using another TLC with an S/V ratio of 120m−1. Chl a fluorescence measurements (in situ and off-line) were carried out to monitor the photosynthetic performance of these cultures. Simultaneous measurement of irradiance and effective quantum yield through the day allowed the determination of daily electron transport rate (ETR), which led to the estimation of biomass productivity. Calculated data of biomass productivity of microalgal mass cultures were well correlated with the measured values. The E3 culture achieved the highest productivity of the three trials −27gDWm−2d−1. Extrapolating these results to southern Spain, with a longer cultivation period and higher daily dose of the solar energy, and considering a photosynthetic efficiency (PE) of 4.4% (achieved in E3), we obtained a potential productivity of 43metrictonsha−1year−1 if the unit is operated for 8months (from March to October). Realistically, in locations with favorable climate, TLCs can be considered a suitable system for biomass production with high PE as well as easy maintenance and low operation costs. On-line monitoring of in situ Chl a fluorescence provided data that revealed essential information about the photosynthetic performance of the culture. Here, we present a first attempt of estimating biomass productivity based on ETR measurements in microalgal mass cultures that correlate well with the measured values.