Improvement of microalgae biomass productivity and subsequent biogas yield of hydrothermal gasification via optimization of illumination

Abstract

This study examines the light factorial optimization of Chlorella vulgaris microalgae cultivation under different wavelengths and light intensities. RGB light-emitting diodes were applied on microtiter plate and lab scale stirred tank photobioreactors. One-way ANOVA and response surface methodology were adopted to investigate the effects on biomass productivity. The highest biomass productivity is found at 243.5 and 96.8 μmol photon m−2 s−1 in case of red and blue color intensities, respectively. Scaled-up fermentation in stirred tank photobioreactors shows that changing light intensity and aeration settings result in differing biomass productivity and composition. The effects of targeted cultivation are investigated on hydrothermal gasification (HTG) which is carried out in tubular reactor system at 550 °C, 30.0 MPa and average 120 s residence time. It is found that the fermentation of microalgae under optimized light factor levels results in higher H2 yield compared to unoptimized light intensity levels. Throughout the HTG process high H2 yield is achieved (4.38–9.34 mol kg−1) without using any catalyst, which indicates that the efficiency of downstream processing can be increased already at the cultivation stage.