Optimization of spectral light quality for growth and product formation in different microalgae using a continuous photobioreactor

Many parameters for microalgae cultivation are not fully optimized so far. Even though light is one important process parameter, little research is done regarding its spectral composition. In contrast to other published data, mostly with monochromatic or dichromatic illumination, the objective of this study was to investigate the influence of a broad range of different light qualities to the productivity of cell dry weight as well as the productivity of their phycobiliproteins phycoerythrin or phycocyanin, by keeping the overall light intensity constant. Instead of cultivating in batch mode, cultivations were done in continuous mode in closed, thermal sterilizable photobioreactors. A total of 37 light quality conditions are shown in this work. In case of Chlamydomonas reinhardtii a composition of αred : αgreen : αblue of 80:10:10 resulted in the highest biomass productivity, with a value of 252 mg·L− 1·d− 1. A maximum biomass productivity is achieved for Galdieria sulphuraria at pure red light (304 mg·L− 1·d− 1), whereas the highest phycocyanin productivity is reached at a ratio of αred : αgreen : αblue of 60:0:40 (4.99 mg·L− 1·d− 1). The highest biomass and phycoerythrin productivity was achieved for Porphyridium purpureum at αred : αgreen : αblue of 40:40:20, with values of 312 mg·L− 1·d− 1 and 16.93 mg·L− 1·d− 1, respectively. The collected data show clearly the significance to investigate the right mixture of light for every microalgal strain and the desired product of interest individually.