Evaluation of Growth Yield of Spirulina maxima in Photobioreactors

Microalgae biomass has become a valuable material, the attractiveness of which is familiar to a wider group of customers, not only as a biomass (a prepared product), but also as a raw material for the production of a number of valuable substances like ethanol, hydrogen, hormones, biostimulants, and many other. Human nutrition, animal feeding, biofuel production, and sustainable agriculture – these are the branches of industry that are interested in microalgae biomass1,2. The literature on the subject presents various studies on the productivity of different microalgal culture systems3–7. The highest productivity was obtained for Chlorella and Spirulina: 7.70 g L–1 day–1 and 130 g m–2 day–1 for Chlorella, and 4.3 g m–2 day–1 and 51 g L–1 day–1 for Spirulina respectively8. Commercial production of Spirulina, that in the strict sense is not a microalga, but a cyanobacterium1, has gained worldwide attention for its use in human food supplements, animal feed, and pharmaceuticals. The production of Spirulina with reduced costs is necessary when considering a large-scale cultivation for industrial purposes. For microbial cultures, the growth rate and growth yield are equally important. Although there are many papers that deal with the effect of culture conditions on the growth rate9–12, there is little information concerning their influence on the growth yield, and thus the efficiency of the conversion of substrates into biomass. Such knowledge is not only necessary for the efficient cultivation of cells, but also allows for assessment of the economic aspects of the process. The greatest disadvantage incurring the highest cost in microalgae cultivation is the reactor/photobioreactor construction. Many advanced and complicated solutions for the cultivation of microalgae have been proposed12–15. If cheaper construction of a reactor for the cultivation of photoautotrophic organisms with a better utilization of nutrients could be used instead of technically advanced solutions, greater economic sustainability could be achieved16–19. Two reactors that differ in their construction, ratio of illuminated surface (A) to volume (V), and operating costs were used. The aim of this work was to present whether the more advanced construction would bring about better conditions for growth of cells, and at same time, higher nutrients utilization effectiveness. By using two sets of reactors on a large-laboratory and semi-technical scale, the present work aimed at evaluating the growth yield of S. maxima, and estimating the photosynthetic, carbon, and phosphorus utilization efficiencies.