Media Recycling in Commercial Scale Spirulina platensis Cultivation
Author: Alexandria Rae Massey
Year: 2023
Supervisors: Guðrún Sævarsdóttir, Ari Ingimundarson
Abstract:
Algae has been cultivated for various products since the 1940s. Nutrient recycling has been investigated since then to reduce production costs and the environmental impacts of algae cultivation. Majority of these studies have been done in small scale lab scenarios; however, this study is to investigate the impacts that recycling media can have on Arthrospira platensis cultivation at a commercial scale. To recycle the media, harvested culture is sent to a mechanical shaker to separate the product from the media to be reused. The media is then filtered and UV treated before being returned to the production unit. In this thesis it was demonstrated that recycled media could be successfully used for four cycles without nutrient replenishment. After five cycles of recycled media, the phycocyanin (CPC) content of the algae fell from 18% to 4%. The experiment was repeated with nutrient replenishment to see if the media could be recycled for more cycles, but the CPC concentration fell again during the fifth cycle. These two experiments have determined that it is not the nitrate and phosphate concentrations that limit media recycling, but the complete depletion of sulfur. This sulfur depletion results in production of polysaccharides over CPC with little effect on growth rate. VAXA will use the results of this thesis to recycle media for four cycles which will save €94.60 in nutrient costs for each cycle in a 6200 L bioreactor.