Good practices for the industrial cultivation of the cyanobacterium Arthrospira platensis under a greenhouse in a temperate zone (northern Italy)

Arthrospira, Spirulina, and Limnospira are cyanobacteria widely known as food supplements or additives and cultivated worldwide under the commercial name of spirulina. Many studies have been focused on the improvement of operational conditions for optimizing cell growth and harvesting. At present, greater attention is paid to obtaining a good-quality, possibly food-grade, product that can be added to different food formulations and to reducing the environmental impact by saving water and avoiding or minimizing the release of mineral salts in the environment. A few studies have addressed these aspects although, in most cases, through laboratory experiments or pilot plants. This study focused on the effects of medium recycling, monitored at each harvesting step, and nutrient replenishment on Arthrospira platensis growth, biomass, biochemical composition, and extracellular polysaccharide (EPS) production, in a production plant located in a temperate zone (northeastern Italy). Four out of the seven largest ponds (11,000 L each) of the plant were followed for a three-month semi-continuous cultivation, which included the period with the highest biomass productivity. Recycling the culture medium after biomass harvest effectively allowed the best nutritional status of the cells. Biomass productivity increased from June to August 2023 (mean values: 0.029 and 0.038 g L-1 d-1 at 25–26 °C and 27–29 °C, respectively). Protein, polysaccharides, and C-phycocyanin contents were 62, 22, and 12%, respectively, while EPS was < 7 mg L-1. The biochemical composition did not vary during the cultivation period, differently from previous studies performed with small culture volumes and for a short time.