Microalgae cultivation is a promising alternative to traditional agriculture in arid—semi-arid areas. The aim of this study is to assess the viability of long-term cultivation of native Arthrospira platensis in Gran Canaria. Maximum culture productivity (0.08 g/L/day) and optimal concentration range (0.6–0.9 g/L) were firstly determined in 8000 L raceway under a greenhouse. Afterwards, a stable productivity of 0.06 g/L/day (6.0 g/m²/day) was obtained by reusing the culture medium during 26 days of cultivation, with consistent biomass biochemical composition. Outdoor temperature and daily solar irradiation ranged between 17.9–30.7 °C and 79.2–274.8 W/m², while culture pH and salinity were in the range 9.42–10.77 and 11.2–14.9 g/L, respectively. Protein (>60%), potassium (1.8 g/100 g) and C-phycocyanin (7.2%) content is in the high-range of commercial Spirulina, which makes BEA 1257B promising for food and extraction of natural pigments/antioxidants. The dried biomass complies with international standards for human consumption, because of low heavy metal content and no pathogens presence. Product quality can be improved by reducing ash (≃12%) and sodium (1.5%) content through biomass washing optimization and/or further dewatering step. Other microorganisms can be prevented by high alkaline conditions and mild chemical treatments. These results pave the way for a sustainable microalgae-based blue bioeconomy in the Canary Islands.

Algal–bacterial interactions play a major role in shaping diversity of algal associated bacterial communities. Temporal variation in bacterial phylogenetic composition reflects changes of these complex interactions which occur during the algal growth cycle as well as throughout the lifetime of algal blooms. Viruses are also known to cause shifts in bacterial community diversity which could affect algal bloom phases. This study investigated on changes of bacterial and viral abundances, bacterial physiological status, and on bacterial successional pattern associated with the harmful benthic dinoflagellate Ostreopsis cf. ovata in batch cultures over the algal growth cycle. Bacterial community phylogenetic structure was assessed by 16S rRNA gene ION torrent sequencing. A comparison between bacterial community retrieved in cultures and that one co‐occurring in situ during the development of the O. cf. ovata bloom from where the algal strain was isolated was also reported. Bacterial community growth was characterized by a biphasic pattern with the highest contributions (~60%) of highly active bacteria found at the two bacterial exponential growth steps. An alphaproteobacterial consortium composed by the Rhodobacteraceae Dinoroseobacter (22.2%–35.4%) and Roseovarius (5.7%–18.3%), together with Oceanicaulis (14.2‐40.3%), was strongly associated with O. cf. ovata over the algal growth. The Rhodobacteraceae members encompassed phylotypes with an assessed mutualistic‐pathogenic bimodal behavior. Fabibacter (0.7%–25.2%), Labrenzia (5.6%–24.3%), and Dietzia (0.04%–1.7%) were relevant at the stationary phase. Overall, the successional pattern and the metabolic and functional traits of the bacterial community retrieved in culture mirror those ones underpinning O. cf. ovata bloom dynamics in field. Viral abundances increased synoptically with bacterial abundances during the first bacterial exponential growth step while being stationary during the second step. Microbial trends also suggest that viruses induced some shifts in bacterial community composition.

The goal of this study was to determine the feasibility of the large-scale cultivation of locally isolated Tetraselmis striata in different open ponds in Gran Canaria. The biomass productivities were 24.66 ± 0.53 kg_DW in 32 days (28.9 t/ha/year) for 8000 L indoors, 42.32 ± 0.81 kg_DW in 43 days (38.8 t/ha/year) for an 8000 L pond outdoors, and 54.9 ± 0.58 kg_DW in 28 days (19.6 t/ha/year) for a 45,000 L pond outdoors. The photosynthetic efficiencies were 1.45 ± 0.03% for an 8000 L pond indoors, 1.95 ± 0.04% for 8000 L outdoors. and 1.10 ± 0.01% for a 45,000 L pond outdoors. The selected strain was fast-growing (µ = 0.21 day⁻¹) and could be rapidly scaled up to 45,000 L; it formed healthy cultures that maintained high photosynthetic activity during long-term cultivation and provided stable biomass productivities, able to grow on urea, which acted as a cheap and effective grazer control. The obtained biomass is a good source of proteins and has an FA profile with a high content of some nutritionally important fatty acids: oleic, α-linolenic (ALA) and EPA. The high ash content in the biomass (>35%) can be reduced by the implementation of additional washing steps after the centrifugation of the culture.

Biomass harvesting represents one of the main bottlenecks in microalgae large-scale production. Solid–liquid separation of the biomass accounts for 30% of the total production costs, which can be reduced by the use of flocculants as a pre-concentration step in the downstream process. The natural polymer chitosan and the two chemical flocculants FeCl₃ and AlCl₃ were tested on freshwater Chlorella sorokiniana and two marine algae, Dunaliella tertiolecta and Tetraselmis striata. A preliminary screening at the laboratory scale was performed to detect the most suitable doses of flocculants. On the basis of these results, selected doses were tested on the pilot scale, using the flocculants for a pre-concentration step and the centrifugation as a second step to confirm the effectiveness of flocculants in a realistic operational environment. The biomass recoveries (R_pilot, %) of 100 L cultures were as follows: (1) for T. striata, R_pilot = 94.6% for 0.08 g/L AlCl₃, 88.4% for 0.1 g/L FeCl₃, and 68.3% for 0.04 g/L chitosan; (2) for D. tertiolecta, R_pilot = 81.7% for 0.1 g/L AlCl₃, 87.9% for 0.2 g/L FeCl₃, and 81.6% for 0.1 g/L chitosan; and (3) for C. sorokiniana, R_pilot = 89.6% for 0.1 g/L AlCl₃, 98.6% for 0.2 g/L FeCl₃, and 68.3% for 0.1 g/L chitosan. Flocculation reduced the harvesting costs by 85.9 ± 4.5% using chemical flocculants. Excesses of aluminum and iron in the biomass could be solved by decreasing the pH in the biomass combined with washing. This is the first study, to the best of our knowledge, that investigates the pilot-scale flocculation of three native Canarian microalgal strains. A pilot-scale pre-concentration step before centrifugation can improve the yield and reduce costs in the microalgae harvesting process.

Protein and phycocyanin production is challenged by freshwater scarcity in arid coastal regions. This study assessed and optimized the cultivation of Limnospira platensis BEA 1257B in full seawater. Eight cultivation phases were conducted in 10,000 L raceways under a greenhouse to evaluate the effects of seawater content, nutrient availability, shading, CO₂ supply, and medium recycling on biomass productivity and biochemical composition. Freshwater, energy, and fertilizer savings, together with effluent characteristics of the optimized full-seawater recirculation strategy (SWR), were evaluated against a conventional freshwater cultivation process. Lower productivity was associated with high salinity and irradiance. Under long-term optimized conditions (615 days), the strain achieved stable productivities of 4.1 ± 1.4 gDW m⁻² day⁻¹ (14.8 ± 5.0 tDW ha⁻¹ year⁻¹). Increasing salinity promoted carbohydrate accumulation in the biomass (26.0% AFWD), while protein (64.4%) and C-phycocyanin (9.9%) moderately decreased. Nevertheless, protein quality, phycocyanin, and essential fatty acids remained high. Spray-dried biomass exhibited nutritionally relevant contents of K, Mg, Ca, Fe, and Mn, and complied with international food safety standards. SWR reduced energy demand by 10.5% and freshwater consumption by 12% on a surface basis, although these advantages were partially offset when expressed per unit of product, while clearly supporting environmentally sustainable and regulatory-compliant Limnospira production.