Optimization of a low-cost fertilizer-based medium for large-scale cultivation of the coastal diatom Conticribra weissflogii using response surface methodology and its effects on biomass composition

Diatoms are widely studied because of their potential in aquaculture and in the pharmaceutical and nutraceutical industries due to the production of bioactive compounds such as fatty acids and pigments. However, for this potential to be achieved, it is necessary to make their large-scale cultivation economically viable, with a significant reduction in the cost of the medium. The objective of this work was to optimize a fertilizer-based medium to cultivate the marine diatom Conticribra weissflogii, a potential producer of the fatty acids eicosapentaenoic acid (C20:5) and docosahexaenoic acid (C22:6) and pigments like fucoxanthin. For this, a Plackett–Burman screening experiment was performed to eliminate non-essential nutrients and the response surface methodology was employed to optimize concentrations of the essential nutrients considering two responses, growth and cost–benefit. After optimization, media validation, and cost analysis were performed, the optimized medium was tested outdoors on a pilot scale in 330-L photobioreactors and in 1800-L circular tanks, and the growth rate was compared with the bench scale. Lastly, the biomass composition was analyzed. The screening experiments showed that among the evaluated nutrients, only urea, calcium phosphate, metasilicate, and biotin were relevant for the growth of C. weissflogii, and the concentrations of these elements have been optimized to obtain the greatest growth and the best cost–benefit ratio. Conticribra weissflogii presented similar results of growth and cost–benefit among treatments, although the medium developed to test the cost–benefit was 32.4% cheaper. Moreover, compared to the laboratory f/2 medium, the costs of this medium were 79.43% lower. The produced biomass in the cost–benefit medium had reduced ash contents, whereas protein, lipids, and fucoxanthin were the same in comparison to the regular culture medium. No difference was observed in the percentage of eicosapentaenoic acid. Thus, the results showed improved production of C. weissflogii at a commercial scale by reducing the medium costs without compromising the biomass quality.