Microalgae are considered a promising resource of proteins, lipids, carbohydrates, and other functional biomolecules for food and feed markets. Competitive drying solutions are required to meet future demands for high-quality algal biomass while ensuring proper preservation at reduced costs. Since often used drying methods, such as freeze or spray drying, are energy and time consuming, more sustainable processes remain to be developed. This study tested an indirect and hybrid solar dryer as an alternative to conventional freeze drying of industrially produced Tetraselmis chui and Nannochloropsis oceanica wet paste. The effects of the drying method on biomass quality parameters, including biochemical profiles, functional properties, and microbial safety, were assessed. No significant differences were found between the applied drying technologies for total proteins, carbohydrates, lipids, and fatty acid profiles. On the other hand, some pigments showed significant differences, displaying up to 44.5% higher contents in freeze-dried samples. Minor differences were also registered in the mineral profiles (<10%). Analyses of microbial safety and functional properties of the solar-dried biomass appear adequate for food and feed products. In conclusion, industrial solar drying is a sustainable technology with a high potential to preserve high-quality microalgal biomass for various markets at expected lower costs.

S. costatum and C. calcitrans are two cosmopolitan high-value centric diatoms, with a rich nutritional profile. The following work optimised the culture medium of S. costatum and C. calcitrans cultures, respectively, in a stepwise process as follows: 2.4 mM and 1.2 mM of silicate, 4 mM of nitrate, 100 µM of phosphate, 20 and 80 µM iron, and 0.5 mL L−1 of micronutrients. The results that were obtained revealed an increase in biomass productivity with a 1.8- and 3.2-fold increase in biomass that was produced by S. costatum and C. calcitrans, respectively. The biochemical profile showed an increase in high-value PUFAs such as 2.6-fold and 2.3-fold increase in EPA for S. costatum and C. calcitrans, respectively, whilst a 2.6-fold increase in DHA was detected in S. costatum cultures. The present work provides the basic tools for the industrial cultivation of S. costatum and C. calcitrans with enhanced productivity as well as improved biomass quality, two factors which are highly relevant for a more effective application of these diatoms to aquaculture and nutraceutical production.

The continuous growth of the world population has imposed major challenges on agriculture. Consequently, farmers generalized the overuse of synthetic fertilizers and pesticides to meet the global food demand. Although these products have helped many developing countries increase their crop yield, they have simultaneously resulted in many issues, mainly the decline of soil fertility and degradation of local ecosystems due to soil, water, and air contamination, combined with their non-renewable nature and increased costs. For agriculture to become more sustainable, the use of alternative biological products, with recognized beneficial effects on plant yield and health, must be expanded. In this context, microalgae and cyanobacteria are rich sources of nutrients and bioactive metabolites, which have been gaining attention from researchers and companies for their ability to improve plant nutrition, growth, and tolerance to stress. This review gives an overview of the research work that has been done in the last two decades, regarding the use of microalgae and cyanobacteria (blue-green algae) as biofertilizers, biostimulants, and biopesticides. This work identified trends and challenges and highlights the use of microalgae to recycle the nutrients from wastewater to improve plant productivity while reducing the fertilizer and water footprint for more sustainable agriculture practices.