The outdoor production of marine microalgae biomass in pilot scale flat panels photobioreactors, under not sterile conditions and using centrate as nutrients source, was studied. Experiments were performed modifying the centrate percentage, dilution rate and orientation of the photobioreactors. The strain Geitlerinema sp. was that one prevailing independently of the culture conditions. The higher productivity of 47.7 g_biomass m^-2·day^-1 dry weight and photosynthetic efficiency of 2.8%, was achieved when using 20% centrate and a dilution rate of 0.3 day^-1, whatever the orientation of the reactor, maximal nutrient removal capacities of 82%, 85% and 100% for carbon, nitrogen and phosphorus being obtained. Under non-optimal conditions up to 80% of the nitrogen and 60% of the phosphorus were lost by stripping and precipitation, respectively. Carbohydrates was the major component of the biomass followed by proteins and lipids. These results support the possibility to produce microalgae biomass below 0.59 €/kg, useful to produce biofertilizers and animal feed.

The production of marine microalgae provides a sustainable solution for agriculture, acting as biostimulants to enhance seed germination, vigor, and early growth. In the present work, the parameters of pH, airflow, and dilution speed were established to produce biomass of two species of marine algae (Nannochloropsis gaditana and Thalassiosira sp.); in addition, its capacity to stimulate the germination of bean seeds was evaluated. The experimental treatments included three biomass concentrations (C_b) of both microalgae species (0.5, 1, and 1.5 g·L⁻¹) and a control (distilled water) at two temperatures (25 and 35 °C). The rate, index, average time, time at 50% germination, and vigor were evaluated. The results indicated that the highest yield of microalgae biomass was obtained with D = 0.3 day⁻¹ for N. gaditana and 0.2 day⁻¹ for Thalassiosira sp. Microalgae biomass showed activity as a biostimulant on germination, improving the germination rate and reducing the germination time with better vigor for the seedlings at each of the evaluated concentrations.

The west coast of Saudi Arabia borders the Red Sea, which maintains high average temperatures and increased salinity compared to other seas or oceans. Summer conditions in the Arabian Peninsula may exceed the temperature tolerance of most currently cultivated microalgae. The Cyanidiales are polyextremophilic red algae whose native habitats are at the edges of acidic hot springs. Cyanidioschyzon merolae 10D has recently emerged as an interesting model organism capable of high-cell density cultivation on pure CO ₂ with optimal growth at 42 °C and low pH between 0.5-2. C. merolae biomass has an interesting macromolecular composition, is protein rich, and contains valuable bio-products like heat-stable phycocyanin, carotenoids, β-glucan, and starch. Here, photobioreactors were used to model C. merolae 10D growth performance in simulated environmental conditions of the mid-Red Sea coast across four seasons, it was then grown at various scales outdoors in Thuwal, Saudi Arabia during the Summer of 2022. We show that C. merolae 10D is amenable to cultivation with industrial-grade nutrient and CO ₂ inputs outdoors in this location and that its biomass is relatively constant in biochemical composition across culture conditions. We also show the adaptation of C. merolae 10D to high salinity levels of those found in Red Sea waters and conducted further modeled cultivations in nutrient enriched local sea water. It was determined that salt-water adapted C. merolae 10D could be cultivated with reduced nutrient inputs in local conditions. The results presented here indicate this may be a promising alternative species for algal bioprocesses in outdoor conditions in extreme desert summer environments.

Agricultural inputs based on microalgae have been successfully tested at different stages of the crop cycle, from sowing to harvest, to enhance crop performance. In this study, biomass from Nannochloropsis gaditana and Thalassiosira sp. was obtained to evaluate its effect on wheat seed germination under two temperature conditions. Microalgal biomass was produced under controlled conditions (neutral pH, air flow of 1 L·min⁻¹, and a dilution rate of 0.2 day⁻¹). The biomass was characterized for its lipid, carbohydrate, protein, and ash content. Subsequently, its effect on germination, as well as on glucose and amylose content in wheat seedlings, was assessed. Four biomass concentrations were tested (0.0 [distilled water], 0.5, 1.0, and 1.5 g·L⁻¹) at two incubation temperatures (25 and 35 °C). Results showed that Thalassiosira sp. lightly promoted the germination rate more than N. gaditana. Germination parameters were negatively affected by high temperature, but treatments with Thalassiosira sp. alleviated this effect, showing values comparable to those obtained at the optimal temperature. Vigor parameters were improved compared with the control in both temperatures. Glucose and amylose contents exhibited irregular but consistent patterns. However, at a temperature of 35 °C, a slight conversion of starch to glucose could be observed. Overall, microalgal biomass did not significantly improve germination or its time variables, but it could exert a protective effect against high-temperature stress, particularly in the case of Thalassiosira sp.

The use of cattle manure wastewater for microalgae cultivation is beneficial, as it contains nutrients such as N, P, K, Mg, Zn, and Fe. Therefore, different species of algae were isolated and cultivated, and nutrient analyses were conducted, including microalgae Watanabea sp., which resulted in higher biomass production (1.5 g L⁻¹), 36% protein, and 40% carbohydrates, although the ash fraction was only 8%, the lowest. In a TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) analysis, this species was selected from among the isolates because it demonstrated the best performance for use as a biostimulant for chili germination. After that, optimal conditions were established for cultivating Watanabea sp. microalgae in six polypropylene photobioreactors with a capacity of 2.9 L were used and tested at pH values of 7.0, 7.5, 8.0, 8.5, 9.0, and 9.5, at T = 25 °C, under constant light at 850 µE∙m⁻²∙s⁻¹, and different dilution rates from 0.1 until 0.9%. The highest biomass production was achieved at pH 7.5 and a dilution rate of 0.1%, indicating that slightly alkaline conditions favored biomass accumulation. These conditions were associated with enhanced nitrate and phosphate assimilation. Furthermore, the effect of Watanabea sp. biomass on stimulating the germination of agricultural chili (Capsicum annuum L.) seeds was evaluated. Three methods of application (grounding and ungrounding freeze-lyophilized and fresh biomass) and concentrations of microalgal biomass (0.5, 1.0, and 1.5 g L⁻¹) and a control (distilled water) were used at two temperatures (25 and 35 °C). The microalgae Watanabea sp. grounding freeze-lyophilized and treated chili seeds increased the final germination percentage and slightly earlier with better vigor and root growth at both temperatures. Further studies are needed to evaluate its effects on seedling establishment and field performance.