Study of growth performance, protein, and pigments in Spirulina (Arthrospira sp.) using low-cost culture media

The most important limitation of the mass production of Spirulina microalgae in the world is the high cost of its culture medium. The present study was carried out with the aim of evaluating the cultivation mediums based on chemicals and commercial fertilizers and comparing the growth  characteristics, pigments, and the amount of protein in the produced spirulina in comparison with the Zarrouk’s medium. In order to meet the nutritional needs of Spirulina species, low-cost fertilizers were used in the form of 18 treatments and three replications. In all treatments, commercial sodium bicarbonate at 16.8 g/L, sea salt at 0.5 g/L, and the commercial liquid fertilizer (K:P, 20:20) were used to meet the phosphorus and potassium needs of the microalgae. To supply nitrogen in the treatments, three sources of sodium nitrate, urea, and a 50:50 combination of both were used. In all three groups, 6 substances were used in the form of 6 treatments (control, potassium, iron, a combination of potassium and iron, magnesium, and micronutrients). According to the results, the growth of Spirulina was higher in the control group (Zarrouk’s medium) than other treatments until the 20th day, but after that, the sodium nitrate -magnesium (N-Mg) treatment showed a higher growth rate than the control group. Also, the highest specific growth rate, cell density of algae, and the lowest doubling time were measured in the treatment containing sodium nitrate source. The highest algal cell density and specific growth rate were significantly (p<0.05) observed in sodium nitrate-magnesium (N-Mg) and sodium nitrate-micronutrients (N-Mic) treatments, which were significantly different from the control group (Zarrouk’s medium). The maximum chlorophyll a, chlorophyll b, and total pigment were obtained significantly in sodium nitrate-micronutrients (N-Mic) treatment (p<0.05). The highest amount of protein was obtained in the combined sodium nitrate-urea group with iron and potassium sources. To sum up, the highest growth rate and the highest cell density were obtained in the culture medium containing sodium nitrate, which is comparable to Zarrouk’s culture medium that can be used on a commercial scale.