Production and characterization of Spirulina sp. LEB 18 cultured in reused Zarrouk's medium in a raceway-type bioreactor.

The objective was to evaluate the effect of reusing Zarrouk's medium on a Spirulina sp. LEB 18 culture by determining kinetic parameters, chemical composition, biofuels, and thermal characterization. Cultivation was performed in a raceway bioreactor for 7 days, the supernatant was reused for four cycles. Culturing the microalga in the reused medium resulted in a cellular yield of 2.30 g L-1 (control) and 2.04, 1.89, 1.73, and 1.15 g L-1 for four cycles with no influence on cell growth and productivity. Biomass with high contents of carbohydrates (58.00%, 3rd cycle), phycocyanin (2.47 mg mL-1, 1st cycle), and saturated fatty acids (60.13%, 4th cycle) were obtained with an increase in the profiles of C16:0 (45.85%) and C18:2n6 (47.40%) in the 1st cycle. The reuse of Zarrouk's medium allowed obtaining biomass with reduced cost and differentiated characteristics, allowing the exploration of commercially important biomolecules by the completion of up to four cycles.