Avaliação da utilização do dióxido de carbono proveniente da fermentação alcoólica no cultivo de Spirulina (Arthrospira) platensis: uso simultâneo de nitrato de sódio e sulfato de amônio como fontes de nitrogênio em fotobiorreator aberto / Evaluation of the use of carbon dioxide from alcoholic fermentation on Spirulina (Arthrospira) platensis cultivation: simultaneous use of sodium nitrate and ammonium sulphate as nitrogen sources in open photobioreactor

Mayla Santos Rodrigues

The main objective of this work was the evaluation of the potential of using carbon dioxide from alcoholic fermentation on Spirulina (Arthrospira) platensis cultivation, aiming to prove the feasibility of applying an effluent gas in the production of high added-value microbial biomass. In order to do so, the cyanobacterium was cultivated in laboratorial-scale open raceway tanks at temperature 30 ± 1 °C and light intensity 156 ± 20 µmol photons m-2 s-1. After the study of several cultivation variables, the following conditions were set: inoculum concentration 400 ± 20 mg L-1; pH 9,0 ± 0,3, controlled by the addition of carbon dioxide from cylinders; Schlösser medium, modified as to contain 0,497 and 16,4 g L-1 sodium carbonate and bicarbonate, respectively, and only 5,9 mM sodium nitrate; addition of 7,5 mM ammonium sulphate throughout 13 days, at exponentially increasing amounts, by the fed-batch cultivation process. Under such conditions, the following results were obtained: maximum cell concentration Xm = 2990 mg L-1, cell productivity PX = 185 mg L-1 d-1, maximum specific growth rate µm = 0,42 d-1, cell to nitrogen conversion factor YX/N = 8,85 mg mg-1, final chlorophyll content CLf = 4,3 mg g-1, and content of proteins (PTN) and lipids (LIP) of 35 and 21 %, respectively. Objectiving further optimized A. platensis growth, it was chosen to increase the light intensity from 156 to 192 or 252 ± 20 µmol photons m-2 s-1 on the 5th, 8th or 11th day of cultivation. The best results in terms of growth (Xm = 3954 mg L-1, PX = 253 mg L-1 d-1) and biomass content (CLf = 4,2 mg g-1, PTN = 28 %, LIP = 19 %) were reached with increasing the light intensity to 192 ± 20 µmol photons m-2 s-1 on the 8th day of cultivation. The runs carried out under such optimum conditions, but using carbon dioxide from alcoholic fermentation, led to the following results: Xm = 3298 mg L-1, PX = 206 mg L-1 d-1, CLf = 4,0 mg g-1, PTN = 28 %, LIP = 17 %. Conclusively, the use of carbonic acid gas from alcoholic fermentation on A. platensis cultivation was found viable. It would be valuable to further study the influence of this industrial effluent gas on the metabolism and growth of such photosynthetic microorganism, in order to make it possible reaching cell concentration and productivity results as high as those obtained using pure carbon dioxide.

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