Effect of the light emitting diodes intensity and photoperiod in the optimization of the Spirulina (Arthrospira) biomass production

Abstract

Biomass (ф) production from Spirulina sp. batch cultures was optimized in laboratory scale photobioreactors (LPB) of 0.2 L, by the effect of X1: intensity of light emitting diodes (LEDs) and X2: photoperiod, between 1.25-41.7 klux and 12/12-24/0 hours of light/dark (L/D) respectively using a central composite rotational design (CCRD) and response surface methodology (RSM). The hydraulic characteristics and ф value from Spirulina batch cultures were also evaluated in a closed-loop channel photobioreactor open to the atmosphere (PB-CLOA) by the effect of the lighting LED of 8.3±1.9 klux and photoperiod of 12/12 and 24/0 h L/D. Two optimal zones of ф in LPB were identified, both with a 21.5 klux LED intensity and photoperiod relationship of 12/2 and 24/0 h L/D, with values of 1.65 and 1.62 ф respectively. The mathematical model which indicated the optimal zones was of 2nd order, which had a high significance (p = 0.000396 < 0.05) achieving a predictive value of R2 = 0.92. In the PB-CLOA, the cultivation of Spirulina sp. with photoperiod of 12/12 h L/D, showed a ф value of 0.72, a more rapid adaptation of λ = 4.62 h, a higher specific growth rate of μmax=0.033 h-1 and reduced time energy consumption of 74.05 h; compared to culture developed with photoperiod 24/0 h L/D. The PB-CLOA hydraulic parameters were: operation volume 2.5 L, flow velocity 0.26 m/s, numbers of Reynolds (Re) 15488, Froude (Fr) 0.60 and Vedernikov (Ved) 0.90.