Enlightening the dark side of Arthrospira maxima cultivation: evaluation of carbon supply modes and performance at optimal growth conditions

Abstract

Night biomass loss due to respiratory activity can significantly impact the phytoplankton biomass productivity and the yield of specific biomolecules. A decrease in biomass loss can be achieved by cyclic two-stage cultivation (CTSC) employing an organic carbon source during the dark phase of the photoperiod. Thus, sugarcane vinasse was used as carbon supply in CTSC to influence the Arthrospira maxima growth. The impact of carbon supply on CTSC was assessed and the results show that splitting the supplementation volume of 60 mL supplemented vinasse into three doses of 20 mL during the dark phase increased biomass productivity by 35.4%, although the maximum exponential growth rate was unaffected. The cyanobacterium also takes up CO₂ (supplied in the light phase) as ${\mathrm{HCO}}_3^{-}$, high concentrations of which increase biomass loss. Thus, carbon assimilation in CTSC is higher when the concentration of dissolved inorganic carbon is reduced. Optimization of organic and inorganic carbon supply in CTSC with the response surface methodology resulted in an increased growth rate (from 0.73 to 1.18–1.62 day⁻¹) and a reduction of cultivation time (from 7 to 5 days), thus producing a synergistic effect of reduced night biomass loss and vinasse treatment. After cultivating A. maxima for 5 days under optimal conditions (culture medium with 6.81 g L⁻¹ of NaHCO₃ and adding 1.5% (v/v) vinasse every 4 h during the dark phase), the reduction of chemical oxygen demand and electrical conductivity demonstrates that removal of organic matter present in the vinasse was due to cell growth during CTSC.