Impact of salinity on the kinetics of CO2 fixation by Spirulina platensis cultivated in semi-continuous photobioreactors

Abstract

In this research, the physiological response of the microalgae Spirulina platensis to salinity stress (1 and 100 g L-1 ) was investigated. Spirulina platensis and Spirulina platensis (adapted to high salt concentration) were operated at laboratory scale in a semi-continuous photobioreactors. The responses examined were within 0.5 to 10% CO2 concentration, temperatures from 10 to 40 oC, light intensities from 60 to 200 μmol m-2 s -1 and presented better results in terms of all kinetic parameters. The highest rate of CO2 biofixation for Spirulina platensis was 25.1 gCO2 m-3 h -1 , and the maximum specific growth (μmax) achieved was 0.44 d-1 - 0.67 d-1 at 2.5% CO2, 150 µmol m-2 s -1 at 25 oC. Corresponding determined values of Spirulina platensis adapted were 18.2 gCO2 m-3 h -1 , 0.31 d-1 - 0.58 d-1 at 2.5% CO2, 60 µmol s-1 m-2 and 28 oC. However, both microalgae exhibited experimental limiting growth factors, CO2 10%, 40 oC and 200 µmol m-2 s -1 , conditions under which photosynthetic CO2 biofixation may be inhibited and photoinhibition of photosynthesis may be enhanced by salinity. The efficiency of 2.5% CO2 removal by Spirulina platensis achieved 99%, whereas Spirulina platensis adapted to 96%, respectively. The kinetic parameters estimated for Spirulina platensis can be used to improve photobioreactor design for reducing of atmospheric carbon dioxide.

Investigation of Hydrodynamic Parameters in an Airlift Photobioreactor on CO2 Biofixation by Spirulina sp.

“…strain was sourced from Science and Technology Park, Bushehr, Iran, and it was cultivated in BG-11 culture medium [32], which is described in Table 1. The stock culture was maintained in a 500 mL Erlenmeyer flask containing 250 mL of the medium at 27 • C under 60 µmol m −2 s −1 of light intensity and a 12/12 h day/night cycle [15].…”

“…For this purpose, experiments, which were repeated three times, conducted at six different gas velocities of (0.185, 0.524, 0.857, 1.176, 1.593, and 1.936 cm/s) (Table 2), to find out the range of the bubbly flow (homogenous regime) for optimum cyanobacterial growth. [15,33] was sparged at the bottom of the reactor. Two separate experiments were carried out for 7 days at gas velocities of 0.185 and 0.524 cm/s corresponding to flow rates of 0.87 and 2.47 L/min or 0.054 and 0.154 volume of air per medium volume per minute (vvm), respectively.…”

“…The initial concentration of cyanobacteria was about 0.5 g L −1 . The light intensity was 150 µmol photons m −2 s −1 with a 12:12 light-dark (LD) cycle, and the temperature was 30 ± 1 • C [15,34]. The pH of the culture medium was adjusted to 9.5 ± 0.02 using 6 M NaOH [19,35].…”

“…Each day, a 20 mL sample from the ALR was withdrawn to measure the growth medium optical density at 680 nm (OD 680 ) [15,40] using a spectrophotometer (DR 5000, Hach, Loveland, HQ, USA).…”

“…is an ideal candidate due to its resistance to harsh environmental conditions, high CO 2 fixation ability, and growth rate [13,14]. For instance, the removal efficiency of CO 2 fixation by Spirulina platensis at 5% CO 2 in the feed gas was found to be 81% in a semi-continuous process [15]. Also, using 6% and 12% CO 2, the maximum CO 2 biofixation by Spirulina sp.…”