Using an innovative pH-stat CO₂ feeding strategy to enhance cell growth and C-phycocyanin production from Spirulina platensis

Spirulina platensis can mitigate CO₂ emissions and simultaneously produce an antioxidant called C-phycocyanin (C-PC), which is a high value nutraceutical product. An innovative pH control system was used to cultivate S. platensis, in which CO₂ feeding, instead of acid/alkaline titration, was used to control the pH of the culture. The optimum culture pH was 9.5. Compared to continuous CO₂ feeding system, the pH control system improved the CO₂ removal efficiency from 13.6% to 62.3%. The C-PC content and productivity were also enhanced to 16.8% and 0.17 g/L/d, respectively. Therefore, the proposed pH control system is economic and sustainable as it avoids the use of acid/alkaline and reduces the overall CO₂ emissions. A two-stage C-PC purification process combining fractional precipitation and ion exchange chromatography could achieve the highest purity (A₆₁₅/A₂₈₀) of 4.33 with a 33% C-PC recovery.