Fig. 1
From: High cell density cultivation by anaerobic respiration
Principle of anaerobic high cell density culturing (HCDC) as fed-batch. A The culture is fed by peristaltic pumping of HNO3- and glucose-solutions, and by manual injection of trace element solutions. The feed rate is controlled by measured pH, ensuring that pH is kept within a narrow interval. The culture is sparged with N2 to remove CO2. B The respiratory reduction of HNO3 to N2 raises the pH, which is compensated by pumping a dose of HNO3. C Based on the titration curve of the growth medium, the pH interval translates into an HNO3 concentration interval. Our results indicated that the relationship between pH and HNO3 concentration could be obscured by high CO2 concentrations (lowering the pH), which would require a refined control algorithm taking monitored CO2 concentrations into account