FIG. 1.

Parameter profiles in a photobioreactor culture of C. tepidum with thiosulfate (12 mM) as the preferred electron source. Medium 1 with 12 mM thiosulfate was used for this culture. H₂S gas was used primarily as the medium reductant and the obligatory required reduced-sulfur source. It was supplied by using the following strategy. Before inoculation, the redox potential of the medium was lowered to −320 mV by using manually controlled flow of H₂S into the vessel. From then on, the H₂S flow rate was regulated by a control system with a set point of −300 ± 20 mV for the culture redox potential. NaOH (2 M) was added via a control system to maintain the pH at 6.8 ± 0.2.