ACTUAL AND POTENTIAL RATES OF HYDROGEN PHOTOPRODUCTION BY CONTINUOUS-CULTURE OF THE PURPLE NONSULFUR BACTERIUM RHODOBACTER-CAPSULATUS

The influence of (NH4)(2)SO4 concentration and dilution rate (D) on ac tual and potential H-2 photoproduction has been studied in ammonium-li mited chemostat cultures of Rhodobacter capsulatus B10. The actual H-2 production in a photobioreactor was maximal (approx. 80 ml h(-1) l(-1 )) at D = 0.06 h(-1) and 4 mM (NH4)(2)SO4 However, it was lower than t he potential H-2 evolution (calculated from hydrogen evolution rates i n incubation vials), which amounted to 100-120 ml h(-1) l(-1) at D = 0 .03-0.08 h(-1). Taking into account the fact that H-2 production in th e photobioreactor under these conditions was not limited by light or l actate, another limiting (inhibiting) factor should be sought. One pos sibility is an inhibition of H-2 production by the H-2 accumulated in the gas phase. This is apparent from the non-linear kinetics of H-2 ev olution in the vials or from its inhibition by the addition of H-2; in itial rates were restored in both cases after the vials had been refil led with argon. The actual H-2 production in the photobioreactor at D = 0.06 h(-1) was shown to increase from approximately 80 ml h(-1) l(-1 ) to approximately 100 ml h(-1) l(-1) under an argon flow at 100 ml mi n(-1). Under maximal H-2 production rates in the photobioreactor, up t o 30% of the lactate feedstock was utilised for H-2 production and 50% for biomass synthesis.