Optimisation of culture conditions for biological hydrogen production by Citrobacter freundii CWBI952 in batch, sequenced-batch and semicontinuous operating mode

Investigations were carried out to determine the effect of the pH, the nitrogen source, iron
and the dilution rate (h 1) on fermentative hydrogen production from glucose by the newly
isolated strain Citrobacter freundii CWBI952. The hydrogen production rate (HPR), hydrogen
yield, biomass and soluble metabolites were monitored at 30 C in 100 mL serum bottles
and in a 2.3 L bioreactor operated in batch, sequenced-batch and semicontinuous mode.
The results indicate that hydrogen production activity, formate biosynthesis and glucose
intake rates are very sensitive to the culture pH, and that additional formate bioconversion
and production of hydrogen with lower biomass yields can be obtained at pH 5.9. In
a further series of cultures casein peptone was replaced by (NH4)2SO4, a low cost alternative
nitrogen source. The ammonia-based substitute was found to be suitable for H2
production when a concentration of 0.045 g/L FeSO4 was provided. Optimal overall
performances (ca. an HPR of 33.2 mL H2/L h and a yield of 0:83 molH2 =molglucose) were
obtained in the semicontinuous culture applying the previously optimized parameters for
pH, nitrogen, and iron with a dilution rate of 0.012 h 1 and degassing of biogas by N2 at
a 28 mL/min flow rate.