Performance intensification of a stirred bioreactor for fermentative biohydrogen production

In this study, the biohydrogen (bioH₂) production of a microbial consortium was optimized by adjusting the type and configuration of two impellers, the mixing regimen and the mass transfer process (K_La coefficients). A continuous stirred-tank reactor (CSTR) system, with a nonstandard geometry, was characterized. Two different mixing configurations with either predominant axial (PB4 impeller) or radial pumping (Rushton impeller) were assessed and four different impeller configurations to produce bioH₂. The best configuration for an adequate mixing time was determined by an ANOVA analysis. A response surface methodology was also used to fully elucidate the optimal configuration. When the PB4 impellers were placed in best configuration, c/Dt = 0.5, s/Di = 1, the maximum bioH₂ productivity obtained was 440 mL L⁻¹ hr⁻¹, with a bioH₂ molar yield of 1.8. The second best configuration obtained with the PB4 impellers presented a bioH₂ productivity of 407.94 mL L⁻¹ hr⁻¹. The configurations based on Rushton impellers showed a lower bioH₂ productivity and bioH₂ molar yield of 177.065 mL L⁻¹ hr⁻¹ and 0.71, respectively. The experiments with axial impellers (PB4) showed the lowest K_La coefficient and the highest bioH₂ production, suggesting that mixing is more important than K_La for the enhanced production of bioH_2.