Biotechnological Products and Process Engineering

Hydrogen gas (∼60% H2) was produced in a continuous flow bioreactor inoculated with heat-treated soil, and fed synthetic wastewater containing glucose (9.5 g l). The pH in the bioreactor was maintained at 5.5 to inhibit consumption of H2 by methanogens. The objective of this study was to characterize bacterial communities in the reactor operated under two different hydraulic retention times (HRTs of 30-h and 10-h) and temperatures (30°C and 37°C). At 30-h HRT, the H2 production rate was 80 ml h and yield was 0.91 mol H2/ mol glucose. At 10-h HRT, the H2 production rate was more than 5 times higher at 436 ml h, and yield was 1.61 mol H2/mol glucose. Samples were removed from the reactor under steady-state conditions for PCR-based detection of bacterial populations by ribosomal intergenic spacer analysis (RISA). Populations detected at 30-h HRT were more diverse than at 10-h HRT and included representatives of Bacillaceae, Clostridiaceae, and Enterobacteriaceae. At 10-h HRT, only Clostridiaceae were detected. When the temperature of the 10-h HRT reactor was increased from 30°C to 37°C, the steady-state H2 production rate increased slightly to 463 ml h and yield was 1.8 mol H2/mol glucose. Compared to 30°C, RISA fingerprints at 37°C from the 10-h HRT bioreactor exhibited a clear shift from populations related to Clostridium acidisoli (subcluster Ic) to populations related to Clostridium acetobutylicum (subcluster Ib).