Bio-hydrogen production from ground wheat starch by continuous combined fermentation using annular-hybrid bioreactor

Continuous combined fermentation of ground wheat starch was realized in an annular-hybrid bioreactor (AHB) for hydrogen gas production. A mixture of pure cultures of Clostridium beijerinkii (DSMZ-791) and Rhodobacter sphaeroides-RV were used as seed cultures in combined fermentation. The feed contained 5 g L⁻¹ ground wheat with some nutrient supplementation. Effects of hydraulic residence time (HRT) on the rate and yield of hydrogen gas formation were investigated. Steady-state daily hydrogen production decreased but, hydrogen yield increased with increasing HRT. The highest hydrogen yield was 90 ml g⁻¹ starch at HRT of 6 days. Hydrolysis of starch and fermentation of glucose to volatile fatty acids (VFA) were readily realized at all HRTs. However, slow conversion of VFAs to H₂ and CO₂ by photo-fermentation caused accumulation of VFAs in the medium. Specific and volumetric rates of hydrogen formation also decreased with increasing HRT. High hydrogen yields obtained at high HRTs are due to partial fermentation of VFAs by Rhodobacter sp. The system should be operated at HRTs longer than 5 days for effective hydrogen gas formation by the dark and photo-fermentation bacteria.