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The feasibility of hydrogen production from distillers grains substrate, an industrial cellulosic waste, was investigated. A substrate concentration of 80 g/L gave the maximum production at 50 °C and pH of 6.0 using sewage sludge. Four controllable factors with three levels: seed sludge (two sewage sludges and cow dung), temperature (40, 50, and 60 °C), pH (6, 7 and 8) and seed pretreatment (none, heat, and acid) were selected in Taguchi experimental design to optimize fermentation conditions. The peak hydrogen and ethanol productions were found with heat-treated cow dung seed, substrate concentration 80 g/L, 50 °C and pH 6. The peak hydrogen production rate and hydrogen yield were 7.9 mmol H2/L/d and 0.40 mmol H2/g-COD respectively whereas the peak ethanol production was 3050 mg COD/L and rate 0.22 g EtOH/L/d. A total bioenergy yield of 41 J/g substrate was obtained which was 21% and 79% from hydrogen and ethanol respectively.

Biohydrogen production from untreated rice straw using different heat-treated sludge, initial cultivation pH, substrate concentration and particle size was evaluated at 55 °C. The peak hydrogen production yield of 24.8 mL/g TS was obtained with rice straw concentration 90 g TS/L, particle size

The effect of effluent recycle on hydrogen production in an anaerobic continuous stirred tank reactor (CSTR) was investigated. The CSTR was fed on sucrose (20 g chemical oxygen demand (COD)/L) and at hydraulic retention time (HRT) of 12 h. The pH and temperature were regulated around 6.7 and 35 °C, respectively. The effluent was then recycled at recycle ratios of 0, 0.2, 0.4, 0.6, 0.8 and 1.0. When the recycle ratios increased, the volatile suspended solid (VSS) concentration also increased with a peak of 14.2% at the recycle ratio 0.4 compared with the VSS 3.52 g/L without effluent recycle. However, a drastic drop in hydrogen production performance was observed with increased recycle ratio. The strategy of increasing organic loading rate by increasing the substrate concentration and shorting the HRT was then applied keeping a recycle ratio of 0.2. VSS concentration increased with increasing substrate concentration but as the HRT was shortened from 12 h to 2 h stepwise, VSS concentration increased first and then decreased at HRT 8 h. The maximal hydrogen production was obtained at sucrose concentration of 20 g COD/L and HRT 6 h (organic loading rate (OLR) 66.7 g COD/L-d) with recycle ratio 0.2. The hydrogen yield, hydrogen production rate and specific hydrogen production rate values also peaked at the same conditions (sucrose 20 g COD/L and HRT 6 h) with 3.88 mol H 2 /mol sucrose, 807 mmol H 2 /L-d and 244.3 mmol H 2 /g VSS-d, respectively. This study showed peak hydrogen production performance at OLR 66.7 g COD/L-d in the recycled continuous anaerobic biohydrogen production system by controlling HRT. Thus, effluent recycling at the optimum ratio along with optimum HRT and substrate concentration can maximize the hydrogen production performance in an anaerobic biohydrogen production system.