Continuous thermophilic hydrogen production from cheese whey powder solution in an anaerobic fluidized bed reactor: Effect of hydraulic retention time and initial substrate concentration

The focus of this study is the use of an anaerobic fluidized bed reactor (AFBR) to continuously produce hydrogen under thermophilic conditions (55 °C) using a range of cheese whey (CW) concentrations and hydraulic retention times (HRTs). The following combinations of tests parameters were evaluated: a fixed concentration of 4900 ± 200 mg lactose L−1 and HRTs of 8, 6, 4, 2, 1 and 0.5 h in AFBR1 and a fixed HRT of 6 h and influent CW concentrations of 2800 ± 100, 4900 ± 200, 6800 ± 300, 9800 ± 300 and 14,600 ± 300 mg lactose L−1 in AFBR2. For AFBR1, the maximum hydrogen production rate (HPR) obtained was 4.1 ± 0.2 L H2 h−1 L−1 in the HRT of 0.5 h, and maximum hydrogen yield (HY) of 3.67 ± 0.59 mol H2 mol lactose−1 in the HRT of 4 h. For AFBR2, the maximum HPR was 0.85 ± 0.12 L H2 h−1 L−1 at a concentration of 6800 ± 300 mg lactose L−1, and the maximum HY was 2.64 mol H2 mol lactose−1 at a concentration of 2800 ± 100 mg lactose L−1. In both reactors, the main metabolic products were acetic acid and butyric acid. Based on 16S rRNA clone analysis of the bacterial community, the identified sequences were affiliated with relative abundances of 48.42% (Thermoanaerobacterium and Thermohydrogenium kirishiense) and 75.53% (Thermoanaerobacterium thermosaccharolyticuum and T. kirishiense) in AFBR1 and AFBR2, respectively.