Thermophilic biohydrogen production using a UASB reactor: performance during long‐term operation

BACKGROUND: The efficiency of H₂ production by dark fermentation described in the literature is around 50% of the maximum theoretical value and the experiments are mostly carried out over short‐term operations. This present study evaluated H₂ production in a UASB (upflow anaerobic sludge blanket) reactor operated at 55 °C for 366 days using a synthetic substrate based on sucrose. The reactor response to an increased organic loading rate (OLR) was assessed by applying three different hydraulic retention times (HRTs): 12 h (211 days), 6 h (71 days), and 2 h (84 days). RESULTS: CH₄ was observed in the biogas during startup. The highest average values of the molar H₂ flow rate (MHFR), volumetric H₂ production rate (VHPR), and H₂ yield (HY) were achieved at a HRT of 2 h, and were, respectively, 14.00 ± 5.24 mmol h⁻¹, 75.33 ± 24.65 mL H₂ L⁻¹.h⁻¹, and 1.73 ± 1.14 mol–H₂ mol‐suc⁻¹. Considering only the unstable steady‐state period, HY average at a HRT of 2 h was 2.56 ± 0.84 mol–H₂ mol‐suc⁻¹. CONCLUSION: Operational conditions were found to be the main factors responsible for removing methanogenic microorganisms from the system. Increase in the OLR enhanced H₂ production and the ethanol pathway proved to be favorable for H₂ production. © 2015 Society of Chemical Industry