Effect of upflow velocity and hydraulic retention time in anaerobic fluidized-bed reactors used for hydrogen production

The present study evaluated the influence of upflow velocity (Vup) applied to an anaerobic fluidized-bed reactor used for hydrogen production. For comparison, two reactors were used with different velocities: 1.24 cm s−1 (R124) and 1.88 cm s−1 (R188). Expanded clay was used as a support material for immobilization along with synthetic wastewater containing glucose as the main carbon source (5000 mg L−1). The reactor R124, which operated at the minimum fluidization velocity (1.24 cm s−1), had the best values for hydrogen production. The maximum hydrogen production rate was 2.21 L h−1 L−1 for a hydraulic retention time (HRT) of 1 h, while the best hydrogen yield was 2.55 mol H2 mol−1 glucose for an HRT of 2 h. The hydrogen content in the biogas was around 40.53–67.57%. A high amount of ethanol was produced, suggesting that a metabolic pathway via ethanol was preferable. In general, the reactor under the minimum velocity fluidization (R124) presented a greater production of hydrogen than R188 showing that should have a limit point in Vup till the hydrogen production is maximized.

► The present study evaluated the influence of upflow velocity (Vup) applied to an anaerobic fluidized-bed reactor used for hydrogen production. ► For comparison, two reactors were used with different velocities: 1.24 cm s−1 (R124) and 1.88 cm s−1 (R188). ► The results showed that an increase in the Vup has not been effect to increase the hydrogen yield neither the hydrogen production rate. ► A high amount of ethanol was produced, suggesting that a metabolic pathway via ethanol was preferable. ► In general, the reactor under the minimum velocity fluidization (R124) presented a greater production of hydrogen than R188 showing that should have a limit point in Vup till the hydrogen production is maximized.