Biological hydrogen production by Clostridium acetobutylicum in an unsaturated flow reactor

A mesophilic unsaturated flow (trickle bed) reactor was designed and tested for H₂ production via fermentation of glucose. The reactor consisted of a column packed with glass beads and inoculated with a pure culture (Clostridium acetobutylicum ATCC 824). A defined medium containing glucose was fed at a flow rate of 1.6 mL/min (0.096 L/h) into the capped reactor, producing a hydraulic retention time of 2.1 min. Gas-phase H₂ concentrations were constant, averaging 74±3% for all conditions tested. H₂ production rates increased from 89 to 220 mL/h L of reactor when influent glucose concentrations were varied from 1.0 to 10.5 g/L. Specific H₂ production rate ranged from 680 to 1270 mL/g glucose per liter of reactor (total volume). The H₂ yield was 15-27%, based on a theoretical limit by fermentation of 4 moles of H₂ from 1 mole of glucose. The major fermentation by-products in the liquid effluent were acetate and butyrate. The reactor rapidly (within 60-72 h) became clogged with biomass, requiring manual cleaning of the system. In order to make long-term operation of the reactor feasible, biofilm accumulation in the reactor will need to be controlled through some process such as backwashing. These tests using an unsaturated flow reactor demonstrate the feasibility of the process to produce high H₂ gas concentrations in a trickle-bed type of reactor. A likely application of this reactor technology could be H₂ gas recovery from pre-treatment of high carbohydrate-containing wastewaters.