A microbial fluidized electrode electrolysis cell (MFEEC) was used to enhance hydrogen gas production from dissolved organic matter. Flowable granular activated carbon (GAC) particles were used to provide additional surface area for growth of exoelectrogenic bacteria. The use of this exoelectrogenic biofilm on the GAC particles with fluidization produced higher current densities and hydrogen gas recoveries than controls (no recirculation or no GAC), due to intermittent contact of the capacitive particles with the anode. The total cumulative charge of 1688C m(-2) with the MFEEC reactor (a recirculation flow rate of 19 mL min(-1)) was 20% higher than that of the control reactor (no GAC). The highest hydrogen gas yield of 0.82 +/- 0.01 mol-H-2/mol-acetate (17 mL min(-1)) was 39% higher than that obtained without recirculation (0.59 +/- 0.01 mol-H-2/mol-acetate), and 116% higher than that of the control (no GAC, without recirculation). These results show that flowable GAC particles provide a useful approach for enhancing hydrogen gas production in bioelectrochemical systems. (C) 2014 Elsevier B.V. All rights reserved.