Biohydrogen production in a three-phase fluidized bed bioreactor using sewage sludge immobilized by ethylene–vinyl acetate copolymer

Ethylene–vinyl acetate (EVA) copolymer was used to immobilize H2-producing sewage sludge for H2 production in a three-phase fluidized bed reactor (FBR). The FBR with an immobilized cell packing ratio of 10% (v/v) and a liquid recycle rate of 5 l/min (23% bed expansion) was optimal for dark H2 fermentation. The performance of the FBR reactor fed with sucrose-based synthetic medium was examined under various sucrose concentration (Cso) and hydraulic retention time (HRT). The best volumetric H2 production rate of 1.80 ± 0.02 H2 l/h/l occurred at Cso = 40 g COD/l and 2 h HRT, while the optimal H2 yield (4.26 ± 0.04 mol H2/mol sucrose) was obtained at Cso = 20 g COD/l and 6 h HRT. The H2 content in the biogas was stably maintained at 40% or above. The primary soluble metabolites were butyric acid and acetic acid, as both products together accounted for 74–83% of total soluble microbial products formed during dark H2 fermentation.