Exploring biohydrogen-producing performance in three-phase fluidized bed bioreactors using different types of immobilized cells

In this study, the spherical activated carbon (AC) and silicone gel (SC) were used as the primary matrices to immobilize H₂-producing activated sludge. The experiments were carried out in two different types of three-phase fluidized beds; namely, conventional fluidized bed reactor (FBR) and draft tube fluidized bed reactor (DTFBR). The solid volume of AC and SC immobilized cells was 10 vol.% for both FBR and DTFBR. Sucrose (at 20000 mg COD/l) was used as the carbon substrate for H2 production. The H ₂-producing performance was examined at different hydraulic retention times (HRT = 8, 6, 4, 2, 1, and 0.5 h). The results show that the best volumetric H2 production rate was 1.23 ± 0.08 l/h/l (HRT = 2 h) and 2.33 ± 0.22 l/h/l (HRT = 0.5 h) for fluidized beds containing AC and SC immobilized cells, respectively. The highest H₂ yield was 3.37 mol H₂/mol sucrose (HRT = 6 h) and 4.07 mol H₂/mol sucrose (HRT = 4 h) for fluidized beds with AC and SC immobilized cells, respectively. The H₂ content in the biogas was stably maintained at 35% or higher for all the reactors, while the primary soluble metabolites in the cultures were acetic acid and butyric acid.