Fermentative hydrogen production with a draft tube fluidized bed reactor containing silicone-gel-immobilized anaerobic sludge

A draft tube fluidized bed reactor (DTFBR) containing immobilized cell particles was designed to produce H2 continuously. A synthetic polymer (silicone gel; SC) was used as the primary material to immobilize acclimated anaerobic sludge for H2 production in DTFBR with a working volume of 8 L. The DTFBR system was operated at a hydraulic retention time (HRT) of 2.2–8.9 h and an influent sucrose concentration ( C s ) of 5–40 g COD/l. The results show that in general decreasing HRT or increasing sucrose concentration led to a marked increase in the volumetric H2 production rate ( v H 2 ) , but a gradual decrease in the H2 yield ( Y H 2 ) . The best v H 2 ( 2.27 ± 0.13 l / h / l ) occurred at C s = 40 g COD/l and HRT = 2.2 h , whereas the highest Y H 2 ( 4.98 ± 0.18 mol H2/mol sucrose) was obtained at C s = 40 g COD/l and HRT = 8.9 h . The correlation between the production rate and the organic loading rate (OLR) can be satisfactorily described by Monod-type models. There was no universal trend of the dependence between the H2 yield and OLR. The H2 content in the biogas was stably maintained at over 40%. The major soluble products were butyric acid and acetic acid, as they accounted for 62–73% and 16–22% of total soluble microbial products (SMPs), respectively. The H2-producing performance in the DTFBR system can be stably maintained and reproducible in long-term operations, while unstable operations can be quickly recovered via proper thermal treatment at 70–80 °C.