Research On Carrier Optimization And Operation Characteristics Of Photo-Hydrogen Producing Anaerobic Fluidized Bed Reactor

The low biomass, utilization rate of substrate and light conversion efficiency were the main barriers in continuous photo-hydrogen production. Hence, in this paper, a novel bio-carrier, activated carbon fiber, was firstly applied to immobilize the photo-fermentation bacteria for photo-hydrogen production and to overcome the above problems. The optimum amount, length, specific surface area and modified method of ACF were ascertained, and then the modified ACF was used in the photo-hydrogen producing anaerobic fluidized bed reactor. The optimal operation and control strategy of the reactor were established, which could provide the theory and the technical guidance for the development of bio-hydrogen production.The results showed that ACF was an excellent immobilized carrier for photo-fermentation bacteria with good biocompatibility and high immobilization ability. The hydrogen production increased with increasing the specific surface area, but the hydrogen production was inhibited when the amount and length of ACF were too high. When the specific surface area, length and amount of ACF was 1500 m²/g, 1 mm and 0.8 g/L in the batch tests, the maximum hydrogen yield of 3.05 molH₂/mol acetate was obtained, which was about 12.4⁴7.3 % higher than that of the traditional carriers(clay and activated carbon). These demonstrated that ACF was an ideal carrier for the bacterial immobilization.The hydrogen production of HNO3 modified ACF was much better than those KOH and H₂O₂ modified ACF. The optimal concentration of HNO3 modification was 6 mol/L when the reaction time was 1 h. The maximum hydrogen production rate was 35.94 ml/L/h and the maximum hydrogen yield was 3.30 molH₂/mol acetate, which was 36 % higher than the control.The content of surface oxygenic functional groups had strong influence on the photo-hydrogen production. After HNO3 modification, the content of carbon, oxygen and nitrogen were changed visibly and meanwhile surface oxygenic functional groups increased. The main oxygenic functional groups on the ACF surface were C-OH, C=O and C-OOH, and C=O played a decisive role in the bacterial immobilization and hydrogen production.The hydrogen production of anaerobic fluidized bed reactor was restrained when HRT, acetate concentration, glutamate concentration and light intensity were in high level. The initial pH was the most important factor in influencing hydrogen production. When initial pH was 6.0, the hydrogen yield and hydrogen production rate were both decreased greatly and the hydrogen production was observed until 72 h. The optimum conditions of the reactor with the best hydrogen production performance as follows: HRT 48 h, acetate concentration 50 mmol/L, glutamate concentration 10 mmol/L, initial pH 7.0 and light intensity 4000 lux. The maximum hydrogen yield and hydrogen production rate of the reactor were 2.26 molH₂/mol acetate and 25.8 ml/L/h, respectively.