Biohydrogen Production by Modified Anaerobic Fluidized Bed Reactor (AFBR) Using Mixed Bacterial Cultures in Thermophilic Condition

Abstract

Hydrogen production represents a vital foundation for a hydrogen economy. Research, development, and demonstration, however, must continue in order to bring down the cost, increase the efficiency, and address the emissions issues associated with hydrogen production technologies. Dark fermentation using AFBR considered recently being promising and highly efficient in producing hydrogen gas in quantities exceeding even the theoretical values of 4 mol H / mol glucose if certain modification in the bioreactor design and process are made. Thermophilic fermentative biohydrogen production was studied in the anaerobic fluidized bed reactor (AFBR) operated at 65ºC with sucrose as a substrate. Theoretically, the maximum hydrogen yield (HY) is 4 mol H /mol glucose when glucose is completely metabolized to acetate, H and CO . But somehow, under most bioreactor design and operation conditions the maximum possible hydrogen yield (HY) as generally been observed not to exceed or reach 70-100% of the maximum theoretical hydrogen yield. In this study further modification in anaerobic fluidized bed reactor namely the decrease in the total liquid volume to 3.3L, in addition to the application of external work in the form of high temperatures, high dilution rates and high rates of de-gassed effluent recycling were investigated as a means to overcome the thermodynamic constrains preventing the simultaneous achievement of high hydrogen yield (HY) and hydrogen productivity (HP) in an AFBR reactor. Bacterial granulation was successfully induced under a thermophilic temperature of 65 C. The bacterial granules consisted of a multispecies bacterial consortium comprised of thermophilic consortium . At a hydraulic retention time (HRT) of 1 h and effluent recycle rate of 3.6 L/ min, with V/F equal to 0.91 min, hydrogen production rate (HPR) of7.57 LH / h and hydrogen yield of 5.8 mol H / mol glucose were achieved. This was greater than the yield achieved in a previous study conducted on 2012 , where the yield was 3.55 mol H / mol glucose under similar experimental conditions.