Anaerobic biohydrogen production by a fluidized granular bed bioreactor under thermophilic condition
Year: 2011
Type: dissertation
Abstract: There is now a critical need for development of full-scale practical application of \nfermentation technologies for energy generation (e.g. hydrogen production) that would be \ndependent on carbon neutral fuels such as biomass or wastewaters containing organic \nmaterials. Thermophilic fermentative biohydrogen production was studied in the \nanaerobic fluidized bed reactor (AFBR) operated at 65ºC with sucrose as a substrate. \nTheoretically, the maximum hydrogen yield (HY) is 4 mol H2.mol-1 glucose when \nglucose is completely metabolized to acetate, H2 and CO2. But somehow, under most \nbioreactor design and operation conditions the maximum possible hydrogen yield (HY) \nhas generally been observed not to exceed or reach 70-100% of the maximum theoretical \nhydrogen yield. In this study the application of external work in the form of high \ntemperatures, high dilution rates and high rates of de-gassed effluent recycling were \ninvestigated as a means to overcome the thermodynamic constrains preventing the \nsimultaneous achievement of high hydrogen yield (HY) and hydrogen productivity (HP) \nin an AFBR reactor. Bacterial granulation was successfully induced under a thermophilic \ntemperature of 65 oC within a period ranging from 7 to 14 days. The bacterial granules \nconsisted of a multispecies bacterial consortium comprised of thermophilic clostridial and \nenterobacter species. At a hydraulic retention time (HRT) of 1.67 h and effluent recycle \nrate of 3.5 L min-1, hydrogen production rate (HPR) of 32.7 L H2/h and hydrogen yield \n(HY) of 3.91 mol H2/ mol glucose were achieved. The design and operation of our bench \nscale AFBR system has also resulted in HYs greater than 4 mol H2/mol glucose. The \nmaximum substrate conversion efficiency was 95%. However, it was noted that at very \nlow HRTs (< 1h) the bioreactor substrate conversion efficiency dropped to 55%. This \nwork demonstrated that the application of external work to a bioreactor in the form of \nhigh temperatures, high dilution rates and high rates of de-gassed effluent recycling could \nbe used to overcome the thermodynamic constraints preventing the simultaneous \nachievement of high HYs and high HPs.
Author: Phumlani Masilela
Language: English
Field: Energy
Domain: Physical Sciences
Open Access status: green
Funder: National Research Foundation
OpenAlex ID: W199796374