title: Influence of substrate concentration on the stability and yield of continuous biohydrogen production.
abstract: The effect of substrate concentration (sucrose) on the stability and yield of a continuous fermentative process producing hydrogen was studied. High substrate concentrations are attractive from an energy standpoint as they would minimise the energy required for heating. The reactor was a CSTR; temperature was maintained at 35 degrees C; pH was controlled between 5.2 and 5.3, and the hydraulic retention time (HRT) was 12 h. Online measurements were taken for ORP, pH, temperature, %CO2, gas output and %H2, and data logged using a MatLAB data acquisition toolbox. Steady-state operation was obtained at 10, 20 and 40 g/L of sucrose in the influent, but a subsequent step change to 50 g/L was unsustainable. The hydrogen content ranged between 50% and 60%. The yield of hydrogen decreased as the substrate concentration increased from 1.7 +/- 0.2 mol/mol hexose added at 10 g/L, to 0.8 +/- 0.1 mol/mol at 50 g/L. Sparging with nitrogen improved the hydrogen yield by at least 35% at 40 g/L and at least 33% at 50 g/L sucrose. Sparging also enabled steady-state operation at 50 g/L sucrose. Addition of an extra 4 g/L of n-butyric acid to the reactor operating at 40 g/L sucrose increased the butyrate concentration from 9,830 to 18,900 mg/L, immediately stopping gas production and initiating the production of propionate, whilst the addition of 2 g/L taking the butyrate concentration to 12,200 mg/L did not do so. It was shown that operation at 50 g/L sucrose in a CSTR in butyrate fermentation is possible.
authors.affiliation: School of Applied Sciences, University of Glamorgan, Pontypridd, Mid Glamorgan CF37 1DL, United Kingdom. gkyazze@glam.ac.uk
authors.forename: G
authors.initials: G
authors.lastname: Kyazze
authors.forename: N
authors.initials: N
authors.lastname: Martinez-Perez
authors.forename: R
authors.initials: R
authors.lastname: Dinsdale
authors.forename: G C
authors.initials: GC
authors.lastname: Premier
authors.forename: F R
authors.initials: FR
authors.lastname: Hawkes
authors.forename: A J
authors.initials: AJ
authors.lastname: Guwy
authors.forename: D L
authors.initials: DL
authors.lastname: Hawkes
mesh_terms: D019342:Acetic Acid / Q000378:metabolism; D019149:Bioreactors / Q000382:microbiology*; D020148:Butyric Acid / Q000378:metabolism; D004563:Electrochemistry; D005285:Fermentation; D006859:Hydrogen / Q000378:metabolism*; D009584:Nitrogen / Q000737:chemistry; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D012722:Sewage / Q000382:microbiology*; D013395:Sucrose / Q000378:metabolism
chemical_list: D012722:Sewage; D020148:Butyric Acid; D013395:Sucrose; D006859:Hydrogen; D009584:Nitrogen; D019342:Acetic Acid; D010100:Oxygen