title: Performance characteristics of a two-stage dark fermentative system producing hydrogen and methane continuously.
abstract: The performance of a mesophilic two-stage system generating hydrogen and methane continuously from sucrose (10-30 g/L) was investigated. A hydrogen-generating CSTR followed by an upflow anaerobic filter were both inoculated with anaerobically digested sewage sludge, and ORP, pH, gas output, %H(2), %CH(4) and %CO(2) monitored. pH was controlled with NaOH, KOH or Ca(OH)(2). Using NaOH as alkali with 10 g/L sucrose, yields of 1.62 +/- 0.2 mol H(2)/mol hexose added and 323 mL CH(4)/gCOD added to the hydrogen and methane reactors respectively were achieved. The overall chemical oxygen demand (COD) reduction was 92.6% with 0.90 +/- 0.1 g/L sodium and 316 +/- 40 mg/L residual acetate in the methane reactor. Operation at 20 g/L sucrose and NaOH as alkali led to impaired volatile fatty acid (VFA) degradation in the methane reactor with 2.23 +/- 0.2 g/L sodium, 1,885 mg/L residual acetate, a hydrogen yield of 1.47 +/- 0.1 mol/mol hexose added, a methane yield of 294 mL/gCOD added and an overall COD reduction of 83%. Using Ca(OH)(2) as alkali with 20 g/L sucrose gave a hydrogen yield of 1.29 +/- 0.3 mol/mol hexose added, a methane yield of 337 mL/gCOD added and improved the overall COD reduction to 91% with residual acetate concentrations of 522 +/- 87 mg/L. Operation at 30 g/L sucrose with Ca(OH)(2) gave poorer overall COD reduction (68%), a hydrogen yield of 1.47 +/- 0.2 mol/mol hexose added, a methane yield of 138 mL/gCOD added and residual acetate 7,343 +/- 715 mg/L. It was shown that sodium toxicity and overloading are important issues for successful anaerobic digestion of effluent from biohydrogen reactors in high rate systems.
authors.affiliation: School of Applied Sciences, University of Glamorgan, Pontypridd, Mid Glamorgan CF37 1DL, UK. gkyazze@glam.ac.uk
authors.forename: G
authors.initials: G
authors.lastname: Kyazze
authors.forename: R
authors.initials: R
authors.lastname: Dinsdale
authors.forename: A J
authors.initials: AJ
authors.lastname: Guwy
authors.forename: F R
authors.initials: FR
authors.lastname: Hawkes
authors.forename: G C
authors.initials: GC
authors.lastname: Premier
authors.forename: D L
authors.initials: DL
authors.lastname: Hawkes
mesh_terms: D001421:Bacteria, Anaerobic / Q000502:physiology; D001673:Biodegradation, Environmental; D019149:Bioreactors / Q000382:microbiology*; D002245:Carbon Dioxide / Q000378:metabolism; D005232:Fatty Acids, Volatile / Q000378:metabolism; D005285:Fermentation; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008697:Methane / Q000096:biosynthesis*; D012722:Sewage / Q000737:chemistry / Q000382:microbiology*; D013379:Substrate Specificity; D013395:Sucrose / Q000378:metabolism; D013696:Temperature
chemical_list: D005232:Fatty Acids, Volatile; D012722:Sewage; D002245:Carbon Dioxide; D013395:Sucrose; D006859:Hydrogen; D008697:Methane