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UBC Theses and Dissertations

Anaerobic fermentation for biological hydrogen production in a sequencing batch reactor Won, Seung Gun

Abstract

Biological hydrogen production via anaerobic fermentation of organic waste can be potentially a greener and sustainable technology. Thus far, most research has been conducted using continuous stirred tank reactors (CSTR). Anaerobic sequencing batch reactors (ASBR) have advantages over CSTR, but there are disadvantages in terms of their operation. The overall goal of the thesis research is to enhance hydrogen production by optimizing the operational conditions in an ASBR using agri-food wastewater as substrate. An ASBR with 6-L working volume was inoculated with sewage sludge from the anaerobic zone of a sewage treatment facility and was not pretreated to select the hydrogen-producing bacteria. Hydrogen productivity was estimated by hydrogen content (%), hydrogen production rate (HPR) and hydrogen yield as the performance indicators in response to changes in pH, hydraulic retention time (HRT), organic loading rate (OLR), and cyclic duration (CD) as the key operational parameters. Using dairy wastewater as substrate, the suppression of methanogenesis was feasible without pretreatment of inoculum under the conditions of higher OLR and shorter HRT, which favoured hydrogen production. With carbohydrate-rich synthetic wastewater as substrate, the combination of relatively low pH 4.5 and HRT 30 hr was found to be the optimal condition for hydrogen production. For higher hydrogen production, ethanol-to-acetic acid ratio of 1.25 and food-to-microorganism ratio of 0.84 were revealed as threshold values. Higher hydrogen productivity at longer CD was not necessarily accompanied with higher microbial growth that occurred at shorter CD. Subsequently, real sugar refinery wastewater was used in the tests for biohydrogen production. Based on statistical analysis and curve fitting by the modified Gompertz model of the data as well as microbial identification, the operational setting of (pH 5.5, HRT 10 hr, OLR 15 kg/m³.d) was concluded to be optimal with the performance indicators of (71.8±10.5% H₂, HPR 2.11±0.31 L H₂/L reactor.d and yield 0.95±0.13 mol H₂/mol sucrose). Taxonomic analysis confirmed the presence of dominant hydrogen-producing bacteria among the diverse microbial genera, and in particular, the Clostridia spp. without the pretreatment of inocula. Further studies with the optimization of operational conditions would contribute towards making the best possible decision for ASBR.

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