The effect of chemical oxygen demand/sulfate (COD/SO42-) ratio on fermentative hydrogen production using enriched mixed microflora has been studied. The chemostat system maintained with a substrate (glucose) concentration of 15 g COD L-1 exhibited stable H2 production at inlet sulfate concentrations of 0-20 g L-1 during 282 days. The tested COD/SO42- ratios ranged from 150 to 0.75 (with control) at pH 5.5 with hydraulic retention time (HRT) of 24, 12 and 6 h. The hydrogen production at HRT 6 h and pH 5.5 was not influenced by decreasing the COD/SO42- ratio from 150 to 15 (with control) followed by noticeable increase at COD/SO42- ratios of 5 and 3, but it was slightly decreased when the COD/SO42- ratio further decreased to 1.5 and 0.75. These results indicate that high sulfate concentrations (up to 20,000 mg L-1) would not interfere with hydrogen production under the investigated experimental conditions. Maximum hydrogen production was 2.95, 4.60 and 9.40 L day-1 with hydrogen yields of 2.0, 1.8 and 1.6 mol H2 mol-1 glucose at HRTs of 24, 12 and 6 h, respectively. The volatile fatty acid (VFA) fraction produced during the reaction was in the order of butyrate > acetate > ethanol > propionate in all experiments. Fluorescence In Situ Hybridization (FISH) analysis indicated the presence of Clostridium spp., Clostridium butyricum, Clostridium perfringens and Ruminococcus flavefaciens as hydrogen producing bacteria (HPB) and absence of sulfate reducing bacteria (SRB) in our study.
Bibliographical noteFunding Information:
This work was supported by 21st Frontier research project (Sustainable Water Resources Research Center 3-4-3), 2006 Research Grant from Kangwon National University and Global Research Laboratory (GRL) project by Korean Institute of Geoscience and Mineral Resources (KIGAM), NP2008-019. Authors are also thankful to Prof. Cha for his continuous support and guidance throughout this research work.
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- COD/SO ratio
- Fluorescence In Situ Hybridization
- Hydraulic retention time
- Hydrogen producing bacteria
- Sulfate reducing bacteria