Gi Cheol Cha

Effect of COD/SO42−ratio and Fe(II) under the variable hydraulic retention time (HRT) on fermentative hydrogen production

The effect of chemical oxygen demand/sulfate (COD/SO(4)(2-)) 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 H(2) production at inlet sulfate concentrations of 0-20 g L(-1) during 282 days. The tested COD/SO(4)(2-) ratios ranged from 150 to 0.75 (with control) at pH 5.5 with hydraulic retention time (HRT) of 24, 12 and 6h. The hydrogen production at HRT 6h and pH 5.5 was not influenced by decreasing the COD/SO(4)(2-) ratio from 150 to 15 (with control) followed by noticeable increase at COD/SO(4)(2-) ratios of 5 and 3, but it was slightly decreased when the COD/SO(4)(2-) 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 H(2) mol(-1) glucose at HRTs of 24, 12 and 6h, 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.

Suppression of acidogenic activities due to rapid temperature drop in anaerobic digestion

A rapid temperature drop during anaerobic acidogenesis in an anaerobic reactor system resulted in the sharp suppression of carbohydrate decomposition and production of volatile fatty acids. When the temperature was dropped from 30°C to 25, 20, 15°C sequentially, the numbers of bacteria were slowly reduced without showing temperature shock. The acidogenesis, however, was dramatically affected after each temperature drop; the removal efficiency of carbohydrate was reduced from 92% to 84%, 72%, 25% with showing the minima of 78%, 52% and 10% due to the rapid temperature drop respectively. This indicates that the acidogens lose the activities momentarily during the rapid temperature drop and require certain period of time to recover the activities at the adjusted fermentation temperature.A rapid temperature drop during anaerobic acidogenesis in an anaerobic reactor system resulted in the sharp suppression of carbohydrate decomposition and production of volatile fatty acids. When the temperature was dropped from 30°C to 25, 20, 15°C sequentially, the numbers of bacteria were slowly reduced without showing temperature shock. The acidogenesis, however, was dramatically affected after each temperature drop; the removal efficiency of carbohydrate was reduced from 92% to 84%, 72%, 25% with showing the minima of 78%, 52% and 10% due to the rapid temperature drop respectively. This indicates that the acidogens lose the activities momentarily during the rapid temperature drop and require certain period of time to recover the activities at the adjusted fermentation temperature.