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Batch tests were conducted to select a good natural mixed microflora seed source and determine its optimal initial cultivation pH to elevate hydrogen production from xylose (20 g-COD/L). Hydrogen production efficiency was evaluated using the hydrogen yield (HY) and maximum hydrogen production rate (HPR m ). Sewage sludge was shown to have higher HY and HPR m than other biological sludges collected from distillery, food and paper mill wastewater treatment plants. The experiments of pH effect were conducted at pH 5–8 and 35 °C. The experimental results indicate that the initial cultivation pH markedly affected HY, HPR m , liquid fermentation product concentration and distribution, butyrate/acetate concentration (HBu/HAc) ratio and metabolic pathway. For sewage sludge, its optimal initial cultivation pH for hydrogen production was 6.5 with peak values of HY 1.3 mol-H 2 /mol-xylose, HPR m 0.25 mol-H 2 /L-day, butyrate concentration 5780 mg-COD/L and HBu/HAc ratio 4. However, a pH change of 0.5 units from pH 6.5 decreased hydrogen production efficiency by 23%. Strategies based on the experimental results for optimal hydrogen production from xylose are proposed. |
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