Three continuous stirred tank reactors (CSTR) were operated under mesophilic (37. ±. 1. °C), thermophilic (55. ±. 1. °C) and hyper-thermophilic (80. ±. 1. °C) temperatures for 164. days to investigate the effect of temperature and temperature shock on the cellulosic-dark hydrogen fermentation by mixed microflora. During steady state condition, the sudden decreases in the fermentation temperature occurred twice in each condition for 24. h. The results show that the 55. ±. 1 and 80. ±. 1. °C presented stable hydrogen yields of 12.28 and 9.72. mmol/g cellulose, respectively. However, the 37. ±. 1. °C presented low hydrogen yield of 3.56. mmol/g cellulose and methane yield of 5.4. mmol/g cellulose. The reactor performance under 55. ±. 1 or 80. ±. 1. °C appeared to be more resilient to the sudden decreases in the fermentation temperature than 37. ±. 1. °C. The experimental analysis results indicated that the changing in soluble by-products could explain the effect of temperature and temperature shock, and the thermophilic temperature is expected having a better economic performance for cellulosic-hydrogen fermentation.
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