As is known to all, hydrogen production is usually accompanied with the formation of volatile fatty acids (VFAs) and alcohol as metabolic products, which leads to a sharp drop of medium pH. In order to buffer the change of medium Alisertib during hydrogen fermentation, the effect of phosphate buffer concentration on hydrogen production by FZ11 was investigated at the fixed corn stalk 15 g/l, urea 6 g/l and initial pH 6.47, and the result was depicted in Fig. 4. As illustrated in Fig. 4, the Ps and Rm increased along with the increase of phosphate buffer concentration from 0 M to 0.15 M. The Ps of 85.7 ml/g and Rm of 6.3 ml/g h−1 occurred at the phosphate buffer concentration of 0.15 M. After that, the Ps and Rm decreased gradually with increasing phosphate buffer concentration. Meanwhile, the final pH changed from 4.1 to 5.98 with increasing phosphate buffer concentration ranging from 0 M to 0.3 M. These results showed that phosphate buffer solution could buffer medium pH in a certain range of acidity, and alleviate medium acidification. However, on the other hand, the high content of the phosphate would result in the increase of cytoplasmic osmotic pressure, in that case, the hydrogen production and cell growth would be partially suppressed.