Failure of biohydrogen production by low levels of substrate and lactic acid accumulation

To identify causes affecting the stability of biohydrogen production from the microbial community perspective, a fermentor was operated using galactose as a substrate for 30 days. The fermentor demonstrated that hydrogen production yield gradually increased with concomitant decrease of galactose concentration until day 27. Meanwhile, hydrogen producing clostridia gradually increased their proportion to 75% of bacteria analyzed until day 11, and then gradually decreased to 23% with increases in other groups of bacteria such as Bacilli. After day 27, hydrogen production abruptly failed without deterioration of galactose utilization. At that time, lactic acid accumulated to 920 mg COD/L and Ruminococcaceae increased its proportion to 30%. In conclusion, low substrate levels, beginning on day 11, provided a selective disadvantage to the hydrogen producing clostridia and proliferated other groups of bacteria, which resulted in accumulation of lactic acid and, ultimately, failure of hydrogen production.