Biohydrogen production from household solid waste (HSW) at extreme-thermophilic temperature (70 degrees C) - Influence of pH and acetate concentration

Hydrogen production from household solid waste (HSW) was performed via dark fermentation by using an extreme-thermophilic mixed culture, and the effect of pH and acetate on the biohydrogen production was investigated. The highest hydrogen production yield was 257 +/- 25 mL/gVS(added) at the optimum pH of 7.0. Acetate was proved to be inhibiting the dark fermentation process at neutral pH, which indicates that the inhibition was caused by total acetate concentration not by undissociated acetate. Initial inhibition was detected at acetate concentration of 50 mM, while the hydrogen fermentation was seriously inhibited at acetate concentration of 200 mM. At 200 mM acetate concentration, the hydrogen yield was 36 +/- 25 mL/gVS(added), which was almost 7 times lower than the yield of 254 +/- 13 mL/gVS(added), which was achieved at lower acetate concentration (5-25 mM). Additional to the negative effect on the hydrogen yield, acetate was resulting in the longer lag phase during batch fermentations. The lag phase was more than 100 h at acetate concentration of more than 150 mM, while it was only 3-4 h at 5-25 mM acetate.