Abstract
The Influence of volatile fatty acids on hydrogen fermentation from an organic waste by a mixed microflora was investigated in a batch experiment. The batch reactor with a working volume of 1.0 liter was operated at 35°C and a constant p H (5.5 or 6.5) for each experimental run. Dog food was used as the substrate. The seed microflora was a mixed culture obtained by acclimatizing a thermophilic digested sludge by treating the organic fraction of municipal solids waste using glucose as the substrate. The experiments were conducted by changing the initial concentrations of acetic acid and butyric acid from 0 to 50,000mg·l-1 at the substrate concentrations of TS2% to evaluate the substrate decomposition, gas production and metabolic production under each condition. Hydrogen production potential, gas production rate and hydrogen content in the biogas decreased with the increase in the initial concentration of volatile fatty acid. The inhibition effect at a pH of 5.5 was much stronger than that at a pH of 6.5 for a same fatty acid concentration. It was also found that the inhibition caused by fatty acids depends on not only the concentration, but also the type of fatty acid. Butyric acid exerted a stronger inhibition effect than acetic acid. In addition, it was found that an un-ionized fatty acid is a more powerful inhibitor and that hydrogen fermentation is significantly inhibited at an un-ionized fatty acid concentration higher than 200mg·l-1.
