Effects of propionic acid concentration on anaerobic digestion of pig manure.
Résumé
The effect of propionic acid concentration on anaerobic digestion was studied, with emphasis on the acidogenic step. No inhibitory effect, either on the methanogenic or on the acetogenic step, was noted, up to concentrations of 6 g litre−1 when the pH was ⩾ 7·4. Propionic acid, when present at 4 g litre−1 or more, reduced the rate of the acidogenic step, but the effect was small. Our results together with literature data show that propionic acid accumulation in anaerobic digesters must be considered mainly as a warning and not as a cause of a disturbance.