Stable performance of anaerobic digestion in the presence of a high concentration of propionic acid

An automatically controlled, glucose-fed, anaerobic digester was deliberate ly inhibited by addition of phenol. To overcome the phenol inhibition the f eed dilution rate was lowered in such a way that the methane yield from glu cose was kept the same as that under normal conditions. The concentrations of acetic and butyric acids remained below 100 mg/l, however, propionic aci d accumulated to 2750 mg/l. Phenol apparently inhibited all tropic groups o f organisms and it was shown that the propionic acid was formed from the me tabolism of phenol. From the nature of the operating strategy, it was deduc ed that the digester continued to convert all the glucose that was supplied to methane showing that propionic acid accumulation did not inhibit conver sion of glucose to methane. Therefore, propionic acid accumulation map be a n effect and not a cause of inhibition of the anaerobic digestion process. (C) 2001 Elsevier Science Ltd. All rights reserved.