Abstract
The effects of low pressures (down to 0.01 MPa) on the mesophilic anaerobic fermentation of glucose (10 g COD·l-1) were examined in this fundamental study. The anaerobic fermentation was developed to produce either low-molecular-weight fatty acids, lactic acid, hydrogen or methane as the primary product, by adjusting HRT, temperature and characteristics of the seed sludge. In the fermentation experiments producing acids and hydrogen, lactic acid and propionic acid concentrations decreased and acetic acid concentration increased in a completely mixed anaerobic reactor as operating pressure was decreased. Also, low-pressure operation yielded more hydrogen. In the fermentation experiment producing methane, the reactor recovered quickly at 0.01 MPa compared with 0.1 and 0.07 MPa. Low-pressure operation is thus considered favorable overall. Most of these observations are in accordance with thermodynamic predictions.
