Evaluation of Effectiveness of Two-Phase Anaerobic Digestion Process Degrading Complex Substrate

The effectiveness of two-phase anaerobic digestion in degrading complex substrates was studied by using a continuous acidogenic reactor and batch experiments. When 4,600 mg COD/l of milk consisting of carbohydrates, proteins and lipids, was fed to the acidogenic reactor, carbohydrates were easily converted to acids although protein degradation was insufficient and lipids were not degraded. The condition which gave greater than 95% carbohydrate degradation was a pH of not less than 4.5 at a constant HRT of 18 hours, and HRT longer than 6 hours at a constant pH of 6.0. Low pH or short HRT within the optimal range brought about the production of more n-butyrate instead of propionate. Degradation of egg albumin in the two-phase system required a longer HRT (about 5 days) than the ordinary acidogenic reactor. Batch experiments using the mixed liquor from the acidogenic reactor suggest that phase separation is not very effective for the degradation of carbohydrates and proteins, but it can prevent the inhibition caused by lipids.