Effect of CO₂ Partial Pressure on the Anaerobic Digestion

Abstract

Effect of CO₂ partial pressure on the anaerobic digestion of starch and production of methane were investigated by using anaerobic chemostat type reactor at 35°C. The CO₂ partial pressure in the atmosphere of the reactors was controlled in a series of bioreactor from 0.1 to 0.8atm. Since the partial pressure of CO₂ in an uncontrolled condition was about 0.4atm, N₂ was added to the reactors controlled at CO₂ partial pressure of between 0.1 and 0.4atm. At CO₂ partial pressure of 0.5atm, the methane production was approximately 20% more than that in an uncontrolled condition of CO₂. Based on the carbon mass balance, it was concluded that methane production was related to the removal of dissolved organic carbon and consumption of CO₂. The number of acetate consuming methanogenic bacteria, enumerated by the most probable number method, decreased significantly when CO₂ partial pressure exceeded 0.7atm. Homoacetogenic bacteria were increased with increasing CO₂ partial pressure increased from 0.1 to 0.6atm, however, decreased slightly at CO₂ partial pressure above 0.6atm. The number of acidogenic, H₂ consuming methanogenic bacteria, propionate and butyrate degraders were not much influenced by the partial pressure of CO₂. The potential methanogenic activity and potential substrate utilizing activity of acetate, increased at CO₂ partial pressure between 0.5atm and 0.6atm, however, decreased significantly when CO₂ partial pressure exceeded 0.7atm.