Estimation of Oxygen Concentration in the Slurry in Biogas Production Without O2 Removal in Initial Process

The existence of free molecular oxygen in the biogas production process will inhibit strict anaerobic methanogenic bacteria. The estimation of O2 concentration in the slurry is needed to see if the oxygen methanogenic inhibition happens in the biogas production without oxygen removal in initial process. The calculation begin with determine the digester volume, the gas space volume fraction in the digester, and the operation condition, i.e. the temperature and the pressure according to the good condition in the biogas production process. Based on the liquid-gas equilibrium principle, and with the assumption that the air consist of 80% of nitrogen and 20% of oxygen, it is obtained the equilibrium oxygen concentration in the slurry in various gas space volume fraction in the digester. The result of the calculation show that the oxygen concentrations in the slurry in all of gas space volume fraction in the digester are much higher than the methanogenic inhibition limit, indicating the possibility the happen of the methanogenic inhibition in the system. The inhibition possibility will be higher by the greater of the gas space volume fraction in the digester.