Methanation method in a bioreactor under continuous cell-retention conditions

A method to convert H2 and CO2 into methane or a methane enriched gas composition with a Methanothermobacter thermoautotrophicus methanogenic microorganism—in a bioreactor comprising:

• (i) culturing the methanogenic microorganism in a liquid culture medium;
• (ii) supplying a nitrogen source to the liquid culture medium for cell division and cell growth of the methanogenic microorganism;
• (iii) culturing the methanogenic microorganism under cell retention conditions;
• (iv) contacting the methanogenic microorganism with at least one feeding gas comprising CO2 and H2;
• (v) reducing or stopping the supply of the nitrogen source to the culture medium wherein the supply of the nitrogen source is reduced to a concentration of 0.2 mol/L/day to 0 mol/L/day;
• (vi) continuously removing metabolic water in the culture medium from the bioreactor;
• and
• (vii) collecting methane or a methane enriched gas composition.