Biogas upgraded to biomethane can be utilized as a renewable energy source to substitute LPG in households and industry. This study explored biogas upgrading by CO2 removal from 20 - 75 % CO2-N2 simulated biogas mixture. The experimental unit using the microbubble technique combined with the water absorption column was set up and used for CO2 removal from the gas. Microbubble sizes of 20 - 30 µm were generated by a venturi ejector and measured with an automated bubble size measurement. The experiments confirmed that a microbubble with an inline mixer could enhance the effectiveness of the absorption process. The tests demonstrated over 85.80 % removal of CO2 from the simulated biogas by the experimental unit. The effects of various parameters, including the size of venturi ejector, gas flow rate, water flow rate, liquid-gas ratio, and initial concentration of CO2, were investigated. The results revealed that 2 L/min gas flow rate, 15 L/min water flow rate, L/G ratio 7.5, and venturi ejector size 0.50 inches are the optimum conditions. The use of the tube absorber gave much higher CH4 recovery than an absorption column. The appropriate operating conditions gave over 96 % CH4 concentration or less than 4 % CO2 concentration, matching the CH4 purity required by biomethane specifications. The results indicated that the new technique demonstrated in this study can upgrade biogas to biomethane.