The invention presents a method for the treatment of combustion exhaust gas / waste gas comprising carbon monoxide and carbon dioxide. In the process that the product gas is obtained after the purification. This product gas can supplied for combustion again or to a natural gas network. At the first step of this process, which a mixture of at least carbon monoxide and carbon dioxide is removed. Those gases is a first product and the second step of this process is conversion the carbon monoxide to pure Hydrogen in the water shift reaction unit (WGS) . The third step of this process is converted carbon dioxide after capture and purification unit of this gas to bur methane, which is the reaction between pure hydrogen and carbon dioxide to higher level of purity and product of Bio methane.