Economic estimation of an environmental-friendly biomethanation process based on economic values of consumed and produced gases would be a unique attitude. In this paper, time and space dependent concentration profiles of components involved in a batch process, designed for biomethanation, were predicted through a mass transfer modelling. The reaction terms used in the modeling required bio-kinetic parameters of μ max, m, kL, YC/L, YX/L, and YP/L which were globally optimized via a predefined algorithm using some experimental data as 0.0987 day-1, 0.1374 day-1, 1.5422mole m-3, -1.3636, -0.0183, -0.0908. Upon model verification, process income was calculated for a long-term scenario under a variety of factors and maximized through response surface methodology. The maximum income achieved was $-0.4/m3 bioreactor. A term carbon subsidy was considered in the income equation in order to find a break-even income for subsidy value of $363/ton CO2. Sensitivity analysis revealed that the amount of carbon subsidy directly influenced the selection of low or high levels of some process parameters to make the process profitable. In addition, it was found that pressure and liquid volume were the most important factors to achieve maximum income when $30 and $300/ton CO2 carbon subsidy were allocated to the process, respectively.