We optimized the operation of the process that reforms biogas with CO2 and/or steam for the production of methanol using a mathematical optimization approach. The raw biogas is cleaned up before reforming. Part of the biogas is used to provide energy for the process. Next, the unreacted hydrocarbons and CO2 are removed. Subsequently, syngas composition may be adjusted, using either water gas shift reaction or membrane-pressure swift adsorption. Finally, methanol is synthesized. The process is modeled using mass and energy balances, chemical and phase equilibria, and rules of thumb. The problem is formulated as an NLP problem with simultaneous heat integration for the optimal biogas composition and methanol production. Two objective functions are considered: a simplified production cost and an environmental one developed based on carbon footprint. Biogas is expected to have around 50-52% of CH4 and 45-47% of CO2 depending on the objective function. The production cost of methanol is $1.75/gal, for a plant size that uses 10% of the potential biogas to be produced in Madrid, Spain, with an investment of $46 MM.