The finding the biomass to make the methane from is the non-scalable, energy intensive part. You have to collect the biomass, load it on to a truck, ship it ar

The finding the biomass to make the methane from is the non-scalable, energy intensive part. You have to collect the biomass, load it on to a truck, ship it around on a truck, and then unload it and dispose of it after it's depleted. If you only need air, electricity and water to make the synthetic fuel, that's going to be scalable to a civilizational level scale.