Biogas is by definition a product of excess biomass production. The net potential can be estimate by the net agricultural (and perhaps forestry) primary production within a country.
To a rough first approximation based on food intake, biomass is the residual of undigested food caloric energy in the waste stream, which I believe runs at about 25% of the input calories.
You can estimate this for a population by taking roughly 2,000 kilocalories/day * population * 0.25. Ignoring any collection or processing losses, for the US this translates to about 700,000 GJ, 110,000 barreloil, or 200 GWh electricity (assuming no generation or transmission losses, in actuality about 1/3 this amount).
Actual US energy consumption is closer to 45 million barreloil day (equivalent, only 18.3 million barrels of actual oil), or roughly 400 times the maximum amount of energy available in food waste.
There may be other biomass wastestreams available (say: the input feedstock for livestock, pork, dairy, and poultry), though this won't add up to the 400-fold increase necessary as typically the trophic loss is about 10x in a given foodchain level. Even were all US food consumption in the form of animal products, the wastestream would be 40x short of present energy consumption levels.
It's not clear if the artist here is aware of what they're demonstrating, but the process of methane harvesting employed is not dissimilar to how fossil fuels formed in the first place, with biomass settling to the bottoms of shallow seas and, over the course of hundreds of millions of years, being transformed to petroleum and natural gas.
We're presently consuming that bounty at roughly 5 million times its rate of formation. The fact that it takes 8 hours to produce fuel sufficient for 20km of travel is actually millions of times more efficient than the net energy cost of fossil fuels.
Jeffrey S. Dukes, "Burning Buried Sunshine" (2003) details this with exquisite clarity.
https://www-legacy.dge.carnegiescience.edu/DGE/Dukes/Dukes_C...