Don’t a lot of places capture methane from their landfills for energy? How can the quantities be unknown when you’re capturing and messing the output gases? This can’t be some magical surprise.
Probably better to just burn the trash? You get some energy, no (lingering, at least) methane leaks and you can capture and bury the really nasty stuff which is not combusted.
And you'll permanently lose whatever compounds are in that garbage by burning it - everything disintegrates into co2, water, nitrous oxide and a few other basic elements. On top of that, burning anything will always result in particulate matter emissions and solid residue, which is highly toxic as it concentrates everything that doesn't burn.
Now imagine in 20 years we find some way of cheaply separating plastic polymers into raw precursors, say by designing some bacteria or fungus that selectively targets a specific polymer. Had we just burned all of the old trash, we'd be out of luck - but assuming we find such a process, old landfills just became gold mines.
They do, but the gas (which is half CO2, half methane) is contaminated with silicon-containing gases (derived from silicones, including from parchment paper and cosmetics!) If you try to burn the gas in a turbine the silicon coats the combustors and turbine blades with glass.
The amount of methane generated from landfills can vary and decreases over time.
Here's a 40+ year old landfill that didn't generate enough methane to operate its original flaring station, but still generated a significant amount of methane so the station had to be replaced:
I believe they do gather the methane, but the article mentions leaks, suggesting that the cap over the waste which is used to collect the methane allowed some of it to leak out (thus not being accounted for).
https://www.politico.eu/article/denmark-garbage-gamble-amage...