Neither I nor Don can give you the proof you're looking for since the Ukraine is a country where research is not as easy as internet access.
Ukraine has long been known for their dilemmas with sufficient gas supplies as the Ruskies are their primary source for NG and the Ruskies have not been entirely friendly and fair with them. This has lead them to be unusually resourceful with what they have to work with. They make their landfill gas go as far as can go. This is why their technology is so advanced. They have little choice. Since they have the mental capacities and capabilities of solving many of their problems, the elimination of CO2 from their landfill methane was an option probably somewhat simple for them to overcome.
The U.S. on the other hand, has ample NG, so the need to purify their methane from landfills has been no big deal. In the U.S., we're such a throw-away society, we look at landfills (for energy needs) as a joke, in large part. Our people are not freezing their butts off in large enough numbers. It's totally different in Ukraine, where the average household income is no where near ours.
When you're freezing your tail off, where there's a will, there's a way, and with sufficient technological intelligence, Ukraine found the ability to remove the CO2 from LFG a rather easy way to convert an inexpensive resource into a valuable commodity.
I'm sure the U.S. could have mastered the processes much sooner, but again, it comes down to supply and demand. My guess is, Don probably did not reply because the efforts required to substantiate were beyond practicality for him, given the nature of researching Ukraine.
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