Coal is simply trees that spent their lives producing oxygen, too. They were just slow in going back to their constituent parts.

I completely understand and agree with your choice based on economic self-interest. Back in the olden days I tried making biogas. I got a flammable product but it was highly contaminated with other gases, especially CO2 because I had no efficient way to separate CO2 from methane. Also, I had no compressor so all I got was a weak yellowish flame. I was proud of it, but it wasn't worth the effort.

Since then I've thought of a way to scrub the CO2 that uses another waste product -- wood ash. Passing hot water through wood ashes puts potassium into solution forming KOH -- potassium hydroxide. This is why ashes make a good garden additive, plants like potassium.

It occurred to me that bubbling the biogas through the KOH solution would scrub CO2 (and sulfides and sulfates) from the system H2O + CO2 -> H2CO3 while H2CO3 + 2KOH -> K2CO3 + H2O. Potassium carbonate and water. KCO3 has low solubility in water and would mostly ppt out. This leaves the methane (and other aliphatics) untouched. Also, the K2CO3 would be less soluble in the soil, too. This would result in a slower release, lower toxicity fertlizer than aqueous KOH right out of the ashes.

Anybody have any comments?

B