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Should I encourage my neighbors to send their food waste to a biogas plant instead of the current incineration facility? I have Googled around and it does not seem like it is clear that it is better to produce biogas than to burn waste in a district heat (I live in cold Sweden) or especially a co generation plant.

I would think the high water content of food waste would mean a lot of energy goes to evaporating the water while in a biogas facility maybe more of the energy in the food could be captured?

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  • But when the the water vapor is condensed again during the energy extraction process, that evaporating energy will be recovered, so it isn't lost either, right?
    – adius
    Commented Dec 8, 2021 at 10:45

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I can only answer regarding the actual plant. If food wastes need to be trucked all around Sweden when the incinerator is down the road, the picture may be different.

Biogasification of food wastes, market wastes and similar stuff is certainly better, for the reason you describe in your last paragraph: Kitchen wastes are typically 70-80% moisture.

Typically biogas plants use co-generation. I would estimate that such a waste to energy plant uses about 20-30% of its generated electricity and maybe 50% of its heat.

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  • I appreciate your answer @mart, do you have any references? And do you have any energy budgets for these two types of approaches, even back-of-the-envelope? E.g. 1 kg food waste contains 2.5 MJ of energy (by burning) and 2 MJ is required to boil off the water so every 1kg of food can be turned into 0.5 MJ of heat. For biogas maybe the gas produced from 1 kg of food contains 0.7 MJ if all converted to heat, but can also be used in engines (at around 25% efficiency) to produce kinetic energy or electricity.
    – Uli Alskelung Von Hornbol
    Commented Feb 14, 2017 at 20:31
  • I'll see what I find.
    – mart
    Commented Feb 15, 2017 at 8:29
  • Were you able to find anything?
    – Uli Alskelung Von Hornbol
    Commented Apr 15, 2017 at 11:42
  • I became curious and did another round of Googling and came across this: link.springer.com/article/10.1007/s40518-014-0018-1 This analysis seems to suggest that incineration is just as efficient if not more efficient when looking at combined heat and power. I guess the only reason to have digesters then would be if one really wants to produce sustainable fuel for airplanes.
    – Uli Alskelung Von Hornbol
    Commented May 2, 2017 at 16:41
  • thanks, I'll have a look - also reminder to self that I need to dig up more numbers for my answer ...
    – mart
    Commented May 3, 2017 at 6:55

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