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If a household puts all its organic waste, from both the kitchen and the bathroom, into a biodigester, will it produce enough methane for the household's space heating in a low -25 °C to high -15 °C climate?

References to some real experiments are very much appreciated.

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    A colleague in India uses a biogas digester to produce cooking fuel for his family of three. They occasionally require supplemental propane, for instance when expecting company. He does not produce enough for heating, but in the climate where he lives there is no need for heating. I will see if he has collected any data on his production/usage.
    – LShaver ♦
    Jun 14 '17 at 21:19
  • Do you really mean a temperature range from -25 to -15 °C? Or is it -25 to +15 °C? Also can you please add how much space needs to be heated?
    – THelper ♦
    Jun 15 '17 at 7:04
  • -15. Let's say 1000 sqft single-story, well insulated house together with heat recovery ventilator.
    – George Chen
    Jun 15 '17 at 13:25
  • If anyone has done anything like that and has collected numbers, that'll be a solid starting point for a realistic estimation.
    – George Chen
    Jun 15 '17 at 14:55
  • You mean you want to heat during very cold winter. First calculate how much energy you need.
    – J. Chomel
    Jun 16 '17 at 6:29
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Let's see:

This paper states numbers for organic waste production from 0.14 - 0.32 kg/ person day for developing countries. Elsewhere it is said that the total amount of organic wastes differs little between high- and low income countries, but the composition changes: More kitchen scraps, peelings etc. in low incom countries vs. meal leftovers in high income ocuntries.

To calculatio biogas yield, we need to know the specific yield in Nl / kg VS (Normliter per kg volatile solids), the VS as percentage of TS (Total Solids) and the TS.

This study investigates heating a student dorm in Sweden, using organic wastes & biodigestion. They give these ranges for organic wastes:

  • TS 15-35 %
  • VS 80-96% (of TS)
  • biogas yield:303 - 435 Nl / kg VS

Note the huge variability - waste is not waste and every project will need a local sampling campaign to get the actual biogas potential.

Let's assume the middle of each range for a rough approximation:

  • 0.23 kg / day organic waste
  • 27 % TS - 0,062 kg TS / day
  • 88 % VS - 0,055 kg VS / day
  • 370 Nl / kg VS - 20 Nl / day biogas production

20 Nl / day, with methane content of 55% (again an average value) turns (@ ~10 kWh/m³ methane) out to be 0.11 kWh usable energy per day. Let's say 0.5 kWh/d for a 4 person household as an optimistic value. This does not take into account own energy demand of digestion (which can be 0-30 % of the heat produced).

In Germany a typical 4 person household needs 70 kWh/d for heating, a low value is 30 kWh/d.

Energy demand for heationg in a temperate cliamte is by orders of magnitude higher than what can be derived from household waste, when applied at household level. Organic waste will be produced year round, while most heat demand will be in winter.

However, 0.5 kWh/d would be not too far aaway from the cooking needs of a household (~1.5 kWh/day for Germany), so here biogas could at least supplement conventional energy usage.

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    One should add that a lot of food waste and organic waste is produced outside private households.
    – mart
    Jun 17 '17 at 18:49
  • Hello I know it's been a while, but do you have a source for your 0-30% of heat produced number?
    – Curtis
    Jun 7 '18 at 1:59
  • I used to design biogas plants and found 20% to be fairly typical, smaller digeters will typically need more heat and there's some flexibility in process temepratures. but no source right now.
    – mart
    Jun 7 '18 at 7:10

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