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.