In an off-grid situation where electricity and fossil fuels are unavailable, producing hot water for bathing, washing, and cleaning becomes challenging. One solution is to build a simple system that uses the natural process of anaerobic digestion to produce methane gas from organic waste. This gas can then be captured and burned to heat water.
Anaerobic digestion occurs when organic matter like food scraps, crop residues, or animal manure breaks down in an oxygen-free environment. Methane-producing bacteria convert the materials into biogas, which contains 50-75% methane. Capturing this gas to use as a fuel source takes advantage of waste products and provides a reliable energy supply using only basic equipment.
Gathering Feedstock
The first step is collecting organic waste to feed the digester. Good feedstocks are plentiful in a homesteading situation:
- Food scraps from the kitchen
- Crop residues and garden waste
- Manure and bedding from livestock pens
It’s best to avoid meat, bones, and fatty foods, as these can cause problems in the digester.
Chopping or grinding the waste helps it break down faster. Aim for pieces 1 inch or smaller in size.
Building the Digester
The digester is an air-tight container where the organic waste is loaded. An example design:
- 55 gallon metal drum for the main digestion chamber
- 5 gallon bucket nested inside to collect the methane gas
- Feedstock inlet pipe allows waste loading
- Outlet pipe transports gas to the burner
Ensure the drum is sealed using gaskets or caulk to prevent oxygen exposure. Add water until the drum is 30% full to help start the digestion process. The bucket should have about 2 inches of water in it to create a water seal for gas collection via displacement.
Starting Digestion
“Seed” the digester by adding a shovel full of finished compost or soil. This introduces the methane-producing bacteria.
Begin loading feedstock through the inlet pipe every few days. Expect full digestion and maximum gas production to take 2-4 weeks. Agitate the drum occasionally to prevent clogs.
Monitor the water level in the bucket to check gas production. Refill the water as it gets displaced by accumulating methane.
Using the Methane
Once sufficient gas is being produced, start burning it for water heating.
Pipe the gas from the outlet to a simple burner. Place a pot full of water above the flame. The methane will combust, heating the water.
Capture excess gas in an additional bucket or bladder instead of wasting it through atmospheric release. This storage allows water heating on demand rather than needing constant gas production.
Safety
Methane gas is highly flammable. Take precautions:
- Check components for leaks
- Burn gas in a well-ventilated area
- Keep flames and sparks away from the digester
Why Water Displacement?
Water displacement is a simple, low-tech method to capture methane gas produced from organic waste in a closed anaerobic digester system. This allows productive use of the methane as a fuel source rather easily even with low to no available resources.
Advantages
- Does not require electricity or specialized equipment
- Captures methane for use as a fuel source instead of wasting it
Suitable Containers
- Glass jars or bottles
- Metal drums or tanks
- Buckets nested inside larger vessels
- Bladders, bags, or storage tanks for excess gas
How Water Displacement Works
- A container filled with water is inverted in a larger water-filled vessel
- As methane accumulates, it displaces the water in the inner container
- Water creates a seal to contain the pressurized gas
- Change in water levels indicates gas production volumes
Conclusion
Water displacement provides a simple, effective solution for capturing methane gas for productive use as a fuel source in an off-grid or low-tech context. This prevents wasted methane emissions while generating usable biogas energy.
With simple homemade equipment and appropriate safety measures, generating methane from compost can be a reliable source of off-grid hot water.
Citations:
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5517374/
[2] https://www.instructables.com/Biogas-Digester/
[3] https://drawdown.org/solutions/landfill-methane-capture
[4] https://www.nrdc.org/bio/pierre-delforge/methane-math-gas-tankless-water-heaters
[5] https://www.researchgate.net/figure/Water-displacement-eBMP-method-for-at-biogas-measurement_fig2_347342612
[6] https://www.homebiogas.com/blog/how-to-make-biogas-at-home/
[7] https://drawdown.org/solutions/landfill-methane-capture/technical-summary
[8] https://www.energy.gov/fecm/methane-hydrate-production-feasibility
[9] https://www.sciencedirect.com/science/article/abs/pii/S0921344918302052
[10] https://attra.ncat.org/publication/micro-scale-biogas-production-a-beginners-guide/
[11] https://energypost.eu/using-captured-methane-to-make-all-the-worlds-fishmeal-a-profitable-revenue-stream/
[12] http://dec.vermont.gov/air-quality/permits/source-categories/anaerobic-digesters
[13] https://www.youtube.com/watch?v=V4cWzY2HaWw
[14] https://sustainability.stanford.edu/news/removing-methane-atmosphere
[15] https://www.biocycle.net/control-of-heat-generation-during-composting/
[16] https://extension.psu.edu/on-farm-anaerobic-digestion-biogas-production-in-pennsylvania-30-years
[17] https://www.researchgate.net/figure/Off-grid-power-to-gas-system-scheme_fig2_317305856
[18] https://www.mdpi.com/2227-9717/7/9/635
[19] https://waste-management-world.com/resource-use/what-about-small-scale-anaerobic-digesters/
[20] https://archive.epa.gov/climatechange/kids/solutions/technologies/methane.html
[21] https://www.sciencedirect.com/science/article/pii/S2772912522000094
[22] https://www.inspirationhub.org.uk/solutions/16000/how-to-install-an-anaerobic-digester
[23] https://www.iea.org/reports/methane-tracker-2020/methane-abatement-options
[24] https://www.porkbusiness.com/news/hog-production/look-3-successful-hog-farm-anaerobic-digesters
[25] https://www.climatecommission.govt.nz/public/Evidence-21/Evidence-CH-12-Long-term-scenarios-to-meet-the-2050-target.pdf
