Biogas Digester: Turning Waste Into Energy

Find out how you could turn your household waste into renewable energy with a biogas digester.

There is a simple way to make your own renewable energy at home and use it for cooking, heating and lighting.

It’s called biogas, and the concept is – add your kitchen scraps or animal manures to a large tank called a “digester” and the anaerobic bacteria that live in the tank will breakdown or “digest” these wastes and convert them to methane gas.

The gas is stored in a bag and can flow straight into your gas cooker in your kitchen, or your outdoor BBQ. The bacteria in the tank need to be fed every day and will not only produce biogas, but also a liquid fertiliser for your garden, and a solid material which is great for growing mushrooms on.

Many people around the world are making their own biogas at home, including millions of people in developing countries.

To become part of this off-the-grid power movement you can make your own DIY unit for very little cost, or buy a ready- made unit that can be used in any city-suburban backyard.

Homemade biogas has immense potential to improve the ecological, ethical, economic and carbon footprint of homes and neighbourhoods throughout Australia, turning existing household and garden waste into heating, electricity and natural biogas.

We can think of biogas in permaculture terms of one element (waste) performing many functions (biogas, fertiliser and greenhouse gas carbon sequestration).

The yield of your biogas digester

Biogas systems can be fed continuously. A few kilos of kitchen scraps a day will supply gas for two to three hours of cooking, even through a cold winter. If you go away on holiday for a few weeks your biogas unit will simply stop producing gas until you get back and begin feeding the bacteria again.

They are run on monthly cycles. At the end of each cycle you can empty out some of the solids from the bottom of the digester to make room for more waste.

Getting your biogas digester started

When you start up your unit you will need to fill your digester with water and add 100kg of animal manures. Ruminant manures work best. Then you will enter the “activation” phase, which takes about three weeks.

Once the bacteria are starting to produce gas and the gas bag is full you can begin the daily feeding of food scraps. Your biogas unit will need to have some warmth for the bacteria to work effectively in the activation phase.

Placing the unit in full sun will be enough for some climates. In cooler areas you may need to warm the digester using an aquarium heater, or have the unit inside a green house.

The homemade IBC (Intermediate Bulk Container) biogas unit is the simplest and most productive setup. Best run on garden waste and animal manure, if heated the system can even handle meat (but not bones).

If heat-treated it is the perfect material for growing pink, white and yellow oyster mushrooms—the oyster mushrooms then eat the dead anaerobic bacteria to produce a living mycelium mushroom compost.

The production of your biogas system ultimately depends on what you feed it and the efficiency of the energy source.

Home biogas systems are relatively easy to make, only needing a few simple items. These include a 44 gallon drum or IBC (International Bulk Container), plumbing parts and a pump.

I won’t go into detail about how to make a biogas system as there are numerous examples on the internet and it’s a fairly involved process, but here are some things to keep in mind.

The minimum requirement for home scale biogas is one cow or the equivalent in household foods scraps and garden waste (25kg-50kg a week). It also needs a minimum running temperature of 24°C – this can be achieved with a hot house, insulation and a large aquarium pump.

DIY home biogas digester tips

  • Start small and simple with one IBC or 44 gallon drum system to understand the biogas system’s principles and operation.
  • Make sure all gas fittings are airtight.
  • Install a simple water vapour trap to improve the burning of gas.
  • Insulate the outside of the biodigester to improve gas quantity.
  • Heat the biodigester to 36°C with a large aquarium heat- er to improve the gas quantity.
  • Set up a composting or outdoor mushroom system to handle the waste.

biogas

Learn more…

While home scale biogas is simple enough to set up, optimising the DIY biogas digester to its full potential involves a bit of testing and technical know-how.

This can be developed through reading books on the subject, watching YouTube DIY biogas videos, joining Facebook Groups and doing further online research. There are also a few great online open-source DIY biogas groups you can check out.

The developing area of DIY biogas holds a lot of potential and promise. It can provide a local and small-scale solution for the bigger global problems of climate change and fossil fuel replacements. To do so, this needs to involve communities and government agencies supporting each other in an ongoing and productive debate.

There is a huge amount of potential from permaculture design thinking to contribute to biogas and the renewable energy sector. Ethical social enterprise and DIY biogas has a fundamental, multi-faceted role to play in addressing climate change and inequality.

Stuart Muir Wilson is the founding director of Bullock Proof Energy.

You can find the full version of this article in Issue #12 of Pip Magazine, which is available here.

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