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Biogas: Creating Power From Waste

diagram
Biogas system diagram. Illustration by Grace West

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 readymade 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).

biogas
Home biogas system. Photo by Isaac Marquez and Home Power magazine

YIELD

Biogas systems can be fed continuously. A few kilos of kitchen scraps a day will supply gas for 2-3 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.

When you start up your unit you will need to fill your digester with water and add 100 kg 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.

FEEDSTOCKBIOGAS YIELD
Cattle slurry15-25 m3 per tonne
Green grass and garden clippings160-200 m3 per tonne

GLOBAL PERSPECTIVE

Biogas is an ancient way of generating gas for heating, lighting and cooking purposes. Many isolated rural farmers throughout the Middle East and Asia have been using biogas for the last 300 years (see figure 3).

Last year in Shenzhen, China, 1.2 million domestic scale biogas systems were installed and are now operational. From one cow, they produce domestic power, cooking, lighting and heating, providing enough biogas for one subsistence family. As shown in this example, biogas has the potential to increase rural resilience for farms and households.

An additional benefit is improvement in literacy and numeracy rates because children and adults can now study at night with biogas lighting. Deforestation has dramatically decreased because subsistence farmers do not have to cut down timber to burn for heating and cooking. Clean fuel has also decreased respiratory infections significantly and improved rural air quality.

PETROLEUM GAS

While biogas can be created from animal and food waste, the extraction of petroleum ‘natural’ gas can be extremely damaging to the environment. Petroleum gas is tapped from the top of fossil fuel oil reserves. This process has a devastating impact on the global climate and pristine ecosystems (see figure 2). The environmental and ethical impact is extreme, as petroleum gas emits greenhouse gases that contribute to global warming.

The extraction processes of petroleum gas involve fracking, a process that destroys underground water supplies with chemicals and oil pollutants and also risks gas leaks. The full impact of this industry in the Kimberley and Great Australian Bight has been devastating on life-giving river ecosystems and greenhouse gas emissions.

However, biogas can allow for a carbon positive process (better then neutral), allowing us to store carbon back in the soil through the solid and living carbon chain, making it available to grasses and flora as fertiliser. The gas can also be run through an aquaponics system, making it available to plants or algae.

Biogas is safe to use because of its low pressure, but because it is flammable, precautions (such as using the services of a licensed gas plumber) should be taken.

digester
An IBC biogas digester in Amazonia. Photo by Resex Tapajós-Arapiuns

PERMACULTURE ETHICS

There can be a downside to biogas. In Germany, for example, it has been tied to industrial agriculture and government subsidies, causing energy crops such as corn and rapeseed to occupy large swathes of prime agricultural land. This is a contentious ecological and land use issue. If these energy crops were produced as part of a biodynamic/permaculture system, yields on all fronts would be much higher, benefiting ecologies and ecosystems alike.

It’s possible however to utilise the permaculture ethics of earth care, people care and fair share (limits to growth) to inform ethical small-scale biogas systems, which consume only by-products or existing waste streams, adding to the carbon positive savings of the DIY or commercial biogas systems.

If biogas systems are developed consciously within the three permaculture ethics, the effect could be a deep and profound impact on the home footprint of waste, energy, carbon and ethics. These would meet permaculture’s ethics, with care of people (community energy), care of earth (closing the biomethane cycle) and fair share (energy justice) distribution.

‘Though the problems are increasingly complex, the solutions remain embarrassingly simple’ – Bill Mollison.

DIY
DIY biogas system. Photo by Habibullah Esmaili

MAKE YOUR OWN

The simplest way to address the global problems we face is to start at home. 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 (25 kg – 50 kg 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 quick 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 heater to improve the gas quantity.
  • Set up a composting or outdoor mushroom system to handle the waste.

Ideas for further DIY biogas plug-in development:

  • Aquaponics for complete C02 recovery. By plumbing C02 into the water it’s converted directly into the biomass of algae and aquaponic life forms.
  • Add mixer or grinder to increase the edges available for micro bacteria to attach onto their food.
  • Add biochar to compost in order to perfect chemistry by achieving a neutral pH of 7.0.
  • Add a starter culture with the correct biology from organic cow manure (fresh from a dairy).
  • Add C02 at the start to kickstart the process, injecting with a small cylinder and pipe to the base of the biodigester.

While home scale biogas is simple enough to set up, optimising the DIY biogas system 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.

diy-biogas
A DIY biogas system. Photo by David Blaisdell

HOW A BIOGAS SYSTEM CAN BENEFIT THE HOME AND ENVIRONMENT:

  • Reduce or eliminate gas power bills. Provide peak load (on demand) high volume electricity.
  • Take greenhouse gases out of the atmosphere and into living soils. Increase microbiology and mycelium (mushroom) activity in the soil.
  • Increase soil living carbon chains.
  • Eliminate fossil fuel dependency from coal seam gas (fracking and oil extraction).
  • Reduce rainforest deforestation for oil and ‘natural’ gas extraction.

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

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