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Let's 'AD' it up

Posted Tuesday 8th January 2013, 4:00pm
Let's 'AD' it up

Let's continue with understanding the science of Poo Power!

To refresh: we know that there are different forms of bioenergy, including biogas, and from the last post ("Blast Off!") we also know some of its common uses. But there's a missing piece to the puzzle - how do we get the energy from the waste? If you came to our launch event last year you may have picked up one of our flyers that explains the process called anaerobic digestion, or 'AD' for short.

Poo Power! flyers

Currently, much of our biodegradable waste such as food, green waste, paper and dog poo (!!) is sent to landfill where it breaks down to release methane. Anaerobic digestion is the process that composts this waste to produce biogas that can be used to as a renewable source of energy. A biogas generator is the system we use to control and accelerate this natural process:

  • ensuring it occurs in an oxygen-free environment, i.e. 'anaerobic'
  • the added water needed, approximately 2 parts water for 1 part waste
  • methane-producing bacteria to inoculate the waste.

The temperature is also quite important because methane-producing bacteria work best at temperatures between 30-40'C or 50-60'C, depending on which type you use. It can take from 2 to 8 weeks to digest a load of waste, depending on the temperature and waste type, but it can start as quickly as 24-48 hours from inoculation.

Biogas is then stored and depending on the system used it can be combusted to run a generator producing electricity and heat (in a co-generation system), burned as a fuel in a boiler or furnace, or cleaned and used as a replacement for natural gas.

Lastly the leftover sludge or 'digestate' is removed for use as a fertiliser or soil conditioner as it contains valuable plant nutrients like nitrogen and potassium.

One of the advantages of biogas generation is that its size can vary from a domestic system to a large commercial plant of several thousand cubic metres. Some are large lagoons, others are tank systems. They can sit above ground, or underground. Batch, or continuous systems. Their scalability and adaptability makes them a very desirable technology as it can be customised for a number of different settings.

It's amazing to think that this technology has been around since 900 B.C. when the Assyrians used it to heat their bath water.

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About Diesel

Diesel

Diesel is an inspiration. Plus he makes some of the poo. Diesel is proof that one pooch can make a difference.

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  • Green Nation
  • Yarra Energy Foundation
  • Melbourne Water
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