How do they make energy from food waste?

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Piddlehinton AD 3The Anaerobic Digester at Piddlehinton can process up to 20 000 tonnes of food waste per year, and produces enough energy to power the nearby feed mill

Despite what you might think the method of turning food waste into energy is relatively simple; the waste is left to break down in the absence of oxygen, the chemical reactions that take place produce methane and carbon dioxide (Biogas1), which can then be harvested and used for energy.

The process can be broken into three main stages:

1. Pre-treatment – When food waste first arrives at the plant it needs to be screened, and all contaminants such as plastic packaging need to be removed. This process is difficult and very, very dirty, which is why it is so important to make sure only food goes in food waste bins.

2. Digestion – After pre-treatment the waste is fed into the digester, which is basically a large air-tight tank (see above). The biogas is produced as the waste breaks down; this is then harvested and stored until needed.

3. Digestate– Once the ‘digestion’ process is complete all that is left is digestate. The liquid portion of this is ready to use, and is spread on nearby farms as a fertiliser; the solid matter is processed further and turned into compost.

Sending food waste from Dorset to be recycled at the Piddlehinton AD helps to reduce green house gas emissions and cut down on waste sent to landfill.

Biogas1 is a bi-product of the breakdown of organic matter in the absence of oxygen. It is made of mainly methane and carbon dioxide.

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