About anaerobic digestion (AD)

Anaerobic digestion (AD) is a proven, safe biological process where organic materials are broken down by micro-organisms in the absence of oxygen, to produce renewable energy and a nutrient-rich biofertiliser.
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Tamar's anaerobic digestion (AD) solutions enable the safe, cost-effective disposal of unavoidable organic waste with minimal environmental and community impact.

Anaerobic digestion recycles food waste to produce low cost, low carbon renewable energy, divert waste from landfill and incineration, reduces carbon emissions, displaces the need for (and cost of) petro-chemical derived fertiliser and returns valuable nutrients to the soil.


The AD process

 Click here for a larger version of the AD cycle above

In 2015, there were over 200 operational AD plants (outside of water sector) in the UK, with a combined capacity 210 MW – enough to generate power for over 500,000 homes.

AD plays a role in the supply and security of the UK’s energy, as it produces cost-effective 24/7 baseload, low carbon energy. This is different to the intermittent sources of energy from other renewable power sources, like tidal or wind. 

There are over 15 million tonnes of food waste each year in the UK, 7.2 million tonnes coming from households. Approximately 40% of this food waste ends up in the residual waste stream and is either sent to landfill or incinerated. AD is also a cost-effective, environmentally responsible waste management solution that recycles the food waste, rather than it being burned or buried. 

The AD process produces biofertiliser, worth £200 million and proven to increase crop yields, while also recycling essential nutrients to the land.

The AD sector could reduce the UK’s total greenhouse gas emissions by over 2%, create 35,000 jobs and contribute £3bn to UK economy.

What happens inside an AD plant? 

1. The food waste delivered to the facility is weighed at the weighbridge.

2. The fully enclosed pre-treatment building has measures in place to control noise, dust and odour. Once inside, lorries tip their load into a designated tipping area. All received material is inspected and any unsuitable items (contaminants, such as metals or plastic) are removed.  

3. Following pre-treatment (shredding), the organic matter is fed into the digestion process. From this point forward, it is entirely contained within sealed pipework and tanks.

4. The material is pasteurised to ensure that all pathogens and undesirable bacteria are killed.

5. The digesters are completely sealed to create an oxygen free environment needed for the bacteria to thrive. Each digester is fed by a pumped pipework system. Within the digestion tanks, material is digested at around 55°C to produce biogas and a compost-like product. The digestion process takes around a month, after which the gas is extracted.

6. Biogas produced from the digestion process is extracted from the top of each digester and taken to a Combined Heat and Power (CHP) unit, where it is used to generate renewable energy. This process generates heat, which is captured for use on site for space heating or in neighbouring buildings. The electricity generated provides all the on-site power required for the plant, with the majority sent to the local electricity network. 

7. At the end of the process, a stable, nutrient-rich biofertiliser is created. The process meets stringent requirements set by the British Standards Institute PAS110, the Environment Agency and ABPR (Government regulations for animal by products).


Watch a video of an AD plant being constructed. 
Watch what happens inside a typical AD plant. 

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