Anaerobic digestion

Anaerobic digestion (AD) is a safe biological process in which food waste and other organic materials are broken down by micro-organisms in the absence of light and oxygen, to produce renewable energy and a nutrient-rich biofertiliser.

In summary, Anaerobic Digestion is based on a straightforward, natural process. If managed correctly, in a well-constructed and reliable plant, it is a consistent and sustainable source of renewable baseload energy.

AD turns the problem of organic waste into two valuable resources:

  • Bio-fertilisers help farmers enrich the soils without using petrochemical fertilisers, which are costly to the environment.
  • Green electricity is produced to power local homes and businesses.

AD Process

The AD process is sometimes referred to as the "concrete cow" because, in straightforward terms, we are replicating many aspects of the digestion system of a cow.

The Agrivert AD process follows these simple steps:

  • Food waste is fed into the bunker where it is stored. Then the food waste is cleaned and prepared to be fed into the beginning of the digestion process.

  • Next, the food is de-packaged. Any non-organic contamination that shouldn't be fed into the digester is removed. Like a cow's mouth, the de-packaging technology shreds the materials and separates the packaging and any other contamination away from the food. This makes the organic fraction as readily available as possible to aid digestion.

  • Then a small amount of liquid is added. This is usually waste liquids sourced from food and drink manufacturers. The liquid helps wash the food away from the packaging and make it into a pumpable consistency. The clean, packaging-free substrate is sometimes called "soup". This is the bit the "mechanical cow" is interested in eating.

  • The soup is fed into the digester tanks (the mechanical cow's stomach).

  • The heat generated by the engines gently warms the material within the digesters. It also gently and consistently stirs the material to prevent any inedible crusts or sediments from forming.

  • From here, biology takes over. Just as within a cow's stomach, a culture of bugs and healthy bacteria develop and physically digest the materials inside the tank.

  • Whilst these micro-organisms eat the food, they produce biogas. This gas is rich in methane.

  • The biogas is captured in the roof of the digester tanks and pushed through a Combined Heat and Power Gas engine.

  • The engines burn the gas and use the energy to turn a generator, thus creating renewable electricity.

  • The heat the engine produces during the process is used to heat various tanks and pipework within the AD plant.

  • A small amount of the electricity produced is used to power the AD plant, thus ensuring the plant is self-sufficient. The remainder can be supplied onto the National Grid to power local homes and businesses.

  • The power produced by AD benefits energy companies as it is not intermittent like some other renewable power sources. AD power production is not dependent on weather conditions, as is the case for solar and wind-generated power. The industry terms this steady, continuous power supply as "baseload energy supply".

  • Once the gas is harvested, we are left with a rich organic bio-fertiliser known as digestate.

  • The Digestate is filtered and then pasteurised to ensure that it doesn't contain harmful bacteria or anything else that shouldn't be put back into the soil. All of Agrivert's passed AD plants were PAS 110 accredited, meaning they passed and maintained stringent standards regarding Digestate quality.

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