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Digestate is a nutrient-rich substance produced by anaerobic digestion that can be used as a fertiliser. It consists of left over indigestible material and dead micro-organisms - the volume of digestate will be around 90-95% of what was fed into the digester. By using digestate instead of synthetic fertilisers derived from natural gas, we can reduce consumption of fossil fuels and reduce our carbon footprint.
All the nitrogen, phosphorous and potassium present in the feedstock will remain in the digestate as none is present in the biogas. Typical values for nutrients are:
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Nitrogen: 2.3 - 4.2 kg/tonne
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Phosphorous: 0.2 - 1.5 kg/tonne
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Potassium: 1.3 - 5.2 kg/tonne
However, the nutrients are considerably more bioavailable than in raw slurry, meaning it is easier for plants to make use of the nutrients. This can be particularly valuable for land within Nitrate Vulnerable Zones (NVZ) where applications of organic nitrogen are restricted.
Digestate can be used straight from the digester, in which case it is called whole digestate. Alternatively it can be separated in to liquor and fibre. Digestate is not compost, although it has some similar characteristics. Compost is produced by aerobic micro-organisms, meaning they require oxygen from the air.
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