Digestate

This allows sewage sludge and animal manure to be good candidates for co-digestion together with other feedstocks to produce a better digestate for agricultural purposes as well as increased biogas production.

[2] During this stage, the acidifying bacteria convert water-soluble chemical substances, including products of hydrolysis, to short-chain organic acids, such as formic, acetic, propionic, butyric, and pentanoic, alcohols, such as methanol and ethanol, aldehydes, carbon dioxide, and hydrogen.

This process can also lower pH inside the biodigester over time causing the microbes to not to be able to function.

The methanogenic microbes are fairly sensitive to pH changes and prefer a range from 5.0-8.5 depending on the species.

[2] This is why in some biodigesters the chambers for the different anaerobic digestions stages will be separated for optimal biogas production.

The liquid fraction constitutes up to 90% of the digestate by volume, contains 2–6% dry matter, particles <1.2 mm in size, and most of the soluble nitrogen and potassium, while the solid fraction retains most of the digestate phosphorus, and contains dry matter content ˃ 15%.

[3] Combining the two into a whole digestate allows for increased availability of a wide array of nutrients that can be useful for agricultural activities.

Some anaerobic biodigesters will only have one digestion chamber allowing these two digitates to mix together on their own without further intervention.

All this together makes digestate a potentially viable source for agricultural soil amendments of certain crops.

Acidogenic digestate can also be used as an environmentally friendly filler to give structure to composite plastics.

Chemical quality needs to be considered in terms of heavy metals and other inorganic contaminant, persistent organic compounds and the content of macro-elements such as nitrogen, phosphorus and potassium.

Depending on their source, biowastes can contain pathogens, which can lead to the spreading of human, animal or plant diseases if not appropriately managed.

If a biogas plant meets the standard, its digestate will be regarded as having been fully recovered and to have ceased to be waste, and it can be sold with the name "bio-fertiliser".