Digestate product definitions

Whole Digestate

This is the processed material as it is unloaded from the digester.

To distinguish one product from another, definitions regarding DM content are necessary. The German RAL standard, for instance, defines whole digestate as a pumpable material with <12% Dry Matter (DM).

Separated Liquor

This is the liquid resulting from passing whole digestate through a separator or centrifuge to remove the coarse fibres. A large number of different types of separator are utilised for digestate separation, and each of these are capable of producing separated products with different qualities.

One of the values of removing the coarse fibres from the digestate, is that it produces a thin liquid that runs easily off the leaf of the plant, leaving virtually no surface residue, thus making it highly suitable for growing crop application.  This can help to minimise the loss of nitrogen through volatilisation after spreading and through other paths of nitrogen loss. Therefore it is important that both the particle size and Dry Matter (DM) are defined. Liquor containing up to 6% DM material is normally acceptable, provided that the particle size is <1.2mm, for example as can be defined by the hole size in the screen of the separator used.

Separated Fibre

This is the fibre produced by the separator.

Separated fibre can be used fresh as a soil conditioner or after further aerobic composting to stabilise it, a material suitable for making into a compost product. To enable it to be aerobically composted it is generally accepted that the DM will need to be between 25% and 35%. The German RAL standard requires solid digestate products to be >20% DM to enable the fibre to be spread evenly as a soil conditioner.

The EA, WRAP and the REA are developing a quality protocol and Digestate standard PAS 110 - follow this link to view the latest developmetns and current documnets.