What Waste Code
D8

D8: Biological treatment not specified elsewhere in this Annex which results in final compounds or mixtures which are discarded by means of any of the operations numbered D1 to D12

Annex I of the consolidated Waste Framework Directive (2008/98/EC)  opens in a new tab.

Applying this code

D and R codes describe the operation, not the waste itself and not site acceptance.

Classify the waste first using the Waste classification technical guidance (WM3) — GOV.UK  opens in a new tab, then check permit conditions before applying a code operationally.