The BioProject metadata accession was orginally an initiative of the NIH NCBI. In EMBL they are more generally referred to as a Study and receive a secondary accession number assigned by EMBL as well as the NCBI BioProject accession number.
Here is an example in the EMBL ENA database: ERP193236 and the same example in NCBI: PRJEB111370
How to register a BioProject/Study¶
Sign in to the ENA Webin Portal
Click “Register Study” in the “Studies (Projects)” panel
Provide the Submission Details (Release date, Study Name, Short description, Abstract)
After submission your accession may take several days to propogate to the NCBI databases, but should be immediately visible from the EMBL Search if made public.