primary treatment
as defined in Council Directive of 21 May 1991 concerning urban waste water treatment…, Article 2, point (7)
7.
‘primary treatment’ means treatment of urban waste water by a physical and/or chemical process involving settlement of suspended solids, or other processes in which the BOD5 of the incoming waste water is reduced by at least 20 % before discharge and the total suspended solids of the incoming waste water are reduced by at least 50 %;