primary treatment
as defined in Council Directive 91/271/EEC of 21 May 1991 concerning urban waste-water…, Article 2, point (7)
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 %