This European Standard specifies requirements, test methods, the marking and evaluation of conformity for a packaged and/or site assembled tertiary treatment unit (see Figure 1). It applies for tertiary treatment units that are placed on the market as complete units used for the tertiary treatment of domestic wastewater by biological, physical, chemical, electrical processes and coming from: a) units in accordance with EN 12566-3 or EN 12566-6; b) installations designed and constructed in accordance with CEN/TR 12566-5. Equivalent secondary treated effluent may come from existing systems. Package and/or site assembled tertiary treatment units according to this standard consist of one or more watertight tanks without any direct infiltration into the ground, made of concrete, corrosion resistant or coated steel, un-plasticised poly-vinyl chloride (PVC-U), polyethylene (PE), glass reinforced thermosetting plastics (GRP) based on polyester resin (UP) (GRP-UP), polypropylene (PP), polydicyclopentadiene (PDCPD) and flexible sheets (HDPE, PP, PVE and EPDM). This standard applies to tertiary treatment units for use above ground (outside the building) or buried in the ground where no vehicle loads are applied to the unit. This standard does not apply to tertiary treatment systems forming part of units covered by EN 12566-3 and EN 12566-6. This standard does not cover the systems for microorganism reduction.