This European Standard specifies requirements, test methods, evaluation of conformity and marking for prefabricated secondary treatment units used for the treatment of effluent from septic tanks according to EN 12566-1 or EN 12566-4 in small wastewater treatment systems for up to 50 PT. NOTE Equivalent septic effluent may come from existing septic tanks. It applies to the prefabricated secondary treatment unit, where all its components are packaged or site-assembled and placed on the market as a kit by one manufacturer. The prefabricated secondary treatment unit consists of one or more tanks made of concrete, steel, unplasticised polyvinylchloride (PVC-U), polyethylene (PE), glass reinforced polyester (GRP-UP), polypropylene (PP), polydicyclopentadiene (PDCPD) or container made of flexible sheets (HDPE, PP, PVC, EPDM). Other components specified by the manufacturer, such as pipes, pumps and filter material will be considered as part of the unit. This European Standard establishes the performance of the prefabricated secondary treatment units needed to verify their suitability for the end use conditions for which the test methods are specified. This European Standard applies for the packaged and/or site assembled secondary treatment units for use on the top of the ground (outside the building) or buried in the ground where no vehicle loads are applied to the unit. This European Standard does not cover: non watertight secondary treatment units with direct infiltration into the ground; retrofit kits (see definition in 3.1.7).