An apparatus for the extraction of phosphorus from wastewater that includes a precipitation module and a retention module. The precipitation module includes a crystallization vessel, one or more inlets disposed in a lower region of the precipitation module and at least one outlet disposed in an upper region of the precipitation module. The retention module includes a sedimentation vessel, at least one inlet disposed in an upper region of the retention module and at least one outlet disposed in a lower region of the retention module. At least one outlet of the precipitation module is connected to at least one inlet of the retention module and at least one outlet of the retention module is connected to at least one inlet of the precipitation module. The volume VS of the sedimentation vessel is greater than/equal to 0.6 times the volume VC of the crystallization vessel (VS≥0.6·VC).