The separator according to the invention comprises: a tank (1) for receiving waste material and containing fluid to separate waste material by density into floating and settled material; automatic feed means (18, 37), for example, a double screen (18) to feed waste material to the tank (1); motorised conveyor belts (3, 4) divided into a floating waste material conveyor (3) and a settled waste material conveyor (4) to extract floating or settled waste material from the tank (1): and a blower-type sorting device (21) comprising: a turbine (22) that provides an airflow; and a branched duct (23) divided into: a riser duct (26) to transport part of the airflow to a diffuser (39) beneath the automatic feed means (18, 37) to raise light-weight waste material; and a discharge duct (27) to transport and horizontally expel another part of the airflow in order to remove previously raised waste material. The separator according to the invention may incorporate bubble-making means, with injectors (2) to facilitate floatability and remove floating waste material.