Abstract: The inventions refer to a mixer assembly for generating and maintaining a movement within waste water, comprising a hub (3) and at least two blades (4), which are disengageably connected to said hub (3), the hub (3) in a rear end being arranged to be connected to a drive shaft and thereby being arranged to be driven in rotation about an axially extending centre axis. According to the invention the hub (3) comprises a seat (9) for each of said at least two blades (4), each seat (9) comprising an axially extending first engagement means (10), and that each blade (4) comprises an axially extending second engagement means (11), said first engagement means (10) and said second engagement means (11) together being arranged to admit axial mutual displacement of said hub (3) and each of said blades (4) during mounting/demounting of the propeller assembly, and is thereto arranged to prevent radial mutual displacement of said hub (3) and each of said blades (4) when the mixer assembly is in an assembled condition.