A waste water treatment works (92, 112) including a liquid mixing and pumping system (88) for a first reservoir (20) operatively containing liquid (46), the system including a mixer (68), operatively submerged in the liquid contained in the first reservoir and rotatable about a vertical rotational axis (30), the mixer including an arrangement of vanes (44, 70) arranged peripherally around the rotational axis and being spaced from all sides of the first reservoir; a horizontally disposed vane carrier plate (42); drive means (32) for operatively rotating the mixer; a vertical shaft (26) for the mixer, extending upwardly from the mixer; an upright sleeve (72) disposed around the vertical shaft; and a transfer pipe (76) having an outlet in communication with a passage defined in the sleeve; the transfer pipe having its inlet (78) in a second reservoir (64) and serving to transfer liquid from the second reservoir to the first reservoir.