Abstract: A vortex grit trap comprising a generally vertically extending tank of circular cross-section including a separation zone having an inlet and an outlet for liquid flow to and from the tank, and in which liquid is circulated about a longitudinal axis of the tank, and, a grit collection zone positioned beneath the separation zone in use, the trap being characterized by a generally circular tank divider centered on the vertical longitudinal axis of the tank and extending transverse thereto, the divider defining a notional boundary between the separation and collection zones of the tank and being of smaller diameter than the adjacent region of the tank so as to define with the adjacent tank wall an annulus through which grit passes from the separation zone to the collection zone in use, and, means for generating a cloud of gas bubbles migrating in use upwardly through substantially the whole of said annulus whereby substantially all grit passing from the separation zone into the collection zone passes through the