Abstract: Separator apparatus and method for treatment of a contaminated liquid by injecting air/gas to lower the specific gravity of the contaminated liquid by at least 20% and rotating the contaminated liquid to separate contaminants by centrifugal forces. The separator includes a swirl chamber defining a longitudinal axis; at least one injector for, in use, introducing: (i) liquid entrained with air/gas; (ii) air/gas-entrained liquid; or (iii) air/gas, into the swirl chamber; a first outlet located at or near the operative bottom of the swirl chamber for, in use, removing sludge from the swirl chamber; a second outlet located operatively above the first outlet for, in use, removing liquid from the swirl chamber; circulating means to, in use, circulate liquid in the swirl chamber; and an elongate body that extends from or near the operative top of the swirl chamber, along the longitudinal axis of the swirl chamber, beyond the level of the at least one injector.