An apparatus for treating a liquid includes: (a) a pump volute or hydrocyclone head having an inlet and an outlet, (b) a throat having a first opening, a second opening and a central axis, wherein the first opening is connected to the outlet of the pump volute or hydrocyclone head, (c) a tank connected to the second opening of the throat, and (d) a wave energy source having a first electrode within the pump volute or hydrocyclone head that extends through the outlet into the first opening of the throat along the central axis of the throat, and a second electrode within the tank that is spaced apart and axially aligned with first electrode. The liquid is supplied to the inlet of the pump volute or hydrocyclone head, and is irradiated with one or more wave energies produced by the wave energy source.