An apparatus for treating a liquid includes: (a) a pump volute or hydrocyclone head having an inlet and a throat having an outlet and a central axis, (b) a tank connected to the outlet of the throat, wherein the tank has a maximum inner diameter that is larger than an inner diameter of the outlet of the throat, and (c) a wave energy source having a first electrode within the pump volute or hydrocyclone head that extends through the outlet of the throat along the central axis, and a second electrode within the tank that is spaced apart and axially aligned with first electrode along the central axis. 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.