The invention relates to a cavitation and electrocoagulation reactor comprising a hollow cylindrical cathode having a cylindrical anode coaxially disposed therein to form an annular interelectrode gap between the contact surfaces. An inlet sleeve and an outlet sleeve disposed in the respective inlet and outlet of the cathode and abutting against opposite ends of the anode seal the interelectrode gap from the respective inlet and outlet of the cathode. A set of channels disposed in the wall of the inlet sleeve connect the inlet to the interelectrode gap. Similarly, a set of openings disposed in the outlet sleeve connect the interelectrode gap to the cathode outlet. An electrical source has first and second terminals respectively connected to the anode and the cathode. The method for removing contaminants from a contaminated fluid flow involves the simultaneous application of hydrodynamic cavitation and electrocoagulation to the contaminated fluid flow.