Apparatus for step-wise purification treatment of contaminated polar liquid, such as water, by the procedure of U.S. Pat. No. 4,224,148, comprising successive flow-connected container units, electrically insulated from the ground, the sequential units providing: (a) macerating/distributing means for producing suspension of selected small-particle-size contaminant which will accept a galvanic charge, (b) means for maintaining acidic pH of 2 to 2.5 in presence of gaseous oxidizing agent, (c) source of soluble metal ions adapted to impart a galvanic charge on the small particles, plus subsequent aeration means, (d) means for introducing alkaline reagent while air blowing to restrain precipitation, (e) means for alkaline flocculation of separable particles, including pH control means and switch means for electrically grounding the liquid medium.