Abstract: An apparatus and method for removing charged ions from solution by treating the solution with electrodialysis followed by Donnan dialysis. One of many applications is for treating the baths associated with the metal finishing, e.g. plating, anodizing, or etching, industry. For example, charged ions can be removed from the rinse baths of a plating line by treating the rinse water of a first rinse bath following the plating bath with an electrodialysis unit and returning the concentrated solution to the plating bath, and treating a second rinse bath following the first rinse bath with a Donnan dialysis unit to produce an additional concentrated solution and a diluted effluent which may be either discharged into a sewer or stream, or readily destroyed.