A method and apparatus for the high-pressure electrocoagulative treatment of aqueous and viscous fluids and sludge is provided. The apparatus includes a plate and frame design utilizing mechanical closure on a plurality of recessed, gasketed, non-electrically conductive electrocoagulation spacer plates that completely enclose and isolate all fluids, electrical contacts, and electrodes within the confines of the apparatus. The spacer plates include intergral supports that position and support said plates with enclosed electrodes on top of the side rails of the supporting frame of the apparatus allowing said plates to be separated for electrode replacement and maintenance and conversly closed, pressured and put into service. The apparatus includes a baffled influent and effluent chamber at both ends for the addition and flash mixing of chemical reagents and/or flocculants and to provide a means of fluid communication between fluid conduits and chambers formed within the apparatus.