Abstract: Automatic marine sewage treatment through a pair of tanks with salt water based sewage fed to the first tank after removal of solids above a predetermined size. Circulation means responsive to liquid levels in the tanks cause batch transfer of liquids from the first tank to the second tank and multiply circulate a stream of liquids from and to the second tank while filling the first tank. Electrolytic treatment subjects the stream to D.C. current flow, producing treating chemicals. Treated liquids are discharged from the second tank when the first tank reaches a control level, delivering a predetermined fraction of the treated liquids to the first tank.