Abstract: Process and apparatus for continuously obtaining separate outflows of pure water and sterile sludge when starting with various aqueous slurries containing organic or oxidizable contaminants (as exemplified by domestic sewage or industrial waste) and first treating the flowing mixture with sulfur dioxide and iron under conditions of closely controlled acidity and in the absence of oxygen. The invention provides a multiple-stage, closed, operating system, a primary segment of which is thus characterized by a self-contained, continuously recycling oxygen-free gaseous flow comprising sulfur dioxide gas which moves through an iron reaction bed concurrent with the contaminant stream.