Abstract: An apparatus for oxidizing organic residues in an aqueous stream, comprising a chamber having a top, a bottom, an inlet for introducing a liquid thereinto, and an outlet for removing liquid therefrom, a plurality of dividers in the chamber between the inlet and the outlet dividing the chamber into a plurality of subchambers, a plurality of ultraviolet lamps in the subchambers, means for directing liquid flow through the chamber in a serpentine fashion, a plurality of separate subcovers over the subchambers and the lamps, which subcovers may be individually opened and closed, conductors for supplying electrical current to the lamps, and means for interrupting the flow of current to the lamps under each subcover when the subcover is open while simultaneously permitting such current flow to lamps which are not under an open subcover.