Abstract: In accordance with the present invention, the chromium content of an aqueous waste containing significant amounts of at least one soluble chromium compound, such as blowdown waters from cooling towers utilizing chromium-containing materials as corrosion inhibitors is reduced, by contacting the chromium-containing waste water with an aqueous waste containing sodium sulfides, particularly spent caustic utilized in a desulfurization of petroleum fractions, to precipitate a substantial amount of the chromium and, thereafter, separating the precipitated chromium from the mixture as a sludge, to produce a waste water which can be safely disposed of to the earth's surface in a sewer or the like.