Systems and methods for process stream treatment. The treatment system may generally include an oxidation unit coupled to a downstream demineralization unit. The oxidation unit may oxidize organic and reduced sulfur contaminants in the process stream to facilitate downstream treatment. The demineralization unit may convert a product of the oxidation unit to generate a mineral stream. In some examples, the process stream may be a spent caustic stream from an industrial operation, such as an ethylene production facility or a petroleum refinery. A fresh caustic stream, such as a sodium hydroxide stream, may be isolated in the demineralization step and returned to the industrial operation for use.