A continuous method for the treatment of a spent aqueous caustic stream used to scrub a hydrocarbon process stream to remove oxidizable sulfur-containing compounds includes: a. mixing an oxidizing hypochlorous acid stream produced from an aqueous brine solution with the aqueous caustic stream to form a reactive mixed feedstream; b. contacting the reactive mixed feedstream with at least one catalyst to promote the oxidation of the sulfur-containing compounds and the neutralization of the sodium hydroxide; and c. recovering a neutral treated product stream comprising aqueous sodium sulfate, sodium carbonate and sodium chloride that is odorless, non-toxic and environmentally acceptable for discharge into the sea or into a conventional sewage treatment system. Preferably, the hypochlorous acid is produced by an electrolyzer that also produces a (1) hydrogen stream that is directed to a PEM fuel cell to generate at least a portion of the electrical power requirement of the electrolyzer, and (2) water that is combined with fresh sodium hydroxide from the electrolyzer to form a fresh caustic stream for use in scrubbing the hydrocarbon process stream.