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Sodium hydroxide (caustic) continues to be one of the primary reagents used in refineries and petrochemical plants to extract hydrogen sulfide, mercaptans, and organic acids from hydrocarbon streams. A local refinery had accumulated $5000 m 3 of spent caustics containing cresylic and naphthenic compounds. The chemical oxygen demand (COD) concentrations must be reduced to less than 1 g/L prior to discharge to biotreatment. A simple and safe treatment system for this high volume and high concentration of COD is desired. Bench-scale treatment of spent caustic by the Fenton's reagent process had a total COD removal of greater than 95%, and the effluent COD was lower than 1 g/L. The process was operated at a temperature lower than 808C and ambient pressure. The capital cost was thus lower than that of the wet air oxidation (WAO) process that normally operates at 2008C and 28 bars. The cost of exporting spent caustic to a full-service company in USA was $1.21 per gallon that was competitive with treatment at the individual generation sites on a short-term basis.

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