Wet air oxidation (WAO) is commonly used to treat spent caustic wastewater streams. The process achieves complete oxidation of reduced sulfur species such as sulfides, and mercaptides. At more aggressive treatment conditions, complex organic contaminants such as phenol, cresyols and naphthenates can be broken down to biodegradable short chain organics. By applying WAO, odor issues can be eliminated and the treated spent caustic is suitable for discharge to a conventional biological treatment process.

For the over 20 years, spent caustic treatment has been one of Siemens’ lead commercial applications of the Zimpro® WAO technology. Systems can be found in many of the newly-constructed ethylene facilities and refineries worldwide. Siemens has supplied custom-designed, specification-compliant spent caustic treatment systems for some of the largest facilities in the United States, Middle East, Europe, Taiwan, India, Korea, Africa, South America and China.