Abstract: The invention relates to the treatment of chemical process wastewaters and chemical waste landfill leachates containing obnoxious and hazardous halogenated organic chemicals by the use of a combination of physical, chemical and biological processes to produce a liquid discharge acceptable to the environment in an efficient and economical manner.

Abstract: The addition of a small amount of hydrogen or a hydrogen-liberating compound such as a metal hydride to a caustic solution serves to suppress the corrosive effect of the solution on nickel-based surfaces. Typical nickel-based surfaces include caustic evaporator surfaces which contain a caustic solution maintained at a temperature of from about 130.degree. C. to about 180.degree. C. A preferred metal hydride is sodium borohydride which is preferably present in an amount of from about 5 ppm to about 100 ppm. Concentrated caustic solutions containing less than 0.5 ppm of nickel can be prepared by this process.