Spent sulfidic caustic, which is difficult to treat and to dispose of due to its noxious properties, can be regenerated employing a new method, which is a combination of chemical, physical, and microbiological processes. After simple physical separation, advanced neutralization is applied to clarify and deodorize the caustic, resulting in a quality sufficient for microbial polishing. Based on the analysis results of the waste, this process would be highly economical and safe, as the product may be used in liquefied petroleum gas treatment units, depending on the concentration of the regenerated caustic and inclusion of the original catalyst. With this method, in addition to waste prevention, a considerable amount of caustic and catalyst can be saved.