Abstract

Several industries are generating an enormous volume of wastewater contaminated with a number of toxic and persistent organic compounds (POPs) such as phenols, cresols, naphthenic compounds, lignin, mercaptans, and inorganic disulfides. These contaminants enter waste streams from chemical processing and handling operations and from refineries and petrochemical units. A number of such contaminants are biorefractory and toxic to microbial species, and therefore require some kind of pretreatment before being sent to conventional biological treatment methods. This entry focuses on the wet oxidation (WO) process that can be used for the treatment of waste streams containing POPs and other inorganics that are biorefractories. WO is an oxidation process mainly used for the degradation of organic and inorganic compounds at elevated temperature and pressure conditions (up to 320°C and 20 MPa, respectively), converting them into less harmful gaseous products and water-soluble innocuous products. The process is suitable for moderate- to high-strength wastewaters having a chemical oxygen demand ranging from 10,000 to 100,000 mg/L. The process is applicable for the treatment of low-volume wastewaters emanating from various chemical and process industries. The WO process is also an alternative solution for the regeneration of spent activated carbon and the desulfurization of coal. Several commercial WO processes are available in the market; however, their use is limited to developed countries as the processes are capital intensive and are carried out under severe operating conditions. This entry deals with the WO process, its mechanistic aspects and commercial processes, and the challenges for the process to become acceptable in wastewater treatment.