Industrial wastewaters are usually treated by a combination of chemical and biological treatment methods. In some cases, COD and BOD levels are too high to be treated by these conventional methods and are sent directly for incineration which is often energy-intensive and costly. Supercritical water oxidation (SCWO) is a technology that is capable of oxidizing the toughest organic compounds in wastewater. Wastewater is mixed with oxygen and raised beyond the critical point of water (221 bar and 374oC). At supercritical conditions, oxygen rapidly and completely oxidizes all organic pollutants in the supercritical wastewater in a span of seconds to form water nitrogen and carbon dioxide. SCWO can be used to treat highly hazardous waste that cannot be handled by conventional technologies including brine, industrial wastewater, hazardous organic material or sludge from water treatment plants containing non-biodegradable pollutants.
In the supercritical region, organic compounds largely insoluble in water at ambient conditions are highly soluble in supercritical water allowing organic compounds and oxidants to mix homogeneously in the supercritical phase enabling efficient oxidation of the compounds. Inorganic compounds such as salt and heavy metals are dramatically less soluble in supercritical water compared to water forming salt concentrate and residue. SCWO is an exothermic process and may sometimes generate sufficient energy to heat up the incoming feed via a heat exchanger thereby reducing the operating cost.
SCWO is effective in dealing with high concentrations of hard to degrade organics and can be applied in industries such as:
There has been an increasing demand for advanced oxidation technologies like SCWO that can guarantee complete destruction of hardly degradable pollutants. Several tests were performed with complete removal of per- and polyfluoroalkyl substances (PFAS) from leachate and problematic wastewater with great success. The PFAS group of chemicals includes substances such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) that have been identified with growing concern as highly carcinogenic contaminants. These chemicals are used in a wide range of products, e.g. fire retardants, non-stick frying pans, pizza-boxes, and water-resistant coatings for textiles.