Wet and supercritical oxidation for landfill leachate treatment: A short review

Modern societies are characterized by an increasing production of wastes, which are often dumped in landfills. This practice is widespread in several countries and leads to the formation of a highly polluted dark liquid called leachate. Landfill leachate may contain a variety of high-toxic contaminants, including refractory organic compounds, ammonia-nitrogen compounds, heavy metals, inorganic salts and organo-chloro compounds and poses significant risks to public health. Therefore, significant efforts have been made the last decades to develop efficient methods for leachate disposition and treatment. In recent years, Advanced Oxidation Processes (AOPs) have been widely adopted for landfill leachate purification. Among them, wet and supercritical oxidation processes are of particular interest due to their unique characteristics and exceptional efficiencies, and therefore, have been widely reported as promising, environment-friendly technology for the destruction of recalcitrant organic compounds and the treatment of landfill leachate. This review article is an original literature update providing meaningful information progress made about both processes on their existing applications with emphasis on performance, expressed by the reduction of environmental indicators like COD, TOC or ammonia. Efficiencies can be considered quite high, especially in the case of supercritical oxidation where COD removal can reach up to 99%. Additionally, catalysts and promoters that have been utilized are presented and their influence on treatment's efficiency is discussed. Finally, the emerging prospects by the combination of supercritical oxidation with ozonation and adsorption processes are highlighted. The information and perspectives provided in this review will provide guidance and better understanding to promote the application of wet and supercritical oxidation processes in landfill leachate treatment.