Anchoring catalytic wet air oxidation to biomass waste management with focus on distillery stillage

Wet air oxidation is an advanced chemical reaction process involving the use of moisture and air and is applied to purposes such as to degrade existing and emerging pollutant, especially to waste types of too liquid for combustion process but too solid for biodigestion. The traditional wet air oxidation process operates on a temperature of 150–300 °C and a pressure of 0.5–20 bar whereas the supercritical oxidation applies a temperature > 374 °C and a pressure of > 2.2 bar. Wet air oxidation process technology is well matured; however, it is still a flashpoint to researchers, especially on economizing the system from applying catalysts and their supports. Wet air oxidation process catalysis is performed to improve reaction efficiency performing it at lower temperature and pressure. Such catalyzed processes are preferred based on the catalyst’s selective activity and stability as well as recoverability while economizing the process energy requirement. Consequently, a catalyzed subcritical wet air oxidation is considered as an environmentally friendly and economically feasible alternative. In the past decades, plenty of studies have been done on wet air oxidation but are performed piece by piece, not comprehensively. Additionally, biologically coupled wet air oxidation of pollutants is not well revised. This paper uniquely elucidates the recent advancements in wet air oxidation and it is integral with other waste treatments to an environmentally friendly management. Structurally, this review presents the basics and state of the art of wet air oxidation, the chemical process, its catalytic and catalyst support progresses, and its application in waste and bioenergy with focus to stillage.