Catalytic wet-air oxidation of a chemical plant wastewater over platinum-based catalysts

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.

Heterogeneous catalytic wet air oxidation of refractory organic pollutants in industrial wastewaters: a review

Catalytic wet air oxidation (CWAO) is one of the most economical and environmental-friendly advanced oxidation process. It makes a promising technology for the treatment of refractory organic pollutants in industrial wastewaters. Various heterogeneous catalysts including noble metals and metal oxides have been extensively studied to enhance the efficiency of CWAO. The present review is concerned about the literatures published in this regard. Phenolics, carboxylic acids, and nitrogen-containing compounds were taken as model pollutants in most cases, and noble metals such as Ru, Rh, Pd, Ir, and Pt as well as oxides of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, and Ce were applied as heterogeneous catalysts. Reports on their characterization and catalytic performances for the CWAO of aqueous pollutants are reviewed. Discussions are also made on the reaction mechanisms and kinetics proposed for heterogeneous CWAO and also on the typical catalyst deactivations in heterogeneous CWAO, i.e. carbonaceous deposits and metal leaching.

Treatment of phenol wastewater using hydroxyl radical produced by micro-gap discharge plasma technique

Hydroxyl radical produced by non-equilibrium plasma, which was induced by micro-gap dielectric barrier discharge, was used for the treatment of phenol wastewater. The advantage of this method was that chemicals and catalysts were not involved when hydroxyl radical was generated from water and oxygen. A proportional efficiency of phenol removal was observed with the hydroxyl radical increasing. The removal efficiency was higher in a basic condition than in an acidic condition, which was enhanced with the pH value of the solution increasing from 3.6 to 11.2. It was rational to adjust the pH value between 9.0 and 10.0. The removal efficiency of phenol was reduced when the conductivity of the solution increased from 0 to 200 micros x cm(-1); the highest was found in the solution without Na2CO3. The UV spectral absorption in the process indicated that few organic compounds with a conjugated structure were included in the treated wastewater.