Biodegradability enhancement of phenolic compounds by Hydrogen Peroxide Promoted Catalytic Wet Air Oxidation

Abstract

The aim of this work is to study the viability of the H 2O 2 Promoted Catalytic Wet Air Oxidation (PP-CWAO) process, using activated carbon (AC) as catalyst, to increase the biodegradability of phenolic aqueous solutions. Seventy-two hours experiments were performed in a trickle bed reactor at 140 °C and 2 bar of oxygen partial pressure. Feed concentrations, in terms of theoretical chemical oxygen demand (ThCOD), were 11.8 g COD l −1 for phenol, 12.6 g COD l −1 for o-cresol and 8.0 g COD l −1 for p-nitrophenol. Air was used as main oxidant and 20% of the stoichiometric amount of H 2O 2 needed for pollutant complete mineralisation was added as oxidation promoter. Adding H 2O 2 to the CWAO process not only increases pollutant removal but also leads to higher mineralisation of the remaining oxidation products. For instance, removal of phenol, o-cresol and p-nitrophenol increase from 45, 33 and 15% in the CWAO process to 64, 64 and 49% in the PP-CWAO process. In addition, the PP-CWAO process leads to better biodegradability enhancements, when compared to CWAO, as demonstrated by the respirometric tests. However, it is still necessary to improve the oxidation step in order to assure more biodegradable effluents that could be combined with a subsequent biological wastewater plant.