Ozonation of o-phenylenediamine in the presence of hydrogen peroxide by high-gravity technology

Abstract

The study herein investigated the effectiveness of simultaneous use of ozone and hydrogen peroxide (O3/H2O2 process) to degrade o-phenylenediamine (o-PDA) in a simulated wastewater. A rotor–stator reactor (RSR) was employed to create a high-gravity environment in order to enhance ozone-liquid mass transfer rate and possibly improve the degradation rate of o-PDA. The degradation efficiency of o-PDA (η) as well as the overall gas-phase volumetric mass transfer coefficient (KGa) were determined under different operating conditions of H2O2 concentration, initial o-PDA concentration, temperature of reaction, initial pH and rotation speed of RSR in attempt to establish the optimal conditions. Chemical oxygen demand reduction rate (rCOD) of wastewater treated at a particular set of conditions was also analyzed. Additionally, the intermediate products of degradation were identified using a gas chromatography-mass spectrometer (GC/MS) to further evaluate the extent of o-PDA degradation as well as establish its possible degradation pathway. Results were validated by comparison with those of sole use of ozone (O3 process), and it was noted that η, KGa and rCOD achieved by O3/H2O2 process was 24.4%, 31.6% and 25.2% respectively higher than those of O3 process, indicating that H2O2 can greatly enhance ozonation of o-PDA. This work further demonstrates that an RSR can significantly intensify ozone-liquid mass transfer rate and thus provides a feasible intensification means for the ozonation of o-PDA as well as other recalcitrant organics.