Influences of pH, temperature and activated carbon properties on the interaction ozone/activated carbon for a wastewater treatment process

The influence of experimental parameters (T, pH) and activated carbon (AC) properties on the intensity and the nature (molecular or radical) of the ozone (O3) /AC interaction was studied to optimize an O3/AC wastewater treatment process. This interaction was investigated by studying the dissolved O3 decomposition kinetics in the presence of two commercial AC (Pica 150 and Picaflo), whose chemical and structural properties were previously determined by using different analyses (Boehm method, nitrogen adsorption at 77 K). The kinetic study showed that a first order model is the most suitable to describe O3 decomposition in water (r2 > 0.981). Moreover, the influence of the experimental parameters was demonstrated. An increase in temperature limits the O3/AC interaction by favouring ozone self decomposition in water. An increase in pH leads to deprotonated surface groups (when pH > pHPZC) which favour radical mechanisms but limits the interaction by electrostatic repulsion. Further, the contribution of the radical mechanism in ozone decomposition was evaluated by adding terbutyl alcohol (tBuOH) as radical scavenger. This contribution varied with the pH and the nature of the AC: it operates from 7% (pH = 3) to 76% (pH = 7) for Pica 150 and from 10% (pH = 3) to 86% (pH = 7) for Picaflo.The comparison of kinetic rate constants obtained in the presence of both types of AC revealed the importance of the chemical and structural properties of AC, especially the number of acid functions.