Influences of pH, temperature and activated carbon properties on the interaction ozone/activated carbon for a wastewater treatment process
Résumé
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 (r2N0.981). 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 pHNpHPZC) 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.