Degradation kinetics of DEP in water by ozone/activated carbon process: Influence of pH

Abstract

Efficiency of the ozone (O3)/Activated Carbon (AC) process to remove phthalates was studied by investigating the degradation kinetics of diethylphthalate (DEP) chosen as model pollutant. The influence of pH was determined by performing experiments at five pH values (2.5<pH<7.2). The kinetic contribution of radical mechanisms (δHO•) was estimated by using a radical scavenger (tert-butyl alcohol). Single ozonation of DEP was first performed. Pseudo-first order modelling shows that the reaction depends on pH, with kinetic constants varying from 0.0036min−1 (pH=2.5) to 0.6129min−1 (pH=7.2). Ozonation was then performed in the presence of a commercial AC (Pica L27), whose chemical and textural properties had been previously determined. Pseudo-first-order modelling shows a significant increase in DEP degradation kinetics: kinetic constants rose from 0.290min−1 (pH=2.5) to 0.866min−1 (pH=7.2). Estimation of the kinetic contribution of heterogeneous reactions to DEP removal (δhetero) shows that in acidic conditions, reactions are essentially located on the AC surface (δhetero=98.7% at pH=2.5) and occur in the bulk liquid when pH increases (δhetero=29.2% at pH=7.5). Lastly, estimation of the kinetic contribution of radical mechanisms (δHO•) shows that the increase in the DEP degradation kinetics is mainly due to radical reactions, with δHO• increasing from 87.9% (pH=2.5) to 92.0% (pH=7.5). These radical reactions may be promoted by deprotonated acid groups present on the AC surface.