Use of ozone/activated carbon coupling to remove diethyl phthalate from water: Influence of activated carbon textural and chemical properties

Abstract : The presence of phthalates in the environment and especially in surface waters and sediments is a major environmental concern. The aim of this work was to study diethyl phthalate (DEP) removal by a water treatment process based on the coupling of ozone (O$_3$) and activated carbon (AC). The main objective was to study the influence of AC properties on the process efficiency and on the coupling mechanism (nature and location of reactions). DEP degradation kinetics by O$_3$/AC coupling was studied by using four commercial ACs whose chemical and textural properties had been previously determined (Boehm titration, N$_2$ adsorption isotherm at 77 K, $pH_{PZC}$ determination). Degradation kinetics was correctly modelled by a pseudo-first order kinetic model based on the sum of all the effects occurring during the treatment (r$^2$ > 0.987). Results show that degradation efficiency depends both on textural properties (microporous and external surfaces favour this treatment) and chemical functions (both acid and basic functions favour radical hydroxyl generation). Experiments performed with a radical scavenger show that in all the experimental conditions used, DEP is mainly degraded by radical reactions. Moreover, it is demonstrated that AC acts more as a radical initiator and promoter and a reaction support than as an adsorbent material. The influence of pH on the reaction efficiency and mechanism is also proved: in acidic conditions (pH < 5) radical reactions are due to O$_3$/AC interactions, and they are due to indirect ozonation in the bulk liquid for higher pH.