Adsorption of organic pollutants from water on high silica zeolites and regeneration by ozone

Abstract

This work investigates the removal of refractory organic compounds or micropollutants from water using a three-phase process combining adsorption onto hydrophobic zeolites and in situ regeneration by oxidation with ozone. Nitrobenzene (NB), toxic, non-biodegradable and refractory to ozonation, was chosen as a paradigm to assess the efficiency of the process. First, the adsorption equilibrium isotherms of NB onto various zeolites led to select the best adsorbent for removing NB from water. It was evidenced that zeolites with a high Si/Al ratio were the most efficient although their adsorption capacity stayed beyond that of activated carbon, except at low concentrations. This capacity depended on the Si/Al ratio but also on the zeolite pore size, i.e. on the structure. In a sequential process coupling adsorption and ozonation, NB was completely removed from water by adsorption and oxidized by ozone. However, no catalytic effect was evidenced but oxidation implies a concentration effect for NB. In addition, it was possible to restore totally the initial adsorption capacity of the zeolite.