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This paper presents a study on the integration of two advanced treatment processes for the removal of priority organic processes from wastewaters: catalytic oxidation (Fenton homogenous process) followed by ultrafiltration. The aim of this study was to assess the removal efficiency for 4-chlorophenol (used as model pollutant), as well as the decrease in effluent toxicity in various processes conditions. The experiments have mainly focused on studying the effect of the oxidant dose of the catalytic oxidation process on the performance of the ultrafiltration process and on the toxicity of the final effluents. Furthermore, the mechanisms of the Fenton homogenous oxidation processes and the removal of heavy molecular weight compounds in ultrafiltration were studied. The results have shown that the toxicity of the effluents decreases significantly through catalytic oxidation, while the ultrafiltration process mainly contributes in removing the oxidation intermediates, especially the high molecular weight compounds.

Chlorophenols were selected for this study because most of them are toxic and difficult to biodegrade. They represent a particular group of priority toxic pollutants listed by the US EPA in the Clean Water Act and by the European Decision 2455/2001/EC. The efficiency of advanced oxidation processes for degradation of chlorophenols has been extensively documented. The catalytic wet hydrogen peroxide oxidation process, involving oxidation with H 2 O 2 and solid catalysts in mild reaction conditions, was found to be very attractive for different pollutants; however, data regarding the degradation of chlorophenols are very scarce. The aims of this paper were: (i) to prepare and characterize a series of iron-exchanged montmorillonites and (ii) to assess their catalytic performances in a Fenton-like process for the oxidation of para-chlorophenol. DR-UV-VIS spectroscopy was tentatively used to elucidate the structure of the iron oxo sites intervening in the reaction. This approach has been used previously for ion-exchanged zeolites and was able to distinguish between isolated Fe(III) species and Fe x O y clusters of different nuclearity. The catalytic tests, performed at room temperature, showed that all iron-containing clays were very active, leading to the complete oxidation of parachlorophenol and a significant reduction of TOC values. 4-chlorocatechol was the major reaction intermediate found in the CWHPO of 4-CP, followed by hydroquinone and traces of benzoquinone, 5-chloro-1,2,4-benzenetriol, 1,2,4-benzenetriol and 3-chloro-muconic acid. The leaching test indicates that the catalytic activity is mainly due to leached iron ions, at least in the second part of the process.

The increased concentrations of priority pollutants in wastewaters have imposed the completion of conventional treatment with advanced treatment stages (such as catalytic oxidation, membrane processes, adsorption, ion exchange, etc.) for their removal by chemical degradation and/or physical separation. In this study, 4-chlorophenol (4-CP) is proposed as model-pollutant for the priority organic pollutants present in synthetic wastewaters and several processes which can act as advanced treatment stages for this type of effluents have been analyzed. The concept was to analyze under a unitary framework the performances of a Fenton type oxidation process, in the presence of iron catalyst and hydrogen peroxide and an adsorption process on surfactant modified natural zeolites (SMZs) for the removal of 4-CP. The results have shown that the combined catalytic oxidation (homogeneous Fenton process) and adsorption process can be used to eliminate priority organic pollutant from wastewater (removal efficiencies of 100% 4-CP, 85% TOC and 89% COD for the combined process). The adsorption process is very efficient in removing the oxidation intermediates, significantly eliminating the effluent toxicity (between 78 and 100%).