Single and catalytic ozonation for phenolic wastewaters remediation

Aiming the improvement of single ozonation of a mixture of six phenolic acids normally present in Olive Mill Wastewaters, Manganese and Cerium oxides based catalysts were used in the catalytic ozonation process. Regarding the total phenolic content degradation no significant differences were found in the activity of MnO2, CeO2 and the bimetallic catalyst with a molar ratio Mn/Ce of 70/30. However, concerning the total organic carbon removal, the best results were obtained for the Mn/Ce catalyst explained by the synergetic effect between Mn and Ce. During the preparation of the catalysts, the increase of the calcination temperature leads to a decrease in the Brunauer-Emmet-Teller area resulting in a slight inhibitory effect over the total organic carbon removal. A higher importance of the catalyst in the organic intermediates mineralization than in the parent phenolic compounds degradation was observed. The comparison between single ozonation and catalytic ozonation in the presence of the Mn-Ce-O (70/30) catalyst revealed a higher enhancement in both total phenolic content and total organic carbon oxidation. After 120 min of reaction low carbon adsorption was detected in the recovered catalyst meaning that the pollutants removal occurred by oxidation and not by adsorption to the solid phase. Moreover, a low Mn quantity was detected in the liquid phase confirming the stability of the catalyst in what concerns leaching behaviour of the active phase to the liquid. Therefore, Mn-Ce-O showed to be an interesting catalyst to improve the efficiency of ozonation in the treatment of phenolic wastewaters.