Abstract
The conventional wastewater treatments are inadequate for emerging contaminants detoxification. Photocatalytic ozonation with suitable catalyst can be considered as a suitable solution on the removal of these compounds. The aim of this study was to verify the effect of Ag, Pd and Pt with different loadings (0.1, 0.5 and 1% wt %) onto TiO2 surface for the degradation of a mixture of parabens (methyl, ethyl, propyl, butyl and benzyl) through photocatalytic ozonation. Chemical oxygen demand (COD) and total organic carbon (TOC) was also analyzed after treatments, as well as the effect of the treatment on the samples toxicity over different species, including bacteria, clams and plants. The effect of metal loading on the parabens degradation; COD and TOC removal is very dependent upon the type of noble metal used. This can be related with the different pathways influenced by the metal load. On the one hand, it can be related with the reduction of electron–hole recombination phenomenon, and, on the other hand, the trapping of electrons by the metals reduces the amount of ozonide and hydroxyl radicals produced. In terms of toxicity, apparently the best results were achieved with the intermediate noble metal load. However, the effect of noble metal load must be analyzed case to case.
Highlights
The conventional municipal wastewater treatments seem to be inefficient regarding the degradation of some specific compounds [1]
The presence of gold, platinum and silver at 1 wt % load does not change the diffractive peaks of anatase phase from TiO2 [11]. These studies reveal that the lack of detection in the X-Ray diffraction (XRD) analysis of diffractive peaks of noble metals for different loads used in our study could be explained by the low doped dose and/or small size of noble metals’ nanoparticles
An increase of metal load promotes a slight improvement in the Chemical oxygen demand (COD) removal, even using lower transferred ozone dose (TOD), which is in accordance with the results achieved for parabens degradation
Summary
The conventional municipal wastewater treatments seem to be inefficient regarding the degradation of some specific compounds [1]. The so called emerging contaminants encompass compounds usually used on pharmaceuticals and personal care products and are progressively appearing on natural aquatic resources and on the wastewater treatment plants [1]. Bearing in mind the low efficiency of the traditional municipal wastewater treatment processes on the degradation of these compounds, scientific efforts have been made to find a suitable solution to their degradation [4,5] In this way, advanced oxidation processes (AOPs) appear as promising technologies. Molecular ozone reactions can be a source of refractory by-products no longer reactive with ozone, leading to low mineralization levels [7]
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