Emerging Pollutants That Can Be Transformed into PCDD/Fs

Abstract

AbstractWater and soil pollution is one of the top problems of environmental concern that has been worsened in the last years due to the lack of available water and overall resources. Owing to the difficulty in eliminating pollutants from the environment, applying cost-effective treatments to the anthropogenic sources of origin (i.e., wastewaters and industrial effluents) before they are discharged to the environment becomes a very good alternative. The presence of emerging pollutants (EPs) deserves special attention and is being considered in new regulations due to their adverse effects and/or persistence. Among them, a group with increasing presence is that related to the use of Pharmaceutical and Personal Care Products (PPCPs). Triclosan (TCS; 5-Chloro-2-(2,4-dichlorophenoxy)phenol) is an emerging antimicrobial contaminant that belongs to PPCPs. The extensive use of TCS has caused its presence in different water sources, especially in WWTPs effluents, lakes, rivers, and also in sediments throughout the world, posing a risk to the environment and human health. Advanced Oxidation Processes (AOPs), defined as aqueous phase oxidation technologies based on the formation of highly reactive species, such as hydroxyl radicals (•OH), have been successfully applied to the remediation of wastewaters containing recalcitrant organic compounds. However, depending on the operating conditions, AOPs can lead to the generation of by-products during the degradation of the primary pollutants that may increase the final toxicity of the treated water. In this way, TCS, along with its degradation/oxidation routes, has been related to the formation of persistent organic pollutants (POPs) such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Specifically, this chapter focuses on the potential of electrochemical and photocatalytic oxidation, in terms of TCS degradation rate and by-products formation, paying special attention to the potential formation of PCDD/Fs. The role of two electrolytes widely applied in electrochemical oxidation, NaCl and Na2SO4, as well as the influence of the concentration of a catalyst (TiO2), on the photocatalytic medium, has been analyzed. The toxicity in the treated waters was assessed through the toxic equivalents (TEQ) expressed as the 2,3,7,8-TCDD TEQ concentration, where 2,3,7,8-TCDD is the most toxic congener (NATO Committee on the Challenges of Modern Society (NATO/CCMS)). After complete TCS degradation, TEQ reached a maximum value of 4.78 pg L−1 in electrochemically remediated waters, using NaCl as electrolyte (19 times higher with respect to untreated water containing TCS), whereas the value of the photocatalytically treated waters with TiO2 0.75 g L−1 was 6.25 pg L−1 (more than 25 times higher with respect to untreated water containing TCS). These results emphasize the importance of the quantitative traceability of the formation of by-products and the resulting toxicity (PCDD/Fs, TEQ,) when applying AOPs to polluted waters containing EPs, especially organochlorines, considered precursors of PCDD/Fs.KeywordsAdvanced oxidation processes (AOPs)Electrochemical oxidationEmerging pollutants (EPs)Pharmaceutical and personal care products (PPCPs)PhotocatalysisPolychlorinated dibenzo-p-dioxins and Polychlorinated dibenzofurans (PCDD/Fs)Triclosan (TCS)