Emergent pollutants are compounds from natural or synthetic sources that have known or suspected adverse effects on the environment and human health. Benzotriazoles (BTA) are emergent pollutants that are acutely toxic to certain bacteria and aquatic organisms. Alkylphenol ethoxylates (APEO) and their stable degradation products alkylphenols (AP) are pollutants that are acutely and chronically toxic to algae, fish and invertebrates. In vertebrates, they bind to estrogen receptors and act as endocrine disruptors. Current methods for removing emerging contaminants from the environment, such as biological degradation and adsorption, have not proven to be the most effective methods and may produce products that are even more toxic than the original contaminants. A new approach for removing emergent pollutants from the aqueous environment, especially wastewater, is the use of so-called advanced oxidation processes (AOP), including electro-oxidation (EO) and ozonation, which are based on the formation of reactive oxygen species at room temperature that then oxidise the pollutants.
For BTA, the performance of EO using different anode materials, namely the boron-doped diamond (BDD) anode and the RuO2 and RuO2/IrO2 mixed-metal oxide (MMO) anodes, was monitored. BDD was found to be the most efficient anode, with 81.1% BTA degradation after 60 min. The formation of 1H-BTA-4,7-dione, BTA-OH, BTA-(OH)2 and BTA-(OH)3 was identified with all electrodes. The BDD anode was then used for EO of BTA in model wastewater with the addition of H2SO4, Na2SO4 and NaCl as supporting electrolytes. H2SO4 was found to be the most effective electrolyte, with 97.7% BTA degradation after 60 min. With the addition of H2SO4 and Na2SO4, the formation of BTA-OH, BTA-(OH)2 and BTA-(OH)3 was identified among the EOs, while the latter metabolites were not observed with the addition of NaCl. With the addition of NaCl, the formation of BTA-Cl was identified during EO.
To monitor the ozonation of AP, I have developed an HPLC-DAD method and a GC-MS/MS method. The HPLC-DAD method was linear in the range between 0.5 mg/L and 50 mg/L with an injection RSD below 6.4%. The GC-MS/MS method was linear in the range between 10 µg/L and 500 µg/L with an injection RSD between 1.2% and 8.3%. I also optimised the SPE, with C18 proving to be the most efficient column with extraction recoveries between 47.7% and 86.5%. pH had no significant effect on the recoveries, while the addition of electrolytes slightly increased the recoveries for 4-t-octylphenol and lowered them for the other APs. The optimum MeOH eluent volume was 2 mL. The breakthrough volume was 500 mL. The ozonation efficiency of real wastewater containing AP was monitored by adding two different heterogeneous zeolite catalysts, ZEO and ZEO(Fe). ZEO(Fe) proved to be a much more efficient catalyst, with complete AP mineralisation achieved after 40 min, while in the case of ZEO, complete AP mineralisation was achieved after 110 min.
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