The role of the wastewater matrix in the degradation of Metoprolol by photo- Fenton process at circumneutral pH

Abstract

Increasingly, human activities and lifestyles of developed countries are jeopardizing the viability of ecosystems, especially with the expansion of the chemical industry and the production of so-called emerging contaminants, including cleaning products, cosmetics, pharmaceuticals etc. Metoprolol (MET) is a type of beta-blocking drug increasingly consumed in Spain. Although these contaminants are only present in minute concentrations (ppm or ppb) they could seriously affect aquatic ecosystems if they are not removed from the wastewater. The most common treatment techniques used for removing contaminants in wastewaters have no influence on the degradation of emerging contaminants. This, coupled with the increasing demands on water quality imposed by the Water Framework Directive (2000/60/CE) makes necessary to use alternative techniques that enable the degradation of the contaminants. This is where the advanced oxidation processes (AOPs) come into play. In this project the photo-Fenton process has been applied to degrade MET, added to mineral water and wastewater from membrane bioreactor system (MBR) treatment from Gavà wastewater treatment plant (WWTP). The optimal pH of this process is 2.8 but in this project the experiments will be assessed at circumneutral pH to improve the process to all levels, not only industrial. In order to maintain the iron in solution different chelating agents have been assessed. Different concentrations of hydrogen peroxide and iron have been tested (25, 150 mg/L H2O2 and 2.5, 5.0 and 10.0 mg/L Fe2+). All experiments were carried out in the period of 60 minutes and the following variables were assessed: MET degradation, total organic carbon (TOC) and chemical oxygen demand (COD) reduction, specific UV absorption (SUVA) and toxicity. It has been proved that MET does not suffer photolysis. In mineral water ethylenediaminetetraacetic acid (EDTA) has acted as a chelating agent. The highest MET degradation and COD, SUVA and toxicity reduction in mineral water were obtained for the highest concentrations of iron and hydrogen peroxide (Fe2+:H2O2 10:150) with a values of 100%, 45.4%, 54.8%, 91.9% respectively. This is because the increase in the H2O2 dose enhances the reaction rate due to higher OH· production. Regarding the reduction of TOC it was highest under the conditions Fe2+:H2O2 5:150. Wastewater from MBR treatment was also investigated. The method applied in mineral water does not work so EDTA had to be changed by ethylenediamine-N,N′-disuccinic acid (EDDS). No significant differences in MET degradation have been observed when different concentrations of iron and hydrogen peroxide were assessed. The highest COD reduction was obtained for the highest concentrations of iron and hydrogen peroxide (Fe2+:H2O2 5:150) with a value of 46.8%. Higher toxicity reduction was achieved when the concentration of iron was the lowest (2.5 mg/L) with a value of 90.4%. Regarding TOC reduction, it was highest when hydrogen peroxide concentration was highest (150 mg/L). In order to compare the efficiency of the process under sunlight conditions an experiment was carried out in a compound parabolic collector (CPC) reactor.