| Abstract [eng] |
There has been an increasing concern about the occurrence, fate, and adverse effects of pharmaceutical residues in the aquatic environment in recent years. Some of the most widely and frequently used drug classes, eg. antibiotics, are used in quantities similar to those of pesticides and, in some countries, they are even sold without the prescription. Nevertheless, pharmaceuticals are not tested for low-doses vs. long-term exposure. Therefore the full extent and consequences of the presence of these compounds in the environment are still poorly known (Fatt-Kassinos, Meric, Nikolaou, 2011). Three different pharmaceuticals were selected for this research - diclofenac, ketoprofen and carbamazepine, that are quite widely found in the treated wastewater (Ternes, 1998; Ternes et al. 2001,) and the surface water (Ahrer, Scherwenik, Buchberger, 2001; Soulet et al., 2002) or even groundwater (Sacher et al., 2001). Therefore, it is essential not only to examine the effects of those materials for water ecosystems and human health, but also to find ways to stop the medications access into water cycle. One or several combined advanced oxidation methods before or after biological treatment operations can significantly reduce levels of active medicinal substances in treated wastewater or drinking water. They can also contribute to the destruction of resistant bacteria’s, which is the result of low concentrations of the medicament in water (Schwartz et al., 2003). In order to determine optimal conditions for medicines oxidation (i. e. optimal reactor power and air flow rate), the experiment was conducted using 10 mg/l diclofenac solution. It was noted that the optimal conditions required to obtain the maximum decomposition efficiency were quite similar for all intermediates (UV analysis) and just for diclofenac (HPLC analysis). The best result was achieved when the air flow was ≈8 l/min and capacity varied from 22 to 24 %. However, since one of the goals was to analyze complex water treatment method using UV radiation and TiO2 catalyst, the optimal experimental conditions were not focused on the most effective division for the DBD reactor. As optimum conditions air flow rate and reactor power of 7 l/min., and 20 % (50.1 W) were selected respectively. After selection of optimal reactor operating conditions, combination of 7 additional methods were used to determine their influence on decomposition processes. After the initial semi-decomposition in first reactor cylinder solution was pumped to the second reactor, where the influence on decomposition processes of methods combinations was observed. In all cases, the decomposition efficiency was highest with the present of O3 in the reactor. It confirms the appropriateness of this method for water purification. In case of diclofenac, the effectiveness distribution curves were almost perfectly compatible with the theoretical one, i. e. decomposition was preferably carried out using the combination of O3, TiO2 catalyst, and UV radiation, but removal of one of the factors had an opposite effect. In cases of ketoprofen and carbamazepine this trend was not so clear. Here, all curves were located relatively evenly, so UV radiation or TiO2 catalyst did not have large effect for the decomposition of these medications. In order to choose the optimal conditions for decomposition by obtaining the lowest mortality of the chironomus larvae, it was observed that the lowest mortality rate was achieved when oxidation process was carried for 2.5 minutes and O3 and catalyst were used in the second reactor. Although it is necessary to stress that this was only an intermediate point. The mortality increased again after 5 min of experiment. Therefore, oxidation process in DBD reactor should last no less than 5 minutes. Extension of the time interval was as efficient as ozone alone. Because the latest method is relatively energy efficient it can be stated that drug decomposition in DBD reactor is optimal. Nevertheless, an unambiguous conclusion about cannot be limited by the research of this paper. The by-products of drug decomposition need to be identified so it would be better to assess their potential impact on the environment, also to analysis of a larger group of medications would be needed. Furthermore, because of the fast development of advanced oxidation methods, the comparison of those methods should be done. Only in this way it can be chosen both ecologically and economically optimal water treatment technologies, contributing to a more sustainable world development. The work carried out under the project “synergistic DBI plasma modification technology for industrial wastewater treatment” (MIP024 / 14). DBD reactor was constructed by PhD student Martynas Tichonovas. |
