Fixed-bed thermodynamical analysis of the sorption mechanisms of Pharmaceutically Active Compounds (PhACs) in sandy soil

In the last couple of decades, the utilization of different Pharmaceutically Active Compounds (PhACs) significantly has increased. The applications of the treated wastewater (discharge into surface waterbodies, sewage sludge disposal), have resulted that those PhACs world-wildly can be detected in the environment. Due to the negative effects of these PhACs on ecosystems, it is indispensable to analyze their behavior in the soil environment. In the soil solution systems (SSS) the sorption mechanisms of the PhACs are significantly being influenced by various environmental factors like pH, and temperature. In our research, PhACs with different physicochemical properties have been studied such as 17α-ethynylestradiol (EE2), diclofenac-sodium (DFC), and lidocaine (LID). Owing to these facts, the main questions of our research were: (a) How to estimate the Van’t Hoff equation’ parameters in fixed-bed SSS? (b) How does the temperature change affect the intermolecular reactions of the PhACs on the solid/liquid interface in the single and multi-component systems? Single and multicomponent fixed-bed sorption experiments were carried out. All of the sorption experiments have been investigated at 5 different temperatures. The fixed-bed sorption experiments have been performed at the ploughed layer of calcareous, humic sandy soil. The adsorbate-adsorbate and adsorbent-adsorbate interactions have been evaluated by different empirical formulas. To conduct the results of our study, different statistical analyses (2-way ANOVA, Principal Component analysis, regression analysis, and Pearson correlation have been performed. In the scientific literature, the thermodynamical parameters had been carried out in batch experiments. Nevertheless, this way of sorption analysis in an environmental system often overestimates the equilibrium constant (K_c) in the Van’t Hoff equation. Due to this fact, we hypothesized that if the experiment is implemented in a fixed-bed SSS, the real K_c value can be calculated from the real empirical q_e value, which could provide the optimal results of the thermodynamical parameters. Our results show that in single-component systems EE2, LID, and DFC have got spontaneous endotherm sorption reactions. While in a multicomponent SSS system, the LID and EE2 had an exothermic enthalpy-driven reaction. Furthermore, in all cases, the Gibbs free energy has been decreased when the temperature was increased.

This research was supported by the National Research, Development, and Innovation Office (NKFIH), Hungary (project identification number: 2020–1.1.2-PIACI-KFI-2021-00309; 2021–1.2.4-TÉT-2021-00029, and K-142865). Project no. KDP-1015196 has been implemented with the support provided by the Ministry of Culture and Innovation of Hungary from the National Research, Development and Innovation Fund, financed under the KDP-2020 funding scheme. This study has also been supported by the Doctoral Excellence Program (DKOP-23) of the Ministry for Culture and Innovation, Hungary, from the source of the National Research, Development and Innovation Fund. And The Hungarian National Research, Development and Innovation Fund OTKA-142865