Heterogeneous Photocatalysis of Metronidazole in Aquatic Samples

Application of artificial intelligence for the optimization of advanced oxidation processes to improve the water quality polluted with pharmaceutical compounds

Sulfamethoxazole and metronidazole are emerging pollutants commonly found in surface water and wastewater. These compounds have a significant environmental impact, being necessary in the design of technologies for their removal. Recently, the advanced oxidation process has been proven successful in the elimination of this kind of compounds. In this sense, the present work discusses the application of UV/H2O2 and ozonation for the degradation of both molecules in single and binary systems. Experimental kinetic data from O3 and UV/H2O2 process were adequately described by a first and second kinetic model, respectively. From the ANOVA analysis, it was determined that the most statistically significant variables were the initial concentration of the drugs (0.03 mmol L-1) and the pH = 8 for UV/H2O2 system, and only the pH (optimal value of 6) was significant for degradation with O3. Results showed that both molecules were eliminated with high degradation efficiencies (88-94% for UV/H2O2 and 79-98% for O3) in short reaction times (around 30-90 min). The modeling was performed using a quadratic regression model through response surface methodology representing adequately 90 % of the experimental data. On the other hand, an artificial neural network was used to evaluate a non-linear multi-variable system, a 98% of fit between the model and experimental data was obtained. The identification of degradation byproducts was performed by high-performance liquid chromatography coupled to a time mass detector. After each process, at least four to five stable byproducts were found in the treated water, reducing the mineralization percentage to 20% for both molecules.

Study on the photocatalytic degradation of metronidazole antibiotic in aqueous media with TiO2 under lab and pilot scale

Nowadays, the increased consumption of antibiotics, such as metronidazole (MTZ), leads to their introduction in wastewater as well as in the receiving surface waters due to their incomplete removal by conventional wastewater treatment plants. Heterogeneous photocatalysis is a versatile technology that can efficiently degrade such organic contaminants. In the present research, the photocatalytic degradation of MTZ with TiO₂ P25 was studied under lab and pilot (CPC reactor) conditions. The antibiotic was efficiently removed at high rates in both cases (100 % and 91 %) following pseudo-first order kinetics with rate constants equal to 0.0452 min^-1 (±RSD% = 0.68 % - 2.57 %) and 0.0462 L KJ^-1 (±RSD% = 8.94 % - 21.64 %) respectively. Also, by scavenging lab scale experiments, the contribution of the generated reactive species was investigated and hydroxy radicals (HO^•) were proposed as the predominant species. By applying high resolution mass spectrometry techniques, the transformation products (TPs) were identified and possible transformation pathways were proposed. The ecotoxicity of the TPs was assessed in silico using the ECOSAR software with the results revealing that most of them were less toxic than the parent compound. Similarly, the mutagenicity, developmental toxicity and bioconcentration factors of the TPs were predicted by utilizing the T.E.S.T. software and in their majority, were found to be less mutagenic and developmentally toxic than MTZ. The ecotoxicity monitoring with the Vibrio fischeri bioassay in both laboratory and pilot scale experiments indicated that through heterogeneous photocatalysis it is possible to reduce the toxicity of wastewater containing MTZ. Finally, the stability and reusability of the photocatalyst was investigated through three consecutive catalytic cycles with the results showing that the performance of TiO₂ decreased after each use. For the heterogeneous photocatalysis with TiO₂ to be a "real life" applicable technique, further studies focusing on catalyst regeneration and optimization of the catalytic conditions must be conducted.

Considerations on the Controlled Delivery of Bioactive Compounds through Hyaluronic Acid Membrane

(1) Background: The standard treatment for periodontal disease, a chronic inflammatory state caused by the interaction between biofilms generated by organized oral bacteria and the local host defense response, consists of calculus and biofilm removal through mechanical debridement, associated with antimicrobial therapy that could be delivered either systemically or locally. The present study aimed to determine the effectiveness of a hyaluronic acid membrane matrix as a carrier for the controlled release of the active compounds of a formulation proposed as a topical treatment for periodontal disease, and the influence of pH on the complex system’s stability. (2) Methods: The obtained hyaluronic acid (HA) hydrogel membrane with dispersed melatonin (MEL), metronidazole (MZ), and tetracycline (T) was completely characterized through FTIR, XRD, thermal analysis, UV-Vis and fluorescence spectroscopy, fluorescence microscopy, zeta potential and dielectric analysis. The MTT viability test was applied to check the cytotoxicity of the obtained membranes, while the microbiological assessment was performed against strains of Staphylococcus spp. and Streptococcus spp. The spectrophotometric investigations allowed to follow up the release profile from the HA matrix for MEL, MZ, and T present in the topical treatment considered. We studied the behavior of the active compounds against the pH of the generated environment, and the release profile of the bioactive formulation based on the specific comportment towards pH variation. The controlled delivery of the bioactive compounds using HA as a supportive matrix was modeled applying Korsmeyer–Peppas, Higuchi, first-order kinetic models, and a newly proposed pseudo-first-order kinetic model. (3) Results: It was observed that MZ and T were released at higher active concentrations than MEL when the pH was increased from 6.75, specific for patients with periodontitis, to a pH of 7.10, characterizing the healthy patients. Additionally, it was shown that for MZ, there is a burst delivery up to 2.40 × 10⁻⁵ mol/L followed by a release decrease, while for MEL and T a short release plateau was recorded up to a concentration of 1.80 × 10⁻⁵ mol/L for MEL and 0.90 × 10⁻⁵ mol/L for T, followed by a continuous release; (4) Conclusions: The results are encouraging for the usage of the HA membrane matrix as releasing vehicle for the active components of the proposed topical treatment at a physiological pH.