Feasibility of using UV/H2O2 process to degrade sulfamethazine in aqueous solutions in a large photoreactor

Novel nanocomposite thin film in the efficient removal of antibiotics using visible light: Insights of photocatalytic reactions and stability of thin film in real water implications

Novel clay (bentonite) supported Ag⁰ nanoparticles (NPs) doped TiO₂ nanocomposite (Clay/TiO₂/Ag⁰(NPs)) thin film was obtained by using template synthesis method. The nanocomposite material is decorated with cubical Ag⁰(NPs) and utilised successfully in the photocatalytic degradation of tetracycline (TC) and sulfamethazine (SMZ) from aqueous solutions utilizing visible light and UV-A radiations. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS) analyses were used to characterise the nanocomposite materials. Diffusion reflectance spectroscopy (DRS) was utilised to determine the bandgap energies of the materials and also to confirm that Ag⁰(NPs) was successfully doped with TiO₂. The nanocomposite material showed highly efficient photocatalytic activity for the breaking down of TC/SMZ under visible light irradiation by the enhanced electron-hole separation and adsorption of antibiotics at the vicinity of the catalyst. The oxidative degradation of TC/SMZ were shown to be highly dependent on the pH, initial concentration of TC/SMZ, and various co-existing ions. Reusability test of Clay/Ag⁰(NPs)/TiO₂ nanocomposite revealed that the activity did not decline with repeated use. Treatment of TC and SMZ in real water system further enhanced the application potential of the novel catalysts for the treatment of full-scale wastewater polluted with these antibiotics.

The Influence of Photocatalytic Reactors Design and Operating Parameters on the Wastewater Organic Pollutants Removal—A Mini-Review

The organic pollutants removal by conventional methods (adsorption, coagulation, filtration, microorganism and enzymes) showed important limitation due to the reluctance of these molecules. An alternative to this issue is represented by the photocatalytic technology considered as an advanced oxidation process (AOP). The photoreactors design and concepts vary based on the working regime (static or dynamic), photocatalyst morphology (powders or bulk) and volume. This mini-review aims to provide specific guidelines on the correlations between the photoreactor concept characteristics (working regime, volume and flow rate), irradiation scenarios (light spectra, irradiation period and intensity) and the photocatalytic process parameters (photocatalyst materials and dosage, pollutant type and concentration, pollutant removal efficiency and constant rate). The paper considers two main photoreactor geometries (cylindrical and rectangular) and analyses the influence of parameters optimization on the overall photocatalytic efficiency. Based on the systematic evaluation of the input data reported in the scientific papers, several perspectives regarding the photocatalytic reactors’ optimization were included.

Transformation kinetics and pathways of sulfamonomethoxine by UV/H2O2 in swine wastewater

Sulfamonomethoxine (SMM), as one of the most predominant antibiotics in animal wastewater, is pending for effective control to minimize its environmental risks. Transformation kinetics and pathways of SMM by UV/H₂O₂ in swine wastewater were systematically investigated in this study. Direct UV photolysis (as a dominant role) and ∙OH oxidation contributed to SMM degradation in UV/H₂O₂ system. The less effective reaction rate of SMM in real wastewater than synthetic wastewater (0.1-0.17 vs. ∼0.2-1.5 min^-1, despite higher H₂O₂ dosage and extended reaction time) resulted mainly from the abundant presence of conventional contaminants (indicated by COD, a notable competitor of SMM) in real wastewater. SMM degradation benefited from higher H₂O₂ dosage and neutral and weak alkaline conditions. However, the effect of initial SMM concentration on SMM degradation in synthetic and real wastewater showed opposite trends, owning to the different probability of SMM molecules to interact with UV and H₂O₂ in different matrices. Carbonate had an inhibitory effect on SMM degradation by scavenging ∙OH and pH-variation induced effect, while nitrate promoted SMM degradation by generating more ∙OH. The removal efficiency of SMM in real wastewater reached 91% under the reaction conditions of H₂O₂ of 10 mM, reaction time of 60 min, and pH 6.7-6.9. SMM degradation pathway was proposed as hydroxylation of benzene and pyrimidine rings, and secondary amine, and the subsequent cleavage of S-N bond.

Removal of sulfamethoxazole, sulfadiazine, and sulfamethazine by UV radiation and HO• and SO4•- radicals using a response surface model and DFT calculations

In this work, the degradation of sulfamethazine (SMT), sulfadiazine (SMD), and sulfamethoxazole (SMX) by using UV light, UV/H₂O₂, and UV/S₂O₈^-2 was analyzed. Direct photolysis was studied by varying the lamp power and the solution pH. DFT calculations were carried out to corroborate the efficiency of the degradation as a function of the solution pH. The variation of the apparent rate constant, k_ap, was determined in the indirect photolysis by employing an experimental Box-Behnken-type response surface design. The results evidenced that SMX can be efficiently degraded by applying UV radiation independent of the operating conditions. Nevertheless, the quantum yields for SMT and SMD were close to zero, indicating a low energy efficiency for their photochemical transformation. The effect of the solution pH showed that the photodegradation of sulfonamides depends both on the amount of radiation absorbed as the electronic density. Calculations based on density functional theory and supported by the quantum theory of atoms in molecules allowed to describe fragmentation patterns in the systems under study, proving the lability of S₁₄-C₂, N₁₇-C₁₈, and N₂₂-O₂₂ bonds, for SMT, SMD, and SMX, respectively. From response surface methodology, four statistically reliable equations were obtained to determine the k_ap value as a function of the system operating conditions. Finally, SO₄^•- radicals proved to have a higher reactivity to degrade SMT and SMD compared with HO^• radicals regardless of the operating conditions of the system.

A novel photocatalytic reactor for the extended reuse of W-TiO2 in the degradation of sulfamethazine

In this study, a photocatalytic reactor with a novel engineering design has been used for the extended degradation of sulfamethazine (SMZ). The reactor employed four consecutive stainless-steel plates immobilized by tungsten-dope TiO₂ (W-TiO₂) using polysiloxane. The characterization of W-TiO₂ by X-ray diffraction (XRD), Raman spectroscopy, and energy-dispersive X-ray (EDX) denoted successful doping of tungsten in the lattice of anatase crystals of TiO₂ suggesting a high photocatalytic activity under UV and visible light. A Box-Behnken experimental design was employed for the optimization of the operating parameters such as solution pH, flow rate, and the initial SMZ concentration. The residual SMZ concentration was below the detection limit after 30 min of the photocatalytic reaction under the optimum operating conditions. A highly remarkable degradation of SMZ was observed in five consecutive cycles, which reveals an extended stable photocatalytic activity offered by the reactor design. The transformation products were identified by tandem mass spectrometry, and they were employed to propose the degradation pathway. These results highlight the importance of using the photocatalysts in retained forms and open additional avenues for the practical application of photocatalysis in wastewater treatment.

Advanced Oxidation Processes for the Removal of Antibiotics from Water. An Overview

In this work, the application of advanced oxidation processes (AOPs) for the removal of antibiotics from water has been reviewed. The present concern about water has been exposed, and the main problems derived from the presence of emerging pollutants have been analyzed. Photolysis processes, ozone-based AOPs including ozonation, O3/UV, O3/H2O2, and O3/H2O2/UV, hydrogen peroxide-based methods (i.e., H2O2/UV, Fenton, Fenton-like, hetero-Fenton, and photo-Fenton), heterogeneous photocatalysis (TiO2/UV and TiO2/H2O2/UV systems), and sonochemical and electrooxidative AOPs have been reviewed. The main challenges and prospects of AOPs, as well as some recommendations for the improvement of AOPs aimed at the removal of antibiotics from wastewaters, are pointed out.