UV/H2O2 and UV/PDS Treatment of Trimethoprim and Sulfamethoxazole in Synthetic Human Urine: Transformation Products and Toxicity

Oxidation of Cefalexin by Permanganate: Reaction Kinetics, Mechanism, and Residual Antibacterial Activity

The oxidation of cefalexin (CFX), a commonly used cephalosporin antibiotic, was investigated by permanganate (PM) in water. Apparent second-order rate constant of the reaction between CFX and PM was determined to be 12.71 ± (1.62) M^-1·s^-1 at neutral pH. Lower pH was favorable for the oxidation of CFX by PM. The presence of Cl^- and HCO₃^- could enhance PM-induced oxidation of CFX, whereas HA had negligible effect on CFX oxidation by PM. PM-induced oxidation of CFX was also significant in the real wastewater matrix. After addition of bisulfite (BS), PM-induced oxidation was significantly accelerated owing to the generation of Mn(III) reactive species. Product analysis indicated oxidation of CFX to three products, with two stereoisomeric sulfoxide products and one di-ketone product. The thioether sulfur and double bond on the six-membered ring were the reactive sites towards PM oxidation. Antibacterial activity assessment indicated that the activity of CFX solution was significantly reduced after PM oxidation.

Impact of Chloride Ions on UV/H2O2 and UV/Persulfate Advanced Oxidation Processes

Chloride ion (Cl^-) is one of the most common anions in the aqueous environment. A mathematical model was developed to determine and quantify the impact of Cl^- on the oxidization rate of organic compounds at the beginning stage of the UV/persulfate (PS) and UV/H₂O₂ processes. We examined two cases for the UV/PS process: (1) when the target organic compounds react only with sulfate radicals, the ratio of the destruction rate of the target organic compound when Cl^- is present to the rate when Cl^- is not present (designated as r_R^Cl-/ r_R) is no larger than 1.942%; and (2) when the target organic compounds can react with sulfate radicals, hydroxyl radicals and chlorine radicals, r_R^Cl-/ r_R, can be no larger than 60%. Hence, Cl^- significantly reduces the organic destruction rate in the UV/PS process. In the UV/H₂O₂ process, we found that Cl^- has a negligible effect on the organic-contaminant oxidation rate. Our simulation results agree with the experimental results very well. Accordingly, our mathematical model is a reliable method for determining whether Cl^- will adversely impact organic compounds destruction by the UV/PS and UV/H₂O₂ processes.

Oxidation of steroid estrogens by peroxymonosulfate (PMS) and effect of bromide and chloride ions: Kinetics, products, and modeling

Recently, in situ chemical oxidation (ISCO) using peroxymonosulfate (PMS) for environmental decontamination has received increasing interest. In this study, oxidation kinetics and products of four steroid estrogens (i.e., estrone, 17β-estradiol, estriol, and 17α-ethinylestradiol) by PMS under various conditions were investigated. PMS could fairly degrade steroid estrogens over the pH range of 7-10, and the degradation rate increased with the increase of solution pH. This pH-dependence was well described by parallel reactions between individual acid-base species of steroid estrogens (E and E^-) and PMS (HSO₅^- and SO₅^2-), where specific second-order rate constants for E^- with HSO₅^- and SO₅^2- were in the range of 2.11-5.58 M^-1s^-1 and 0.77-1.25 M^-1s^-1, respectively. Identification of oxidation products by liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometer showed that PMS readily oxidized the phenolic group of steroid estrogens, leading to the generation of hydroxylated and ring-opening products. The presence of bromide and chloride ions (Br^- and Cl^-) at environmentally relevant levels could greatly accelerate the degradation of steroid estrogens by PMS with the formation of halogenated aromatic products. This effect was quantitatively estimated by a kinetic model, where the formation of free bromine and chorine and their rapid electrophilic substitution with steroid estrogens were taken into consideration. Eco-toxicity of transformation products of 17α-ethinylestradiol by PMS treatment in the absence and presence of bromide and chloride was estimated by quantitative structure-activity relationship analysis using ECOSAR. These findings advance the understanding of ISCO using PMS.

Biodegradation of the sulfonamide antibiotic sulfamethoxazole by sulfamethoxazole acclimatized cultures in microbial fuel cells

Microbial fuel cells (MFCs) are known for their ability to enhance the removal rate of toxins while generating power. This research presents a performance assessment of MFCs for power generation and sulfamethoxazole (SMX) degradation using SMX acclimatized cultures. Experiments were performed in MFC batch mode using different SMX concentrations in synthetic wastewater. The experimental results showed that voltage generation was >400mV up to the SMX concentration of 0.20mM (at 400Ω external resistance). Control experiments supported the inference that biodegradation was the main process for SMX removal compared to sorption by SMX acclimatized cultures and that the process results in efficient removal of SMX in MFC mode. The specific removal rates of SMX in MFC with SMX acclimatized sludge were 0.67, 1.37, 3.43, 7.32, and 13.36μm/h at initial SMX concentrations of 0.04, 0.08, 0.20, 0.39, and 0.79mM, respectively. Moreover, the MFC was able to remove >90% of the TOC from the wastewater up to SMX concentrations of 0.08mM. However, this TOC removal produces negative effects at higher SMX concentrations due to toxic intermediates. Microbial community analysis revealed large changes in bacterial communities at the phylum, class, and genus levels after SMX acclimatization and MFC operation. Thauera, a well-known aromatic-degrading bacteria, was the most dominant genus present in post-acclimatized conditions. In summary, this study showed that acclimatized sludge can play an important role in the biodegradation of SMX in MFCs.

UVA-UVB activation of hydrogen peroxide and persulfate for advanced oxidation processes: Efficiency, mechanism and effect of various water constituents

In the present work we investigate the activation efficiency of H₂O₂ and S₂O₈^2- using UVA and UVB radiation. Bisphenol-A (BPA) is used as model pollutants to estimate the oxidative process efficiency in simulated and real sewage treatment plant waters. Particular attention is paid to the BPA removal efficiency and to the radical mechanism involvement considering the effect of typical inorganic water constituents (carbonates and chloride ions) and organic matter. Despite a detrimental effect observed when carbonate ions are in solution using both hydrogen peroxide and persulafate, the presence of high chloride ions concentration was found to improve BPA removal using S₂O₈^2- as radical precursor. This enhancement, investigated combining chemical kinetic model approach and laser flash photolysis experiments, is attributed to the formation of hydroxyl radical and chlorine radical species from sulfate radical. Different transformation products are identified by means of GC-MS and HPLC-MS analyses. Moreover, experiments using sewage treatment plant water (STPW) spiked with BPA are performed in order to assess the efficiency of oxidative processes in a simulated treatment systems activated using UVA + UVB radiations.

Photodegradation of novel oral anticoagulants under sunlight irradiation in aqueous matrices

Kinetics of photodegradation of novel oral anticoagulants dabigatran, rivaroxaban, and apixaban were studied under simulated solar light irradiation in purified, mineral, and river waters. Dabigatran and rivaroxaban underwent direct photolysis with polychromatic quantum yields of 2.2 × 10^-4 and 4.4 × 10^-2, respectively. The direct photodegradation of apixaban was not observed after 19 h of irradiation. Kinetics of degradation of rivaroxaban was not impacted by the nature of the aqueous matrix while photosensitization from nitrate ions was observed for dabigatran and apixaban dissolved in a mineral water. The photosensitized reactions were limited in the tested river water (Isle River, Périgueux, France) certainly due to the hydroxyl radical scavenging effect of the dissolved organic matter. The study of photoproduct structures allowed to identify two compounds for dabigatran. One of them is the 4-aminobenzamidine while the second one is a cyclization product. In the case of rivaroxaban, as studied by very high field NMR, only one photoproduct was observed i.e. a photoisomer. Finally, seven photoproducts were clearly identified from the degradation of apixaban under simulated solar light.

Fate of tetracycline in enhanced biological nutrient removal process

This study investigated the fate of tetracycline at four different concentrations of 20 μg L^-1, 50 μg L^-1, 2 and 5 mg L^-1 in the enhanced biological nutrient removal processes. At the tetracycline concentration below 50 μg L^-1, no obvious inhibition on the biological N&P removal was observed, while the inhibition appeared after the tetracycline concentration was increased to 2 and 5 mg L^-1. It was found that about 44%-87% of tetracycline was removed through biodegradation, while only 3%-6% of removal was due to biosorption. These results clearly suggested that a substantial amount of tetracycline eventually ended up in sludge with the tetracycline content of 23 mg to 4.5 g kg^-1 sludge depending on the tetracycline concentration. Obviously, this could pose an emerging challenge to the post sludge disposal and reuse. Furthermore, phthalic anhydride was detected as a biodegradation byproduct of tetracycline, which has been known to be more toxic than tetracycline to aquatic organisms. Consequently, this study offers in-depth insights into the fate of tetracycline in the enhanced biological nutrient removal process, highlighting on the emerging ecological risks associated with sludge disposal and effluent discharge.

Sulfate radical-induced transformation of trimethoprim with CuFe2O4/MWCNTs as a heterogeneous catalyst of peroxymonosulfate: mechanisms and reaction pathways

Trimethoprim (TMP), a typical antibiotic pharmaceutical, has received extensive attention due to its potential biotoxicity. In this study, CuFe₂O₄, which was used to decorate MWCNTs via a sol–gel combustion synthesis method, was introduced to generate powerful radicals from peroxymonosulfate (PMS) for TMP degradation in an aqueous solution. The results showed that almost 90% of TMP was degraded within 24 min with the addition of 0.6 mM PMS and 0.2 g L⁻¹ CuFe₂O₄/MWCNTs. The degradation rate was enhanced with the increase in initial PMS doses, catalyst loading and pH. A fairly low leaching of Cu and Fe was observed during the reaction, indicating the high potential recyclability and stability of CuFe₂O₄/MWCNTs. Electron paramagnetic resonance analysis confirmed that the CuFe₂O₄/MWCNT-PMS system had the capacity to generate ·OH and SO₄˙⁻, whereas quenching experiments further confirmed that the catalytic reaction was dominated by SO₄˙⁻. A total of 11 intermediate products of TMP was detected via mass spectrometry, and different transformation pathways were further proposed. Overall, this study showed a systematic evaluation regarding the degradation process of TMP by the CuFe₂O₄/MWCNT-PMS system.

The degradation of trimethoprim (TMP) in heterogeneously activated peroxymonosulfate (PMS) oxidation processes using CuFe₂O₄/MWCNTs as the catalyst.

Degradation kinetics and mechanism of pentoxifylline by ultraviolet activated peroxydisulfate

Degradation of pentoxifylline (PTX) by sodium peroxydisulfate (SPDS) assisted by UV irradiation has been investigated in deionized water. The treatment was more favorable over direct photolysis or peroxydisulfate oxidation alone. The effects of various parameters, including different dosage of oxidant agent, PTX concentration, initial solution pH levels, and the presence of inorganic ions like chloride, nitrate and carbonate have been evaluated. The rate of PTX decomposition depends on the oxidant agent dose. The highest degradation was determined at pH 10.5, which can be explained by the generation of additional hydroxyl radicals (HO˙) in the reaction between sulfate radicals and hydroxide ions. The presence of inorganic ions, especially the carbonate ions quench valuable sulfate radicals and have successfully retarded the PTX decomposition. Six PTX oxidation products were identified using UPLC-QTOF-MS for trials in a basic environment. The main degradation product (3,7-dimethyl-6-(5-oxohexyloxy)-3,7-dihydro-2H-purin-2-one) was isolated by column chromatography and identified by ¹HNMR and LC MS analyzes.

Degradation of pentoxifylline (PTX) by sodium peroxydisulfate (SPDS) assisted by UV irradiation has been investigated in deionized water.

Photo-assisted electrochemical degradation of sulfamethoxazole using a Ti/Ru0.3Ti0.7O2 anode: Mechanistic and kinetic features of the process

This study examined the photo-assisted electrochemical degradation and mineralization of the antibiotic contaminant sulfamethoxazole (SMX). All the experiments were perform using a flow electrolytic cell, in which the influence of the current density (10-60 mA cm^-2) and sodium chloride (0.02-0.10 mol L^-1) in the supporting electrolyte composition was analyzed. The results showed that the total SMX and 50% TOC removal was achieved in the current density range used. As expected, the degradation kinetics presented a pseudo first order behavior and the rate constant increased from 0.05 min^-1 to 0.50 min^-1 as the current density raised from 10 to 60 mA cm^-1. In addition, the values of the electrical energy per order (E_EO) increased from 0.67 to 1.06 kW/hm^-3 order^-1 as the current density increased from 10 to 60 mAcm^-2 and drop from 8.82 to 0.57 kW/hm^-3 order^-1 at supporting electrolyte concentration of 0.02-0.1 mol L^-1. The reaction intermediates identified by liquid chromatography-mass spectrometry allowed proposing a mechanism for the degradation. The use of photo assistance in the electrochemical process involved simultaneous reactions, for example, aromatic ring substitutions and hydroxylation. These reactions led to aromatic rings opening that generated simpler organic molecules, making possible the mineralization of the SMX molecule. Probable degradation pathways were proposed and discussed. Comparison of the efficiencies of the photocatalytic, electrochemical (EC) and photo-assisted electrochemical (PAEC) techniques revealed that the combined process showed a synergism for TOC removal.

Sulfate radical-based oxidation of antibiotics sulfamethazine, sulfapyridine, sulfadiazine, sulfadimethoxine, and sulfachloropyridazine: Formation of SO2 extrusion products and effects of natural organic matter

The widespread occurrence of sulfonamide antibiotics in the environment has raised great concerns about their potential to proliferate antibacterial resistance. Sulfate radical (SO₄^•-) based advanced oxidation processes (SR-AOPs) are promising in-situ chemical oxidation (ISCO) technologies for remediation of soil and groundwater contaminated by antibiotics. The present study reported that thermally activated persulfate oxidation of sulfonamides (SAs) bearing six-membered heterocyclic rings, e.g., sulfamethazine (SMZ), sulfapyridine (SPD), sulfadiazine (SDZ), sulfadimethoxine (SDM), and sulfachloropyridazine (SCP), all produced SO₂ extrusion products (SEPs), a phenomenon that is of potential importance, but not systematically studied. As an electrophilic oxidant, SO₄^•- tends to attack the aniline moiety, the reactive site of SAs, via electro-transfer mechanism. The resulting anilinyl radical cations are subjected to further intermolecular Smiles-type rearrangement to produce SEPs. Formation of SEPs is expected to occur in other SR-AOPs as well. The temperature-dependent evolution pattern of SEP of SMZ, 4-(2-imino-4,6-dimethylpyrimidin-1(2H)-yl)aniline, can be well fitted by kinetic modeling concerning sequential formation and transformation of intermediate product. The presence of natural organic matter (NOM) influenced the evolution patterns of 4-(2-imino-4,6-dimethylpyrimidin-1(2H)-yl)aniline significantly. Toxicological effects of SEPs on ecosystem and human health remain largely unknown, thus, further monitoring studies are highly desirable.

Degradation of sulfamethoxazole by UV, UV/H2O2 and UV/persulfate (PDS): Formation of oxidation products and effect of bicarbonate

The frequent detection of sulfamethoxazole (SMX) in wastewater and surface waters gives rise of concerns about their ecotoxicological effects and potential risks to induce antibacterial resistant genes. UV/hydrogen peroxide (UV/H₂O₂) and UV/persulfate (UV/PDS) advanced oxidation processes have been demonstrated to be effective for the elimination of SMX, but there is still a need for a deeper understanding of product formations. In this study, we identified and compared the transformation products of SMX in UV, UV/H₂O₂ and UV/PDS processes. Because of the electrophilic nature of SO₄^-, the second-order rate constant for the reaction of sulfate radical (SO₄^-) with the anionic form of SMX was higher than that with the neutral form, while hydroxyl radical (OH) exhibited comparable reactivity to both forms. The direct photolysis of SMX predominately occurred through cleavage of the NS bond, rearrangement of the isoxazole ring, and hydroxylation mechanisms. Hydroxylation was the dominant pathway for the reaction of OH with SMX. SO₄^- favored attack on NH₂ group of SMX to generate a nitro derivative and dimeric products. The presence of bicarbonate in UV/H₂O₂ inhibited the formation of hydroxylated products, but promoted the formation of the nitro derivative and the dimeric products. In UV/PDS, bicarbonate increased the formation of the nitro derivative and the dimeric products, but decreased the formation of the hydroxylated dimeric products. The different effect of bicarbonate on transformation products in UV/H₂O₂ vs. UV/PDS suggested that carbonate radical (CO₃^-) oxidized SMX through the electron transfer mechanism similar to SO₄^- but with less oxidation capacity. Additionally, SO₄^- and CO₃^- exhibited higher reactivity to the oxazole ring than the isoxazole ring of SMX. Ecotoxicity of transformation products was estimated by ECOSAR program based on the quantitative structure-activity relationship analysis as well as by experiments using Vibrio fischeri, and these results indicated that the oxidation of SO₄^- or CO₃^- with SMX generated more toxic products than those of OH.

Surface-active bismuth ferrite as superior peroxymonosulfate activator for aqueous sulfamethoxazole removal: Performance, mechanism and quantification of sulfate radical

A surface-active Bi₂Fe₄O₉ nanoplates (BF-nP) was prepared using a facile hydrothermal protocol for sulfamethoxazole (SMX) removal via peroxymonosulfate (PMS). The catalytic activity of BF-nP was superior to other catalysts with the following order of performance: BF-nP>Bi₂Fe₄O₉ (nanocubes)>>Co₃O₄>Fe₂O₃ (low temperature co-precipitation method)>Fe₂O₃ (hydrothermal method)∼Bi₂O₃∼Bi³⁺∼Fe³⁺. The empirical relationship of the apparent rate constant (k_app), BF-nP loading and PMS dosage can be described as follows: k_app=0.69[BF-nP]^0.6[PMS]^0.4 (R²=0.98). The GC-MS study suggests that the SMX degradation proceed mainly through electron transfer reaction. The XPS study reveals that the interconversion of Fe³⁺/Fe²⁺ and Bi³⁺/Bi⁵⁺ couples are responsible for the enhanced PMS activation. The radical scavenging study indicates that SO₄^- is the dominant reactive radical (>92% of the total SMX degradation). A method to quantify SO₄^- in the heterogeneous Bi₂Fe₄O₉/PMS systems based on the quantitation of benzoquinone, which is the degradation byproduct of p-hydroxybenzoic acid and SO₄^-, is proposed. It was found that at least 7.8±0.1μM of SO₄^- was generated from PMS during the BF-nP/PMS process (0.1gL^-1, 0.40mM PMS, natural pH). The Bi₂Fe₄O₉ nanoplates has a remarkable potential for use as a reusable, nontoxic, highly-efficient and stable PMS activator.

Kinetics and modeling of sulfonamide antibiotic degradation in wastewater and human urine by UV/H2O2 and UV/PDS

Sulfonamide antibiotics have been frequently detected in the aquatic environment and are of emerging concern due to their adverse bio-effect and potential of inducing antibiotic resistance. This study investigated the degradation kinetics of sulfonamide antibiotics in synthetic wastewater and hydrolyzed human urine by low pressure (LP) UV, UV/H2O2 and UV/peroxydisulfate (PDS). Direct photolysis rates of sulfonamide antibiotics varied and depended on the structures. Sulfonamides with a five-membered heterocyclic group underwent faster direct photolysis. For indirect photolysis processes, second-order rate constants of sulfonamide antibiotics with hydroxyl radical, sulfate radical and carbonate radical were determined, which were (6.21-9.26) × 10(9), (0.77-16.1) × 10(10) and (1.25-8.71) × 10(8) M(-1) s(-1), respectively. A dynamic model was applied and successfully predicted the degradation kinetics of sulfonamides in different water matrices. In synthetic wastewater, carbonate radical contributed to approximately 10% of the overall removal, whereas in synthetic hydrolyzed urine, carbonate radical was the dominant reactive species to degrade sulfonamides. Sulfonamide antibiotics were eliminated more efficiently in synthetic hydrolyzed urine than in synthetic wastewater and UV/PDS was more efficient than UV/H2O2 to degrade most sulfonamides. Energy evaluation showed that UV/PDS costs less energy than LPUV and UV/H2O2 under the experimental conditions applied in this study, particularly for sulfonamides whose indirect photolysis overweighed direct photolysis. By varying UV dose and oxidant dose, the UV/H2O2 process can be optimized to achieve higher efficiency than the UV/PDS process in synthetic wastewater.