Singlet oxygen-mediated fluconazole degradation during the activation of chlorine dioxide with sulfite

Advanced oxidation process with hydrogen peroxide and sulfite for superfast degradation of micro-contaminants in drinking water

Sulfite (S(IV))-based advanced oxidation processes (AOPs) have recently gained attention as viable alternatives to peroxosulfate-based AOPs due to their low toxicity and cost-effectiveness. Hydrogen peroxide (H2O2) is widely recognized as an effective and environmentally friendly oxidant in drinking water treatment. This study introduces a novel H2O2/S(IV) AOP based on the observation of over-stoichiometric consumption of S(IV) by H2O2. This system generates a variety of reactive species (RSs), including sulfate radicals (SO4•-), hydroxyl radicals (•OH), superoxide anion radicals (O2•-), and singlet oxygen (1O2), to achieve rapid degradation of micro-contaminants in drinking water. With dosages of H2O2 and S(IV) set at 0.1 mM and 1.0 mM, respectively, the H2O2/S(IV) system generated concentrations of SO4•-, •OH, O2•- and 1O2 at approximately 10-12, 10-12, 10-13, and 10-13 M. This occurred even in complex water matrices containing bicarbonate (HCO3-), chloride (Cl-), and humic acid (HA) across a pH range of 3.0-11.0. A kinetic model was developed to simulate RS generation and predict the pseudo-first-order degradation rate constants (k) for 15 micro-contaminants in the H2O2/S(IV) system. Theoretical calculations indicated that micro-contaminants with high EHOMO and low ΔE (i.e., ELUMO - EHOMO) are more susceptible to degradation. Compared to UV/H2O2, UV/S(IV), Fe2+/H2O2, and Fe3+/S(IV) systems, the H2O2/S(IV) system demonstrated faster degradation rates, with k values 1-2 orders of magnitude higher, towards micro-contaminants. Additionally, the H2O2/S(IV) system was more effective in controlling disinfection by-product formation during subsequent chlorination, highlighting the application potential of the H2O2/S(IV) system in drinking water treatment.

Nitrogen transformation and bacterial community response in O3-SBR process for treating nitrogen-containing heterocyclic antibiotics

Nitrogen heterocyclic antibiotics (NHAs) pollution poses a significant threat to aquatic ecosystems. Ozonation (O3) pretreatment is beneficial for the removal of total nitrogen (TN) in antibiotics by facilitating subsequent biological treatment. However, nitrogen transformation and bacterial community responses when treating NHAs by O3-coupled biological processes remain unclear. This study utilized an O3-coupled sequencing batch reactor (O3-SBR) to evaluate its treatment efficacy on three typical NHAs, namely fluconazole, sulfamethizole, and acyclovir, and explored nitrogen transformation and the effects of oxidation products (NHAs-OPs) on bacterial communities. The results showed that the O3-SBR process was more effective for treating NHAs than using O3 or SBR alone. O3 pretreatment converted nitrogen in difficult-to-degrade NHAs into inorganic nitrogen and other organic nitrogen compounds, improving the biodegradability of NHAs. Subsequently, NHAs-OPs were used as the nitrogen/carbon source for SBR. Unlike the low TN removal rate of 14.4-23.4% observed when treating pure NHAs wastewater, the TN and total organic carbon removal rates of the SBR treating NHAs-OPs wastewater reached 62.4-85.2% and 65.2-86.4%, respectively. High-throughput sequencing analysis revealed that the enhanced efficacy of the SBR process may be attributed to the dominance of bacterial genera adapted to NHAs-OPs within the system. Additionally, the abundance of denitrification functions under NHAs-OPs stress was found to be higher than that of nitrification functions. These results provide new theoretical support for the treatment of antibiotic production wastewater.

Environmental Fate of the Azole Fungicide Fluconazole and Its Persistent and Mobile Transformation Product 1,2,4-Triazole

Fluconazole is a persistent and mobile pharmaceutical azole fungicide observed in natural waters globally. It does not significantly degrade via traditional wastewater treatment, resulting in likely environmental and human exposure and environmental-origin azole fungicide resistance. Indirect photochemistry is known to degrade many recalcitrant contaminants in natural waters but has not been tested for fluconazole. We systematically measured rates and identified products of the indirect photodegradation of fluconazole in genuine and synthetic surface waters with varying nitrate, bicarbonate, and dissolved organic matter using high resolution mass spectrometry. Degradation half-lives of fluconazole ranged from 2 weeks to a year, indicating indirect photochemistry is slow but competitive with other loss processes. The transformation products 1,2,4-triazole and 1,2,4-triazole-1-acetic acid were produced in 30 to 100% yield during fluconazole degradation. These products are far more resistant to indirect photochemistry than fluconazole, with half-lives for 1,2,4-triazole in the environment of between 1 and 3 years when measurable with our methods. These "very persistent very mobile" contaminants are likely formed by most pharmaceutical and agrochemical azole fungicides, are regularly detected in the US and Denmark in monitoring programs and our exposure modeling demonstrates high potential for human exposure through drinking water with uncertain health implications.

Degradation of levofloxacin by dielectric barrier discharge plasma/chlorine process: Roles of reactive species and control of chlorination disinfection byproducts

In this study, a novel process of dielectric barrier discharge (DBD)/chlorine for levofloxacin (LEV) degradation was investigated. The combined system boosted the degradation efficiency of LEV from 77.8% to 97.5%, improved the reaction rate constant by 2.3 times, and reduced energy consumption by 64.5%. DBD/chlorine process was highly efficient for LEV degradation across a pH range of 3.3-10.8, with removal rates varying from 90.3% to 97.5%. The electron paramagnetic resonance and scavenging experiments demonstrated the generation of reactive oxygen species (ROS, including HO•, 1O2, and O2•-) and reactive chlorine species (RCS) in the DBD/chlorine system, with 1O2 in the nonradical pathway being crucial for LEV removal. Crucially, effective activation of chlorine not only encouraged the production of reactive species but also prevented the formation of disinfection by-products (DBPs), successfully controlling the ecotoxicity of the reaction system. DBD could activate chlorine to form chlorate and HO•, which in turn triggered the production of RCS. The comparison of the LEV degradation pathway was proposed with or without chlorine in the DBD process. Finally, the effects of different water quality and water bodies demonstrated the application prospects of the DBD/chlorine process. This work provided an efficient technique for the elimination of antibiotics by non-thermal plasma/chlorine.

Insights into the Removal of Organic Contaminants by Co-CeO2 Nanocatalysts via CaCO3 Activation: Performance, Kinetic, and Mechanism

The advanced oxidation process based on S(IV) has garnered increasing attention, owing to its efficiency in degrading contaminants. Here, a cobalt-doped cerium oxide catalyst (Co-CeO2) was employed to activate calcium sulfite (CaSO3) for imidacloprid degradation. The Co-CeO2 catalyst was characterized by using SEM, BET, XRD, and XPS techniques to analyze its structural and chemical properties. XPS analysis revealed the presence of Co0, Co2+, and Co3+ species in the Co-CeO2 catalyst. Compared to the CeO2/CaSO3 system, the Co-CeO2/CaSO3 system significantly enhanced the degradation rate of imidacloprid from 5.00% to 94.01%. Scavenging experiments, in conjunction with electron paramagnetic resonance spectroscopy, identified hydroxyl radicals (•OH), sulfate radicals (SO4•-), superoxide radicals (O2•-), sulfite radicals (SO3•-), and singlet oxygen (1O2) as the primary reactive species responsible for the degradation of imidacloprid within the Co-CeO2/CaSO3 system. Density functional theory calculation analysis was employed to investigate the specific sites of imidacloprid attacked by reactive oxygen species, proposing four potential degradation pathways. Furthermore, the Ecological Structure Activity Relationships (ECOSAR) program predicted a significant diminution in the toxicity of intermediate products compared to imidacloprid. Even after five cycles, Co-CeO2 maintained an excellent removal efficiency of 86.35%.

Superior Singlet Oxygen Electrosynthesis via Neighboring Dual Molecular Oxygen Coactivation for Selective Tetracycline Detoxification

Oxygen (O2) electroreduction offers a green approach for singlet oxygen (1O2) synthesis in wastewater contaminants detoxification. However, traditional single O2 activation on single-metal catalytic sites seriously suffers from the kinetically-unfavorable desorption of adsorbed superoxide species (•O2 -*/•OOH*). Here, we demonstrate a novel dual O2 coactivation pathway on shortened Fe1-OV-Ti sites for superior 1O2 electrosynthesis through a rapid disproportionate process between surface-confined •O2 -*/•OOH*. Theoretical calculations combined with in situ electrochemical spectroscopies demonstrated that the shortened distance between Fe single atom and adjacent unsaturated Ti atom facilitates the direct recombination of surface-confined Fe-•OOH and Ti-•OO- to yield 1O2, bypassing the formidable •O2 -*/•OOH* desorption process. Impressively, Fe1-OV-Ti could realize an excellent 1O2 electrosynthesis rate of 54.5 μmol L-1 min-1 with an outstanding 1O2 selectivity of 97.6 % under neutral condition, surpassing that of Fe1-O-Ti (27.1 μmol L-1 min-1, 91.7 %). Using tetracycline (TC) as a model pollutant, the resulting Fe1-OV-Ti electrode achieved nearly 100 % degradation in 120 min at -0.6 V, meanwhile preventing the generation of toxic intermediates. This study provides a new 1O2 electrosynthesis strategy by controlling the distance of adjacent catalytic sites for the coactivation of dual molecular oxygen.

Degradation of UV328 by ozone/peroxymonosulfate system: Performance and mechanisms

2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (UV328) is an emerging persistent organic pollutant ubiquitously found in environmental matrices. Though some advanced oxidation processes have been tested to degrade UV328 in waste streams, the degradation mechanisms are largely unknown. In this study, the degradation of UV328 by ozone (O3) and peroxymonosulfate (PMS) was systemically investigated. At neutral pH, 97.0% UV328 was removed in 5 min with 6.4 mg/min O3 and 2 mM PMS, and the degradation rate was positively correlated with the concentration of oxidants. Hydroxyl radical (•OH), sulfate radical (SO4•-) and singlet oxygen (1O2) participated in the degradation of UV328, in which 1O2 played a key role. Based on the identified transformation intermediates and density functional theory simulations, three degradation pathways of dehydrogenation, cycloaddition and hydroxylation were proposed. •OH and SO4•- radicals could attack UV328 through hydrogen atom abstraction channel. 1O2-mediated cycloaddition reaction is favorable, and •OH could react with UV328 via radical adduct formation pathway. Toxicity assessment indicated that O3/PMS treatment mitigated the ecological risks of UV328.

Degradation of sulfamethazine in coastal aquaculture tailwater by Na2S2O4@iron-electrode electrooxidation combined with ceramic membrane process

Offshore aquaculture's explosive growth improves the public food chain while also unavoidably adding new pollutants to the environment. Consequently, the protection of coastal marine eco-systems depends on the efficient treatment of wastewater from marine aquaculture. For the sulfamethazine (SMZ) of representative sulfonamides and total organic pollutants removal utilizing in-situ high salinity, this work has established an inventive and systematic treatment process coupled with iron-electrode electrochemical and ultrafiltration. Additionally, the activated dithionite (DTN) was being used in the electrochemical and ultrafiltration processes with electricity/varivalent iron (FeII/FeIII) and ceramic membrane (CM), respectively, indicated by the notations DTN@iron-electrode/EO-CM. Quenching experiments and ESR detection have identified plenty of reactive species including SO4·-, ·OH, 1O2, and O2·-, for the advanced treatment. In addition, the mass spectrometry (MS) and the Gaussian simulation calculation for these primary reaction sites revealed the dominate SMZ degradation mechanisms, including cleavage of S-N bond, hydroxylation, and Smile-type rearrangement in DTN@iron-electrode/EO process. The DTN@iron-electrode/EO effluent also demonstrated superior membrane fouling mitigation in terms of the CM process, owing to its higher specific flux. XPS and SEM confirmed the reducing membrane fouling, which showed the formation of a loose and porous cake layer. This work clarified diverse reactive species formation and detoxification with DTN@iron-electrode/EO system and offers a sustainable and efficient process for treating tailwater from coastal aquaculture.

Understanding the pivotal role of ubiquitous Yellow River suspend sediment in efficiently degrading metronidazole pollutants in water environments

Sulfite-based advanced oxidation technology has received considerable attention for its application in organic pollutants elimination. However, the potential of natural sediments as effective catalysts for sulfite activation has been overlooked. This study investigates a novel process utilizing suspended sediment/sulfite (SS/S(IV)) for degradation of metronidazole (MNZ). Our results demonstrate that MNZ degradation efficiency can reach to 93.1 % within 90 min with 12.0 g SS and 2.0 mM sulfite. The influencing environmental factors, including initial pH, SS dosage, S(IV) concentration, temperature, and co-existing substances were systematically investigated. Quenching experiments and electron paramagnetic resonance analyses results indicate that SO3•- is the primary active substance responsible for MNZ degradation, with involvement of SO4•-, SO5•-, and •OH. X-ray photoelectron spectroscopy and Mössbauer spectra reveal that Fe (III)-silicates play a crucial role in activating S(IV). Furthermore, analysis of degradation intermediates and pathways of MNZ is conducted using liquid chromatography with mass spectrometry (LC -MS). The toxicity of MNZ and its intermediates were also systematically evaluated by the T.E.ST. program and wheat seeds germination test. This study offers valuable insight into the activation of sulfite by natural sediments and could contribute to the development of SS-based advanced oxidation processes (AOPs) for the in-situ remediation of antibiotics-contaminated water environments.