UV direct photolysis of sulfamethoxazole and ibuprofen: An experimental and modelling study

pH-modulated oxidation of organic pollutants for water decontamination: A deep insight into reactivity and oxidation pathway

Solution pH is one of the primary factors affecting the efficiency of water decontamination. Although the influence of pH on oxidants activation, catalyst activity, and reactive oxygen species have been widely explored, there is still a scarcity of systemic studies on the changes in the oxidation behavior of organic pollutants at different pH levels. Herein, we report the influence laws of pH on the forms, reactivities, active sites, degradation pathways, and products toxicities of organic pollutants. Changes in pH cause the protonation or deprotonation of organic pollutants and further affect their forms and chemistry (e.g., electrostatic force, hydrophobicity, and oxidation potential). The oxidation potential of organic pollutants follows the order: protonated form > pristine form > deprotonated form. Moreover, protonation or deprotonation can modify the active sites and degradation pathways of organic pollutants, wherein deprotonation renders them more susceptible to electrophilic attack, while protonation reduces their activity against electrophilic and nucleophilic attacks. Additionally, pH adjustments can modify the degradation pathway and the toxicity of transformation products. Overall, pH changes can affect the oxidation fate of organic pollutants by altering their structure, which distinguishes it from the effect of pH on oxidants or oxidant activation processes.

Degradation and mineralization of anti-cancer drugs Capecitabine, Bicalutamide and Irinotecan by UV-irradiation and ozone

The degradation of three anti-cancer drugs (ADs), Capecitabine (CAP), Bicalutamide (BIC) and Irinotecan (IRI), in ultrapure water by ozonation and UV-irradiation was tested in a bench-scale reactor and AD concentrations were measured through ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). A low-pressure mercury UV (LP-UV) lamp was used and degradation by UV (λ = 254 nm) followed pseudo-first order kinetics. Incident radiation in the reactor was measured via chemical actinometry using uridine. The quantum yields (φ) for the degradation of CAP, BIC and IRI were 0.012, 0.0020 and 0.0045 mol Einstein-1, respectively. Ozone experiments with CAP and IRI were conducted by adding ozone stock solution to the reactor either with or without addition of tert-butanol (t-BuOH) as radical quencher. Using this experimental arrangement, no degradation of BIC was observed, so a semi-batch setup was employed for the ozone degradation experiments of BIC. Without t-BuOH, apparent second order reaction rate constants for the reaction of the ADs with molecular ozone were determined to be 3.5 ± 0.8 ∙ 103 L mol-1 s-1 (CAP), 7.9 ± 2.1 ∙ 10-1 L mol-1 s-1 (BIC) and 1.0 ± 0.3 ∙ 103 L mol-1 s-1 (IRI). When OH-radicals (∙OH) were quenched, rate constants were virtually the same for CAP and IRI. For BIC, a significantly lower constant of 1.0 ± 0.5 ∙ 10-1 L mol-1 s-1 was determined. Of the tested substances, BIC was the most recalcitrant, with the slowest degradation during both ozonation and UV-irradiation. The extent of mineralization was also determined for both processes. UV irradiation was able to fully degrade up to 80% of DOC, ozonation up to 30%. Toxicity tests with Daphnia magna (D. magna) did not find toxicity for fully degraded solutions of the three ADs at environmentally relevant concentrations.

Origins of Selective Oxidation in Carbon-Based Nonradical Oxidation Processes toward Organic Pollutants: Quantitative Structure-Activity Relationships (QSARs)

Metal-free carbon material-mediated nonradical oxidation processes (C-NOPs) have emerged as a research hotspot due to their excellent performance in selectively eliminating organic pollutants in aqueous environments. However, the selective oxidation mechanisms of C-NOPs remain obscure due to the diversity of organic pollutants and nonradical active species. Herein, quantitative structure-activity relationship (QSAR) models were employed to unveil the origins of C-NOP selectivity toward organic pollutants in different oxidant systems. QSAR analysis based on adsorption and oxidation descriptors revealed that C-NOP selectivity depends on the oxidation potentials of organic pollutants rather than on adsorption interactions. However, the dominance of electronic effects in selective oxidation decreases with increasing structural complexity of organic pollutants. Moreover, the oxidation threshold solely depends on the inherent electronic nature of organic pollutants and not on the reactivity of nonradical active species. Notably, the accuracy of substituent descriptors (Hammett constants) and theoretical descriptors (e.g., highest occupied molecular orbital energy, ionization potential, and single-electron oxidation potential) is significantly influenced by the complexity and molecular state of organic pollutants. Overall, the study findings reveal the origins of organic pollutant-oriented selective oxidation and provide insight into the application of descriptors in QSAR analysis.

Multiscale computational simulation of pollutant behavior at water interfaces

The investigation of pollutant behavior at water interfaces is critical to understand pollution in aquatic systems. Computational methods allow us to overcome the limitations of experimental analysis, delivering valuable insights into the chemical mechanisms and structural characteristics of pollutant behavior at interfaces across a range of scales, from microscopic to mesoscopic. Quantum mechanics, all-atom molecular dynamics simulations, coarse-grained molecular dynamics simulations, and dissipative particle dynamics simulations represent diverse molecular interaction calculation methods that can effectively model pollutant behavior at environmental interfaces from atomic to mesoscopic scales. These methods provide a rich variety of information on pollutant interactions with water surfaces. This review synthesizes the advancements in applying typical computational methods to the formation, adsorption, binding, and catalytic conversion of pollutants at water interfaces. By drawing on recent advancements, we critically examine the current challenges and offer our perspective on future directions. This review seeks to advance our understanding of computational techniques for elucidating pollutant behavior at water interfaces, a critical aspect of water research.

Effects of wavelength on the treatment of contaminants of emerging concern by UV-assisted homogeneous advanced oxidation/reduction processes

Pollutants of emerging concern in aqueous environments present a significant threat to both the aquatic ecosystem and human health due to their rapid transfer. Among the various treatment approaches to remove those pollutants, UV-assisted advanced oxidation/reduction processes are considered competent and cost-effective. The treatment effectiveness is highly dependent on the wavelength of the UV irradiation used. This article systematically discusses the wavelength dependency of direct photolysis, UV/peroxides, UV/chlor(am)ine, UV/ClO2, UV/natural organic matter, UV/nitrate, and UV/sulfite on the transformation of contaminants. Altering wavelengths affects the photolysis of target pollutants, photo-decay of the oxidant/reductant, and quantum yields of reactive species generated in the processes, which significantly impact the degradation rates and formation of disinfection byproducts. In general, the degradation of contaminants is most efficient when using wavelengths that closely match the highest molar absorption coefficients of the target pollutants or the oxidizing/reducing agents, and the contribution of pollutant absorption is generally more significant. By matching the wavelength with the peak absorbance of target compounds and oxidants/reductants, researchers and engineers have the potential to optimize the UV wavelengths used in UV-AO/RPs to effectively remove pollutants and control the formation of disinfection byproducts.

Decentralized approach toward organic pollutants removal using UV radiation in combination with H2O2-based electrochemical water technologies

The current literature lacks a comprehensive discussion on the trade-off between pollutant degradation/mineralization and treatment time costs in utilizing UV light in combination with H2O2-based electrochemical advanced oxidation processes (EAOPs). The present study sheds light on the benefits of using the photoelectro-Fenton (PEF) process with UVA or UVC for methylparaben (MetP) degradation in real drinking water. Although light boosts the photodegradation of refractory Fe(III) complexes and the photolysis of H2O2 (with UVC only), the energy-intensive nature of light-based treatments is acknowledged. To help tackle the high energy consumption issue, a novel approach was employed: partial application of UVA or UVC light after a predetermined electro-Fenton electrolysis time. The proposed treatment approach yielded satisfactory comparable results to those obtained from the application of PEF/UVA or PEF/UVC in terms of total organic carbon removal (ca. 100%), with notably lower energy consumption (ca. 50%). The study delves into the combined method's feasibility, analyzing pollutant degradation/mineralization process and overall energy consumption. The research identifies possible degradation routes based on intermediate detection and radical quenching experiments. Finally, toxicological assessments evaluate the toxicity levels of MetP and its intermediates. The findings of this study bring meaningful contributions to the fore and point to the highly promising potential of the proposed approach, in terms of sustainability and cost-effectiveness, when applied for decentralized water treatment.

Pharmaceutically active compounds in aqueous environment: recent developments in their fate, occurrence and elimination for efficient water purification

The existence of pharmaceutically active compounds (PhACs) in the water is a major concern for environmentalists due to their deleterious effects on living organisms even at minuscule concentrations. This review focuses on PhACs such as analgesics and anti-inflammatory compounds, which are massively excreted in urine and account for the majority of pharmaceutical pollution. Furthermore, other PhACs such as anti-epileptics, beta-blockers and antibiotics are discussed because they also contribute significantly to pharmaceutical pollution in the aquatic environment. This review is divided into two parts. In the first part, different classes of PhACs and their fate in the wastewater environment are presented. In the second part, recent advances in the removal of PhACs by conventional wastewater treatment plants, including membrane bioreactors (MBRs), activated carbon adsorption and bench-scale studies concerning a broad range of advanced oxidation processes (AOPs) that render practical and appropriate strategies for the complete mineralization and degradation of pharmaceutical drugs, are reviewed. This review indicates that drugs like diclofenac, naproxen, paracetamol and aspirin are removed efficiently by conventional systems. Activated carbon adsorption is suitable for the removal of diclofenac and carbamazepine, whereas AOPs are leading water treatment strategies for the effective removal of reviewed PhACs.

Hydroxyl radical dominated ibuprofen degradation by UV/percarbonate process: Response surface methodology optimization, toxicity, and cost evaluation

Ibuprofen (IBP) is a typical nonsteroidal anti-inflammatory drug with a wide range of applications, large dosages, and environmental durability. Therefore, ultraviolet-activated sodium percarbonate (UV/SPC) technology was developed for IBP degradation. The results showed that IBP could be efficiently removed using UV/SPC. The IBP degradation was enhanced with prolonged UV irradiation time, with the decreasing IBP concentration and the increasing SPC dosage. The UV/SPC degradation of IBP was highly adaptable to pH ranging from 4.05 to 8.03. The degradation rate of IBP reached 100% within 30 min. The optimal experimental conditions for IBP degradation were further optimized using response surface methodology. IBP degradation rate reached 97.3% under the optimal experimental conditions: 5 μM of IBP, 40 μM of SPC, 7.60 pH, and UV irradiation for 20 min. Humic acid, fulvic acid, inorganic anions, and natural water matrix inhibited the IBP degradation to varying degrees. Scavenging experiments of reactive oxygen species indicated that hydroxyl radical played a major role in the UV/SPC degradation of IBP, while carbonate radical played a minor role. Six IBP degradation intermediates were detected, and hydroxylation and decarboxylation were proposed as the primary degradation pathways. An acute toxicity test, based on the inhibition of luminescence in Vibrio fischeri, indicated that the toxicity of IBP during UV/SPC degradation decreased by 11%. An electrical energy per order value of 3.57 kWh m^-3 indicated that the UV/SPC process was cost-effective in IBP decomposition. These results provide new insights into the degradation performance and mechanisms of the UV/SPC process, which can potentially be used for practical water treatment in the future.

Defective TiO2 Nanotube Arrays for Efficient Photoelectrochemical Degradation of Organic Pollutants

Oxygen vacancies (OVs) are one of the most critical factors that enhance the electrical and catalytic characteristics of metal oxide-based photoelectrodes. In this work, a simple procedure was applied to prepare reduced TiO₂ nanotube arrays (NTAs) (TiO_2-x) via a one-step reduction method using NaBH₄. A series of characterization techniques were used to study the structural, optical, and electronic properties of TiO_2-x NTAs. X-ray photoelectron spectroscopy confirmed the presence of defects in TiO_2-x NTAs. Photoacoustic measurements were used to estimate the electron-trap density in the NTAs. Photoelectrochemical studies show that the photocurrent density of TiO_2-x NTAs was nearly 3 times higher than that of pristine TiO₂. It was found that increasing OVs in TiO₂ affects the surface recombination centers, enhances electrical conductivity, and improves charge transport. For the first time, a TiO_2-x photoanode was used in the photoelectrochemical (PEC) degradation of a textile dye (basic blue 41, B41) and ibuprofen (IBF) pharmaceutical using in situ generated reactive chlorine species (RCS). Liquid chromatography coupled with mass spectrometry was used to study the mechanisms for the degradation of B41 and IBF. Phytotoxicity tests of B41 and IBF solutions were performed using Lepidium sativum L. to evaluate the potential acute toxicity before and after the PEC treatment. The present work provides efficient PEC degradation of the B41 dye and IBF in the presence of RCS without generating harmful products.

Analysis of the Comparative Growth Kinetics of Paenarthrobacter ureafaciens YL1 in the Biodegradation of Sulfonamide Antibiotics Based on Substituent Structures and Substrate Toxicity

The high consumption and emission of sulfonamide antibiotics (SAs) have a considerable threat to humans and ecosystems, so there is a need to develop safer and more effective methods than conventional strategies for the optimal removal of these compounds. In this study, four SAs with different substituents, sulfadiazine (SDZ), sulfamerazine (SMR), sulfamethoxazole (SMX), and sulfamethazine (SMZ) were removed by a pure culture of Paenarthrobacter ureafaciens YL1. The effect of the initial SAs concentration on the growth rate of strain YL1 was investigated. The results showed that the strain YL1 effectively removed various SAs in the concentration range of 0.05–2.4 mmol·L−1. The Haldane model was used to perform simulations of the experimental data, and the regression coefficient of the model indicated that the model had a good predictive ability. During SAs degradation, the maximum specific growth rate of strain YL1 was ranked as SMX > SDZ > SMR > SMZ with constants of 0.311, 0.304, 0.302, and 0.285 h−1, respectively. In addition, the biodegradation of sulfamethoxazole (SMX) with a five-membered substituent was the fastest, while the six-membered substituent of SMZ was the slowest based on the parameters of the kinetic equation. Also, density functional theory (DFT) calculations such as frontier molecular orbitals (FMOs), and molecular electrostatic potential map analysis were performed. It was evidenced that different substituents in SAs can affect the molecular orbital distribution and their stability, which led to the differences in the growth rate of strain YL1 and the degradation rate of SAs. Furthermore, the toxicity of P. ureafaciens is one of the crucial factors affecting the biodegradation rate: the more toxic the substrate and the degradation product are, the slower the microorganism grows. This study provides a theoretical basis for effective bioremediation using microorganisms in SAs-contaminated environments.

A kinetic study of the photolysis of sulfamethoxazole with special emphasis on the photoisomer

Abstract

The previously not studied photochemical degradation of sulfamethoxazole (SMX) to the isomer of SMX (ISO) was measured via a polychromatic (Xe) and a monochromatic (Hg) light source and accompanied by quantum chemical DFT calculations. In addition to the $$\mathrm{p}K_\mathrm{a} = \;7.0 \pm 0.1$$ p K a = 7.0 ± 0.1 of ISO, tautomer-dependent properties such as the $$K_\mathrm{OW}$$ K OW were measured and theoretically confirmed by DFT. The kinetics in solutions below and above the $$\mathrm{p}K_\mathrm{a} = 5.6$$ p K a = 5.6 of SMX were studied for the available and quantifiable products SMX, ISO, 3-amino-5-methylisoxazole (AMI), 2-amino-5-methyloxazole (AMO), and sulfanilic acid (SUA). The quantum yields of the neutral ($$\Phi _\mathrm{N}$$ Φ N ) and anionic $$\Phi _\mathrm{A}$$ Φ A ) forms of SMX ($$\Phi _\mathrm{A} = 0.03 \pm 0.001$$ Φ A = 0.03 ± 0.001 , $$\Phi _\mathrm{N} = 0.15 \pm 0.01$$ Φ N = 0.15 ± 0.01 ) and ISO ($$\Phi _\mathrm{A} = 0.05 \pm 0.01$$ Φ A = 0.05 ± 0.01 and $$\Phi _\mathrm{N} = 0.06 \pm 0.02$$ Φ N = 0.06 ± 0.02 ) were found to be wavelength-independent. In a competitive reaction to the formation of ISO from SMX, the degradation product TP271 is formed. Various proposed structures for TP271 described in the literature have been studied quantum mechanically and can be excluded for thermodynamic reasons. In real samples in a northern German surface water in summer 2021 mean concentrations of SMX were found in the range of 120 ng/L. In agreement with the pH-dependent yields, concentrations of ISO were low in the range of 8 ng/L.

Graphical abstract

SARS-CoV-2 pharmaceutical drugs: a critical review on the environmental impacts, chemical characteristics, and behavior of advanced oxidation processes in water

This review summarizes research data on the pharmaceutical drugs used to treat the novel SARS-CoV-2 virus, their characteristics, environmental impacts, and the advanced oxidation processes (AOP) applied to remove them. A literature survey was conducted using the electronic databases Science Direct, Scopus, Taylor & Francis, Google Scholar, PubMed, and Springer. This complete research includes and discusses relevant studies that involve the introduction, pharmaceutical drugs used in the SARS-CoV-2 pandemic: chemical characteristics and environmental impact, advanced oxidation process (AOP), future trends and discussion, and conclusions. The results show a full approach in the versatility of AOPs as a promising solution to minimize the environmental impact associated with these compounds by the fact that they offer different ways for hydroxyl radical production. Moreover, this article focuses on introducing the fundamentals of each AOP, the main parameters involved, and the concomitance with other sources and modifications over the years. Photocatalysis, sonochemical technologies, electro-oxidation, photolysis, Fenton reaction, ozone, and sulfate radical AOP have been used to mineralize SARS-CoV-2 pharmaceutical compounds, and the efficiencies are greater than 65%. According to the results, photocatalysis is the main technology currently applied to remove these pharmaceuticals. This process has garnered attention because solar energy can be directly utilized; however, low photocatalytic efficiencies and high costs in large-scale practical applications limit its use. Furthermore, pharmaceuticals in the environment are diverse and complex. Finally, the review also provides ideas for further research needs and major concerns.

Fabrication of Two Isomorphic and Hyperstable Rare Earth-Based Metal-Organic Frameworks with Efficient Ratiometric Probe and Photocatalytic Performances

Two isomorphic lanthanide compounds {[Ln(ddpp)(H₂O)]·CH₃CN}_n (Ln = Eu and Gd, H₄ddpp = 2,5-di(2',4'-dicarboxylphenyl)pyridine) were synthesized. Complex 1-Eu displays ultrahigh acid-base stability and thermal stability. Furthermore, luminescence measurements revealed that 1-Eu could detect quinolone antibiotics with an ultralow limit of detection in aqueous solution. The ratiometric probe properties for sensing antibiotics could be attributed to the incompletely sensitized Eu³⁺ ion of the ligand. Remarkably, it is interesting that 1-Gd exhibits excellent tetracycline degradation properties under visible light. Ultraviolet-visible diffuse reflectance spectroscopy and valence band X-ray photoelectron spectroscopy were carried out to investigate the photodegradation mechanisms. Moreover, a rational explanation for the fluorescent probe and photocatalysis behavior of these two complexes was also discussed with the assistance of density functional theory calculations.

Enhanced UV Direct Photolysis and UV/H2O2 for Oxidation of Triclosan and Ibuprofen in Synthetic Effluent: an Experimental Study

This study aimed to evaluate the implementation of an advanced oxidation system based on UV radiation and UV/H₂O₂ for degradation of TCS and IBU in synthetic effluent. The assays occurred in a 2-L reactor, protected from external light and equipped with a UV lamp (λ = 254 nm). The effect of contaminant concentration, fractions of chemical species present, and mineralization were evaluated. In the UV/ H₂O₂ system, different concentrations of H₂O₂ were studied for oxidation of the contaminants. The kinetic experiments took place between 75 and 270 min of UV irradiation. The results showed > 99% oxidation of TCS in the direct photolysis system at pH 9.4 after 12 min. The degradation of IBU in the UV/H₂O₂ system, when 10 mg L^-1 of H₂O₂ was used, was 97.39% oxidation. We obtained k' values of 0.189 min^-1 for TCS when its highest oxidation occurred and k' values of 0.0219 min^-1 for IBU. The system was not able to completely mineralize the contaminants, presenting high values of TOC and COD after treatment, thus suggesting the occurrence of phototransformation.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11270-022-05583-z.

Hydrothermal carbonation carbon-based photocatalysis under visible light: Modification for enhanced removal of organic pollutant and novel insight into the photocatalytic mechanism

Hydrothermal carbonation carbon (HTCC) is emerging as a promising alternative for photocatalytic removal of contaminants from water. However, the catalytic activity of HTCC is limited by its poor charge transfer ability, and its photocatalytic mechanism remains unclear. Herein, a unique photosensitization-like mechanism was firstly found on Fe modified HTCC (Fe-HTCC) derived from glucose for effective removal of organic pollutants. Under visible light illumination, the organic pollutant coordinated with Fe-HTCC enabled electrons transfer from its highest occupied molecular orbital (HOMO) to conduction band (CB) of Fe-HTCC, which not only oxidized pollutant itself, but also generated oxygen-centered radical for reducing O₂ into O₂^•- towards pollutant removal. The degradation kinetic constant of sulfamethoxazole (SMX) over Fe-HTCC was about 1024.4 and 20.5 times higher than that of HTCC and g-C₃N₄, respectively. The enhanced performance of Fe-HTCC was originated from dual role of Fe modification: one is to boost the electron-deficient C sites which prefer to coordinate with amino or hydroxyl of pollutants; the other is to enhance the linkage of discrete polyfuran chains in Fe-HTCC for effective electron transfer from pollutant to Fe-HTCC. This work provides new insight into the synthesis and mechanism of HTCC-based high-efficiency photocatalyst for water decontamination.

Insights into naphthalene degradation in aqueous solution and soil slurry medium: Performance and mechanisms

The performance of naphthalene (NAP) degradation in peroxodisulfate (PDS) and peroxymonosulfate (PMS) oxidation systems by nano zero valent iron (nZVI) combined with citric acid (CA) activation was reported in aqueous solution and soil slurry medium. The results in aqueous solution tests indicated that 98.1% and 98.9% of NAP were individually degraded in PDS/nZVI/CA and PMS/nZVI/CA systems within 2 h when the dosages of PDS, PMS, nZVI and CA were 1.0 mM, 0.1 mM, 0.2 mM and 0.1 mM, respectively. The consequences of scavenging tests and electron paramagnetic resonance detection demonstrated that HO• and SO₄^-• were the key factors on NAP removal. The presence of surfactants could consume ROSs and inhibit NAP removal. In addition, GC-MS was applied for the determination of NAP degradation intermediates, and three possible NAP degradation pathways were proposed in PDS oxidation process and two pathways in PMS oxidation process, respectively. The results in soil slurry medium showed that the presence of CA could promote the dissolution of soil minerals and the desorption of NAP from soil medium. 93.5% and 96.8% degradation of NAP were obtained in PDS/nZVI/CA and PMS/nZVI/CA systems within 24 h. Besides, the existence of DOM in soil could promote Fe(II)/Fe(III) cycle and NAP degradation through electron transfer. Based on the NAP degradation performance in the actual groundwater and soil medium, the above findings could provide basis and strong support for the potential application of PDS/nZVI/CA and PMS/nZVI/CA systems in the remediation of NAP contaminated sites.

Ultrasensitive fluorescence detection of norfloxacin in aqueous medium employing a 2D Zn(ii)-based coordination polymer

A 2D fluorescent coordination polymer, {[Zn(L)0.5(mip)] 1.75H2O}n (1), was successfully assembled. 1 was developed as an ultrasensitive fluorescent probe for the sensing of norfloxacin (NOR) in water.

Occurrence, transformation, bioaccumulation, risk and analysis of pharmaceutical and personal care products from wastewater: a review

Almost all aspects of society from food security to disease control and prevention have benefited from pharmaceutical and personal care products, yet these products are a major source of contamination that ends up in wastewater and ecosystems. This issue has been sharply accentuated during the coronavirus disease pandemic 2019 (COVID-19) due to the higher use of disinfectants and other products. Here we review pharmaceutical and personal care products with focus on their occurrence in the environment, detection, risk, and removal.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10311-022-01498-7.

Sustainable ferrate oxidation: Reaction chemistry, mechanisms and removal of pollutants in wastewater

This review is intended to evaluate the use of ferrate (Fe(VI)), being a green coagulant, sustainable and reactive oxidant, to remove micro pollutants especially pharmaceutical pollutants in contaminated water. After a brief description of advanced oxidation processes, fundamental dimensions regarding the nature, reactivity, and chemistry of this oxidant are summarized. The degradation of contaminants by Fe(VI) involves several mechanisms and reactive agents which are critically evaluated. The efficiency and chemistry of Fe(VI) oxidation differs according to the reaction conditions and activation agent, such as soluble Fe(VI) processes, which involve Fe(VI), UV light, and electro-Fe(VI) oxidation. Fe(VI) application methods (including single dose, multiple doses, chitosan coating etc), and Fe(VI) with activating agents (including sulfite, thiosulfate, and UV) are also described to degrade the micro pollutants. Besides, application of Fe(VI) to remove pharmaceuticals in wastewater are intensely studied. Electrochemical prepared Fe(VI) has more wide application than wet oxidation method. Meanwhile, we elaborated Fe(VI) performance, limitations, and proposed innovative aspects to improve its stability, such as the generation of Fe(III), synergetic effects, nanopores entrapment, and nanopores capsules. This study provides conclusive direction for synergetic oxidative technique to degrade the micro pollutants.

Photo-mediated and advanced oxidative processes applied for the treatment of effluents with drugs used for the treatment of early COVID-19: Review

The COVID-19 pandemic is proving to be one of the most challenging health and social crises ever faced by humanity. Several drugs have been proposed as potential antiviral agents for the treatment of COVID-19 since the beginning of the health crisis. Among them are chloroquine (CQ), hydroxychloroquine (HCQ), ivermectin (IVM), and the combination of QC or HCQ and azithromycin (AZI). The use of these and several other drugs has grown sharply, even if there is proof of ineffectiveness in the early treatment or mild cases of COVID-19. Thus, there is great concern about the potential environmental impacts of the effluents released with the presence of these drugs. Therefore, this work aimed to carry out a literature review on wastewater treatment processes, focusing on removing these substances through advanced oxidation process. As the conventional effluent treatment processes do not have high efficiency for removal, it was concentrated in the literature that had as scope advanced and photo-mediated techniques to remove CQ, HCQ, IVM, and AZI. It is expected, with this work, to highlight the importance of conducting research that contributes to the control of pollution and contamination.

Ultraviolet photolysis of four typical cardiovascular drugs: mechanisms, influencing factors, degradation pathways, and toxicity trends

The cardiovascular drugs (CDDs), such as metoprolol (MET), atenolol (ATE), bezafibrate (BZB), and atorvastatin (ATO), have been frequently detected in the water environment. They can cause potential threats to the ecological environment and human health due to their "pseudo-persistence" effect. In this study, the photolysis kinetics, degradation mechanisms, by-products, influencing factors, and acute toxicity of these four typical CDDs under polychromatic ultraviolet irradiation (200-400 nm) were investigated. The results showed that the photolysis of ATE, BZB, MET, and ATO all followed pseudo-first-order kinetics, and their average photon quantum yields of the wavelength studied were 0.14×10^-2, 0.33×10^-3, 0.78×10^-4, and 0.24×10^-4 mol einstein^-1, respectively. Singlet oxygen (¹O₂), hydroxyl radical (·OH), and the triplet-excited state of the cardiovascular drug (³CDD*) were all involved in the photolysis while ¹O₂ was the dominator. The effects of NO₃^-, Cl^-, HCO₃^-, and humic acid (HA) on the photolysis were the combination of light-shielding, quenching, and excitation of reactive species. Seven, four, four, and nine photolysis products of ATO, BZB, ATE, and MET were identified, respectively, and their possible degradation pathways were proposed. The acute toxicity of ATE was basically unchanged during photolysis; however, ATO, BZB, and MET toxicity all increased due to the generation of ketonization and hydroxylation products.

Reactivity and reaction mechanisms of sulfate radicals with lindane: An experimental and theoretical study

Advanced oxidation technologies (AOTs) have been intensely used to eliminate various organic pollutants in engineering waters. In this context, we investigated the kinetics and mechanisms of the sulfate radical (SO₄^-)-mediated degradation of lindane in UV/peroxydisulfate system, and compared results with previous studies on SO₄^--based AOTs for destruction of lindane. The second order rate constant (k) value between SO₄^- and lindane was determined to be (8.95 ± 0.29) × 10⁶ M^-1 s^-1via competition kinetics using p-cyanobenzoic acid as reference compound, which is close to the theoretically calculated value of 4.41 × 10⁷ M^-1 s^-1, that was performed at SMD/M05-2X/6-311++G**//M05-2X/6-31+G** level of theory using density functional theory (DFT) approach. H-atom abstraction pathway was calculated to be thermodynamically favorable and kinetically dominant. In the combined experimental and theoretical study, we aim for a better understanding on the degradation kinetics and mechanisms of lindane, serving as a starting point for more attention to SO₄^--mediated degradation kinetics of cycloaliphatic compounds in future.

Use of Electrocoagulation for Treatment of Pharmaceutical Compounds in Water/Wastewater: A Review Exploring Opportunities and Challenges

Increasing dependency on pharmaceutical compounds including antibiotics, analgesics, antidepressants, and other drugs has threatened the environment as well as human health. Their occurrence, transformation, and fate in the environment are causing significant concerns. Several existing treatment technologies are there with their pros and cons for the treatment of pharmaceutical wastewater (PWW). Still, electrocoagulation is considered as the modern and decisive technology for treatment. In the EC process, utilizing electricity (AC/DC) and electrodes, contaminants become coagulated with the metal hydroxide and are separated by co-precipitation. The main mechanism is charge neutralization and adsorption of contaminants on the generated flocs. The range of parameters affects the EC process and is directly related to the removal efficiency and its overall operational cost. This process only could be scaled up on the industrial level if process parameters become optimized and energy consumption is reduced. Unfortunately, the removal mechanism of particular pharmaceuticals and complex physiochemical phenomena involved in this process are not fully understood. For this reason, further research and reviews are required to fill the knowledge gap. This review discusses the use of EC for removing pharmaceuticals and focuses on removal mechanism and process parameters, the cost assessment, and the challenges involved in mitigation.

Solar photocatalytic degradation of ibuprofen with a magnetic catalyst: Effects of parameters, efficiency in effluent, mechanism and toxicity evolution

The environmental-friendly photocatalytic process with a magnetic catalyst CoFe₂O₄/TiO₂ mediated by solar light for ibuprofen (IBP) degradation in pure water, wastewater effluent and artificial seawater was investigated systematically. The study aims to reveal the efficiency, the mechanism and toxicity evolution during IBP degradation. Hydroxyl radicals and photo-hole (h⁺) were found to contribute to the IBP decay. The presence of SO₄^2- showed no significant effect, while NO₃^- accelerated the photodegradation, and other anions including HCO₃^-, Cl^-, F^-, and Br^- showed significant inhibition. The removal efficiency was significantly elevated with the addition of peroxymonosulfate (PMS) or persulfate (PS) ([Oxidant]₀:[IBP]₀ = 0.4-4), with reaction rate of 5.3-13.1 and 1.3-2.9 times as high as the control group, respectively. However, the reaction was slowed down with the introduction of H₂O₂. A mathematic model was employed to describe the effect of ferrate, high concentration or stepwise addition of ferrate was suggested to play a positive role in IBP photodegradation. Thirteen transformation products were identified and five of them were newly reported. The degradation pathways including hydroxylation, the benzene ring opening and the oxidation of carbon were proposed. IBP can be efficiently removed when spiked in wastewater and seawater despite the decreased degradation rate by 41% and 56%, respectively. Compared to the IBP removal, mineralization was relatively lower. The adverse effect of the parent compound IBP to the green algae Chlorella vulgaris was gradually eliminated with the decomposition of IBP. The transformation product C178a which possibly posed toxicity to rotifers Brachionus calyciflorus can also be efficiently removed, indicating that the photocatalysis process is effective in IBP removal, mineralization and toxicity elimination.

Photo-ammonification of low molecular weight dissolved organic nitrogen by direct and indirect photolysis

The photo-ammonification process plays a crucial role in the transformation of dissolved organic nitrogen (DON) to dissolved inorganic nitrogen (DIN). However, previous studies have primarily focused on DON biotransformation than on abiotic processes. This study investigated the photo-ammonification process of nine model low molecular weight (LMW) DON molecules (e.g., amino acids, nucleotides, and urea) under the influence of different light sources. The results showed that photo-ammonification of model DON was mainly induced by UV light, while negligible contribution by visible light was found. Depending on their molecular structures, amino acids yielded different ammonia amounts, whereas negligible photo-ammonification was observed for nucleotides and urea. As for the reactive species, OH promoted ammonia yields of all the model amino acids; ³CDOM^⁎ contributed to the photo-ammonification of six amino acids; ¹O₂ only had a positive impact on ammonification of tryptophan, histidine, and tyrosine; and CO₃^- accelerated ammonia generation from histidine and methionine. In natural water samples, tryptophan, tyrosine, histidine, and methionine generated significant ammonia. OH and ¹O₂ were speculated as the contributing reactive species based on kinetic studies as well as significant fluorescent humic-like and tyrosine-like substances degradation in irradiated samples compared to the raw samples characterized by the EEM-PARAFAC analysis. The negative linear correlations between photo-ammonification rates and the E_LUMO-E_HOMO of the amino acids emphasized the importance of the role of the molecular structure. Overall, these results revealed the LMW DON photo-ammonification mechanism in sunlit surface waters and highlighted its significance in the nitrogen biogeochemical cycle as well as water quality management.

Photolysis kinetics of cartap and nereistoxin in water and tea beverages under irradiation of simulated sunlight and ultraviolet under laboratory conditions

Cartap applied widely in agricultural crops and tea plants is readily degraded into nereistoxin, resulting in a longer residual period and higher exposure risk to humans. The photolysis kinetics of cartap and nereistoxin in water and tea beverages was firstly investigated to explore the effect and mechanism of pesticide residue removal. Cartap and nereistoxin could be effectively photolyzed by ultraviolet and their photolysis rate increased with light intensity increasing. The photolysis percentage of cartap and nereistoxin in different solutions under ultraviolet irradiation of 200 W mercury lamp reached 81.8%-100.0% within 6 h. Relative to water solution, the water-soluble components in tea had an inhibition effect on the photodegradation of cartap and nereistoxin. This research provided a reference for the development of effective methods for the removal of cartap and its metabolite in water and tea beverages.

UV-activated permanganate process for micro-organic pollutant degradation: efficiency, mechanism and influencing factors

Ultraviolet-activated permanganate (UV/PM) process is a novel advanced oxidation process (AOP), but its application potential remains to be evaluated. This work investigates the degradation of refractory organic pollutant by UV/PM in terms of efficiency, mechanism, and influencing factors. The target compound benzoic acid (BA), which is a micro-organic pollutant and is resistant to PM and UV treatment, can be efficiently degraded by UV/PM. The electron paramagnetic resonance spectra directly supported the formation of hydroxyl radical (HO•) and superoxide radical (O₂^•-) from UV photolysis of PM. Competitive kinetics experiments verified that O₂^•- acted as precursor of HO• and the good degradation performance of BA was due to the involvement of HO• and manganese(V). The rate constants of BA degradation showed a positive linear relationship with PM dosage in the range of 0.5-20 mg·L^-1, and the degradation process was significantly influenced by solution pH and natural organic matters but insensitive to chloride and bicarbonate at environmentally relevant concentrations. Compared to the typical UV-based AOP UV/hydrogen peroxide, UV/PM is a little inferior, indicating that optimization and enhancement is needed for this process before its possible practical application.

Mechanistic insight into the degradation of ibuprofen in UV/H2O2 process via a combined experimental and DFT study

The study investigated the degradation kinetic and transformation mechanism of ibuprofen (IBP) in UV/H₂O₂ process from both experimental and theoretical aspects. Impacts of H₂O₂ dosage, solution pH, quenching agent, and concentration of nitrite (NO₂^-) on IBP degradation in UV/H₂O₂ process were evaluated. Both experimental results and theoretical calculations indicated that ^•OH played an important role in the degradation of IBP and its transformation products. The second-order rate constants of ^•OH and ^•NO₂ with IBP were calculated as 3.93 × 10⁹ M^-1 s^-1 and 5.59 × 10^-3 M^-1 s^-1, based on the transition state theory, which explained the phenomenon that addition of NO₂^- inhibited IBP degradation. Further, according to the results of ultra-high-resolution mass and density functional theory calculations, mechanisms of a detailed degradation pathway for IBP were clarified. Namely, the detailed mechanistic formation pathways for hydroxylated and keto-based products were proposed. Then, possible active sites of the keto-based products, as well as the corresponding subsequent products were predicted by Condensed Fukui Function. Our study can broaden the knowledge of the reactions of emerging contaminants with ^•OH, and provide theoretical foundation for the optimization of UV/H₂O₂ process.

Kinetic and mechanistic investigation into odorant haloanisoles degradation process by peracetic acid combined with UV irradiation

This study reported the kinetics and mechanism of degradation of odorant haloanisoles by peracetic acid combined with UV irradiation (PAA/UV). The removal efficiency of haloanisoles by PAA/UV was more than 92 % after 1 h reaction at pH 5, 25 °C, [HAs] =50 μg/L and [PAA] = 10 mg/L. The degradation of haloanisoles was fitted by the first-order kinetic model, and the rate constants of various haloanisoles followed the order: 2,4,6-tribromoanisole (2,4,6-TBA, (9.25 ± 0.71)×10^-2 s^-1) > 2-monochloroanisole (2-MCA, (8.00 ± 0.34)×10^-2 s^-1) > 2,4-dichloroanisole (2,4-DCA, (6.24 ± 0.55)×10^-2 s^-1) > 2,4,6-trichloroanisole (2,4,6-TCA, (5.05 ± 0.04)×10^-2 s^-1). The contribution of PAA (mainly composed of free radicals produced from PAA activation by UV) to the degradation rate of chloroanisoles in PAA/UV process ranged from 24 % to 36 %, while 25 % to the degradation rate of bromoanisole. Direct photolysis contributed much more to the removal of bromoanisole (42 %) than chloroanisoles (9-14 %). The inhibition of tert-butanol on degradation demonstrated the existence of ·OH, and superoxide radical and carbon-centered radicals were also probably existed in PAA/UV process. Combining density functional theory (DFT) calculation and products analysis, the degradation pathway of haloanisoles in PAA/UV process were determined. The odor and toxicity evaluation indicated PAA/UV process could reduce olfactory discomfort and health risk of haloanisoles.

A novel electrochemical oxidation-methanogenesis system for simultaneously degrading antibiotics and reducing CO2 to CH4 with low energy costs

A novel electrochemical oxidation-methanogenesis (EO-M) system was proposed for the first time to simultaneously achieve antibiotic degradation and a bioelectrochemical conversion of CO₂ to CH₄ with low energy costs. A dual-chamber system was installed with an antimony-doped tin oxide anode (Ti/SnO₂-Sb) for the electrocatalytic generation of hydroxyl radicals to degrade ciprofloxacin (CIP), and a CO₂-reducing methanogenic biocathode was enriched based on a three-dimensional (3D) graphitized granular activated carbon (GGAC) for microbial electromethanogenesis. The anode achieved removal efficiencies as high as 99.99% and 90.53% for CIP (14 mL, 50 mg L^-1) and the chemical oxygen demand (COD, 89 mg L^-1), respectively. The biocathode was rapidly enriched within 15 days and exhibited a methane production rate that stabilized at 15.12 ± 1.82 m³ m^-3 d^-1; additionally, the cathodic coulombic efficiency reached 71.76 ± 17.24%. The energy consumption of CIP degradation was reduced by 3.03 Wh L^-1 compared to that of a single electrochemical oxidation system due to the lower cathodic overpotential of CO₂ bioelectrochemical reduction in the EO-M system. A detailed analysis of the biofilm evolution in the 3D biocathode during the start-up process demonstrated that the enhanced absorption of extracellular polymeric substances by the GGAC cathode accelerated the enrichment of methanogens and induced the formation of methanogens with a large number of flagella. An analysis of the microbial community showed that a high relative abundance of Methanobacterium movens could promote a flagella-mediated direct electron transfer of the biocathode, eventually reducing the cathodic overpotential and energy costs of the EO-M system.

Successive non-radical and radical process of peroxymonosulfate-based oxidation using various activation methods for enhancing mineralization of sulfamethoxazole

To enhance the mineralization of toxic organic pollutants is crucial for the alleviation of environmental pollution. In this study, the successive non-radicals and radicals process (SNRP) of peroxymonosulfate (PMS)-based oxidation was performed using various methods for PMS activation, including UV, ozone, gamma radiation and biochar and applied for enhancing the mineralization of sulfamethoxazole (SMX). The results showed that SNRP-UV could improve the mineralization of SMX, and both SNRP-UV and PMS/UV could completely mineralize SMX. For SNRP-Ozone, SNRP-Radiation and SNRP-Biochar, compared to the sole radical oxidation, all SNRPs could enhance the mineralization of SMX. The biochar-induced SNRP obtained the maximum mineralization increment, followed by gamma irradiation-induced SNRP and ozone-induced SNRP. Sulfate radicals were mainly responsible for SMX mineralization for SNRP-Biochar, while hydroxyl radicals for SNRP-Radiation, and the synergetic effect of ozone and sulfate radicals for SNRP-Ozone. Different degradation intermediate products were identified in different SNRP, further revealing that SNRP induced by different methods had different mineralization capacity. This study further demonstrated that SNRP could be a new strategy for enhancing the mineralization of SMX.

Kinetic and mechanistic insights into the abatement of clofibric acid by integrated UV/ozone/peroxydisulfate process: A modeling and theoretical study

The feasibility of integrated UV/ozone (O₃)/peroxydisulfate (PDS) process for abatement of clofibric acid (CA) was systematically explored in this study with focus on the kinetic simulation and oxidation mechanisms. The results indicated the UV/O₃/PDS process was of prominent treatment capability with pseudo-first-order rate constant of CA degradation increased by 65.9% and 86.0% compared to UV/O₃ and UV/PDS processes, respectively. A chemical kinetic model was developed and successfully employed to predict CA elimination as well as the specific contributions of UV, hydroxyl radical (^•OH) and sulfate radical (SO₄^•-) under different PDS dosage, pH, natural organic matters, bicarbonate and chloride conditions in UV/O₃/PDS process. According to quantum chemical calculation, radical addition on ortho site of isopropoxy substituent and single electron transfer were corroborated to be the dominant reaction channels for the oxidation of CA by ^•OH and SO₄^•-, respectively. Additionally, the reactive sites and transformation pathways of CA were proposed via Fukui function calculation and UPLC-Q-TOF-MS analysis. Moreover, the performance of UV/O₃/PDS process was further evaluated with regard to the energy demand and bromate formation. This study first proposed a kinetic model in UV/O₃/PDS process and elucidated the regioselectivity and products distribution of CA during oxidative treatment.

Synergistic effect of persulfate and g-C3N4 under simulated solar light irradiation: Implication for the degradation of sulfamethoxazole

A method combining g-C₃N₄ and potassium peroxydisulfate (PDS) under simulated sunlight was put forward to effectively degrade sulfamethoxazole (SMX). The SMX removal efficiency was substantially improved compared with the processes involving only g-C₃N₄ or PDS. The kinetic constants for the g-C₃N_4, PDS and g-C₃N₄/PDS systems were 0.0023, 0.0239 and 0.068 min^-1, respectively. The g-C₃N₄/PDS process reached an SMX removal rate of 98.4 % after 60 min of simulated sunlight; in addition, the proposed system showed desirable efficiency for SMX degradation in two different actual water samples as well. The reaction mechanism was illustrated by trapping experiments, which showed that g-C₃N₄ can promote S₂O₈^2- to transfer SO₄^-, S₂O₈^2- favored the generation of O₂^-, and O₂^-, SO₄^- and holes (h⁺) were the main oxidative species for the SMX degradation in the combined reaction process under simulated sunlight. Then, to further explore this mechanism, the intermediates generated during the combined reaction process were analyzed by LC/MS and possible degradation pathways were proposed. The result showed that the breaking of the SN and C-S bonds, the hydroxylation of the benzene ring and the oxidation of the amino group were identified as the main pathways in the SMX degradation process by the g-C₃N₄/PDS system under simulated sunlight.

Experimental and theoretical insights into kinetics and mechanisms of hydroxyl and sulfate radicals-mediated degradation of sulfamethoxazole: Similarities and differences

Hydroxyl radical (^•OH)- and sulfate radical ()-based advanced oxidation technologies (AOTs) have been proven an effective method to remove antibiotics in wastewater treatment plants (WWTPs). This study aims to gain insights into kinetics and mechanisms of neutral sulfamethoxazole (SMX) degradation, a representative antibiotic, by ^•OH and using an experimental and theoretical approach. First, the second-order rate constants (k) of SMX with ^•OH and were determined to be (7.27 ± 0.43) × 10⁹ and (2.98 ± 0.32) × 10⁹ M^-1 s^-1 in UV/H₂O₂ and UV/persulfate (UV/PS) systems, respectively. The following theoretical calculations at the M06-2X level of theory revealed that addition of radicals to the benzene ring is the most favorable first-step reaction for both ^•OH and , but that exhibits higher energy barriers and selectivity than ^•OH due to steric hindrance. We further analyzed subsequent reactions and, interestingly, our findings closely corroborated HOMO/LUMO distributions of SMX to the oxidation pathways. Finally, the estimation of energy consumption for UV alone, ^•OH-, and -mediated oxidation processes was compared. These comparative results, for the first time, provide insights into the similarities and differences of degradation of SMX by ^•OH/ at the molecular level and can help improve antibiotics removal using radical based AOTs in WWTPs.

New insight into the substituents affecting the peroxydisulfate nonradical oxidation of sulfonamides in water

The large consumption and discharge of sulfonamides (SAs) have potentially induced antibiotic resistance genes, posing inestimable threats to humans and ecosystems. In the present study, five SAs with different substituents were regarded as target compounds to be degraded using the nonradical dominated peroxydisulfate (PDS) activation process by the combination of ¹O₂ oxidation and direct electron transfer. The degradation rates, toxicities and pathways of SAs largely varied with their substituents. For instance, sulfathiazole with five-membered substituent had the highest degradation rate of 0.19 min^-1, which was 3.8 times as the rate of sulfanilamide (0.05 min^-1) without substituent. Then the theoretical calculation was adopted to further confirm that different substituents on the SAs could influence the molecular orbital distribution and their stability, thus resulting in the different removal rate of SAs. Finally, the products of different SAs were concisely deduced to take insight into the effects of different substituents on SAs degradation pathways. It was demonstrated that the geometrical differences among various SAs caused by the different substituents contributed to the different degradation pathways of SAs. Representatively, the special Smiles-type rearrangement pathway was occurred in the six-membered SAs instead of in the five-membered SAs, which inversely resulted in the slower degradation rate of six-membered SAs than the five-membered SAs. Thus, the present study provides a valuable insight into the effects of substituents on the degradation rate and transformation pathways of SAs in the nonradical PDS activation process.

Experimental and theoretical insight into hydroxyl and sulfate radicals-mediated degradation of carbamazepine

Carbamazepine (CBZ), a widely detected pharmaceutical in wastewaters, cannot currently be treated by conventional activated sludge technologies, as it is highly resistant to biodegradation. In this study, the degradation kinetics and reaction mechanisms of CBZ by hydroxyl radical (OH) and sulfate radical ()-based advanced oxidation processes (AOPs) were investigated with a combined experimental/theoretical approach. We first measured the UV absorption spectrum of CBZ and compared it to the theoretical spectrum. The agreement of two spectra reveals an extended π-conjugation system on CBZ molecular structure. The second-order rate constants of OH and with CBZ, measured by competition kinetics method, were (4.63 ± 0.01) × 10⁹ M^-1 s^-1 and (8.27 ± 0.01) × 10⁸ M^-1 s^-1, respectively at pH 3. The energetics of the initial steps of CBZ reaction with OH and were also calculated by density functional theory (DFT) at SMD/M05-2X/6-311++G**//M05-2X/6-31 + G**level. Our results reveal that radical addition is the dominant pathway for both OH and . Further, compared to the positive ΔG_R⁰ value for the single electron transfer (SET) reaction pathway between CBZ and OH, the ΔG_R⁰ value for SET reaction between CBZ and is negative, showing that this reaction route is thermodynamically favorable. Our results demonstrated the remarkable advantages of AOPs for the removal of refractory organic contaminants during wastewater treatment processes. The elucidation of the pathways for the reaction of OH and with CBZ are beneficial to predict byproducts formation and assess associated ecotoxicity, providing an evaluation mean for the feasibility of AOPs application.