Kinetic removal of acetaminophen and phenacetin during LED-UV365 photolysis of persulfate system: Reactive oxygen species generation

Solar-driven persulfate degradation of caffeine and cephradine in synthetic human urine

Urine source separation, as an innovative concept for the reuse of microlevel nutrients in human urine, has drawn increasing attention recently. Consequently, removing coexisting pharmaceuticals in urine is necessary for further reuse. This study is the first to apply the solar-driven persulfate process (Solar/PS) to the investigation of cephradine (CFD) and caffeine (CAF) degradation in synthetic human urine. The results showed that significantly more degradation of CFD and CAF occurs with the Solar/PS process than with persulfate oxidation and direct sunlight photolysis, respectively. The generated reactive species ·OH, SO4·-, O2·- and 1O2 were identified in the Solar/PS process. While SO4·- played a dominant role at pH 6, it played a minor role at pH 9 due to the lower amount generated under alkaline conditions. The presence of chloride and ammonia negatively impacted the photodegradation of both compounds. In contrast, bicarbonate exhibited no effect on CAF but enhanced CFD degradation owing to its amino-acid-like structure, which has a higher reactivity toward CO3·-. Although total organic carbon (TOC) was partially mineralized after 6 h of operation, no Microtox® toxicity was observed.

Peracetic acid as an alternative disinfectant for micropollutants degradation and disinfection byproducts control in outdoor swimming pools

Peracetic acid (PAA) has garnered significant interest as a novel alternative to chlorine-based disinfectants for water treatment due to its broad-spectrum antimicrobial activity and its ability of reactive species generation when exposed to UV light. However, limited studies have investigated micropollutant degradation in the presence of PAA under solar irradiation. This is the first study to comprehensively investigate the photodegradation of caffeine (CAF) and 4-methylbenzylidene camphor (4-MBC) and the removal of disinfection byproducts (DBPs) in the presence of PAA under simulated solar light. The study revealed that the photodegradation of CAF and 4-MBC was significantly enhanced in the presence of PAA, following pseudo-first-order kinetics (R2 > 0.98) with reaction rates (kobs) of 0.220 and 0.111 h-1, respectively. In addition, substantial reduction of 21 DBPs, including trihalomethanes, haloacetic acids and haloacetonitriles, and no DBPs formation were observed in the presence of PAA and simulated solar irradiation. The proportion of coexisting H2O2 in the PAA solution considerably influenced target compounds degradation. CAF and 4-MBC were degraded faster under acidic conditions than under alkaline conditions. Hydroxyl radicals (·OH) dominated the degradation of CAF at different pH values, while direct photolysis and other reactive species played a major role in the degradation of 4-MBC.

Advanced oxidation of bio-treated incineration leachate by persulfate combined with heat, UV254 nm, and UV365 nm: Kinetics, mechanism, and toxicity

This study compared and evaluated the ultraviolet/persulfate (UV/PS) at 254 or 365 nm and heat/persulfate (heat/PS) systems for advanced treatment of biologically pre-treated incineration leachate. The UV365 nm/PS system with the highest removal reduced chemical oxygen demand (COD) by 81.7%, total organic carbon by 73.8%, NH3-N by 96.8%, total nitrogen by 47.3%, and color by 98.6% within 24 h, separately. Kinetics tests suggested that a highest concentrations of 4.8 × 10-10 M for [SO4·-]ss and 2.8 × 10-11 M for [·OH]ss were reported in UV365/PS and UV254/PS systems, respectively. Characterization of leachate organic matter species revealed that low molecular weight organic matter < 5 kDa was preferentially degraded in three systems. Ketones are relatively easily degraded by both heat/PS and UV/PS systems, whereas esters were the most recalcitrant. Three-dimensional fluorescence analysis revealed > 99% humic acid and fulvic acid removal in all three systems. In practical applications, it is crucial to consider the pH and toxicity of SR-AOPs in the treatment of bio-treated incineration leachate. Furthermore, the ecotoxicity of MBR effluent treated by the heat/PS system and UV365 nm/PS system increased, which was caused by the strong acidity exhibited in the systems. In addition, we found that PS could interfere with 3.3% of the COD's detection. The findings of this study suggest that secondary effects of PS on water quality at high doses should be investigated in future research.

Ozone- and Hydroxyl Radical-Induced Degradation of Micropollutants in a Novel UVA-LED-Activated Periodate Advanced Oxidation Process

In this study, novel light emitting diode (LED)-activated periodate (PI) advanced oxidation process (AOP) at an irradiation wavelength in the ultraviolet A range (UVA, UVA-LED/PI AOP) was developed and investigated using naproxen (NPX) as a model micropollutant. The UVA-LED/PI AOP remarkably enhanced the degradation of NPX and seven other selected micropollutants with the observed pseudo-first-order rate constants ranging from 0.069 ± 0.001 to 4.50 ± 0.145 min-1 at pH 7.0, demonstrating a broad-spectrum micropollutant degradation ability. Lines of evidence from experimental analysis and kinetic modeling confirmed that hydroxyl radical (•OH) and ozone (O3) were the dominant species generated in UVA-LED/PI AOP, and they contributed evenly to NPX degradation. Increasing the pH and irradiation wavelength negatively affected NPX degradation, and this could be well explained by the decreased quantum yield (ΦPI) of PI. The degradation kinetics of NPX by the UVA-LED/PI AOP in the presence of water matrices (i.e., chloride, bicarbonate, and humic acid) and in real waters were examined, and the underlying mechanisms were illustrated. A total of nine transformation products were identified from NPX oxidation by the UVA-LED/PI AOP, mainly via hydroxylation, dealkylation, and oxidation pathways. The UVA-LED/PI AOP proposed might be a promising technology for the treatment of micropollutants in aqueous solutions. The pivotal role of ΦPI during light photolysis of PI may guide the future design of light-assisted PI AOPs.

Mechanistic insights into UV photolysis of carbamazepine and caffeine: Active species, reaction sites, and toxicity evolution

The pseudo-persistence of pharmaceutical and personal care products (PPCPs)in the aqueous environment may pose potential risks to human health and ecosystems. The UV disinfection in wastewater treatment plants is one of the essential processes before PPCPs enter the water environment, so it is crucial to elucidate the photolytic behavior and mechanism of PPCPs under UV radiation. In this work, carbamazepine (CBZ) and caffeine (CAF) were selected as typical pollutants to investigate the effect of water matrixes, humic acid, inorganic ions, and pH on the UV radiation performance. Hydroxyl radical (•OH) and singlet oxygen (¹O₂) were identified by quenching experiments and electron paramagnetic resonance (EPR) spectra as playing a dominant role in the degradation process. UPLC-TOF/MS was conducted to identify 13 and 14 possible intermediates of CBZ and CAF, respectively. Moreover, combining density functional theory (DFT) calculations (Frontier Molecular Orbital and Fukui index), hydroxylation, oxidation, and ring cleavage were proposed as the main degradation pathways of the contaminants, which occurred first at the C(7C), N(17 N) and O(18O) sites of CBZ and at the C(9C) site of CAF. The bio-acute toxicity experiment and the Ecological Structure-Activity Relationships (ECOSAR) program were performed to analyze and predict the toxicity of the intermediates of CBZ and CAF under UV radiation, respectively. The results showed that the acute toxicity of both solutions increased after UV radiation and followed with the combined toxicity. This work has great scientific value and practical environmental significance for evaluating the UV disinfection process and managing PPCPs in the aqueous environment.

Degradation of iopamidol by UV365/NaClO: Roles of reactive species, degradation mechanism, and toxicology

The degradation of iopamidol (IPM) was investigated using a UV₃₆₅/NaClO system. The reactive species (HO·, ClO·, ozone, Cl·, and Cl₂^-·) in the system were identified, and the changing trends of the percentage contributions of these reactive species to IPM removal under various conditions were systematically evaluated. The results showed that ClO· and HO· played the most significant roles in the apparent pseudo-first-order rate constants of IPM degradation (k_obs, min^-1) in the control experiment, and their percentage contributions to k_obs were 41.31% and 34.45%, respectively. In addition, Cl· and Cl₂^-· together contributed 22% to the k_obs. Furthermore, the contribution of ozone to the IPM removal could be neglected. The concentrations of these species increased significantly when the concentration of NaClO was increased from 50 µM to 200 µM, while the percentage contribution of ClO· to k_obs was greatly increased. The concentrations and percentage contributions of HO· and ClO· decreased significantly as the solution pH increased from 5 to 9, with Cl₂^-· playing a greater role in the degradation of IPM under alkaline conditions. While Cl^- or HCO₃^-/CO₃^2- significantly promoted the generation of Cl₂^-· or CO₃^-·, neither had an obvious effect on k_obs, suggesting that Cl₂^-· and CO₃^-· should have a certain reactivity with IPM. Compared with that of Cl₂^-·, the percentage contribution of ClO· and Cl· to k_obs was more likely to be inhibited by NOM. In addition, the organic and inorganic oxidation products of IPM were detected. The oxidation mechanisms of IPM degradation in the UV₃₆₅/NaClO system, such as the H-extraction reaction, deiodination, substitution reaction, amide hydrolysis, and amine oxidation, were proposed according to the obtained 15 organic products. No effect on acute toxicity towards Vibrio fischeri and Photobacterium phosphoreum was detected during the oxidation of IPM by the UV₃₆₅/NaClO system. Furthermore, the engineering feasibility of the oxidation system was demonstrated, by the effective degradation of IPM in actual water. However, HOI rapidly accumulated during the removal of IPM in the UV₃₆₅/NaClO system, which poses certain environmental risks and will needs to be investigated.

Nitrogen-doped carbon nanosheets with Fe-based nanoparticles for highly efficient degradation of antibiotics and sulfate ion enhancement effect

Developing Fe-based catalysts with high-effective and environmentally friendly features in Fenton-like system for treating wastewater is still a challenge. Novel nitrogen-doped carbon nanosheets with Fe⁰/Fe₃C nano-particles (Fe@NCS-900) were prepared through a simple solvent-free strategy by pyrolyzing the mixture of 2,6-diaminopyridine and ferric chloride hexahydrate under 900 °C. The Fe@NCS-900 possessed almost 100% removal efficiency and 66.5% mineralization rate for the degradation of CBZ in 10 min. Moreover, the Fe@NCS-900 exhibited an apparent first-order constant as high as 0.8809 min^-1, which is 22 and 29 times higher than that of the commercial Fe⁰ and traditional Fenton system, respectively, which could be attribute to the high graphitization degree and rich nitrogen content. Besides, the results of the radical quenching experiments, electron paramagnetic resonance (EPR) and the probe experiments demonstrated that a large number of high valent iron species (Fe (IV)) besides singlet oxygen (¹O₂) and superoxide radicals (O₂^•-) existed and contributed to the CBZ degradation. More interestingly, the addition of coexisting anion SO₄^2- in the reaction system could significantly boost the concentration of •OH and SO₄^•- by 28.3 times and 9.7 times, respectively, resulting in the increase of the apparent first-order constant by 5.9 times (5.1733 min^-1), which was entirely different from previous reports that SO₄^2- had no effect on the catalytic activity or even displayed slightly inhibitory effect. In addition, the catalyst exhibited broad pH adaptability in the pH range of 2-9. The intermediate products of CBZ degradation were investigated by liquid chromatography mass spectrometry (LC-MS) and the degradation pathway was proposed. This paper provides new insights for developing a promising Fe-based nitrogen-doped catalyst for practical wastewater treatment.

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.

Feasibility of micropollutants removal by solar-activated persulfate: Reactive oxygen species formation and influence on DBPs

As a natural source of visible light and a type of renewable energy, solar energy is extensively used in the field of photochemistry. In this study, solar was employed to activate persulfate (PS) to degrade typical micropollutants. The removal kinetics of aspirin (ASA) and flunixin meglumine (FMME) in the solar/PS system were well fitted by pseudo-first-order models (R² > 0.99). In the system containing 1.0 mM PS activated by solar irradiation at a fluence of 1.14 × 10^-4 E·m^-2·s^-1, 72.6% and 97.5% of ASA and FMME were degraded, and the corresponding kinetic constants were 6.8-9.8 × 10^-2 and 1.6-9.8 × 10^-1 min^-1, respectively. Qualitative and quantitative analyses of the reactive oxygen species (ROS) indicated that sulfate radical (SO₄^·-) played a major role in degradation, with the maximum contributions of 77.7% and 88.8% for the degradation of ASA and FMME, whereas the maximum contributions of hydroxyl radical (·OH) were only 11.6% and 6.5%, respectively. The contributions of singlet oxygen (¹O₂) were less than 15% at pH 5.5, but increased to 25.6% and 45.5% at pH 8.5, respectively. Solar/PS pre-oxidation increased disinfection byproducts (DBPs) (95.8% for trihalomethanes (THMs) and 47.9% for haloacetic acids (HAAs) at pH 7.0) after chlorination in deionized water, and an opposite trend was found in systems coexisting with natural organic matter (NOM). Residual PS after oxidation resulted in a high aquatic toxicity, with an inhibition rate of 18.70% to algae growth. Economic analysis showed that the electrical energy per order values of the system ranged from 23.5 to 86.5 kWh·m^-3·order^-1, indicating that the solar/PS system shows promise for practical applications.

Photo-Fenton-like degradation of antibiotics by inverse opal WO3 co-catalytic Fe2+/PMS, Fe2+/H2O2 and Fe2+/PDS processes: A comparative study

Advanced oxidation processes (AOPs) such as Fenton and Fenton-like process for pollutant removal have been widely reported. However, most papers choose one of the popular oxidants (H₂O₂, peroxymonosulfate (PMS) or peroxydisulfate (PDS)) as the oxidant via AOPs for pollutant degradation. The purpose of this work is to compare the degradation rates of the Fe²⁺/PMS, Fe²⁺/H₂O₂ and Fe²⁺/PDS processes. Furthermore, to solve the problem of slow regeneration of Fe²⁺, the visible light irradiation and inverse opal WO₃ cocatalyst were added to the Fenton/Fenton-like process. The IO WO₃ co-catalytic visible light assisted Fe²⁺/PMS, Fe²⁺/H₂O₂ and Fe²⁺/PDS processes greatly improved the degradation efficiency of norfloxacin (NOR), reaching about 30 times, 9 times and 12 times that of the homogeneous Fenton/Fenton-like process, respectively. On average, the TOC removal rates of PMS-based, H₂O₂-based and PMS-based processes for the five pollutants were 71.6%, 54.0%, and 59.6% within 60 min, and the corresponding co-catalyst treatment efficiencies were 0.215 mmol/g/h, 0.162 mmol/g/h, and 0.179 mmol/g/h, respectively. ¹O₂ and •O₂^- have been proven to play a vital role in the degradation of NOR via all the three IO WO₃ co-catalytic photo-Fenton-like processes. In addition, the effects of different reaction parameters on the activity of degrading norfloxacin were explored. The IO WO₃ co-catalytic visible light assisted Fe²⁺/PMS, Fe²⁺/H₂O₂ and Fe²⁺/PDS processes for removal of different persistent organic pollutants and norfloxacin in different actual wastewater have also been studied. Nonetheless, this study proves that IO WO₃ co-catalytic visible light assisted Fe²⁺/PMS, Fe²⁺/H₂O₂ and Fe²⁺/PDS processes could effectively remove antibiotics from wastewater.

Simultaneous mitigation of disinfection by-product formation and odor compounds by peroxide/Fe(II)-based process: Combination of oxidation and coagulation

To remove disinfection by-product (DBP) precursors and mitigate odor compounds, peroxide (peroxymonosulfate and persulfate)/Fe(II)-based process was applied as a combination of coagulation and oxidation. Compared with traditional Fe-based salt coagulation (FeSO₄ and FeCl₃), peroxide/Fe(II)-based process was more efficient in dissolved organic carbon, UV₂₅₄ and turbidity removal, and peroxymonosulfate showed better performance than persulfate. The better coagulation performance arose from a combination of enhanced neutralization and different characteristics of flocs. Even though the combined process would increase the bromine substitution factor of DBPs, DBP formation and DBP-associated toxicity after peroxide/Fe(II)-based process were 9.2-38.8% and 5.2-27.2% lower than that after conventional Fe(III) coagulation. Both enhanced dissolved organic matter removal and oxidation of DBP precursors played vital roles in DBP control. Conventional Fe-based salt coagulation could hardly remove odor compounds (less than 10%, generally), whereas 28.2-84.9% of odor compounds were degraded during peroxide/Fe(II)-based process, due to free radical formation. This study demonstrated that PMS/Fe(II)-based process might be a promising treatment process for simultaneous DBP control and odor removal in source water.