RESUMO
The absolute radical quantum yield (Φ) is a critical parameter to evaluate the efficiency of radical-based processes in engineered water treatment. However, measuring Φ is fraught with challenges, as current quantification methods lack selectivity, specificity, and anti-interference capabilities, resulting in significant error propagation. Herein, we report a direct and reliable time-resolved technique to determine Φ at pH 7.0 for commonly used radical precursors in advanced oxidation processes. For H2O2 and peroxydisulfate (PDS), the values of Φâ¢OH and ΦSO4â¢- at 266 nm were measured to be 1.10 ± 0.01 and 1.46 ± 0.05, respectively. For peroxymonosulfate (PMS), we developed a new approach to determine Φâ¢OHPMS with terephthalic acid as a trap-and-trigger probe in the nonsteady state system. For the first time, the Φâ¢OHPMS value was measured to be 0.56 by the direct method, which is stoichiometrically equal to ΦSO4â¢-PMS (0.57 ± 0.02). Additionally, radical formation mechanisms were elucidated by density functional theory (DFT) calculations. The theoretical results showed that the highest occupied molecular orbitals of the radical precursors are O-O antibonding orbitals, facilitating the destabilization of the peroxy bond for radical formation. Electronic structures of these precursors were compared, aiming to rationalize the tendency of the Φ values we observed. Overall, this time-resolved technique with specific probes can be used as a reliable tool to determine Φ, serving as a scientific basis for the accurate performance evaluation of diverse radical-based treatment processes.
Assuntos
Radical Hidroxila , Sulfatos , Sulfatos/química , Radical Hidroxila/química , Purificação da Água/métodos , Oxirredução , Peróxido de Hidrogênio/químicaRESUMO
Dissolved organic matter (DOM) has a dual role in indirect phototransformations of aquatic contaminants by acting both as a photosensitizer and an inhibitor. Herein, the pH dependence of the inhibitory effect of DOM and the underlying mechanisms were studied in more than 400 kinetic irradiation experiments over the pH range of 6-11. Experiments employed various combinations of one of three DOM isolates, one of two model photosensitizers, the model antioxidant phenol, and one of nine target compounds (TCs), comprising several aromatic amines, in particular anilines and sulfonamides, and 4-cyanophenol. Using model photosensitizers without antioxidants, the phototransformation of most TCs increased with increasing pH, even for TCs for which pH did not affect speciation. This trend was attributed to pH-dependent formation yields of TC-derived radicals and their re-formation to the parent TC. Analogous trends were observed with DOM as a photosensitizer. Comparison of model and DOM photosensitizer data sets showed increasing inhibitory effects of DOM on TC phototransformation kinetics with increasing pH. In systems with anilines as a TC and phenol as a model antioxidant, pH trends of the inhibitory effect could be rationalized based on the reduction potential difference (ΔEred) of phenoxyl/phenol and anilinyl/aniline couples. Our results indicate that the light-induced transformation of aromatic amines in the aquatic environment is governed by the pH-dependent inhibitory effects of antioxidant phenolic moieties of DOM and pH-dependent processes related to the formation of amine oxidation intermediates.
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Poluentes Ambientais , Poluentes Químicos da Água , Concentração de Íons de Hidrogênio , Cinética , Oxirredução , Fotólise , Poluentes Químicos da Água/análiseRESUMO
Azulene is a bicyclic aromatic chromophore that absorbs in the visible region. Its absorption maximum undergoes a hypsochromic shift if a conjugated electron-withdrawing group is introduced at the C1 position. This fact can be exploited in the design of a colorimetric chemodosimeter that functions by the transformation of a dithioacetal to the corresponding aldehyde upon exposure to Hg2+ ions. This chemodosimeter exhibits good chemoselectivity over other metal cations, and responds with an unambiguous colour change clearly visible to the naked eye. Its synthesis is concise and its ease of use makes it appropriate in resource-constrained environments, for example in determing mercury content of drinking water sources in the developing world.
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Two-photon fluorescence microscopy has become an indispensable technique for cellular imaging. Whereas most two-photon fluorescent probes rely on well-known fluorophores, here we report a new fluorophore for bioimaging, namely azulene. A chemodosimeter, comprising a boronate ester receptor motif conjugated to an appropriately substituted azulene, is shown to be an effective two-photon fluorescent probe for reactive oxygen species, showing good cell penetration, high selectivity for peroxynitrite, no cytotoxicity, and excellent photostability.
Assuntos
Azulenos/química , Corantes Fluorescentes/química , Microscopia de Fluorescência por Excitação Multifotônica/métodos , Espécies Reativas de Nitrogênio/análise , Espécies Reativas de Oxigênio/análise , Azulenos/toxicidade , Sobrevivência Celular/efeitos dos fármacos , Corantes Fluorescentes/toxicidade , Células HeLa , Humanos , Limite de DetecçãoRESUMO
Dissolved organic matter (DOM) is a natural photosensitizer that contributes to the inactivation of microbial pathogens. In constructed treatment wetlands with open water areas DOM can promote sunlight disinfection of wastewater effluent, but a better understanding of DOM spectroscopic and photochemical properties and how they are impacted by different unit process wetlands is needed to inform design. The goals of this study were: (1) to investigate whether DOM isolates realistically represent the photochemistry of the source DOM in its original water and (2) to observe how changes of DOM along a treatment wetland affect its photochemistry, including pathogen inactivation. A pilot scale unit process wetland was studied that consisted of three different cells (open water, cattail, and bulrush) fed by secondary wastewater effluent. DOM was isolated using solid-phase extraction (SPE), photochemically characterized, and compared to the original water samples and standard DOMs. For MS2 coliphage, a virus indicator, the most efficient photosensitizer was the wastewater DOM isolated from the influent of the wetland, while for the bacterial indicator Enterococcus faecalis, inactivation results were comparable across wetland isolates. SPE resulted in isolation of 47% to 59% of whole water DOM and enriched for colored DOM. Singlet oxygen precursors were efficiently isolated, while some excited triplet state precursors remained in the extraction discharge. DOM processing indicators such as SUVA254, SUVA280, and spectral slopes including E2/ E3 ratios were reflected in the isolates. Photoinactivation of MS2 was significantly lower in both the reconstituted water samples and isolates compared to the original water sample, possibly due to disturbance of the trans-molecular integrity of DOM molecules by SPE that affects distance between MS2 and DOM sites with locally higher singlet oxygen production. For E. faecalis, results were similar in original water samples and isolates. Higher sorption of DOM to E. faecalis was roughly correlated with higher photoinactivation rates. To enhance sunlight disinfection in unit process wetlands, there is no advantage to placing open water cells after vegetated cells, as passage through the vegetated cells led to increased light absorption and lower singlet oxygen and triplet-state quantum yields and steady state concentrations.
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Fármacos Fotossensibilizantes , Áreas Alagadas , Oxigênio Singlete , Luz Solar , Águas ResiduáriasRESUMO
As water scarcity intensifies, point-of-use and point-of-entry treatment may provide a means of exploiting locally available water resources that are currently considered to be unsafe for human consumption. Among the different classes of drinking water contaminants, toxic trace elements (e.g., arsenic and lead) pose substantial operational challenges for distributed drinking water treatment systems. Removal of toxic trace elements via adsorption onto iron oxides is an inexpensive and robust treatment method; however, the presence of metal-complexing ligands associated with natural organic matter (NOM) often prevents the formation of iron precipitates at the relatively low concentrations of dissolved iron typically present in natural water sources, thereby requiring the addition of iron which complicates the treatment process and results in a need to dispose of relatively large amounts of accumulated solids. A point-of-use treatment device consisting of a cathodic cell that produced hydrogen peroxide (H2O2) followed by an ultraviolet (UV) irradiation chamber was used to decrease colloid stabilization and metal-complexing capacity of NOM present in groundwater. Exposure to UV light altered NOM, converting â¼6 µM of iron oxides into settable forms that removed between 0.5 and 1 µM of arsenic (As), lead (Pb), and copper (Cu) from solution via adsorption. After treatment, changes in NOM consistent with the loss of iron-complexing carboxylate ligands were observed, including decreases in UV absorbance and shifts in the molecular composition of NOM to higher H/C and lower O/C ratios. Chronoamperometric experiments conducted in synthetic groundwater revealed that the presence of Ca2+ and Mg2+ inhibited intramolecular charge-transfer within photoexcited NOM, leading to substantially increased removal of iron and trace elements.
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Água Potável , Oligoelementos , Poluentes Químicos da Água , Purificação da Água , Humanos , Peróxido de Hidrogênio , Fotólise , Diálise RenalRESUMO
It is presently unknown to what extent the endogenous direct, endogenous indirect, and exogenous indirect mechanisms contribute to bacterial photoinactivation in natural surface waters. In this study, we investigated the importance of the exogenous indirect mechanism by conducting photoinactivation experiments with eight health-relevant bacterial species (Bacteroides thetaiotaomicron, Campylobacter jejuni, Enterococcus faecalis, Escherichia coli K12, E. coli O157:H7, Salmonella enterica serovar Typhimurium LT2, Staphylococcus aureus, and Streptococcus bovis). We used three synthetic photosensitizers (methylene blue, rose bengal, and nitrite) and two model natural photosensitizers (Suwannee River natural organic matter and dissolved organic matter isolated from a wastewater treatment wetland) that generated singlet oxygen and hydroxyl radical. B. thetaiotaomicron had larger first order rate constants than all other organisms under all conditions tested. The presence of the synthetic photosensitizers generally enhanced photoinactivation of Gram-positive facultative anaerobes (Ent. faecalis, Staph. aureus, and Strep. bovis). Among Gram-negative bacteria, only methylene blue with E. coli K12 and rose bengal with C. jejuni showed an enhancing effect. The presence of model natural photosensitizers either reduced or did not affect photoinactivation rate constants. Our findings highlight the importance of the cellular membrane and photosensitizer properties in modulating the contribution of the exogenous indirect mechanism to the overall bacterial photoinactivation.
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Bactérias Gram-Negativas , Staphylococcus aureus , Azul de Metileno/química , Fármacos Fotossensibilizantes/química , Rosa BengalaRESUMO
Dissolved organic matter (DOM) is both a promoter and an inhibitor of triplet-induced organic contaminant oxidation. This dual role was systematically investigated through photochemical experiments with three types of DOM of terrestrial and aquatic origins that were preoxidized to varying extents by ozonation. The inhibitory effect of DOM was assessed by determining the 4-carboxybenzophenone photosensitized transformation rate constants of two sulfonamide antibiotics (sulfamethoxazole and sulfadiazine) in the presence of untreated or preoxidized DOM. The inhibitory effect decreased with the increasing extent of DOM preoxidation, and it was correlated to the loss of phenolic antioxidant moieties, as quantified electrochemically, and to the loss of DOM ultraviolet absorbance. The triplet photosensitizing ability of preoxidized DOM was determined using the conversion of the probe compound 2,4,6-trimethylphenol (TMP), which is unaffected by DOM inhibition effects. The DOM photosensitized transformation rate constants of TMP decreased with increasing DOM preoxidation and were correlated to the concomitant loss of chromophores (i.e., photosensitizing moieties). The combined effects of DOM preoxidation on the inhibiting and photosensitizing properties were assessed by phototransformation experiments of the sulfonamides in DOM-containing solutions. At low extents of DOM preoxidation, the sulfonamide phototransformation rate constants remained either unchanged or slightly increased, indicating that the removal of antioxidant moieties had larger effects than the loss of photosensitizing moieties. At higher extents of DOM preoxidation, transformation rates declined, mainly reflecting the destruction of photosensitizing moieties.
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Compostos Orgânicos/química , Ozônio/química , Processos Fotoquímicos , Poluentes Químicos da Água/análise , Benzofenonas/química , Elétrons , Cinética , Oxirredução , Fenóis/química , Solubilidade , Sulfadiazina/química , Sulfametoxazol/químicaRESUMO
The fate of anthropogenic trace organic contaminants in surface waters can be complex due to the occurrence of multiple parallel and consecutive transformation processes. In this study, the removal of five antiviral drugs (abacavir, acyclovir, emtricitabine, lamivudine and zidovudine) via both bio- and phototransformation processes, was investigated in laboratory microcosm experiments simulating an open-water unit process wetland receiving municipal wastewater effluent. Phototransformation was the main removal mechanism for abacavir, zidovudine, and emtricitabine, with half-lives (t1/2,photo) in wetland water of 1.6, 7.6, and 25 h, respectively. In contrast, removal of acyclovir and lamivudine was mainly attributable to slower microbial processes (t1/2,bio = 74 and 120 h, respectively). Identification of transformation products revealed that bio- and phototransformation reactions took place at different moieties. For abacavir and zidovudine, rapid transformation was attributable to high reactivity of the cyclopropylamine and azido moieties, respectively. Despite substantial differences in kinetics of different antiviral drugs, biotransformation reactions mainly involved oxidation of hydroxyl groups to the corresponding carboxylic acids. Phototransformation rates of parent antiviral drugs and their biotransformation products were similar, indicating that prior exposure to microorganisms (e.g., in a wastewater treatment plant or a vegetated wetland) would not affect the rate of transformation of the part of the molecule susceptible to phototransformation. However, phototransformation strongly affected the rates of biotransformation of the hydroxyl groups, which in some cases resulted in greater persistence of phototransformation products.
Assuntos
Fenômenos Microbiológicos , Fotoquímica , Água/química , Áreas Alagadas , Aciclovir , Antivirais/química , Biodegradação Ambiental , Biotransformação , Concentração de Íons de Hidrogênio , Cinética , Teoria Quântica , Águas Residuárias/química , Poluentes Químicos da Água/análiseRESUMO
Sunlight inactivation is an important mode of disinfection for viruses in surface waters. In constructed wetlands, for example, open-water cells can be used to promote sunlight disinfection and remove pathogenic viruses from wastewater. To aid in the design of these systems, we developed predictive models of virus attenuation that account for endogenous and exogenous sunlight-mediated inactivation mechanisms. Inactivation rate models were developed for two viruses, MS2 and poliovirus type 3; laboratory- and field-scale experiments were conducted to evaluate the models' ability to estimate inactivation rates in a pilot-scale, open-water, unit-process wetland cell. Endogenous inactivation rates were modeled using either photoaction spectra or total, incident UVB irradiance. Exogenous inactivation rates were modeled on the basis of virus susceptibilities to singlet oxygen. Results from both laboratory- and field-scale experiments showed good agreement between measured and modeled inactivation rates. The modeling approach presented here can be applied to any sunlit surface water and utilizes easily measured inputs such as depth, solar irradiance, water matrix absorbance, singlet oxygen concentration, and the virus-specific apparent second-order rate constant with singlet oxygen (k2). Interestingly, the MS2 k2 in the open-water wetland was found to be significantly larger than k2 observed in other waters in previous studies. Examples of how the model can be used to design and optimize natural treatment systems for virus inactivation are provided.
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Modelos Biológicos , Luz Solar , Inativação de Vírus/efeitos da radiação , Vírus/efeitos da radiação , Purificação da Água/métodos , Raios Ultravioleta , Águas Residuárias/virologiaRESUMO
Two aquatic fulvic acids and one soil humic acid were irradiated to examine the resulting changes in the redox and photochemical properties of the humic substances (HS), the relationship between these changes, and their relationship to changes in the optical properties. For all HS, irradiation caused photooxidation, as shown by decreasing electron donating capacities. Photooxidation was accompanied by decreases in specific UV absorbance and increases in the E2/E3 ratio (254 nm absorbance divided by that at 365 nm). In contrast, photooxidation had little effect on the samples' electron accepting capacities. The coupled changes in optical and redox properties for the different HS suggest that phenols are an important determinant of aquatic HS optical properties and that quinones may play a more important role in soil HS. Apparent quantum yields of H2O2, ·OH, and triplet HS decreased with photooxidation, thus demonstrating selective destruction of HS photosensitizing chromophores. In contrast, singlet oxygen ((1)O2) quantum yields increased, which is ascribed to either decreased (1)O2 quenching within the HS microenvironment or the presence of a pool of photostable sensitizers. The photochemical properties show clear trends with SUVA and E2/E3, but the trends differ substantially between aquatic and soil HS. Importantly, photooxidation produces a relationship between the (1)O2 quantum yield and E2/E3 that differs distinctly from that observed with untreated HS. This finding suggests that there may be watershed-specific correlations between HS chemical and optical properties that reflect the dominant processes controlling the HS character.
Assuntos
Benzopiranos/química , Substâncias Húmicas , Benzopiranos/efeitos da radiação , Substâncias Húmicas/análise , Peróxido de Hidrogênio/química , Oxirredução , Fotodegradação , Processos Fotoquímicos , Oxigênio Singlete/química , Solo/química , Espectrofotometria UltravioletaRESUMO
Chlorite (ClO2-) is a regulated byproduct of chlorine dioxide water treatment processes. The transformation of chlorite under UV irradiation into chloride (Cl-) and chlorate (ClO3-) involves reactive species chain reactions that could enhance chlorine dioxide water treatment efficiency while reducing residual chlorite levels. This study conducted a mechanistic investigation of chlorite phototransformation by analyzing reaction intermediates and stable end products, including chlorine dioxide (ClO2), free chlorine (HOCl/OCl-), hydroxylradical (â¢OH), Cl-, and ClO3- through combined experimental and modeling approaches. Experiments were performed at UV254 irradiation in pure buffered water within the pH range of 6 to 8. Results indicated that the apparent quantum yields for chlorite phototransformation increased from 0.86 to 1.45, and steady-state â¢OH concentrations at 1 mM initial chlorite concentration rose from 8.16 × 10-14 M - 16.1 × 10-14 M with decreasing pH values. It was observed that under UV irradiation, chlorite acts as both a significant producer and consumer of reactive species through three distinct reaction pathways. The developed kinetic model, which incorporates optimized intrinsic chlorite quantum yields Φchloritein ranging from 0.33 to 0.39, effectively simulated the loss of oxidants and the formation of major products. It also accurately predicted steady-state concentrations of various species, including â¢OH, â¢ClO, Cl⢠and O3. For the first time, this study provides a comprehensive transformation pathway scheme for chlorite phototransformation. The findings offer important insights into the mechanistic aspects of product and oxidizing species formation during chlorite phototransformation.
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Advanced oxidation processes (AOPs) are a growing research field with a large variety of different process variants and materials being tested at laboratory scale. However, despite extensive research in recent years and decades, many variants have not been transitioned to pilot- and full-scale operation. One major concern are the inconsistent experimental approaches applied across different studies that impede identification, comparison, and upscaling of the most promising AOPs. The aim of this tutorial review is to streamline future studies on the development of new solutions and materials for advanced oxidation by providing guidance for comparable and scalable oxidation experiments. We discuss recent developments in catalytic, ozone-based, radiation-driven, and other AOPs, and outline future perspectives and research needs. Since standardized experimental procedures are not available for most AOPs, we propose basic rules and key parameters for lab-scale evaluation of new AOPs including selection of suitable probe compounds and scavengers for the measurement of (major) reactive species. A two-phase approach to assess new AOP concepts is proposed, consisting of (i) basic research and proof-of-concept (technology readiness levels (TRL) 1-3), followed by (ii) process development in the intended water matrix including a cost comparison with an established process, applying comparable and scalable parameters such as UV fluence or ozone consumption (TRL 3-5). Subsequent demonstration of the new process (TRL 6-7) is briefly discussed, too. Finally, we highlight important research tools for a thorough mechanistic process evaluation and risk assessment including screening for transformation products that should be based on chemical logic and combined with complementary tools (mass balance, chemical calculations).
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Free-living (FL) and particulate-associated (PA) communities are distinct bacterioplankton lifestyles with different mobility and dissemination routes. Understanding spatio-temporal dynamics of PA and FL fractions will allow improvement to wastewater treatment processes including pathogen and AMR bacteria removal. In this study, PA, FL and sediment community composition and antimicrobial resistance gene (ARG; tetW, ermB, sul1, intI1) dynamics were investigated in a full-scale municipal wastewater free-water surface polishing constructed wetland. Taxonomic composition of PA and FL microbial communities shifted towards less diverse communities (Shannon, Chao1) at the CW effluent but retained a distinct fraction-specific composition. Wastewater treatment plant derived PA communities introduced the bulk of AMR load (70 %) into the CW. However, the FL fraction was responsible for exporting over 60 % of the effluent AMR load given its high mobility and the effective immobilization (1-3 log removal) of PA communities. Strong correlations (r2>0.8, p < 0.05) were observed between the FL fraction, tetW and emrB dynamics, and amplicon sequence variants (ASVs) of potentially pathogenic taxa, including Bacteroides, Enterobacteriaceae, Aeromonadaceae, and Lachnospiraceae. This study reveals niche differentiation of microbial communities and associated AMR in CWs and shows that free-living bacteria are a primary escape route of pathogenic and ARG load from CWs under low-flow hydraulic conditions.
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Microbiota , Áreas Alagadas , Antibacterianos/farmacologia , Farmacorresistência Bacteriana , Águas Residuárias , Bactérias/genética , Eliminação de Resíduos LíquidosRESUMO
The combination of urbanization and global warming leads to urban overheating and compounds the frequency and intensity of extreme heat events due to climate change. Yet, the risk of urban overheating can be mitigated by urban green-blue-grey infrastructure (GBGI), such as parks, wetlands, and engineered greening, which have the potential to effectively reduce summer air temperatures. Despite many reviews, the evidence bases on quantified GBGI cooling benefits remains partial and the practical recommendations for implementation are unclear. This systematic literature review synthesizes the evidence base for heat mitigation and related co-benefits, identifies knowledge gaps, and proposes recommendations for their implementation to maximize their benefits. After screening 27,486 papers, 202 were reviewed, based on 51 GBGI types categorized under 10 main divisions. Certain GBGI (green walls, parks, street trees) have been well researched for their urban cooling capabilities. However, several other GBGI have received negligible (zoological garden, golf course, estuary) or minimal (private garden, allotment) attention. The most efficient air cooling was observed in botanical gardens (5.0 ± 3.5°C), wetlands (4.9 ± 3.2°C), green walls (4.1 ± 4.2°C), street trees (3.8 ± 3.1°C), and vegetated balconies (3.8 ± 2.7°C). Under changing climate conditions (2070-2100) with consideration of RCP8.5, there is a shift in climate subtypes, either within the same climate zone (e.g., Dfa to Dfb and Cfb to Cfa) or across other climate zones (e.g., Dfb [continental warm-summer humid] to BSk [dry, cold semi-arid] and Cwa [temperate] to Am [tropical]). These shifts may result in lower efficiency for the current GBGI in the future. Given the importance of multiple services, it is crucial to balance their functionality, cooling performance, and other related co-benefits when planning for the future GBGI. This global GBGI heat mitigation inventory can assist policymakers and urban planners in prioritizing effective interventions to reduce the risk of urban overheating, filling research gaps, and promoting community resilience.
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Excited triplet states of aromatic ketones and quinones are used as proxies to assess the reactivity of excited triplet states of the dissolved organic matter ((3)DOM*) in natural waters. (3)DOM* are crucial transients in environmental photochemistry responsible for contaminant transformation, production of reactive oxygen species, and potentially photobleaching of DOM. In recent photochemical studies aimed at clarifying the role of DOM as an inhibitor of triplet-induced oxidations of organic contaminants, aromatic ketones have been used in the presence of DOM, and the question of a possible interaction between their excited triplet states and DOM has emerged. To clarify this issue, time-resolved laser spectroscopy was applied to measure the excited triplet state quenching of four different model triplet photosensitizers induced by a suite of DOM from various aquatic and terrestrial sources. While no quenching for the anionic triplet sensitizers 4-carboxybenzophenone (CBBP) and 9,10-anthraquinone-2,6-disulfonic acid (2,6-AQDS) was detected, second-order quenching rate constants with DOM for the triplets of 2-acetonaphthone (2AN) and 3-methoxyacetophenone (3MAP) in the range of 1.30-3.85 × 10(7) L mol(C)(-1) s(-1) were determined. On the basis of the average molecular weight of DOM molecules, the quenching for these uncharged excited triplet molecules is nearly diffusion-controlled, but significant quenching (>10%) in aerated water is not expected to occur below DOM concentrations of 22-72 mg(C) L(-1).
Assuntos
Conformação Molecular , Compostos Orgânicos/química , Absorção Fisico-Química , Antraquinonas/química , Benzofenonas/química , Soluções Tampão , Concentração de Íons de Hidrogênio , Cinética , Fotoquímica , Fármacos Fotossensibilizantes/química , Solubilidade , Análise Espectral , Água/químicaRESUMO
In water treatment dissolved organic matter (DOM) is typically the major sink for chemical oxidants. The resulting changes in DOM, such as its optical properties have been measured to follow the oxidation processes. However, such measurements contain only limited information on the changes in the oxidation states of and the reactive moieties in the DOM. In this study, we used mediated electrochemical oxidation to quantify changes in the electron donating capacities (EDCs), and hence the redox states, of three different types of DOM during oxidation with chlorine dioxide (ClO2), chlorine (as HOCl/OCl(-)), and ozone (O3). Treatment with ClO2 and HOCl resulted in comparable and prominent decreases in EDCs, while the UV light absorbances of the DOM decreased only slightly. Conversely, ozonation resulted in only small decreases of the EDCs but pronounced absorbance losses of the DOM. These results suggest that ClO2 and HOCl primarily reacted as oxidants by accepting electrons from electron-rich phenolic and hydroquinone moieties in the DOM, while O3 reacted via electrophilic addition to aromatic moieties, followed by ring cleavage. This study highlights the potential of combined EDC-UV measurements to monitor chemical oxidation of DOM, to assess the nature of the reactive moieties and to study the underlying reaction pathways.
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Antioxidantes/química , Benzopiranos/química , Compostos Clorados/química , Cloro/química , Substâncias Húmicas , Óxidos/química , Ozônio/química , Oxirredução , Purificação da ÁguaRESUMO
[This corrects the article DOI: 10.1039/D2RA06730G.].
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ZnO is a widely studied photocatalyst, but practical use is hindered by its low resistance to photocorrosion in water, which leads to metal leaching and loss of performance over time. In this work, highly porous and mechanically stable ZnO foams, called MolFoams, were doped by adding 1% or 2% Co, Ni or Cu salts to the starting Zn salt, followed by air insufflation during a sol-gel rection and sintering. The resulting doped foams showed a major increase in stability, with a 60-85% reduction in Zn2+ leaching after irradiation, albeit with a reduction in photocatalytic activity. A systematic analysis using XRD, Raman, XPS and XANES allowed for the identification of dopant species in the foams revealing the presence of Co3O4, NiO and Cu2O within the ZnO lattice with doping leading to a reduced band gap and significant increases in the resistance to photocorrosion of ZnO while identifying the cause of the reduction in photocatalytic activity to be shifting of the band edge positions. These results provide a pathway to significantly reduce the photocorrosion of ZnO in water, with further work required to maintain the photocatalytic activity of undoped ZnO.
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This study investigates microplastic (MPs) dynamics of a recently established surface flow 2100 population equivalent polishing constructed wetland (CW) receiving 1.4 ML per day of secondary treated wastewater. MPs type, size ranges and concentrations were measured along the CW at a 2-months sampling campaign. The CW received an average of 5·106 MPs per day (6 MPs per liter), mostly 100-1000 µm-sized synthetic fibers followed by fragments in the same size range. 95 % of MPs were retained, resulting in 0.30 ± 0.09 MPs per liter in CW effluent. Most MPs (97 %) were trapped within the first 20 % of the CW which consisted of a settling pond and shallow vegetated treatment cells and provided an areal removal rate > 4000 MP m-2 d-1. Data and microscopic analysis indicate MPs erosion and fragmentation in the CW. Turbidity and suspended solids were no indicator for MP removal due to water fowl activity, algal growth, and preferential flow conditions. This is the first study on MP dynamics in an independently operating full scale free water surface CW incorporated into a municipal wastewater treatment scheme. Surface flow CWs can retain MPs effectively but accumulation in CW sediments and substrate needs to be considered when further utilized or recycled.