array(23 items)0 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=22653, pid=124)originalId => protected22653 (integer)
authors => protected'Gulde, R.; Rutsch, M.; Clerc, B.; Schollée, J. E.; von Gunten, U.; McArdell, C. S.' (123 chars)
title => protected'Formation of transformation products during ozonation of secondary wastewate r effluent and their fate in post-treatment: from laboratory- to full-scale' (151 chars)
journal => protected'Water Research' (14 chars)
year => protected2021 (integer)
volume => protected200 (integer)
issue => protected'' (0 chars)
startpage => protected'117200 (16 pp.)' (15 chars)
otherpage => protected'' (0 chars)
categories => protected'ozone; granular activated carbon; powdered activated carbon; sand filter; mi cropollutants; structure elucidation' (112 chars)
description => protected'Ozonation is increasingly applied in water and wastewater treatment for the abatement of micropollutants (MPs). However, the transformation products for med during ozonation (OTPs) and their fate in biological or sorptive post-tr eatments is largely unknown. In this project, a high-throughput approach, co mbining laboratory ozonation experiments and detection by liquid chromatogra phy high-resolution mass spectrometry (LC-HR-MS/MS), was developed and appli ed to identify OTPs formed during ozonation of wastewater effluent for a lar ge number of relevant MPs (total 87). For the laboratory ozonation experimen ts, a simplified experimental solution, consisting of surrogate organic matt er (methanol and acetate), was created, which produced ozonation conditions similar to realistic conditions in terms of ozone and hydroxyl radical expos ures. The 87 selected parent MPs were divided into 19 mixtures, which enable d the identification of OTPs with an optimized number of experiments. The fo llowing two approaches were considered to identify OTPs. (1) A screening of LC-HR-MS signal formation in these experiments was performed and revealed a list of 1749 potential OTP candidate signals associated to 70 parent MPs. Th is list can be used in future suspect screening studies. (2) A screening was performed for signals that were formed in both batch experiments and in sam ples of wastewater treatment plants (WWTPs). This second approach was ultima tely more time-efficient and was applied to four different WWTPs with ozonat ion (specific ozone doses in the range 0.23-0.55 gO<sub>3</sub>/gDOC), leadi ng to the identification of 84 relevant OTPs of 40 parent MPs in wastewater effluent. Chemical structures could be proposed for 83 OTPs through the inte rpretation of MS/MS spectra and expert knowledge in ozone chemistry. Forty-e ight OTPs (58%) have not been reported previously. The fate of the verified OTPs was studied in different post-treatment steps. During sand filtration, 87-89% of the OTPs were ...' (2420 chars)
serialnumber => protected'0043-1354' (9 chars)
doi => protected'10.1016/j.watres.2021.117200' (28 chars)
uid => protected22653 (integer)
_localizedUid => protected22653 (integer)modified_languageUid => protectedNULL
_versionedUid => protected22653 (integer)modifiedpid => protected124 (integer)1 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=22256, pid=124)originalId => protected22256 (integer)
authors => protected'Wünsch, R.; Mayer, C.; Plattner, J.; Eugster, F.; Wüls er, R.; Gebhardt, J.; Hübner, U.; Canonica, S.; Wintgen s, T.; von Gunten, U.' (183 chars)
title => protected'Micropollutants as internal probe compounds to assess UV fluence and hydroxy l radical exposure in UV/H<sub>2</sub>O<sub>2</sub> treatment' (137 chars)
journal => protected'Water Research' (14 chars)
year => protected2021 (integer)
volume => protected195 (integer)
issue => protected'' (0 chars)
startpage => protected'116940 (13 pp.)' (15 chars)
otherpage => protected'' (0 chars)
categories => protected'OH-radical exposure; UV/H2O2 AOP; in-situ probe compounds; kinetic modeling; sensitivity analysis; water treatment' (114 chars)
description => protected'Organic micropollutants (MPs) are increasingly detected in water resources, which can be a concern for human health and the aquatic environment. Ultravi olet (UV) radiation based advanced oxidation processes (AOP) such as low-pre ssure mercury vapor arc lamp UV/H<sub>2</sub>O<sub>2</sub> can be applied to abate these MPs. During UV/H<sub>2</sub>O<sub>2</sub> treatment, MPs are ab ated primarily by photolysis and reactions with hydroxyl radicals (<sup>•< /sup>OH), which are produced <em>in situ</em> from H<sub>2</sub>O<sub>2</sub > photolysis. Here, a model is presented that calculates the applied UV flue nce (<em>H</em><sub>calc</sub>) and the <sup>•</sup>OH exposure (<em>CT</e m><sub>•OH,calc</sub> ) from the abatement of two selected MPs, which act as internal probe compounds. Quantification of the UV fluence and hydroxyl r adical exposure was generally accurate when a UV susceptible and a UV resist ant probe compound were selected, and both were abated at least by 50 %, e.g ., iopamidol and 5-methyl-1H-benzotriazole. Based on these key parameters a model was developed to predict the abatement of other MPs. The prediction of abatement was verified in various waters (sand filtrates of rivers Rhine an d Wiese, and a tertiary wastewater effluent) and at different scales (labora tory experiments, pilot plant). The accuracy to predict the abatement of oth er MPs was typically within ±20 % of the respective measured abatement. The model was further assessed for its ability to estimate unknown rate constan ts for direct photolysis (<em>k</em><sub>UV</sub>,<sub>MP</sub>) and reactio ns with <sup>•</sup>OH (<em>k</em>•<sub>OH</sub>,<sub>MP</sub>). In most cases, the estimated rate constants agreed well with published values, cons idering the uncertainty of kinetic data determined in laboratory experiments . A sensitivity analysis revealed that in typical water treatment applicatio ns, the precision of kinetic parameters (<em>k</em><sub>UV</sub>,<sub>MP</su b> for UV susceptible an...' (2086 chars)
serialnumber => protected'0043-1354' (9 chars)
doi => protected'10.1016/j.watres.2021.116940' (28 chars)
uid => protected22256 (integer)
_localizedUid => protected22256 (integer)modified_languageUid => protectedNULL
_versionedUid => protected22256 (integer)modifiedpid => protected124 (integer)2 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=21433, pid=124)originalId => protected21433 (integer)
authors => protected'Rougé, V.; von Gunten, U.; Allard, S.' (53 chars)
title => protected'Efficiency of pre-oxidation of natural organic matter for the mitigation of disinfection byproducts: electron donating capacity and UV absorbance as sur rogate parameters' (169 chars)
journal => protected'Water Research' (14 chars)
year => protected2020 (integer)
volume => protected187 (integer)
issue => protected'' (0 chars)
startpage => protected'116418 (10 pp.)' (15 chars)
otherpage => protected'' (0 chars)
categories => protected'electron donating capacity (EDC); chemical pre-oxidation; natural organic ma tter (NOM); disinfection byproduct (DBP); UV absorbance (UV 254); chlorine d isinfection' (163 chars)
description => protected'Pre-oxidation is often used before disinfection with chlorine to decrease th e reactivity of the water matrix and mitigate the formation of regulated dis infection byproducts (DBPs). This study provides insights on the impact of o xidative pre-treatment with chlorine dioxide (ClO<sub>2</sub>), ozone (O<sub >3</sub>), ferrate (Fe(VI)) and permanganate (Mn(VII)) on Suwannee River Nat ural Organic Matter (SRNOM) properties characterized by the UV absorbance at 254 nm (UV<sub>254</sub>) and the electron donating capacity (EDC). Change s in NOM reactivity and abatement of DBP precursors are also assessed. The i mpact of pre-oxidants (based on molar concentration) on UV<sub>254</sub> aba tement ranked in the order O<sub>3</sub> > Mn(VII) > Fe(VI)/ClO<sub>2< /sub>, while the efficiency of pre-oxidation on EDC abatement followed the o rder Mn(VII) > ClO<sub>2</sub> > Fe(VI) > O<sub>3</sub> and two pha ses were observed. At low specific ClO<sub>2</sub>, Fe(VI) and Mn(VII) doses corresponding to < 50% EDC abatement, a limited relative abatement of UV <sub>254</sub> compared to the EDC was observed (~ 8% EDC abatement per 1% U V<sub>254</sub> abatement). This suggests the oxidation of phenolic-type moi eties to quinone-type moieties which absorb UV<sub>254</sub> and don't contr ibute to EDC. At higher oxidant doses (> 50% EDC abatement), a similar ab atement of EDC and UV<sub>254</sub> (~ 0.9-1.2% EDC abatement per 1% UV<sub> 254</sub> abatement) suggested aromatic ring cleavage. In comparison to the other oxidants, O<sub>3</sub> abated the relative UV<sub>254</sub> more effe ctively, due to a more efficient cleavage of aromatic rings. For a pre-oxida tion with Mn(VII), ClO<sub>2</sub> and Fe(VI), similar correlations between the EDC abatement and the chlorine demand or the adsorbable organic halide ( AOX) formation were obtained. In contrast, O<sub>3</sub> pre-treatment led t o a lower chlorine demand and AOX formation for equivalent EDC abatement. Fo r all oxidants<sub>,</su...' (2360 chars)
serialnumber => protected'0043-1354' (9 chars)
doi => protected'10.1016/j.watres.2020.116418' (28 chars)
uid => protected21433 (integer)
_localizedUid => protected21433 (integer)modified_languageUid => protectedNULL
_versionedUid => protected21433 (integer)modifiedpid => protected124 (integer)3 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=21462, pid=124)originalId => protected21462 (integer)
authors => protected'Li, J.; Jiang, J.; Manasfi, T.; von Gunten, U.' (66 chars)
title => protected'Chlorination and bromination of olefins: kinetic and mechanistic aspects' (72 chars)
journal => protected'Water Research' (14 chars)
year => protected2020 (integer)
volume => protected187 (integer)
issue => protected'' (0 chars)
startpage => protected'116424 (12 pp.)' (15 chars)
otherpage => protected'' (0 chars)
categories => protected'free available chlorine (FAC); bromine (HOBr); olefin; chlorine (Cl2); chlor ine monoxide (Cl2O); bromine monoxide (Br2O)' (120 chars)
description => protected'Hypochlorous acid (HOCl) is typically assumed to be the primary reactive spe cies in free available chlorine (FAC) solutions. Lately, it has been shown t hat less abundant chlorine species such as chlorine monoxide (Cl<sub>2</sub> O) and chlorine (Cl<sub>2</sub>) can also influence the kinetics of the abat ement of certain organic compounds during chlorination. In this study, the c hlorination as well as bromination kinetics and mechanisms of 12 olefins (in cluding 3 aliphatic and 9 aromatic olefins) with different structures were e xplored. HOCl shows a low reactivity towards the selected olefins with speci es-specific second-order rate constants <1.0 M<sup>−1</sup>s<sup>−1</ sup>, about 4-6 orders of magnitude lower than those of Cl<sub>2</sub>O and Cl<sub>2</sub>. HOCl is the dominant chlorine species during chlorination of olefins under typical drinking water conditions, while Cl<sub>2</sub>O and Cl<sub>2</sub> are likely to play important roles at high FAC concentration near circum-neutral pH (for Cl<sub>2</sub>O) or at high Cl<sup>−</sup> con centration under acidic conditions (for Cl<sub>2</sub>). Bromination of the 12 olefins suggests that HOBr and Br<sub>2</sub>O are the major reactive spe cies at pH 7.5 with species-specific second-order rate constants of Br<sub>2 </sub>O nearly 3-4 orders of magnitude higher than of HOBr (ranging from < ;0.01 to >10<sup>3</sup> M<sup>−1</sup>s<sup>−1</sup>). The reactivit ies of chlorine and bromine species towards olefins follow the order of HOCl < HOBr < Br<sub>2</sub>O < Cl<sub>2</sub>O ≈ Cl<sub>2</sub>. Gen erally, electron-donating groups (e.g., CH<sub>2</sub>OH- and CH<sub>3</sub> -) enhances the reactivities of olefins towards chlorine and bromine species by a factor of 3-10<sup>2</sup>, while electron-withdrawing groups (e.g., C l-, Br-, NO<sub>2</sub>-, COOH-, CHO-, -COOR, and CN-) reduce the reactiviti es by a factor of 3-10<sup>4</sup>. A reasonable linear free energy relation ship (LFER) between the ...' (2529 chars)
serialnumber => protected'0043-1354' (9 chars)
doi => protected'10.1016/j.watres.2020.116424' (28 chars)
uid => protected21462 (integer)
_localizedUid => protected21462 (integer)modified_languageUid => protectedNULL
_versionedUid => protected21462 (integer)modifiedpid => protected124 (integer)4 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=21200, pid=124)originalId => protected21200 (integer)
authors => protected'Walpen, N.; Houska, J.; Salhi, E.; Sander, M.; von Gunte n, U.' (86 chars)
title => protected'Quantification of the electron donating capacity and UV absorbance of dissol ved organic matter during ozonation of secondary wastewater effluent by an a ssay and an automated analyzer' (182 chars)
journal => protected'Water Research' (14 chars)
year => protected2020 (integer)
volume => protected185 (integer)
issue => protected'' (0 chars)
startpage => protected'116235 (12 pp.)' (15 chars)
otherpage => protected'' (0 chars)
categories => protected'secondary-treated wastewater; ozonation; micropollutant abatement; electron donating capacity; UV absorbance' (108 chars)
description => protected'Ozonation of secondary wastewater treatment plant effluent for the abatement of organic micropollutants requires an accurate process control, which can be based on monitoring ozone-induced changes in dissolved organic matter (DO M). This study presents a novel automated analytical system for monitoring c hanges in the electron donating capacity (EDC) and UV absorbance of DOM duri ng ozonation. In a first step, a quantitative photometric EDC assay was deve loped based on electron-transfer reactions from phenolic moieties in DOM to an added chemical oxidant, the radical cation of 2,2′-azino-bis(3-ethylben zothiazoline-6-sulfonate) (ABTS<sup>·</sup><sup>+</sup>). The assay is high ly sensitive (limit of quantification ∼0.5 mg<sub>DOC</sub>·L<sup>-</sup> <sup>1</sup>) and EDC values of model DOM isolates determined by this assay were in good agreement with values determined previously by mediated electro chemical oxidation (slope = 1.01 ± 0.07, <em>R</em><sup>2</sup> = 0.9 8). In a second step, the photometric EDC measurement method was transferred onto an automated fluidic system coupled to a photometer (EDC analyzer). Th e EDC analyzer was then used to monitor changes in EDC and UV absorbance of secondary wastewater effluent treated with ozone. While both parameters exhi bited a dose-dependent decrease, a more pronounced decrease in EDC as compar ed to UV absorbance was observed at specific ozone doses up to 0.4 mg<sub>O< /sub><sub>3</sub>·g<sub>DOC</sub><sup>-1</sup>. The concentration of 17<em> α</em>-ethinylestradiol, a phenolic micropollutant with a high ozone reacti vity, decreased proportionally to the EDC decrease. In contrast, abatement o f less ozone-reactive micropollutants and bromate formation started only aft er a pronounced initial decrease in EDC. The on-line EDC analyzer presented herein will enable a comprehensive assessment of the combination of EDC and UV absorbance as control parameters for full-scale ozonation.' (1961 chars)
serialnumber => protected'0043-1354' (9 chars)
doi => protected'10.1016/j.watres.2020.116235' (28 chars)
uid => protected21200 (integer)
_localizedUid => protected21200 (integer)modified_languageUid => protectedNULL
_versionedUid => protected21200 (integer)modifiedpid => protected124 (integer)5 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=21244, pid=124)originalId => protected21244 (integer)
authors => protected'Remucal, C. K.; Salhi, E.; Walpen, N.; von Gunten, U.' (78 chars)
title => protected'Molecular-level transformation of dissolved organic matter during oxidation by ozone and hydroxyl radical' (105 chars)
journal => protected'Environmental Science and Technology' (36 chars)
year => protected2020 (integer)
volume => protected54 (integer)
issue => protected'16' (2 chars)
startpage => protected'10351' (5 chars)
otherpage => protected'10360' (5 chars)
categories => protected'' (0 chars)
description => protected'Ozonation of drinking and wastewater relies on ozone (O<sub>3</sub>) and hyd roxyl radical (<sup>•</sup>OH) as oxidants. Both oxidants react with disso lved organic matter (DOM) and alter its composition, but the selectivity of the two oxidants and mechanisms of reactivity with DOM moieties are largely unknown. The reactions of O<sub>3</sub> and <sup>•</sup>OH with two DOM is olates were studied by varying specific ozone doses (0.1-1.3 mg-O<sub>3</sub >/mg-C) at pH 7. Additionally, conditions that favor O<sub>3</sub> (i.e., ad dition of an <sup>•</sup>OH scavenger) or <sup>•</sup>OH (i.e., pH 11) w ere investigated. Ozonation decreases aromaticity, apparent molecular weight , and electron donating capacity (EDC) of DOM with large changes observed wh en O<sub>3</sub> is the main oxidant (e.g., EDC decreases 63-77% for 1.3 mg- O<sub>3</sub>/mg-C). Both O<sub>3</sub> and <sup>•</sup>OH react with high ly aromatic, reduced formulas detected using high-resolution mass spectromet ry (O:C = 0.48 ± 0.12; H:C = 1.06 ± 0.23), while <sup>•</sup>OH also oxi dizes more saturated formulas (H:C = 1.64 ± 0.26). Established reactions be tween model compounds and O<sub>3</sub> (e.g., addition of one to two oxygen atoms) or <sup>•</sup>OH (e.g., addition of one oxygen atom and decarboxy lation) are observed and produce highly oxidized DOM (O:C > 1.0). This st udy provides molecular-level evidence for the selectivity of O<sub>3</sub> a s an oxidant within DOM.' (1468 chars)
serialnumber => protected'0013-936X' (9 chars)
doi => protected'10.1021/acs.est.0c03052' (23 chars)
uid => protected21244 (integer)
_localizedUid => protected21244 (integer)modified_languageUid => protectedNULL
_versionedUid => protected21244 (integer)modifiedpid => protected124 (integer)6 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=18628, pid=124)originalId => protected18628 (integer)
authors => protected'Lim, S.; McArdell, C. S.; von Gunten, U.' (60 chars)
title => protected'Reactions of aliphatic amines with ozone: kinetics and mechanisms' (65 chars)
journal => protected'Water Research' (14 chars)
year => protected2019 (integer)
volume => protected157 (integer)
issue => protected'' (0 chars)
startpage => protected'514' (3 chars)
otherpage => protected'528' (3 chars)
categories => protected'aliphatic amines; ozone; reaction kinetics; reaction mechanisms; transformat ion products; nitroalkanes' (102 chars)
description => protected'Aliphatic amines are common constituents in micropollutants and dissolved or ganic matter and present in elevated concentrations in wastewater-impacted s ource waters. Due to high reactivity, reactions of aliphatic amines with ozo ne are likely to occur during ozonation in water and wastewater treatment. W e investigated the kinetics and mechanisms of the reactions of ozone with et hylamine, diethylamine, and triethylamine as model nitrogenous compounds. Sp ecies-specific second-order rate constants for the neutral parent amines ran ged from 9.3 × 10<sup>4</sup> to 2.2 × 10<sup>6</sup> M<sup>−1 </sup>s<sup>−1</sup> and the apparent second-order rate constants at pH 7 for potential or identified transformation products were 6.8 × 10<sup>5 </sup> M<sup>−1</sup>s<sup>−1</sup> for <em>N,N</em>-diethylhydroxylam ine, ∼10<sup>5</sup> M<sup>−1</sup>s<sup>−1</sup> for <em>N</em>-eth ylhydroxylamine, 1.9 × 10<sup>3</sup> M<sup>−1</sup>s<sup>−1</sup > for <em>N</em>-ethylethanimine oxide, and 3.4 M<sup>−1</sup>s<sup>−1 </sup> for nitroethane. Product analyses revealed that all amines were trans formed to products containing a nitrogen-oxygen bond (e.g., triethylamine <e m>N</em>-oxide and nitroethane) with high yields, i.e., 64–100% with regar d to the abated target amines. These findings could be confirmed by measurem ents of singlet oxygen and hydroxyl radical which are formed during the amin e-ozone reactions. Based on the high yields of nitroethane from ethylamine a nd diethylamine, a significant formation of nitroalkanes can be expected dur ing ozonation of waters containing high levels of dissolved organic nitrogen , as expected in wastewaters or wastewater-impaired source waters. This may pose adverse effects on the aquatic environment and human health.' (1813 chars)
serialnumber => protected'0043-1354' (9 chars)
doi => protected'10.1016/j.watres.2019.03.089' (28 chars)
uid => protected18628 (integer)
_localizedUid => protected18628 (integer)modified_languageUid => protectedNULL
_versionedUid => protected18628 (integer)modifiedpid => protected124 (integer)7 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=18571, pid=124)originalId => protected18571 (integer)
authors => protected'Tentscher, P. R.; Lee, M.; von Gunten, U.' (61 chars)
title => protected'Micropollutant oxidation studied by quantum chemical computations: methodolo gy and applications to thermodynamics, kinetics, and reaction mechanisms' (148 chars)
journal => protected'Accounts of Chemical Research' (29 chars)
year => protected2019 (integer)
volume => protected52 (integer)
issue => protected'3' (1 chars)
startpage => protected'605' (3 chars)
otherpage => protected'614' (3 chars)
categories => protected'' (0 chars)
description => protected'The abatement of organic micropollutants during oxidation processes has beco me an emerging issue for various urban water systems such as drinking water, wastewater, and water reuse. Reaction kinetics and mechanisms play an impor tant role in terms of efficiency of these processes and the formation of tra nsformation products, which are controlled by functional groups in the micro pollutants and the applied oxidants. So far, the kinetic and mechanistic inf ormation on the underlying reactions was obtained by experimental studies; a dditionally, predictive quantitative structure–activity relationships (QSA Rs) were applied to determine reaction kinetics for the oxidation of emergin g compounds. Since this experimental approach is very laborious and there ar e tens of thousands potential contaminants, alternative strategies need to b e developed to predict the fate of micropollutants during oxidative water tr eatment. Due to significant developments in quantum chemical (QC) computatio ns in recent years and increased computational capacity, QC-based methods ha ve become an alternative or a supplement to the current experimental approac h. <br/> This Account provides a critical assessment of the current state-of -the-art of QC-based methods for the assessment of oxidation of micropolluta nts. Starting from a given input structure, QC computations need to locate e nergetic minima on the potential energy surface (PES). Then, useful thermody namic and kinetic information can be estimated by different approaches: Expe rimentally determined reaction mechanisms can be validated by identification of transition structures on the PES, which can be obtained for addition rea ctions, heavy atom transfer (Cl<sup>+</sup>, Br<sup>+</sup>, O·) and H atom transfer (simultaneous proton and electron transfer) reactions. However, tr ansition structures in the PES cannot be obtained for e<sup>–</sup>-transf er reactions. <br/> Second-order rate constants <i>k</i> for the reactions o f micropollutants with c...' (3391 chars)
serialnumber => protected'0001-4842' (9 chars)
doi => protected'10.1021/acs.accounts.8b00610' (28 chars)
uid => protected18571 (integer)
_localizedUid => protected18571 (integer)modified_languageUid => protectedNULL
_versionedUid => protected18571 (integer)modifiedpid => protected124 (integer)8 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=18569, pid=124)originalId => protected18569 (integer)
authors => protected'Marron, E. L.; Mitch, W. A.; Gunten, U. von; S edlak, D. L.' (98 chars)
title => protected'A tale of two treatments: the multiple barrier approach to removing chemical contaminants during potable water reuse' (116 chars)
journal => protected'Accounts of Chemical Research' (29 chars)
year => protected2019 (integer)
volume => protected52 (integer)
issue => protected'3' (1 chars)
startpage => protected'615' (3 chars)
otherpage => protected'622' (3 chars)
categories => protected'' (0 chars)
description => protected'In response to water scarcity and an increased recognition of the risks asso ciated with the presence of chemical contaminants, environmental engineers h ave developed advanced water treatment systems that are capable of convertin g municipal wastewater effluent into drinking water. This practice, which is referred to as potable water reuse, typically relies upon reverse osmosis ( RO) treatment followed by exposure to ultraviolet (UV) light and addition of hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>). These two treatment process es individually are capable of controlling many of the chemical and microbia l contaminants in wastewater; however, a few chemicals may still be present after treatment at concentrations that affect water quality. <br/> Low-molec ular weight (<200 Da), uncharged compounds represent the greatest challenge for RO treatment. For potable water reuse systems, compounds of greatest con cern include oxidation products formed during treatment (e.g., <em>N-</em>ni trosodimethylamine, halogenated disinfection byproducts) and compounds prese nt in wastewater effluent (e.g., odorous compounds, organic solvents). Altho ugh the concentrations of most of these compounds decrease to levels where t hey no longer compromise water quality after they encounter the second treat ment barrier (i.e., UV/H<sub>2</sub>O<sub>2</sub>), low-molecular weight com pounds that are resistant to direct photolysis and exhibit low reactivity wi th hydroxyl radical (<strong>·</strong>OH) may persist. While attempts to i dentify the compounds that pass through both barriers have accounted for app roximately half of the dissolved organic carbon remaining after treatment, i t is unlikely that a significant fraction of the remaining unknowns will eve r be identified with current analytical techniques. Nonetheless, the toxicit y-weighted concentration of certain known compounds (e.g., disinfection bypr oducts) is typically lower in RO-UV/H<sub>2</sub>O<sub>2</sub> treated water than conventional drink...' (3217 chars)
serialnumber => protected'0001-4842' (9 chars)
doi => protected'10.1021/acs.accounts.8b00612' (28 chars)
uid => protected18569 (integer)
_localizedUid => protected18569 (integer)modified_languageUid => protectedNULL
_versionedUid => protected18569 (integer)modifiedpid => protected124 (integer)9 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=17187, pid=124)originalId => protected17187 (integer)
authors => protected'Önnby, L.; Salhi, E.; McKay, G.; Rosario-Ortiz, F.  ;L.; von Gunten, U.' (100 chars)
title => protected'Ozone and chlorine reactions with dissolved organic matter - Assessment of o xidant-reactive moieties by optical measurements and the electron donating c apacities' (161 chars)
journal => protected'Water Research' (14 chars)
year => protected2018 (integer)
volume => protected144 (integer)
issue => protected'' (0 chars)
startpage => protected'64' (2 chars)
otherpage => protected'75' (2 chars)
categories => protected'dissolved organic matter; electron donating capacity; oxidant reactivity; oz one; chlorine; disinfection by-products; fluorescence' (129 chars)
description => protected'Oxidation processes are impacted by the type, concentration and reactivity o f the dissolved organic matter (DOM). In this study, the reactions between v arious types of DOM (Suwannee River fulvic acid (SRFA), Nordic Reservoir NOM (NNOM) and Pony Lake fulvic acid (PLFA)) and two oxidants (ozone and chlori ne) were studied in the pH range 2–9 by using a combination of optical mea surements and electron donating capacities. The relationships between residu al electron donating capacity (EDC) and residual absorbance showed a strong pH dependence for the ozone-DOM reactions with phenolic functional groups be ing the main reacting moieties. Relative EDC and absorbance abatements (UV<s ub>254</sub> or UV<sub>280</sub>) were similar at pH 2. At pH 7 or 9, the re lative abatement of EDC was more pronounced than for absorbance, which could be explained by the formation of UV-absorbing products such as benzoquinone from the transformation of phenolic moieties. An increase in fluorescence a batement with increasing pH was also observed during ozonation. The increase in fluorescence quantum yields could not be attributed to formation of benz oquinone, but related to a faster abatement of phenolic moieties relative to fluorophores with low ozone reactivity.<br /> The overall <sup>•</sup>OH yields as a result of DOM-induced ozone consumption increased significantly with increasing pH, which could be related to the higher reactivity of pheno lic moieties at higher pH. The <sup>•</sup>OH yields for SRFA and PLFA wer e proportional to the phenolic contents, whereas for NNOM, the <sup>•</sup >OH yield was about 30% higher.<br /> During chlorination of DOM at pH 7 an efficient relative EDC abatement was observed whereas the relative absorbanc e abatement was much less pronounced. This is due to the formation of chloro phenolic moieties, which exert a significant absorbance, and partly lose the ir electron donating capacity.<br /> Pre-ozonation of SRFA leads to a decrea se of chloroform and hal...' (2283 chars)
serialnumber => protected'0043-1354' (9 chars)
doi => protected'10.1016/j.watres.2018.06.059' (28 chars)
uid => protected17187 (integer)
_localizedUid => protected17187 (integer)modified_languageUid => protectedNULL
_versionedUid => protected17187 (integer)modifiedpid => protected124 (integer)10 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=17288, pid=124)originalId => protected17288 (integer)
authors => protected'Önnby, L.; Walpen, N.; Salhi, E.; Sander, M.; von Gunte n, U.' (86 chars)
title => protected'Two analytical approaches quantifying the electron donating capacities of di ssolved organic matter to monitor its oxidation during chlorination and ozon ation' (157 chars)
journal => protected'Water Research' (14 chars)
year => protected2018 (integer)
volume => protected144 (integer)
issue => protected'' (0 chars)
startpage => protected'677' (3 chars)
otherpage => protected'689' (3 chars)
categories => protected'electron donating capacity; dissolved organic matter; ozonation; chlorinatio n; size exclusion chromatography; flow-injection analysis' (133 chars)
description => protected'Electron-donating activated aromatic moieties, including phenols, in dissolv ed organic matter (DOM) partially control its reactivity with the chemical o xidants ozone and chlorine. This comparative study introduces two sensitive analytical systems to directly and selectively quantify the electron-donatin g capacity (EDC) of DOM, which corresponds to the number of electrons transf erred from activated aromatic moieties, including phenols, to the added chem ical oxidant 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonate) radical c ation (i.e., ABTS<sup>•+</sup>). The first system separates DOM by size ex clusion chromatography (SEC) followed by a post-column reaction with ABTS<su p>•+</sup> and a spectrophotometric quantification of the reduction of ABT S<sup>•+</sup> by DOM. The second system employs flow-injection analysis ( FIA) coupled to electrochemical detection to quantify ABTS<sup>•+</sup> re duction by DOM. Both systems have very low limits of quantification, allowin g determination of EDC values of dilute DOM samples with <1 mg carbon per liter. When applied to ozonated and chlorinated model DOM isolates and real water samples, the two analytical systems showed that EDC values of the trea ted DOM decrease with increasing specific oxidant doses. The EDC decreases d etected by the two systems were in overall good agreement except for one sam ple containing DOM with a very low EDC. The combination of EDC with UV-absor bance measurements gives further insights into the chemical reaction pathway s of DOM with chemical oxidants such as ozone or chlorine. We propose the us e of EDC in water treatment facilities as a readily measurable parameter to determine the content of electron-donating aromatic moieties in DOM and ther eby its reactivity with added chemical oxidants.' (1796 chars)
serialnumber => protected'0043-1354' (9 chars)
doi => protected'10.1016/j.watres.2018.06.060' (28 chars)
uid => protected17288 (integer)
_localizedUid => protected17288 (integer)modified_languageUid => protectedNULL
_versionedUid => protected17288 (integer)modifiedpid => protected124 (integer)11 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=17022, pid=124)originalId => protected17022 (integer)
authors => protected'Schollée, J. E.; Bourgin, M.; von Gunten, U.; McArdell, C. S.; Hollender, J.' (112 chars)
title => protected'Non-target screening to trace ozonation transformation products in a wastewa ter treatment train including different post-treatments' (131 chars)
journal => protected'Water Research' (14 chars)
year => protected2018 (integer)
volume => protected142 (integer)
issue => protected'' (0 chars)
startpage => protected'267' (3 chars)
otherpage => protected'278' (3 chars)
categories => protected'advanced wastewater treatment; ozonation; non-target screening; transformati on products; micropollutants' (104 chars)
description => protected'Ozonation and subsequent post-treatments are increasingly implemented in was tewater treatment plants (WWTPs) for enhanced micropollutant abatement. Whil e this technology is effective, micropollutant oxidation leads to the format ion of ozonation transformation products (OTPs). Target and suspect screenin g provide information about known parent compounds and known OTPs, but for a more comprehensive picture, non-target screening is needed. Here, sampling was conducted at a full-scale WWTP to investigate OTP formation at four ozon e doses (2, 3, 4, and 5 mg/L, ranging from 0.3 to 1.0 gO<sub>3</sub>/gDOC) and subsequent changes during five post-treatment steps (<i>i.e.</i>, sand filter, fixed bed bioreactor, moving bed bioreactor, and two granular activa ted carbon (GAC) filters, relatively fresh and pre-loaded). Samples were mea sured with online solid-phase extraction coupled to liquid chromatography hi gh-resolution tandem mass spectrometry (LC-HRMS/MS) using electrospray ioniz ation (ESI) in positive and negative mode. Existing non-target screening wor kflows were adapted to (1) examine the formation of potential OTPs at four o zone doses and (2) compare the removal of OTPs among five post-treatments. I n (1), data processing included principal component analysis (PCA) and chemi cal knowledge on 31 possible oxidation reactions to prioritize non-target fe atures likely to be OTPs. Between 394 and 1328 unique potential OTPs were de tected in positive ESI for the four ozone doses tested; between 12 and 324 u nique potential OTPs were detected in negative ESI. At a specific ozone dose of 0.5 gO<sub>3</sub>/gDOC, 27 parent compounds were identified and were re lated to 69 non-target features selected as potential OTPs. Two OTPs were co nfirmed with reference standards (venlafaxine <i>N</i>-oxide and chlorothiaz ide); 34 other potential OTPs were in agreement with literature data and/or reaction mechanisms. In (2), hierarchical cluster analysis (HCA) was applied on profiles detected in...' (2489 chars)
serialnumber => protected'0043-1354' (9 chars)
doi => protected'10.1016/j.watres.2018.05.045' (28 chars)
uid => protected17022 (integer)
_localizedUid => protected17022 (integer)modified_languageUid => protectedNULL
_versionedUid => protected17022 (integer)modifiedpid => protected124 (integer)12 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=16875, pid=124)originalId => protected16875 (integer)
authors => protected'von Gunten, U.' (19 chars)
title => protected'Oxidation processes in water treatment: are we on track?' (56 chars)
journal => protected'Environmental Science and Technology' (36 chars)
year => protected2018 (integer)
volume => protected52 (integer)
issue => protected'9' (1 chars)
startpage => protected'5062' (4 chars)
otherpage => protected'5075' (4 chars)
categories => protected'' (0 chars)
description => protected'Chemical oxidants have been applied in water treatment for more than a centu ry, first as disinfectants and later to abate inorganic and organic contamin ants. The challenge of oxidative abatement of organic micropollutants is the formation of transformation products with unknown (eco)toxicological conseq uences. Four aspects need to be considered for oxidative micropollutant abat ement: (i) Reaction kinetics, controlling the efficiency of the process, (ii ) mechanisms of transformation product formation, (iii) extent of formation of disinfection byproducts from the matrix, (iv) oxidation induced biologica l effects, resulting from transformation products and/or disinfection byprod ucts. It is impossible to test all the thousands of organic micropollutants in the urban water cycle experimentally to assess potential adverse outcomes of an oxidation. Rather, we need multidisciplinary and automated knowledge- based systems, which couple predictions of kinetics, transformation and disi nfection byproducts and their toxicological consequences to assess the overa ll benefits of oxidation processes. A wide range of oxidation processes has been developed in the last decades with a recent focus on novel electricity- driven oxidation processes. To evaluate these processes, they have to be com pared to established benchmark ozone- and UV-based oxidation processes by co nsidering the energy demands, economics, the feasibilty, and the integration into future water treatment systems.' (1481 chars)
serialnumber => protected'0013-936X' (9 chars)
doi => protected'10.1021/acs.est.8b00586' (23 chars)
uid => protected16875 (integer)
_localizedUid => protected16875 (integer)modified_languageUid => protectedNULL
_versionedUid => protected16875 (integer)modifiedpid => protected124 (integer)13 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=16828, pid=124)originalId => protected16828 (integer)
authors => protected'Tentscher, P. R.; Bourgin, M.; von Gunten, U.' (65 chars)
title => protected'Ozonation of <i>Para</i>-substituted phenolic compounds yields <i>p</i>‑be nzoquinones, other cyclic <i>α,β</i>-unsaturated ketones, and substituted catechols' (161 chars)
journal => protected'Environmental Science and Technology' (36 chars)
year => protected2018 (integer)
volume => protected52 (integer)
issue => protected'8' (1 chars)
startpage => protected'4763' (4 chars)
otherpage => protected'4773' (4 chars)
categories => protected'' (0 chars)
description => protected'Phenolic moieties are common functional groups in organic micropollutants an d in dissolved organic matter, and are exposed to ozone during drinking wate r and wastewater ozonation. Although unsubstituted phenol is known to yield potentially genotoxic <em>p</em>-benzoquinone during ozonation, little is kn own about the effects of substitution of the phenol ring on transformation p roduct formation. With batch experiments employing differing ozone/target co mpound ratios, it is shown that <em>para</em>-substituted phenols (<em>p</em >-alkyl, <em>p</em>-halo, <em>p</em>-cyano, <em>p</em>-methoxy, <em>p</em>-f ormyl, <em>p</em>-carboxy) yield <em>p</em>-benzoquinones, <em>p</em>-substi tuted catechols, and 4-hydroxy-4-alkyl-cyclohexadien-1-ones as common ozonat ion products. Only in a few cases did <em>para</em>-substitution prevent the formation of these potentially harmful products. Quantum chemical calculati ons showed that different reaction mechanisms lead to <em>p</em>-benzoquinon e, and that cyclohexadienone can be expected to form if no such pathway is p ossible. These products can thus be expected from most phenolic moieties. Ki netic considerations showed that substitution of the phenolic ring results i n rather small changes of the apparent second order rate constants for pheno l–ozone reactions at pH 7. Thus, in mixtures, most phenolic structures can be expected to react with ozone. However, redox cross-reactions between dif ferent transformation products, as well as hydrolysis, can be expected to fu rther alter product distributions under realistic treatment scenarios.' (1590 chars)
serialnumber => protected'0013-936X' (9 chars)
doi => protected'10.1021/acs.est.8b00011' (23 chars)
uid => protected16828 (integer)
_localizedUid => protected16828 (integer)modified_languageUid => protectedNULL
_versionedUid => protected16828 (integer)modifiedpid => protected124 (integer)14 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=15883, pid=124)originalId => protected15883 (integer)
authors => protected'Bourgin, M.; Beck, B.; Boehler, M.; Borowska, E.; Fleine r, J.; Salhi, E.; Teichler, R.; von Gunten, U.; Siegrist , H.; McArdell, C. S.' (188 chars)
title => protected'Evaluation of a full-scale wastewater treatment plant upgraded with ozonatio n and biological post-treatments: abatement of micropollutants, formation of transformation products and oxidation by-products' (202 chars)
journal => protected'Water Research' (14 chars)
year => protected2018 (integer)
volume => protected129 (integer)
issue => protected'' (0 chars)
startpage => protected'486' (3 chars)
otherpage => protected'498' (3 chars)
categories => protected'wastewater treatment; ozonation; granular activated carbon; transformation p roducts; bromate; nitrosamines' (106 chars)
description => protected'<div id="abssec0010"> <p id="abspara0010">To protect the ecosystem and drink ing water resources in Switzerland and in the countries of the downstream ca tchments, a new Swiss water protection act entered into force in 2016 aiming to reduce the discharge of micropollutants from wastewater treatment plants (WWTPs). As a consequence, selected WWTPs must be upgraded by an advanced t reatment for micropollutant abatement with suitable and economic options suc h as (powdered) activated carbon treatment or ozonation. WWTP Neugut (105′ 000 people equivalent) was the first WWTP in Switzerland to implement a long -term full-scale ozonation. Differing specific ozone doses in the range of 0 .35–0.97 g O<sub>3</sub>/g DOC were applied to determine the adequate ozo ne dose to fulfill the requirements of the Swiss water protection act. Based on this assessment, a specific ozone dose of 0.55 g O<sub>3</sub>/g DOC is recommended at this plant to ensure an average abatement of the twelve sele cted indicator substances by ≥80% over the whole treatment. A monitoring o f 550 substances confirmed that this dose was very efficient to abate a broa d range of micropollutants by >79% on average. After ozonation, an additiona l biological post-treatment is required to eliminate possible negative ecoto xicological effects generated during ozonation caused by biodegradable ozona tion transformation products (OTPs) and oxidation by-products (OBPs). Three biological treatments (sand filtration, moving bed, fixed bed) and granular activated carbon (GAC, fresh and pre-loaded) filtration were evaluated as po st-treatments after ozonation. In parallel, a fresh GAC filter directly conn ected to the effluent of the secondary clarifier was assessed. Among the thr ee purely biological post-treatments, the sand filtration performed best in terms of removal of dissolved organic carbon (DOC), assimilable organic carb on (AOC) and total suspended solids (TSS). The fresh activated carbon filtra tion ensured a significa...' (3274 chars)
serialnumber => protected'0043-1354' (9 chars)
doi => protected'10.1016/j.watres.2017.10.036' (28 chars)
uid => protected15883 (integer)
_localizedUid => protected15883 (integer)modified_languageUid => protectedNULL
_versionedUid => protected15883 (integer)modifiedpid => protected124 (integer)15 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=7060, pid=124)originalId => protected7060 (integer)
authors => protected'Skarpeli-Liati, M.; Pati, S. G.; Bolotin, J.; Eustis,&nb sp;S. N.; Hofstetter, T. B.' (118 chars)
title => protected'Carbon, hydrogen, and nitrogen isotope fractionation associated with oxidati ve transformation of substituted aromatic <em>N</em>-alkyl amines' (141 chars)
journal => protected'Environmental Science and Technology' (36 chars)
year => protected2012 (integer)
volume => protected46 (integer)
issue => protected'13' (2 chars)
startpage => protected'7189' (4 chars)
otherpage => protected'7198' (4 chars)
categories => protected'' (0 chars)
description => protected'We investigated the mechanisms and isotope effects associated with the <em>N </em>-dealkylation and N-atom oxidation of substituted <em>N</em>-methyl- an d <em>N,N</em>-dimethylanilines to identify isotope fractionation trends for the assessment of oxidations of aromatic <em>N</em>-alkyl moieties by compo und-specific isotope analysis (CSIA). In laboratory batch model systems, we determined the C, H, and N isotope enrichment factors for the oxidation by M nO<sub>2</sub> and horseradish peroxidase (HRP), derived apparent <sup>13</s up>C-, <sup>2</sup>H-, and <sup>15</sup>N-kinetic isotope effects (AKIEs), a nd characterized reaction products. The N-atom oxidation pathway leading to radical coupling products typically exhibited inverse <sup>15</sup>N-AKIEs ( up to 0.991) and only minor <sup>13</sup>C- and <sup>2</sup>H-AKIEs. Oxidati ve <em>N</em>-dealkylation, in contrast, was subject to large normal <sup>13 </sup>C- and <sup>2</sup>H-AKIEs (up to 1.019 and 3.1, respectively) and sma ll <sup>15</sup>N-AKIEs. Subtle changes of the compound’s electronic prope rties due to different types of aromatic and/or <em>N</em>-alkyl substituent s resulted in changes of reaction mechanisms, rate-limiting step(s), and thu s isotope fractionation trends. The complex sequence of electron and proton transfers during the oxidative transformation of substituted aromatic <em>N< /em>-alkyl amines suggests highly compound- and mechanism-dependent isotope effects precluding extrapolations to other organic micropollutants reacting along the same degradation pathways.' (1556 chars)
serialnumber => protected'0013-936X' (9 chars)
doi => protected'10.1021/es300819v' (17 chars)
uid => protected7060 (integer)
_localizedUid => protected7060 (integer)modified_languageUid => protectedNULL
_versionedUid => protected7060 (integer)modifiedpid => protected124 (integer)16 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=14377, pid=124)originalId => protected14377 (integer)
authors => protected'Bourgin, M.; Borowska, E.; Helbing, J.; Hollender, J.; K aiser, H.-P.; Kienle, C.; McArdell, C. S.; Simon, E .; von Gunten, U.' (174 chars)
title => protected'Effect of operational and water quality parameters on conventional ozonation and the advanced oxidation process O<SUB>3</SUB>/H<SUB>2</SUB>O<SUB>2</SUB> : kinetics of micropollutant abatement, transformation product and bromate f ormation in a surface water' (255 chars)
journal => protected'Water Research' (14 chars)
year => protected2017 (integer)
volume => protected122 (integer)
issue => protected'' (0 chars)
startpage => protected'234' (3 chars)
otherpage => protected'245' (3 chars)
categories => protected'surface water; AOP O3/H2O2; micropollutants; transformation products; bromat e; ozonation reactors' (97 chars)
description => protected'The efficiency of ozone-based processes under various conditions was studied for the treatment of a surface water (Lake Zürich water, Switzerland) spik ed with 19 micropollutants (pharmaceuticals, pesticides, industrial chemical , X-ray contrast medium, sweetener) each at 1 μg L<sup>−1</sup>. Two pilo t-scale ozonation reactors (4–5 m<sup>3</sup> h<sup>−1</sup>), a 4-chamb er reactor and a tubular reactor were investigated by either conventional oz onation and/or the advanced oxidation process (AOP) O<sub>3</sub>/H<sub>2</s ub>O<sub>2</sub>. The effects of selected operational parameters, such as oz one dose (0.5–3 mg L<sup>−1</sup>) and H<sub>2</sub>O<sub>2</sub> dose ( O<sub>3</sub>:H<sub>2</sub>O<sub>2</sub> = 1:3–3:1 (mass ratio)), and sele cted water quality parameters, such as pH (6.5–8.5) and initial bromide co ncentration (15–200 μg L<sup>−1</sup>), on micropollutant abatement and bromate formation were investigated. Under the studied conditions, compound
90%) even for the lowest ozone dose of 0.5 mg/L. Conversely, the abatement e fficiency of sucralose, which only reacts with hydroxyl radicals (<B>·</B>O H), varied between 19 and 90%. Generally, the abatement efficiency increased with higher ozone doses and higher pH and lower bromide concentrations. H<s ub>2</sub>O<sub>2</sub> addition accelerated the ozone conversion to radical <B>·</B>OH, which enables a faster abatement of ozone-resistant micropollu tants. Interestingly, the abatement of micropollutants decreased with higher bromide concentrations during conventional ozonation due to competitive ozo ne-consuming reactions, except for lamotrigine, due to the suspected reactio n of HOBr/OBr<sup>−</sup> with the primary amine moieties. In addition to the abatement of micropollutants, the evolution of the two main transformati on products (TPs) of hyd...' (3133 chars)
serialnumber => protected'0043-1354' (9 chars)
doi => protected'10.1016/j.watres.2017.05.018' (28 chars)
uid => protected14377 (integer)
_localizedUid => protected14377 (integer)modified_languageUid => protectedNULL
_versionedUid => protected14377 (integer)modifiedpid => protected124 (integer)17 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=14276, pid=124)originalId => protected14276 (integer)
authors => protected'Soltermann, F.; Abegglen, C.; Tschui, M.; Stahel, S.; vo n Gunten, U.' (93 chars)
title => protected'Options and limitations for bromate control during ozonation of wastewater' (74 chars)
journal => protected'Water Research' (14 chars)
year => protected2017 (integer)
volume => protected116 (integer)
issue => protected'' (0 chars)
startpage => protected'76' (2 chars)
otherpage => protected'85' (2 chars)
categories => protected'bromide; bromate; ozonation; wastewater treatment; micropollutants' (66 chars)
description => protected'Wastewater treatment plants (WWTPs) are important point sources for micropol lutants, which are harmful to freshwater organisms. Ozonation of wastewater is a powerful option to abate micropollutants, but may result in the formati on of the potentially toxic oxidation by-product bromate in bromide-containi ng wastewaters. This study investigates options to reduce bromate formation during wastewater ozonation by (i) reducing the bromide concentration of the wastewater, (ii) lowering the ozone dose during wastewater treatment and (i ii) adding hydrogen peroxide to limit the lifetime of ozone and quench the i ntermediates of the bromate formation pathway. Two examples demonstrate that a high share of bromide in wastewater can originate from single point sourc es (e.g., municipal waste incinerators or landfills). The identification of major point sources requires laborious sampling campaigns, but may facilitat e the reduction of the bromide load significantly. To reduce the bromate for mation by lowering the ozone dose interferes with the aim to abate micropoll utants. Therefore, an additional treatment is necessary to ensure the elimin ation of micropollutants. Experiments at a pilot-plant illustrate that a com bined treatment (ozone/powdered activated carbon) allows to eliminate microp ollutants with low bromate yields. Furthermore, the addition of hydrogen per oxide was investigated at bench-scale. The bromate yields could be reduced b y ∼50% and 65% for a hydrogen peroxide dose of 5 and 10 mg L<sup>−1</sup >, respectively. In conclusion, there are options to reduce the bromate form ation during wastewater ozonation, however, they are not simple with sometim es limited efficiency.' (1694 chars)
serialnumber => protected'0043-1354' (9 chars)
doi => protected'10.1016/j.watres.2017.02.026' (28 chars)
uid => protected14276 (integer)
_localizedUid => protected14276 (integer)modified_languageUid => protectedNULL
_versionedUid => protected14276 (integer)modifiedpid => protected124 (integer)18 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=14082, pid=124)originalId => protected14082 (integer)
authors => protected'Heeb, M. B.; Kristiana, I.; Trogolo, D.; Arey, J.&n bsp;S.; von Gunten, U.' (103 chars)
title => protected'Formation and reactivity of inorganic and organic chloramines and bromamines during oxidative water treatment' (109 chars)
journal => protected'Water Research' (14 chars)
year => protected2017 (integer)
volume => protected110 (integer)
issue => protected'' (0 chars)
startpage => protected'91' (2 chars)
otherpage => protected'101' (3 chars)
categories => protected'chloramines; bromamines; oxidative water treatment; partial charge; pKa; kin etic modeling' (89 chars)
description => protected'The formation and further reactions of halamines during oxidative water trea tment can be relevant for water quality. In this study, we investigated the formation and reactivity of several inorganic and organic halamines (monochl oramine, <I>N</I>-chloromethylamine, <I>N</I>-chlorodimethylamine, monobroma mine, dibromamine, <I>N</I>-bromomethylamine, <I>N,N</I>-dibromomethylamine, and <I>N</I>-bromodimethylamine) by kinetic experiments, transformation pro duct analysis, and quantum chemical computations. Kinetic model simulations were conducted to evaluate the relevance of halamines for various water trea tment scenarios. Halamines were quickly formed from the reaction of chlorine and bromine with ammonia or organic amines. Species-specific second-order r ate constants for the reaction of chlorine and bromine with ammonia, methyl- and dimethylamine were in the order of 10<SUP>6</SUP>-10<SUP>8</SUP> M<SUP> −1</SUP>s<SUP>−1</SUP>. The formed halamines were found to be reactive t owards phenolic compounds, forming halogenated phenols via electrophilic aro matic substitution (phenol and resorcinol) or quinones via electron transfer (catechol and hydroquinone). At near neutral pH, apparent second-order rate constants for these reactions were in the order of 10<SUP>−4</SUP>-10<SUP >−1</SUP> M<SUP>−1</SUP>s<SUP>−1</SUP> for chloramines and 10<SUP>1</S UP>-10<SUP>2</SUP> M<SUP>−1</SUP>s<SUP>−1</SUP> for bromamines. Quantum chemical computations were used to determine previously unknown aqueous p<I> K</I><SUB>a</SUB> values, gas phase bond dissociation energies (BDE) and par tial atomic charges of the halamines, allowing a better understanding of the ir reactivities. Kinetic model simulations, based on the results of this stu dy, showed that during chlorination inorganic and organic chloramines are th e main halamines formed. However, their further reactions with organic matte r are outcompeted kinetically by chlorine. During ozonation, mainly inorgani c bromamines are formed,...' (2384 chars)
serialnumber => protected'0043-1354' (9 chars)
doi => protected'10.1016/j.watres.2016.11.065' (28 chars)
uid => protected14082 (integer)
_localizedUid => protected14082 (integer)modified_languageUid => protectedNULL
_versionedUid => protected14082 (integer)modifiedpid => protected124 (integer)19 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=14236, pid=124)originalId => protected14236 (integer)
authors => protected'Lee, M.; Blum, L. C.; Schmid, E.; Fenner, K.; von G unten, U.' (90 chars)
title => protected'A computer-based prediction platform for the reaction of ozone with organic compounds in aqueous solution: kinetics and mechanisms' (130 chars)
journal => protected'Environmental Science: Processes and Impacts' (44 chars)
year => protected2017 (integer)
volume => protected19 (integer)
issue => protected'3' (1 chars)
startpage => protected'465' (3 chars)
otherpage => protected'476' (3 chars)
categories => protected'' (0 chars)
description => protected'Ozonation of secondary wastewater effluents can reduce the discharge of micr opollutants by transforming their chemical structures. Therefore, a better u nderstanding of the formation of transformation products during ozonation is important. In this study, a computer-based prediction platform for the kine tics and mechanisms of the reactions of ozone with organic compounds was dev eloped to enable <I>in silico</I> predictions of transformation products. Wi th the developed prediction platform, reaction kinetics expressed as second- order rate constants for the reactions of ozone with selected organic compou nds (<I>k</I><SUB>O<SUB>3</SUB></SUB>, M<SUP>−1</SUP> s<SUP>−1</SUP>) ca n be predicted based on an adapted <I>k</I><SUB>O<SUB>3</SUB></SUB> predicti on model from a previous study (Lee <I>et al., Environ. Sci. Technol.</I>, 2 015, 49 , 9925–9935) (average model error of about a factor of 6 for 14 co mpound classes with 284 model compounds). Ozone reaction mechanisms reported in the literature have been reviewed and, using chemoinformatics tools, enc oded into about 340 individual reaction rules that can be generally applied to predict the transformation products of micropollutants. Predictions for < I>k</I><SUB>O<SUB>3</SUB></SUB> and/or transformation products were overall consistent with the experimental data for three micropollutants used as vali dation compounds (<I>e.g.</I>, carbamazepine, tramadol, and triclosan). Howe ver, limitations of the current <I>k</I><SUB>O<SUB>3</SUB></SUB> prediction platform were also identified: ambiguous assignment of the <I>n</I>-th highe st occupied molecular orbital energy (<I>E</I><SUB>HOMO−<I>n</I></SUB>) to the reactive sites, potential errors associated with the use of a gas-phase geometry, and a poor <I>k</I><SUB>O<SUB>3</SUB></SUB> prediction for certai n compounds (cetirizine). Therefore, the current prediction tool should not be considered as a substitute for experimental studies and experimental data are still required in t...' (2329 chars)
serialnumber => protected'2050-7887' (9 chars)
doi => protected'10.1039/C6EM00584E' (18 chars)
uid => protected14236 (integer)
_localizedUid => protected14236 (integer)modified_languageUid => protectedNULL
_versionedUid => protected14236 (integer)modifiedpid => protected124 (integer)20 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=14134, pid=124)originalId => protected14134 (integer)
authors => protected'Spahr, S.; Cirpka, O. A.; von Gunten, U.; Hofstetter,&nb sp;T. B.' (89 chars)
title => protected'Formation of <I>N</I>-Nitrosodimethylamine during chloramination of secondar y and tertiary amines: role of molecular oxygen and radical intermediates' (149 chars)
journal => protected'Environmental Science and Technology' (36 chars)
year => protected2017 (integer)
volume => protected51 (integer)
issue => protected'1' (1 chars)
startpage => protected'280' (3 chars)
otherpage => protected'290' (3 chars)
categories => protected'' (0 chars)
description => protected'<I>N</I>-Nitrosodimethylamine (NDMA) is a carcinogenic disinfection byproduc t from water chloramination. Despite the identification of numerous NDMA pre cursors, essential parts of the reaction mechanism such as the incorporation of molecular O<SUB>2</SUB> are poorly understood. In laboratory model syste ms for the chloramination of secondary and tertiary amines, we investigated the kinetics of precursor disappearance and NDMA formation, quantified the s toichiometries of monochloramine (NH<SUB>2</SUB>Cl) and aqueous O<SUB>2</SUB > consumption, derived <SUP>18</SUP>O-kinetic isotope effects (<SUP>18</SUP> O-KIE) for the reactions of aqueous O<SUB>2</SUB>, and studied the impact of radical scavengers on NDMA formation. Although the molar NDMA yields from f ive <I>N, N</I>-dimethylamine-containing precursors varied between 1.4% and 90%, we observed the stoichiometric removal of one O<SUB>2</SUB> per <I>N, N </I>-dimethylamine group of the precursor indicating that the oxygenation of N atoms did not determine the molar NDMA yield. Small <SUP>18</SUP>O-KIEs b etween 1.0026 ± 0.0003 and 1.0092 ± 0.0009 found for all precursors as wel l as completely inhibited NDMA formation in the presence of radical scavenge rs (ABTS and trolox) imply that O<SUB>2</SUB> reacted with radical species. Our study suggests that aminyl radicals from the oxidation of organic amines by NH<SUB>2</SUB>Cl and <I>N</I>-peroxyl radicals from the reaction of amin yl radicals with aqueous O<SUB>2</SUB> are part of the NDMA formation mechan ism.' (1524 chars)
serialnumber => protected'0013-936X' (9 chars)
doi => protected'10.1021/acs.est.6b04780' (23 chars)
uid => protected14134 (integer)
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authors => protected'Soltermann, F.; Abegglen, C.; Götz, C.; von Gunten, U.' (75 chars)
title => protected'Bromide sources and loads in Swiss surface waters and their relevance for br omate formation during wastewater ozonation' (119 chars)
journal => protected'Environmental Science and Technology' (36 chars)
year => protected2016 (integer)
volume => protected50 (integer)
issue => protected'18' (2 chars)
startpage => protected'9825' (4 chars)
otherpage => protected'9834' (4 chars)
categories => protected'' (0 chars)
description => protected'Bromide measurements and mass balances in the catchments of major Swiss rive rs revealed that chemical industry and municipal waste incinerators are the most important bromide sources and account for ∼50% and ∼20%, respective ly, of the ∼2000 tons of bromide discharged in the Rhine river in 2014 in Switzerland. About 100 wastewater treatment plants (WWTPs) will upgrade thei r treatment for micropollutant abatement in the future to comply with Swiss regulations. An upgrade with ozonation may lead to unintended bromate format ion in bromide-containing wastewaters. Measured bromide concentrations were <0.05 mg L<SUP>-1</SUP> in ∼75% of 69 WWTPs, while they ranged from 0.4 to ∼50 mg L<SUP>-1</SUP> in WWTPs with specific bromide sources (e.g., munic ipal waste incinerators, landfill leachate, and chemical industry). Wastewat er ozonation formed little bromate at specific ozone doses of ≤0.4 mg O<SU B>3</SUB>/mg DOC, while the bromate yields were almost linearly correlated t o the specific ozone dose for higher ozone doses. Molar bromate yields for t ypical specific ozone doses in wastewater treatment (0.4-0.6 mg O<SUB>3</SUB >/mg DOC) are ≤3%. In a modeled extreme scenario (in which all upgraded WW TPs release 10 μg L<SUP>-1</SUP> of bromate), bromate concentrations increa sed by <0.4 μg L<SUP>-1</SUP> in major Swiss rivers and by several microgra ms per liter in receiving water bodies with a high fraction of municipal was tewater.' (1452 chars)
serialnumber => protected'0013-936X' (9 chars)
doi => protected'10.1021/acs.est.6b01142' (23 chars)
uid => protected10708 (integer)
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authors => protected'Lee, Y.; von Gunten, U.' (33 chars)
title => protected'Advances in predicting organic contaminant abatement during ozonation of mun icipal wastewater effluent: reaction kinetics, transformation products, and changes of biological effects' (181 chars)
journal => protected'Environmental Science: Water Research and Technology' (52 chars)
year => protected2016 (integer)
volume => protected2 (integer)
issue => protected'' (0 chars)
startpage => protected'421' (3 chars)
otherpage => protected'442' (3 chars)
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description => protected'Ozonation of municipal wastewater effluent has been considered in recent yea rs as an enhanced wastewater treatment technology to abate trace organic con taminants (micropollutants). The efficiency of ozonation for micropollutant abatement depends on (1) the reactivity of ozone and OH radical (<B>·</B>OH ) with the target micropollutant, (2) the dosage of ozone and the stability of ozone and <B>·</B>OH in a given water matrix, (3) the removal of undesir able effects (<I>e.g.</I>, biological activities) of a micropollutant after structural transformation, and (4) the biodegradability of transformation pr oducts in biological post-treatment. In this article, recent advances in pre dicting organic micropollutant abatement during ozonation of municipal waste water effluents are reviewed with a focus on (i) principle-based approaches for describing and modeling the reaction kinetics of ozone and <B>·</B>OH, (ii) transformation products and pathways, (iii) changes of biological activ ities, and (iv) biodegradation of transformation products in biological post -treatment. Using the chemical kinetics based on ozone and <B>·</B>OH rate constants (<I>i.e.</I>, compound-specific information) and exposures (<I>i.e .</I>, water matrix-specific information), a generalized prediction of the a batement efficiency of various micropollutants in varying water quality appe ars to be possible. QSAR-type correlations based on Hammett coefficients or quantum chemical energy calculations or (semi)empirical models have been dev eloped for predicting the ozone and <B>·</B>OH rate constants and exposures , respectively. Models based on the ozone and <B>·</B>OH reaction rules can be used to predict the transformation products of micropollutants by ozone and <B>·</B>OH. Reaction rule-based models in combination with the chemical kinetics information will enable the prediction of transformation product e volution during ozonation. The biological activities of transformation produ cts have been assessed b...' (2981 chars)
serialnumber => protected'2053-1400' (9 chars)
doi => protected'10.1039/c6ew00025h' (18 chars)
uid => protected10447 (integer)
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Formation of transformation products during ozonation of secondary wastewater effluent and their fate in post-treatment: from laboratory- to full-scale
Ozonation is increasingly applied in water and wastewater treatment for the abatement of micropollutants (MPs). However, the transformation products formed during ozonation (OTPs) and their fate in biological or sorptive post-treatments is largely unknown. In this project, a high-throughput approach, combining laboratory ozonation experiments and detection by liquid chromatography high-resolution mass spectrometry (LC-HR-MS/MS), was developed and applied to identify OTPs formed during ozonation of wastewater effluent for a large number of relevant MPs (total 87). For the laboratory ozonation experiments, a simplified experimental solution, consisting of surrogate organic matter (methanol and acetate), was created, which produced ozonation conditions similar to realistic conditions in terms of ozone and hydroxyl radical exposures. The 87 selected parent MPs were divided into 19 mixtures, which enabled the identification of OTPs with an optimized number of experiments. The following two approaches were considered to identify OTPs. (1) A screening of LC-HR-MS signal formation in these experiments was performed and revealed a list of 1749 potential OTP candidate signals associated to 70 parent MPs. This list can be used in future suspect screening studies. (2) A screening was performed for signals that were formed in both batch experiments and in samples of wastewater treatment plants (WWTPs). This second approach was ultimately more time-efficient and was applied to four different WWTPs with ozonation (specific ozone doses in the range 0.23-0.55 gO3/gDOC), leading to the identification of 84 relevant OTPs of 40 parent MPs in wastewater effluent. Chemical structures could be proposed for 83 OTPs through the interpretation of MS/MS spectra and expert knowledge in ozone chemistry. Forty-eight OTPs (58%) have not been reported previously. The fate of the verified OTPs was studied in different post-treatment steps. During sand filtration, 87-89% of the OTPs were stable. In granular activated carbon (GAC) filters, OTPs were abated with decreasing efficiency with increasing run times of the filters. For example, in a GAC filter with 16,000 bed volumes, 53% of the OTPs were abated, while in a GAC filter with 35,000 bed volumes, 40% of the OTPs were abated. The highest abatement (87% of OTPs) was observed when 13 mg/L powdered activated carbon (PAC) was dosed onto a sand filter.
Gulde, R.; Rutsch, M.; Clerc, B.; Schollée, J. E.; von Gunten, U.; McArdell, C. S. (2021) Formation of transformation products during ozonation of secondary wastewater effluent and their fate in post-treatment: from laboratory- to full-scale, Water Research, 200, 117200 (16 pp.), doi:10.1016/j.watres.2021.117200, Institutional Repository
Micropollutants as internal probe compounds to assess UV fluence and hydroxyl radical exposure in UV/H2O2 treatment
Organic micropollutants (MPs) are increasingly detected in water resources, which can be a concern for human health and the aquatic environment. Ultraviolet (UV) radiation based advanced oxidation processes (AOP) such as low-pressure mercury vapor arc lamp UV/H2O2 can be applied to abate these MPs. During UV/H2O2 treatment, MPs are abated primarily by photolysis and reactions with hydroxyl radicals (•OH), which are produced in situ from H2O2 photolysis. Here, a model is presented that calculates the applied UV fluence (Hcalc) and the •OH exposure (CT•OH,calc ) from the abatement of two selected MPs, which act as internal probe compounds. Quantification of the UV fluence and hydroxyl radical exposure was generally accurate when a UV susceptible and a UV resistant probe compound were selected, and both were abated at least by 50 %, e.g., iopamidol and 5-methyl-1H-benzotriazole. Based on these key parameters a model was developed to predict the abatement of other MPs. The prediction of abatement was verified in various waters (sand filtrates of rivers Rhine and Wiese, and a tertiary wastewater effluent) and at different scales (laboratory experiments, pilot plant). The accuracy to predict the abatement of other MPs was typically within ±20 % of the respective measured abatement. The model was further assessed for its ability to estimate unknown rate constants for direct photolysis (kUV,MP) and reactions with •OH (k•OH,MP). In most cases, the estimated rate constants agreed well with published values, considering the uncertainty of kinetic data determined in laboratory experiments. A sensitivity analysis revealed that in typical water treatment applications, the precision of kinetic parameters (kUV,MP for UV susceptible and for UV resistant probe compounds) have the strongest impact on the model's accuracy.
Wünsch, R.; Mayer, C.; Plattner, J.; Eugster, F.; Wülser, R.; Gebhardt, J.; Hübner, U.; Canonica, S.; Wintgens, T.; von Gunten, U. (2021) Micropollutants as internal probe compounds to assess UV fluence and hydroxyl radical exposure in UV/H2O2 treatment, Water Research, 195, 116940 (13 pp.), doi:10.1016/j.watres.2021.116940, Institutional Repository
Efficiency of pre-oxidation of natural organic matter for the mitigation of disinfection byproducts: electron donating capacity and UV absorbance as surrogate parameters
Pre-oxidation is often used before disinfection with chlorine to decrease the reactivity of the water matrix and mitigate the formation of regulated disinfection byproducts (DBPs). This study provides insights on the impact of oxidative pre-treatment with chlorine dioxide (ClO2), ozone (O3), ferrate (Fe(VI)) and permanganate (Mn(VII)) on Suwannee River Natural Organic Matter (SRNOM) properties characterized by the UV absorbance at 254 nm (UV254) and the electron donating capacity (EDC). Changes in NOM reactivity and abatement of DBP precursors are also assessed. The impact of pre-oxidants (based on molar concentration) on UV254 abatement ranked in the order O3 > Mn(VII) > Fe(VI)/ClO2, while the efficiency of pre-oxidation on EDC abatement followed the order Mn(VII) > ClO2 > Fe(VI) > O3 and two phases were observed. At low specific ClO2, Fe(VI) and Mn(VII) doses corresponding to < 50% EDC abatement, a limited relative abatement of UV254 compared to the EDC was observed (~ 8% EDC abatement per 1% UV254 abatement). This suggests the oxidation of phenolic-type moieties to quinone-type moieties which absorb UV254 and don't contribute to EDC. At higher oxidant doses (> 50% EDC abatement), a similar abatement of EDC and UV254 (~ 0.9-1.2% EDC abatement per 1% UV254 abatement) suggested aromatic ring cleavage. In comparison to the other oxidants, O3 abated the relative UV254 more effectively, due to a more efficient cleavage of aromatic rings. For a pre-oxidation with Mn(VII), ClO2 and Fe(VI), similar correlations between the EDC abatement and the chlorine demand or the adsorbable organic halide (AOX) formation were obtained. In contrast, O3 pre-treatment led to a lower chlorine demand and AOX formation for equivalent EDC abatement. For all oxidants, trihalomethane formation was poorly correlated with both EDC and UV254. The EDC abatement was found to be a pre-oxidant-independent surrogate for haloacetonitrile formation. These results emphasize the benefits of combining EDC and UV254 measurement to understand and monitor oxidant-induced changes of NOM and assessing DBP formation.
Rougé, V.; von Gunten, U.; Allard, S. (2020) Efficiency of pre-oxidation of natural organic matter for the mitigation of disinfection byproducts: electron donating capacity and UV absorbance as surrogate parameters, Water Research, 187, 116418 (10 pp.), doi:10.1016/j.watres.2020.116418, Institutional Repository
Chlorination and bromination of olefins: kinetic and mechanistic aspects
Hypochlorous acid (HOCl) is typically assumed to be the primary reactive species in free available chlorine (FAC) solutions. Lately, it has been shown that less abundant chlorine species such as chlorine monoxide (Cl2O) and chlorine (Cl2) can also influence the kinetics of the abatement of certain organic compounds during chlorination. In this study, the chlorination as well as bromination kinetics and mechanisms of 12 olefins (including 3 aliphatic and 9 aromatic olefins) with different structures were explored. HOCl shows a low reactivity towards the selected olefins with species-specific second-order rate constants <1.0 M−1s−1, about 4-6 orders of magnitude lower than those of Cl2O and Cl2. HOCl is the dominant chlorine species during chlorination of olefins under typical drinking water conditions, while Cl2O and Cl2 are likely to play important roles at high FAC concentration near circum-neutral pH (for Cl2O) or at high Cl− concentration under acidic conditions (for Cl2). Bromination of the 12 olefins suggests that HOBr and Br2O are the major reactive species at pH 7.5 with species-specific second-order rate constants of Br2O nearly 3-4 orders of magnitude higher than of HOBr (ranging from <0.01 to >103 M−1s−1). The reactivities of chlorine and bromine species towards olefins follow the order of HOCl < HOBr < Br2O < Cl2O ≈ Cl2. Generally, electron-donating groups (e.g., CH2OH- and CH3-) enhances the reactivities of olefins towards chlorine and bromine species by a factor of 3-102, while electron-withdrawing groups (e.g., Cl-, Br-, NO2-, COOH-, CHO-, -COOR, and CN-) reduce the reactivities by a factor of 3-104. A reasonable linear free energy relationship (LFER) between the species-specific second-order rate constants of Br2O or Cl2O reactions with aromatic olefins and their Hammett σ+ was established with a more negative ρ value for Br2O than for Cl2O, indicating that Br2O is more sensitive to substitution effects. Chlorinated products including HOCl-adducts and decarboxylated Cl-adduct were identified during chlorination of cinnamic acid by high-performance liquid chromatography/high resolution mass spectrometry (HPLC/HRMS).
Li, J.; Jiang, J.; Manasfi, T.; von Gunten, U. (2020) Chlorination and bromination of olefins: kinetic and mechanistic aspects, Water Research, 187, 116424 (12 pp.), doi:10.1016/j.watres.2020.116424, Institutional Repository
Quantification of the electron donating capacity and UV absorbance of dissolved organic matter during ozonation of secondary wastewater effluent by an assay and an automated analyzer
Ozonation of secondary wastewater treatment plant effluent for the abatement of organic micropollutants requires an accurate process control, which can be based on monitoring ozone-induced changes in dissolved organic matter (DOM). This study presents a novel automated analytical system for monitoring changes in the electron donating capacity (EDC) and UV absorbance of DOM during ozonation. In a first step, a quantitative photometric EDC assay was developed based on electron-transfer reactions from phenolic moieties in DOM to an added chemical oxidant, the radical cation of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS·+). The assay is highly sensitive (limit of quantification ∼0.5 mgDOC·L-1) and EDC values of model DOM isolates determined by this assay were in good agreement with values determined previously by mediated electrochemical oxidation (slope = 1.01 ± 0.07, R2 = 0.98). In a second step, the photometric EDC measurement method was transferred onto an automated fluidic system coupled to a photometer (EDC analyzer). The EDC analyzer was then used to monitor changes in EDC and UV absorbance of secondary wastewater effluent treated with ozone. While both parameters exhibited a dose-dependent decrease, a more pronounced decrease in EDC as compared to UV absorbance was observed at specific ozone doses up to 0.4 mgO3·gDOC-1. The concentration of 17α-ethinylestradiol, a phenolic micropollutant with a high ozone reactivity, decreased proportionally to the EDC decrease. In contrast, abatement of less ozone-reactive micropollutants and bromate formation started only after a pronounced initial decrease in EDC. The on-line EDC analyzer presented herein will enable a comprehensive assessment of the combination of EDC and UV absorbance as control parameters for full-scale ozonation.
Walpen, N.; Houska, J.; Salhi, E.; Sander, M.; von Gunten, U. (2020) Quantification of the electron donating capacity and UV absorbance of dissolved organic matter during ozonation of secondary wastewater effluent by an assay and an automated analyzer, Water Research, 185, 116235 (12 pp.), doi:10.1016/j.watres.2020.116235, Institutional Repository
Molecular-level transformation of dissolved organic matter during oxidation by ozone and hydroxyl radical
Ozonation of drinking and wastewater relies on ozone (O3) and hydroxyl radical (•OH) as oxidants. Both oxidants react with dissolved organic matter (DOM) and alter its composition, but the selectivity of the two oxidants and mechanisms of reactivity with DOM moieties are largely unknown. The reactions of O3 and •OH with two DOM isolates were studied by varying specific ozone doses (0.1-1.3 mg-O3/mg-C) at pH 7. Additionally, conditions that favor O3 (i.e., addition of an •OH scavenger) or •OH (i.e., pH 11) were investigated. Ozonation decreases aromaticity, apparent molecular weight, and electron donating capacity (EDC) of DOM with large changes observed when O3 is the main oxidant (e.g., EDC decreases 63-77% for 1.3 mg-O3/mg-C). Both O3 and •OH react with highly aromatic, reduced formulas detected using high-resolution mass spectrometry (O:C = 0.48 ± 0.12; H:C = 1.06 ± 0.23), while •OH also oxidizes more saturated formulas (H:C = 1.64 ± 0.26). Established reactions between model compounds and O3 (e.g., addition of one to two oxygen atoms) or •OH (e.g., addition of one oxygen atom and decarboxylation) are observed and produce highly oxidized DOM (O:C > 1.0). This study provides molecular-level evidence for the selectivity of O3 as an oxidant within DOM.
Remucal, C. K.; Salhi, E.; Walpen, N.; von Gunten, U. (2020) Molecular-level transformation of dissolved organic matter during oxidation by ozone and hydroxyl radical, Environmental Science and Technology, 54(16), 10351-10360, doi:10.1021/acs.est.0c03052, Institutional Repository
Reactions of aliphatic amines with ozone: kinetics and mechanisms
Aliphatic amines are common constituents in micropollutants and dissolved organic matter and present in elevated concentrations in wastewater-impacted source waters. Due to high reactivity, reactions of aliphatic amines with ozone are likely to occur during ozonation in water and wastewater treatment. We investigated the kinetics and mechanisms of the reactions of ozone with ethylamine, diethylamine, and triethylamine as model nitrogenous compounds. Species-specific second-order rate constants for the neutral parent amines ranged from 9.3 × 104 to 2.2 × 106 M−1s−1 and the apparent second-order rate constants at pH 7 for potential or identified transformation products were 6.8 × 105 M−1s−1 for N,N-diethylhydroxylamine, ∼105 M−1s−1 for N-ethylhydroxylamine, 1.9 × 103 M−1s−1 for N-ethylethanimine oxide, and 3.4 M−1s−1 for nitroethane. Product analyses revealed that all amines were transformed to products containing a nitrogen-oxygen bond (e.g., triethylamine N-oxide and nitroethane) with high yields, i.e., 64–100% with regard to the abated target amines. These findings could be confirmed by measurements of singlet oxygen and hydroxyl radical which are formed during the amine-ozone reactions. Based on the high yields of nitroethane from ethylamine and diethylamine, a significant formation of nitroalkanes can be expected during ozonation of waters containing high levels of dissolved organic nitrogen, as expected in wastewaters or wastewater-impaired source waters. This may pose adverse effects on the aquatic environment and human health.
Micropollutant oxidation studied by quantum chemical computations: methodology and applications to thermodynamics, kinetics, and reaction mechanisms
The abatement of organic micropollutants during oxidation processes has become an emerging issue for various urban water systems such as drinking water, wastewater, and water reuse. Reaction kinetics and mechanisms play an important role in terms of efficiency of these processes and the formation of transformation products, which are controlled by functional groups in the micropollutants and the applied oxidants. So far, the kinetic and mechanistic information on the underlying reactions was obtained by experimental studies; additionally, predictive quantitative structure–activity relationships (QSARs) were applied to determine reaction kinetics for the oxidation of emerging compounds. Since this experimental approach is very laborious and there are tens of thousands potential contaminants, alternative strategies need to be developed to predict the fate of micropollutants during oxidative water treatment. Due to significant developments in quantum chemical (QC) computations in recent years and increased computational capacity, QC-based methods have become an alternative or a supplement to the current experimental approach. This Account provides a critical assessment of the current state-of-the-art of QC-based methods for the assessment of oxidation of micropollutants. Starting from a given input structure, QC computations need to locate energetic minima on the potential energy surface (PES). Then, useful thermodynamic and kinetic information can be estimated by different approaches: Experimentally determined reaction mechanisms can be validated by identification of transition structures on the PES, which can be obtained for addition reactions, heavy atom transfer (Cl+, Br+, O·) and H atom transfer (simultaneous proton and electron transfer) reactions. However, transition structures in the PES cannot be obtained for e–-transfer reactions. Second-order rate constants k for the reactions of micropollutants with chemical oxidants can be obtained by ab initio calculations or by QSARs with various QC descriptors. It has been demonstrated that second-order rate constants from ab initio calculations are within factors 3–750 of the measured values, whereas QSAR-based methods can achieve factors 2–4 compared to the experimental data. The orbital eigenvalue of the highest occupied molecular orbital (EHOMO) is the most commonly used descriptor for QSAR-based computations of k-values. In combination with results from experimental studies, QC computations can also be applied to investigate reaction mechanisms for verification/understanding of oxidative mechanisms, calculation of branching ratios or regioselectivity, evaluation of the experimental product distribution and assessment of substitution effects. Furthermore, other important physical-chemical constants such as unknown equilibria for species, which are not measurable due to low concentrations, or pKa values of reactive transient species can be estimated. With further development of QC-based methods, it will become possible to implement kinetic and mechanistic information from such computations in in silico models to predict oxidative transformation of micropollutants. Such predictions can then be complemented by tailored experimental studies to confirm/falsify the computations.
Tentscher, P. R.; Lee, M.; von Gunten, U. (2019) Micropollutant oxidation studied by quantum chemical computations: methodology and applications to thermodynamics, kinetics, and reaction mechanisms, Accounts of Chemical Research, 52(3), 605-614, doi:10.1021/acs.accounts.8b00610, Institutional Repository
A tale of two treatments: the multiple barrier approach to removing chemical contaminants during potable water reuse
In response to water scarcity and an increased recognition of the risks associated with the presence of chemical contaminants, environmental engineers have developed advanced water treatment systems that are capable of converting municipal wastewater effluent into drinking water. This practice, which is referred to as potable water reuse, typically relies upon reverse osmosis (RO) treatment followed by exposure to ultraviolet (UV) light and addition of hydrogen peroxide (H2O2). These two treatment processes individually are capable of controlling many of the chemical and microbial contaminants in wastewater; however, a few chemicals may still be present after treatment at concentrations that affect water quality. Low-molecular weight (<200 Da), uncharged compounds represent the greatest challenge for RO treatment. For potable water reuse systems, compounds of greatest concern include oxidation products formed during treatment (e.g., N-nitrosodimethylamine, halogenated disinfection byproducts) and compounds present in wastewater effluent (e.g., odorous compounds, organic solvents). Although the concentrations of most of these compounds decrease to levels where they no longer compromise water quality after they encounter the second treatment barrier (i.e., UV/H2O2), low-molecular weight compounds that are resistant to direct photolysis and exhibit low reactivity with hydroxyl radical (·OH) may persist. While attempts to identify the compounds that pass through both barriers have accounted for approximately half of the dissolved organic carbon remaining after treatment, it is unlikely that a significant fraction of the remaining unknowns will ever be identified with current analytical techniques. Nonetheless, the toxicity-weighted concentration of certain known compounds (e.g., disinfection byproducts) is typically lower in RO-UV/H2O2 treated water than conventional drinking water. To avoid the expense associated with managing the concentrate produced by RO, environmental engineers have begun to employ alternative treatment barriers. The use of alternatives such as nanofiltration, ozonation followed by biological filtration, or activated carbon filtration avoids the problems associated with the production and disposal of RO concentrate, but they may allow a larger number of chemical contaminants to pass through the treatment process. In addition to the transformation products and solvents that pose risks in the RO-UV/H2O2 system, these alternative barriers are challenged by larger, polar compounds that are not amenable to oxidation, such as perfluoroalkyl acids and phosphate-containing flame retardants. To fully protect consumers who rely upon potable water reuse systems, new policies are needed to prevent chemicals that are difficult to remove during advanced treatment from entering the sewer system. By using knowledge about the composition of municipal wastewater and the mechanisms through which contaminants are removed during treatment, it should be possible to safely reuse municipal wastewater effluent as a drinking water source.
Marron, E. L.; Mitch, W. A.; Gunten, U. von; Sedlak, D. L. (2019) A tale of two treatments: the multiple barrier approach to removing chemical contaminants during potable water reuse, Accounts of Chemical Research, 52(3), 615-622, doi:10.1021/acs.accounts.8b00612, Institutional Repository
Ozone and chlorine reactions with dissolved organic matter - Assessment of oxidant-reactive moieties by optical measurements and the electron donating capacities
Oxidation processes are impacted by the type, concentration and reactivity of the dissolved organic matter (DOM). In this study, the reactions between various types of DOM (Suwannee River fulvic acid (SRFA), Nordic Reservoir NOM (NNOM) and Pony Lake fulvic acid (PLFA)) and two oxidants (ozone and chlorine) were studied in the pH range 2–9 by using a combination of optical measurements and electron donating capacities. The relationships between residual electron donating capacity (EDC) and residual absorbance showed a strong pH dependence for the ozone-DOM reactions with phenolic functional groups being the main reacting moieties. Relative EDC and absorbance abatements (UV254 or UV280) were similar at pH 2. At pH 7 or 9, the relative abatement of EDC was more pronounced than for absorbance, which could be explained by the formation of UV-absorbing products such as benzoquinone from the transformation of phenolic moieties. An increase in fluorescence abatement with increasing pH was also observed during ozonation. The increase in fluorescence quantum yields could not be attributed to formation of benzoquinone, but related to a faster abatement of phenolic moieties relative to fluorophores with low ozone reactivity. The overall •OH yields as a result of DOM-induced ozone consumption increased significantly with increasing pH, which could be related to the higher reactivity of phenolic moieties at higher pH. The •OH yields for SRFA and PLFA were proportional to the phenolic contents, whereas for NNOM, the •OH yield was about 30% higher. During chlorination of DOM at pH 7 an efficient relative EDC abatement was observed whereas the relative absorbance abatement was much less pronounced. This is due to the formation of chlorophenolic moieties, which exert a significant absorbance, and partly lose their electron donating capacity. Pre-ozonation of SRFA leads to a decrease of chloroform and haloacetic acid formation, however, only after a threshold of > ∼50% abatement of the EDC and under conditions which are not precursor limited. The decrease in chloroform and haloacetic acid formation after the threshold EDC abatement was proportional to the relative residual EDC.
Önnby, L.; Salhi, E.; McKay, G.; Rosario-Ortiz, F. L.; von Gunten, U. (2018) Ozone and chlorine reactions with dissolved organic matter - Assessment of oxidant-reactive moieties by optical measurements and the electron donating capacities, Water Research, 144, 64-75, doi:10.1016/j.watres.2018.06.059, Institutional Repository
Two analytical approaches quantifying the electron donating capacities of dissolved organic matter to monitor its oxidation during chlorination and ozonation
Electron-donating activated aromatic moieties, including phenols, in dissolved organic matter (DOM) partially control its reactivity with the chemical oxidants ozone and chlorine. This comparative study introduces two sensitive analytical systems to directly and selectively quantify the electron-donating capacity (EDC) of DOM, which corresponds to the number of electrons transferred from activated aromatic moieties, including phenols, to the added chemical oxidant 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonate) radical cation (i.e., ABTS•+). The first system separates DOM by size exclusion chromatography (SEC) followed by a post-column reaction with ABTS•+ and a spectrophotometric quantification of the reduction of ABTS•+ by DOM. The second system employs flow-injection analysis (FIA) coupled to electrochemical detection to quantify ABTS•+ reduction by DOM. Both systems have very low limits of quantification, allowing determination of EDC values of dilute DOM samples with <1 mg carbon per liter. When applied to ozonated and chlorinated model DOM isolates and real water samples, the two analytical systems showed that EDC values of the treated DOM decrease with increasing specific oxidant doses. The EDC decreases detected by the two systems were in overall good agreement except for one sample containing DOM with a very low EDC. The combination of EDC with UV-absorbance measurements gives further insights into the chemical reaction pathways of DOM with chemical oxidants such as ozone or chlorine. We propose the use of EDC in water treatment facilities as a readily measurable parameter to determine the content of electron-donating aromatic moieties in DOM and thereby its reactivity with added chemical oxidants.
Önnby, L.; Walpen, N.; Salhi, E.; Sander, M.; von Gunten, U. (2018) Two analytical approaches quantifying the electron donating capacities of dissolved organic matter to monitor its oxidation during chlorination and ozonation, Water Research, 144, 677-689, doi:10.1016/j.watres.2018.06.060, Institutional Repository
Non-target screening to trace ozonation transformation products in a wastewater treatment train including different post-treatments
Ozonation and subsequent post-treatments are increasingly implemented in wastewater treatment plants (WWTPs) for enhanced micropollutant abatement. While this technology is effective, micropollutant oxidation leads to the formation of ozonation transformation products (OTPs). Target and suspect screening provide information about known parent compounds and known OTPs, but for a more comprehensive picture, non-target screening is needed. Here, sampling was conducted at a full-scale WWTP to investigate OTP formation at four ozone doses (2, 3, 4, and 5 mg/L, ranging from 0.3 to 1.0 gO3/gDOC) and subsequent changes during five post-treatment steps (i.e., sand filter, fixed bed bioreactor, moving bed bioreactor, and two granular activated carbon (GAC) filters, relatively fresh and pre-loaded). Samples were measured with online solid-phase extraction coupled to liquid chromatography high-resolution tandem mass spectrometry (LC-HRMS/MS) using electrospray ionization (ESI) in positive and negative mode. Existing non-target screening workflows were adapted to (1) examine the formation of potential OTPs at four ozone doses and (2) compare the removal of OTPs among five post-treatments. In (1), data processing included principal component analysis (PCA) and chemical knowledge on 31 possible oxidation reactions to prioritize non-target features likely to be OTPs. Between 394 and 1328 unique potential OTPs were detected in positive ESI for the four ozone doses tested; between 12 and 324 unique potential OTPs were detected in negative ESI. At a specific ozone dose of 0.5 gO3/gDOC, 27 parent compounds were identified and were related to 69 non-target features selected as potential OTPs. Two OTPs were confirmed with reference standards (venlafaxine N-oxide and chlorothiazide); 34 other potential OTPs were in agreement with literature data and/or reaction mechanisms. In (2), hierarchical cluster analysis (HCA) was applied on profiles detected in positive ESI mode across the WWTP and revealed 11 relevant trends. OTP removal was compared among the five post-treatments and 54–83% of the non-target features that appeared after ozonation were removed, with the two GAC filters performing the best. Overall, these data analysis strategies for non-target screening provide a useful tool to understand the behavior of unknown features during ozonation and post-treatment and to prioritize certain non-targets for further identification.
Schollée, J. E.; Bourgin, M.; von Gunten, U.; McArdell, C. S.; Hollender, J. (2018) Non-target screening to trace ozonation transformation products in a wastewater treatment train including different post-treatments, Water Research, 142, 267-278, doi:10.1016/j.watres.2018.05.045, Institutional Repository
Oxidation processes in water treatment: are we on track?
Chemical oxidants have been applied in water treatment for more than a century, first as disinfectants and later to abate inorganic and organic contaminants. The challenge of oxidative abatement of organic micropollutants is the formation of transformation products with unknown (eco)toxicological consequences. Four aspects need to be considered for oxidative micropollutant abatement: (i) Reaction kinetics, controlling the efficiency of the process, (ii) mechanisms of transformation product formation, (iii) extent of formation of disinfection byproducts from the matrix, (iv) oxidation induced biological effects, resulting from transformation products and/or disinfection byproducts. It is impossible to test all the thousands of organic micropollutants in the urban water cycle experimentally to assess potential adverse outcomes of an oxidation. Rather, we need multidisciplinary and automated knowledge-based systems, which couple predictions of kinetics, transformation and disinfection byproducts and their toxicological consequences to assess the overall benefits of oxidation processes. A wide range of oxidation processes has been developed in the last decades with a recent focus on novel electricity-driven oxidation processes. To evaluate these processes, they have to be compared to established benchmark ozone- and UV-based oxidation processes by considering the energy demands, economics, the feasibilty, and the integration into future water treatment systems.
Ozonation of Para-substituted phenolic compounds yields p‑benzoquinones, other cyclic α,β-unsaturated ketones, and substituted catechols
Phenolic moieties are common functional groups in organic micropollutants and in dissolved organic matter, and are exposed to ozone during drinking water and wastewater ozonation. Although unsubstituted phenol is known to yield potentially genotoxic p-benzoquinone during ozonation, little is known about the effects of substitution of the phenol ring on transformation product formation. With batch experiments employing differing ozone/target compound ratios, it is shown that para-substituted phenols (p-alkyl, p-halo, p-cyano, p-methoxy, p-formyl, p-carboxy) yield p-benzoquinones, p-substituted catechols, and 4-hydroxy-4-alkyl-cyclohexadien-1-ones as common ozonation products. Only in a few cases did para-substitution prevent the formation of these potentially harmful products. Quantum chemical calculations showed that different reaction mechanisms lead to p-benzoquinone, and that cyclohexadienone can be expected to form if no such pathway is possible. These products can thus be expected from most phenolic moieties. Kinetic considerations showed that substitution of the phenolic ring results in rather small changes of the apparent second order rate constants for phenol–ozone reactions at pH 7. Thus, in mixtures, most phenolic structures can be expected to react with ozone. However, redox cross-reactions between different transformation products, as well as hydrolysis, can be expected to further alter product distributions under realistic treatment scenarios.
Tentscher, P. R.; Bourgin, M.; von Gunten, U. (2018) Ozonation of Para-substituted phenolic compounds yields p‑benzoquinones, other cyclic α,β-unsaturated ketones, and substituted catechols, Environmental Science and Technology, 52(8), 4763-4773, doi:10.1021/acs.est.8b00011, Institutional Repository
Evaluation of a full-scale wastewater treatment plant upgraded with ozonation and biological post-treatments: abatement of micropollutants, formation of transformation products and oxidation by-products
To protect the ecosystem and drinking water resources in Switzerland and in the countries of the downstream catchments, a new Swiss water protection act entered into force in 2016 aiming to reduce the discharge of micropollutants from wastewater treatment plants (WWTPs). As a consequence, selected WWTPs must be upgraded by an advanced treatment for micropollutant abatement with suitable and economic options such as (powdered) activated carbon treatment or ozonation. WWTP Neugut (105′000 people equivalent) was the first WWTP in Switzerland to implement a long-term full-scale ozonation. Differing specific ozone doses in the range of 0.35–0.97 g O3/g DOC were applied to determine the adequate ozone dose to fulfill the requirements of the Swiss water protection act. Based on this assessment, a specific ozone dose of 0.55 g O3/g DOC is recommended at this plant to ensure an average abatement of the twelve selected indicator substances by ≥80% over the whole treatment. A monitoring of 550 substances confirmed that this dose was very efficient to abate a broad range of micropollutants by >79% on average. After ozonation, an additional biological post-treatment is required to eliminate possible negative ecotoxicological effects generated during ozonation caused by biodegradable ozonation transformation products (OTPs) and oxidation by-products (OBPs). Three biological treatments (sand filtration, moving bed, fixed bed) and granular activated carbon (GAC, fresh and pre-loaded) filtration were evaluated as post-treatments after ozonation. In parallel, a fresh GAC filter directly connected to the effluent of the secondary clarifier was assessed. Among the three purely biological post-treatments, the sand filtration performed best in terms of removal of dissolved organic carbon (DOC), assimilable organic carbon (AOC) and total suspended solids (TSS). The fresh activated carbon filtration ensured a significant additional micropollutants abatement after ozonation due to sorption. The relative abatement of the indicator substances ranged between 20 and 89% after 27′000 bed volumes (BV) and was still substantial at 50′000 BV. In an identical GAC filter running in parallel and being fed with the effluent of the secondary clarifier, the elimination was less efficient. Seven primary OTPs (chlorothiazide and six N-oxides) formed during ozonation could be quantified thanks to available reference standards. Their concentration decreased with increasing specific ozone doses with the concomitant formation of other OTPs. The seven OTPs were found to be stable compounds and were not abated in the biological post-treatments. They were sorbed in the fresh GAC filter, but less efficiently than the corresponding parent compounds. Two OBPs, bromate (BrO3−) and N-nitrosodimethylamine (NDMA), were formed during ozonation but did not exceeded 5 μg/L for bromate and 30 ng/L for NDMA at the recommended specific ozone dose of 0.55 g O3/g DOC. NDMA was well abated in all post-treatments (minimum 41% during fixed bed filtration, maximum 83% during fresh GAC filtration), while bromate was very stable as expected.
Bourgin, M.; Beck, B.; Boehler, M.; Borowska, E.; Fleiner, J.; Salhi, E.; Teichler, R.; von Gunten, U.; Siegrist, H.; McArdell, C. S. (2018) Evaluation of a full-scale wastewater treatment plant upgraded with ozonation and biological post-treatments: abatement of micropollutants, formation of transformation products and oxidation by-products, Water Research, 129, 486-498, doi:10.1016/j.watres.2017.10.036, Institutional Repository
Carbon, hydrogen, and nitrogen isotope fractionation associated with oxidative transformation of substituted aromatic N-alkyl amines
We investigated the mechanisms and isotope effects associated with the N-dealkylation and N-atom oxidation of substituted N-methyl- and N,N-dimethylanilines to identify isotope fractionation trends for the assessment of oxidations of aromatic N-alkyl moieties by compound-specific isotope analysis (CSIA). In laboratory batch model systems, we determined the C, H, and N isotope enrichment factors for the oxidation by MnO2 and horseradish peroxidase (HRP), derived apparent 13C-, 2H-, and 15N-kinetic isotope effects (AKIEs), and characterized reaction products. The N-atom oxidation pathway leading to radical coupling products typically exhibited inverse 15N-AKIEs (up to 0.991) and only minor 13C- and 2H-AKIEs. Oxidative N-dealkylation, in contrast, was subject to large normal 13C- and 2H-AKIEs (up to 1.019 and 3.1, respectively) and small 15N-AKIEs. Subtle changes of the compound’s electronic properties due to different types of aromatic and/or N-alkyl substituents resulted in changes of reaction mechanisms, rate-limiting step(s), and thus isotope fractionation trends. The complex sequence of electron and proton transfers during the oxidative transformation of substituted aromatic N-alkyl amines suggests highly compound- and mechanism-dependent isotope effects precluding extrapolations to other organic micropollutants reacting along the same degradation pathways.
Skarpeli-Liati, M.; Pati, S. G.; Bolotin, J.; Eustis, S. N.; Hofstetter, T. B. (2012) Carbon, hydrogen, and nitrogen isotope fractionation associated with oxidative transformation of substituted aromatic N-alkyl amines, Environmental Science and Technology, 46(13), 7189-7198, doi:10.1021/es300819v, Institutional Repository
Effect of operational and water quality parameters on conventional ozonation and the advanced oxidation process O3/H2O2: kinetics of micropollutant abatement, transformation product and bromate formation in a surface water
The efficiency of ozone-based processes under various conditions was studied for the treatment of a surface water (Lake Zürich water, Switzerland) spiked with 19 micropollutants (pharmaceuticals, pesticides, industrial chemical, X-ray contrast medium, sweetener) each at 1 μg L−1. Two pilot-scale ozonation reactors (4–5 m3 h−1), a 4-chamber reactor and a tubular reactor were investigated by either conventional ozonation and/or the advanced oxidation process (AOP) O3/H2O2. The effects of selected operational parameters, such as ozone dose (0.5–3 mg L−1) and H2O2 dose (O3:H2O2 = 1:3–3:1 (mass ratio)), and selected water quality parameters, such as pH (6.5–8.5) and initial bromide concentration (15–200 μg L−1), on micropollutant abatement and bromate formation were investigated. Under the studied conditions, compounds with high second-order rate constant kO3>104 M−1 s−1 for their reaction with ozone were well abated (>90%) even for the lowest ozone dose of 0.5 mg/L. Conversely, the abatement efficiency of sucralose, which only reacts with hydroxyl radicals (·OH), varied between 19 and 90%. Generally, the abatement efficiency increased with higher ozone doses and higher pH and lower bromide concentrations. H2O2 addition accelerated the ozone conversion to radical ·OH, which enables a faster abatement of ozone-resistant micropollutants. Interestingly, the abatement of micropollutants decreased with higher bromide concentrations during conventional ozonation due to competitive ozone-consuming reactions, except for lamotrigine, due to the suspected reaction of HOBr/OBr− with the primary amine moieties. In addition to the abatement of micropollutants, the evolution of the two main transformation products (TPs) of hydrochlorothiazide (HCTZ) and tramadol (TRA), chlorothiazide (CTZ) and tramadol N-oxide (TRA-NOX) respectively, was assessed by chemical analysis and kinetic modelling. Both selected TPs were quickly formed initially to reach a maximum concentration followed by a decrease of their concentrations for longer contact times. For the studied conditions, the TP's concentrations at the outlet of the reactors ranged from 0 to 61% of the initial parent compound concentration, CTZ being a more persistent TP than TRA-NOX. Finally, it was demonstrated in both reactors that the formation of bromate (BrO3−), a potentially carcinogenic oxidation by-product, could be controlled by H2O2 addition with a general improvement on micropollutant abatement. Post-treatment by granular activated carbon (GAC) filtration enabled the reduction of micropollutants and TPs concentrations but no changes in bromate were observed. The combined algae assays showed that water quality was significantly improved after oxidation and GAC post-treatment, driven by the abatement of the spiked pesticides (diuron and atrazine).
Bourgin, M.; Borowska, E.; Helbing, J.; Hollender, J.; Kaiser, H.-P.; Kienle, C.; McArdell, C. S.; Simon, E.; von Gunten, U. (2017) Effect of operational and water quality parameters on conventional ozonation and the advanced oxidation process O3/H2O2: kinetics of micropollutant abatement, transformation product and bromate formation in a surface water, Water Research, 122, 234-245, doi:10.1016/j.watres.2017.05.018, Institutional Repository
Options and limitations for bromate control during ozonation of wastewater
Wastewater treatment plants (WWTPs) are important point sources for micropollutants, which are harmful to freshwater organisms. Ozonation of wastewater is a powerful option to abate micropollutants, but may result in the formation of the potentially toxic oxidation by-product bromate in bromide-containing wastewaters. This study investigates options to reduce bromate formation during wastewater ozonation by (i) reducing the bromide concentration of the wastewater, (ii) lowering the ozone dose during wastewater treatment and (iii) adding hydrogen peroxide to limit the lifetime of ozone and quench the intermediates of the bromate formation pathway. Two examples demonstrate that a high share of bromide in wastewater can originate from single point sources (e.g., municipal waste incinerators or landfills). The identification of major point sources requires laborious sampling campaigns, but may facilitate the reduction of the bromide load significantly. To reduce the bromate formation by lowering the ozone dose interferes with the aim to abate micropollutants. Therefore, an additional treatment is necessary to ensure the elimination of micropollutants. Experiments at a pilot-plant illustrate that a combined treatment (ozone/powdered activated carbon) allows to eliminate micropollutants with low bromate yields. Furthermore, the addition of hydrogen peroxide was investigated at bench-scale. The bromate yields could be reduced by ∼50% and 65% for a hydrogen peroxide dose of 5 and 10 mg L−1, respectively. In conclusion, there are options to reduce the bromate formation during wastewater ozonation, however, they are not simple with sometimes limited efficiency.
Soltermann, F.; Abegglen, C.; Tschui, M.; Stahel, S.; von Gunten, U. (2017) Options and limitations for bromate control during ozonation of wastewater, Water Research, 116, 76-85, doi:10.1016/j.watres.2017.02.026, Institutional Repository
Formation and reactivity of inorganic and organic chloramines and bromamines during oxidative water treatment
The formation and further reactions of halamines during oxidative water treatment can be relevant for water quality. In this study, we investigated the formation and reactivity of several inorganic and organic halamines (monochloramine, N-chloromethylamine, N-chlorodimethylamine, monobromamine, dibromamine, N-bromomethylamine, N,N-dibromomethylamine, and N-bromodimethylamine) by kinetic experiments, transformation product analysis, and quantum chemical computations. Kinetic model simulations were conducted to evaluate the relevance of halamines for various water treatment scenarios. Halamines were quickly formed from the reaction of chlorine and bromine with ammonia or organic amines. Species-specific second-order rate constants for the reaction of chlorine and bromine with ammonia, methyl- and dimethylamine were in the order of 106-108 M−1s−1. The formed halamines were found to be reactive towards phenolic compounds, forming halogenated phenols via electrophilic aromatic substitution (phenol and resorcinol) or quinones via electron transfer (catechol and hydroquinone). At near neutral pH, apparent second-order rate constants for these reactions were in the order of 10−4-10−1 M−1s−1 for chloramines and 101-102 M−1s−1 for bromamines. Quantum chemical computations were used to determine previously unknown aqueous pKa values, gas phase bond dissociation energies (BDE) and partial atomic charges of the halamines, allowing a better understanding of their reactivities. Kinetic model simulations, based on the results of this study, showed that during chlorination inorganic and organic chloramines are the main halamines formed. However, their further reactions with organic matter are outcompeted kinetically by chlorine. During ozonation, mainly inorganic bromamines are formed, since ozone quickly oxidizes organic amines. The further reactions of bromamine are typically outcompeted by ozone and thus generally of minor importance. The use of peracetic acid for saline ballast water treatment can result in the formation of substantial amounts of bromamines, which can react with dissolved organic matter and contribute to the formation of brominated products.
Heeb, M. B.; Kristiana, I.; Trogolo, D.; Arey, J. S.; von Gunten, U. (2017) Formation and reactivity of inorganic and organic chloramines and bromamines during oxidative water treatment, Water Research, 110, 91-101, doi:10.1016/j.watres.2016.11.065, Institutional Repository
A computer-based prediction platform for the reaction of ozone with organic compounds in aqueous solution: kinetics and mechanisms
Ozonation of secondary wastewater effluents can reduce the discharge of micropollutants by transforming their chemical structures. Therefore, a better understanding of the formation of transformation products during ozonation is important. In this study, a computer-based prediction platform for the kinetics and mechanisms of the reactions of ozone with organic compounds was developed to enable in silico predictions of transformation products. With the developed prediction platform, reaction kinetics expressed as second-order rate constants for the reactions of ozone with selected organic compounds (kO3, M−1 s−1) can be predicted based on an adapted kO3 prediction model from a previous study (Lee et al., Environ. Sci. Technol., 2015, 49 , 9925–9935) (average model error of about a factor of 6 for 14 compound classes with 284 model compounds). Ozone reaction mechanisms reported in the literature have been reviewed and, using chemoinformatics tools, encoded into about 340 individual reaction rules that can be generally applied to predict the transformation products of micropollutants. Predictions for kO3 and/or transformation products were overall consistent with the experimental data for three micropollutants used as validation compounds (e.g., carbamazepine, tramadol, and triclosan). However, limitations of the current kO3 prediction platform were also identified: ambiguous assignment of the n-th highest occupied molecular orbital energy (EHOMO−n) to the reactive sites, potential errors associated with the use of a gas-phase geometry, and a poor kO3 prediction for certain compounds (cetirizine). Therefore, the current prediction tool should not be considered as a substitute for experimental studies and experimental data are still required in the future to obtain a more robust prediction model. Nonetheless, the developed prediction platform, made available as a stand-alone graphical user interface (GUI) application, will provide useful information about aqueous ozone chemistry to various groups of end-users such as environmental chemists, engineers, or toxicologists.
Lee, M.; Blum, L. C.; Schmid, E.; Fenner, K.; von Gunten, U. (2017) A computer-based prediction platform for the reaction of ozone with organic compounds in aqueous solution: kinetics and mechanisms, Environmental Science: Processes and Impacts, 19(3), 465-476, doi:10.1039/C6EM00584E, Institutional Repository
Formation of N-Nitrosodimethylamine during chloramination of secondary and tertiary amines: role of molecular oxygen and radical intermediates
N-Nitrosodimethylamine (NDMA) is a carcinogenic disinfection byproduct from water chloramination. Despite the identification of numerous NDMA precursors, essential parts of the reaction mechanism such as the incorporation of molecular O2 are poorly understood. In laboratory model systems for the chloramination of secondary and tertiary amines, we investigated the kinetics of precursor disappearance and NDMA formation, quantified the stoichiometries of monochloramine (NH2Cl) and aqueous O2 consumption, derived 18O-kinetic isotope effects (18O-KIE) for the reactions of aqueous O2, and studied the impact of radical scavengers on NDMA formation. Although the molar NDMA yields from five N, N-dimethylamine-containing precursors varied between 1.4% and 90%, we observed the stoichiometric removal of one O2 per N, N-dimethylamine group of the precursor indicating that the oxygenation of N atoms did not determine the molar NDMA yield. Small 18O-KIEs between 1.0026 ± 0.0003 and 1.0092 ± 0.0009 found for all precursors as well as completely inhibited NDMA formation in the presence of radical scavengers (ABTS and trolox) imply that O2 reacted with radical species. Our study suggests that aminyl radicals from the oxidation of organic amines by NH2Cl and N-peroxyl radicals from the reaction of aminyl radicals with aqueous O2 are part of the NDMA formation mechanism.
Spahr, S.; Cirpka, O. A.; von Gunten, U.; Hofstetter, T. B. (2017) Formation of N-Nitrosodimethylamine during chloramination of secondary and tertiary amines: role of molecular oxygen and radical intermediates, Environmental Science and Technology, 51(1), 280-290, doi:10.1021/acs.est.6b04780, Institutional Repository
Bromide sources and loads in Swiss surface waters and their relevance for bromate formation during wastewater ozonation
Bromide measurements and mass balances in the catchments of major Swiss rivers revealed that chemical industry and municipal waste incinerators are the most important bromide sources and account for ∼50% and ∼20%, respectively, of the ∼2000 tons of bromide discharged in the Rhine river in 2014 in Switzerland. About 100 wastewater treatment plants (WWTPs) will upgrade their treatment for micropollutant abatement in the future to comply with Swiss regulations. An upgrade with ozonation may lead to unintended bromate formation in bromide-containing wastewaters. Measured bromide concentrations were <0.05 mg L-1 in ∼75% of 69 WWTPs, while they ranged from 0.4 to ∼50 mg L-1 in WWTPs with specific bromide sources (e.g., municipal waste incinerators, landfill leachate, and chemical industry). Wastewater ozonation formed little bromate at specific ozone doses of ≤0.4 mg O3/mg DOC, while the bromate yields were almost linearly correlated to the specific ozone dose for higher ozone doses. Molar bromate yields for typical specific ozone doses in wastewater treatment (0.4-0.6 mg O3/mg DOC) are ≤3%. In a modeled extreme scenario (in which all upgraded WWTPs release 10 μg L-1 of bromate), bromate concentrations increased by <0.4 μg L-1 in major Swiss rivers and by several micrograms per liter in receiving water bodies with a high fraction of municipal wastewater.
Soltermann, F.; Abegglen, C.; Götz, C.; von Gunten, U. (2016) Bromide sources and loads in Swiss surface waters and their relevance for bromate formation during wastewater ozonation, Environmental Science and Technology, 50(18), 9825-9834, doi:10.1021/acs.est.6b01142, Institutional Repository
Advances in predicting organic contaminant abatement during ozonation of municipal wastewater effluent: reaction kinetics, transformation products, and changes of biological effects
Ozonation of municipal wastewater effluent has been considered in recent years as an enhanced wastewater treatment technology to abate trace organic contaminants (micropollutants). The efficiency of ozonation for micropollutant abatement depends on (1) the reactivity of ozone and OH radical (·OH) with the target micropollutant, (2) the dosage of ozone and the stability of ozone and ·OH in a given water matrix, (3) the removal of undesirable effects (e.g., biological activities) of a micropollutant after structural transformation, and (4) the biodegradability of transformation products in biological post-treatment. In this article, recent advances in predicting organic micropollutant abatement during ozonation of municipal wastewater effluents are reviewed with a focus on (i) principle-based approaches for describing and modeling the reaction kinetics of ozone and ·OH, (ii) transformation products and pathways, (iii) changes of biological activities, and (iv) biodegradation of transformation products in biological post-treatment. Using the chemical kinetics based on ozone and ·OH rate constants (i.e., compound-specific information) and exposures (i.e., water matrix-specific information), a generalized prediction of the abatement efficiency of various micropollutants in varying water quality appears to be possible. QSAR-type correlations based on Hammett coefficients or quantum chemical energy calculations or (semi)empirical models have been developed for predicting the ozone and ·OH rate constants and exposures, respectively. Models based on the ozone and ·OH reaction rules can be used to predict the transformation products of micropollutants by ozone and ·OH. Reaction rule-based models in combination with the chemical kinetics information will enable the prediction of transformation product evolution during ozonation. The biological activities of transformation products have been assessed by an effect-driven approach using in vitro bioassays. Biological activities with specific modes of action (e.g., receptor-binding activities) were found to be quite efficiently removed, upon slight structural modifications by ozone or ·OH. The formation of new biological activities has also been observed, which warrants identification of the responsible toxicophore(s) and quantitative exposure-based risk assessment. Finally, there is only limited experimental information on the biodegradability of transformation products; however, biodegradability probability models can be used to make first estimates. In future research, the discussed principle-based approaches can be more actively applied to determine and predict not only the abatement levels of the parent micropollutants but also the formation of transformation products and the consequent changes of biological activities and biodegradability, which determines the overall treatment efficiency.
Lee, Y.; von Gunten, U. (2016) Advances in predicting organic contaminant abatement during ozonation of municipal wastewater effluent: reaction kinetics, transformation products, and changes of biological effects, Environmental Science: Water Research and Technology, 2, 421-442, doi:10.1039/c6ew00025h, Institutional Repository
Research Activities in Photochemical Transformation Processes
Quantum yields, kinetics and mechanisms of photochemical reactions that lead to the degradation of chemical contaminants.
Photochemical Transformation Processes including pollutants and radicals
Photosensitized degradation of phenolic compounds, anilines, pharmaceuticals and pesticides: the complex role of dissolved organic matter (DOM) as a promoter and inhibitor of oxidation reactions
Photoinduced production and reaction kinetics of oxidizing radicals (sulfate radical, carbonate radical): application to the degradation of contaminants in engineered aquatic systems
Characterizing organic radical oxidants produced by photoirradiation of dissolved organic matter ("OROPHOT")
Photochemical transformation kinetics of organic pollutants
Photooxidants produced by chromophoric dissolved organic matter
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authors => protected'Remke, S. C.; von Gunten, U.; Canonica, S.' (62 chars)
title => protected'Enhanced transformation of aquatic organic compounds by long-lived photooxid ants (LLPO) produced from dissolved organic matter' (126 chars)
journal => protected'Water Research' (14 chars)
year => protected2021 (integer)
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startpage => protected'116707 (10 pp.)' (15 chars)
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categories => protected'DOM; aquatic photochemistry; transformation kinetics; photosensitizer; pheno xyl radicals; organic contaminants' (110 chars)
description => protected'Dissolved organic matter (DOM) plays a crucial role in the photochemical tra nsformation of organic contaminants in natural aquatic systems. The present study focuses on the characterization of a specific effect previously observ ed for electron-rich phenols, consisting in an acceleration of the DOM-photo sensitized transformation of target compounds at low concentrations (< 1 µM). This effect was hypothesized to be caused by DOM-derived "long-lived" photooxidants (LLPO). Pseudo-first-order rate constants for the transformati on of several phenols, anilines, sulfonamide antibiotics and phenylureas pho tosensitized by Suwannee River fulvic acid were determined under steady−st ate irradiation using the UVA and visible wavelengths from a medium-pressure mercury lamp. A significant enhancement (by a factor of 2.4 − 16) of th e first-order transformation rate constant of various electron-rich target c ompounds was observed for an initial concentration of 0.1 <em>μ</em>M compa red to 5 <em>μ</em>M . This effect points to a relevant reactivity of these compounds with LLPO. For phenols and anilines the enhancement effect occurr ed only above certain standard one-electron oxidation potentials. From these data series the standard one-electron reduction potential of LLPO was estim ated to be in the range of 1.0 − 1.3 V versus the standard hydrogen elec trode. LLPO are proposed to mainly consist of phenoxyl radicals formed by ph otooxidation of electron-poor phenolic moieties of the DOM. The plausibility of this hypothesis was successfully tested by studying the photosensitized transformation kinetics of 3,4-dimethoxyphenol in aqueous solutions containi ng a model photosensitizer (2-acetonaphthone) and a model electron-poor phen ol (4-cyanophenol) as DOM surrogates.' (1785 chars)
serialnumber => protected'0043-1354' (9 chars)
doi => protected'10.1016/j.watres.2020.116707' (28 chars)
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authors => protected'Canonica, S.; Schönenberger, U.' (42 chars)
title => protected'Inhibitory effect of dissolved organic matter on the transformation of selec ted anilines and sulfonamide antibiotics induced by the sulfate radical' (147 chars)
journal => protected'Environmental Science and Technology' (36 chars)
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description => protected'Dissolved organic matter (DOM) has been shown to inhibit the oxidation of ar omatic amines initiated by excited triplet states, an effect that was attrib uted to the reduction of oxidation intermediates back to their parent compou nds. The present study focuses on the quantification of an analogous inhibit ory effect of DOM on aqueous oxidations induced by the sulfate radical (SO<s ub>4</sub><sup>·</sup><sup>–</sup>). Second-order rate constants for the SO<sub>4</sub><sup>·</sup><sup>–</sup>-induced transformation of selected anilines and sulfonamide antibiotics were determined by competition kinetic s in the presence and absence of DOM from three different isolates at pH 8. In the presence of 1 mg<sub>C</sub> L<sup>–1</sup> of DOM, a significant reduction in the rate constant was observed for most of the compounds compa red to DOM-free solutions, but for two electron-rich anilines, increases in the rate constant were measured. For 4-cyanoaniline and sulfamethoxazole, th e DOM concentration dependence of the rate constant consisted of a sharp dec rease up to ∼1.0 mg<sub>C</sub> L<sup>–1</sup> of DOM followed by a re gion of slight changes or even increases for higher DOM concentrations (up t o 5 mg<sub>C</sub> L<sup>–1</sup>). This behavior was attributed to the o ccurrence of the aforementioned inhibitory effect and a counteracting accele rated transformation of the contaminants due to reactions with secondary rad ical oxidants resulting from DOM oxidation by SO<sub>4</sub><sup>·</sup><su p>–</sup>. Both effects of inhibition and secondary oxidants should be con sidered when assessing the abatement of aromatic amines in SO<sub>4</sub><su p>·</sup><sup>–</sup>-based advanced oxidation processes.' (1732 chars)
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authors => protected'Leresche, F.; Ludvíková, L.; Heger, D.; Klán, P.; von Gunten, U.; Canonica, S.' (111 chars)
title => protected'Laser flash photolysis study of the photoinduced oxidation of 4-(dimethylami no)benzonitrile (DMABN)' (99 chars)
journal => protected'Photochemical and Photobiological Sciences' (42 chars)
year => protected2019 (integer)
volume => protected18 (integer)
issue => protected'2' (1 chars)
startpage => protected'534' (3 chars)
otherpage => protected'545' (3 chars)
categories => protected'' (0 chars)
description => protected'Aromatic amines are aquatic contaminants for which phototransformation in su rface waters can be induced by excited triplet states of dissolved organic m atter (<sup>3</sup>DOM*). The first reaction step is assumed to consist of a one-electron oxidation process of the amine to produce its radical cation. In this paper, we present laser flash photolysis investigations aimed at cha racterizing the photoinduced, aqueous phase one-electron oxidation of 4-(dim ethylamino)benzonitrile (DMABN) as a representative of this contaminant clas s. The production of the radical cation of DMABN (DMABN<sup>•+</sup>) afte r direct photoexcitation of DMABN at 266 nm was confirmed in accord with pre vious experimental results. Moreover, DMABN<sup>•+</sup> was shown to be p roduced from the reactions of several excited triplet photosensitizers (carb onyl compounds) with DMABN. Second-order rate constants for the quenching of the excited triplet states by DMABN were determined to fall in the range of 3 × 10<sup>7</sup>–5 × 10<sup>9</sup> M<sup>−1</sup> s<sup>−1</sup> , and their variation was interpreted in terms of electron transfer theory u sing a Rehm–Weller relationship. The decay kinetics of DMABN<sup>•+</sup > in the presence of oxygen was dominated by a second-order component attrib
up>•+</sup> leading to photodegradation of DMABN was estimated not to exce ed ≈5 × 10<sup>3</sup> s<sup>−1</sup>.' (1563 chars)
serialnumber => protected'1474-905X' (9 chars)
doi => protected'10.1039/C8PP00519B' (18 chars)
uid => protected18425 (integer)
_localizedUid => protected18425 (integer)modified_languageUid => protectedNULL
_versionedUid => protected18425 (integer)modifiedpid => protected124 (integer)3 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=15613, pid=124)originalId => protected15613 (integer)
authors => protected'Vione, D.; Fabbri, D.; Minella, M.; Canonica, S.' (68 chars)
title => protected'Effects of the antioxidant moieties of dissolved organic matter on triplet-s ensitized phototransformation processes: implications for the photochemical modeling of sulfadiazine' (176 chars)
journal => protected'Water Research' (14 chars)
year => protected2018 (integer)
volume => protected128 (integer)
issue => protected'' (0 chars)
startpage => protected'38' (2 chars)
otherpage => protected'48' (2 chars)
categories => protected'antioxidants; sulfadiazine; electron donating capacity; dissolved organic ma tter; environmental photochemistry' (110 chars)
description => protected'Previous studies have shown that the photodegradation of some pollutants, in duced by the excited triplet states of chromophoric dissolved organic matter (<sup>3</sup>CDOM<sup>*</sup>), can be inhibited by back-reduction processe s carried out by phenolic antioxidants occurring in dissolved organic matter (DOM). Here, for the first time to our knowledge, we included such an inhib ition effect into a photochemical model and applied the model predictions to sulfadiazine (SDZ), a sulfonamide antibiotic that occurs in surface waters in two forms, neutral HSDZ and anionic SDZ<sup>−</sup> (pK<sub>a</sub> = 6 .5). The input parameters of the photochemical model were obtained by means of dedicated experiments, which showed that the inhibition effect was more m arked for SDZ− than for HSDZ. Compared to the behavior of 2,4,6-trimethylp henol, which does not undergo antioxidant inhibition when irradiated in natu ral water samples, the back-reduction effect on the degradation of SDZ was p roportional to the electron-donating capacity of the DOM. According to the m odel results, direct photolysis and ·OH reaction would account for the majo rity of both HSDZ and SDZ<sup>−</sup> photodegradation in waters having lo w dissolved organic carbon (DOC < 1 mgC L<sup>−/1</sup>). With higher DOC values (>3–4 mgC L<sup>−1</sup>) and despite the back-reduction processe s, the <sup>3</sup>CDOM<sup>*</sup> reactions are expected to account for th e majority of HSDZ phototransformation. In the case of SDZ<sup>−</sup> at high DOC, most of the photodegradation would be accounted for by direct phot olysis. The relative importance of the triplet-sensitized phototransformatio n of both SDZ<sup>−</sup> and (most importantly) HSDZ is expected to incre ase with increasing DOC, even in the presence of back reduction. An increase in water pH, favoring the occurrence of SDZ<sup>−</sup> with respect to H SDZ, would enhance direct photolysis at the expense of triplet sensitization . SDZ should be fairly p...' (2140 chars)
serialnumber => protected'0043-1354' (9 chars)
doi => protected'10.1016/j.watres.2017.10.020' (28 chars)
uid => protected15613 (integer)
_localizedUid => protected15613 (integer)modified_languageUid => protectedNULL
_versionedUid => protected15613 (integer)modifiedpid => protected124 (integer)4 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=14086, pid=124)originalId => protected14086 (integer)
authors => protected'Lee, M.; Merle, T.; Rentsch, D.; Canonica, S.; von Gunte n, U.' (86 chars)
title => protected'Abatement of polychoro-1,3-butadienes in aqueous solution by ozone, UV photo lysis, and advanced oxidation processes (O<SUB>3</SUB>/H<SUB>2</SUB>O<SUB>2< /SUB> and UV/H<SUB>2</SUB>O<SUB>2</SUB>)' (192 chars)
journal => protected'Environmental Science and Technology' (36 chars)
year => protected2017 (integer)
volume => protected51 (integer)
issue => protected'1' (1 chars)
startpage => protected'497' (3 chars)
otherpage => protected'505' (3 chars)
categories => protected'' (0 chars)
description => protected'The abatement of 9 polychloro-1,3-butadienes (CBDs) in aqueous solution by o zone, UV–C(254 nm) photolysis, and the corresponding advanced oxidation pr ocesses (AOPs) (i.e., O<SUB>3</SUB>/H<SUB>2</SUB>O<SUB>2</SUB> and UV/H<SUB> 2</SUB>O<SUB>2</SUB>) was investigated. The following parameters were determ ined for 9 CBDs: second-order rate constants for the reactions of CBDs with ozone (<I>k</I><SUB>O<SUB>3</SUB></SUB>) (<0.1–7.9 × 10<SUP>3</SUP> M<SUP >–1</SUP> s<SUP>–1</SUP>) or with hydroxyl radicals (<I>k</I><B>·</B><S UB>OH</SUB>) (0.9 × 10<SUP>9</SUP> – 6.5 × 10<SUP>9</SUP> M<SUP>–1</SU P> s<SUP>–1</SUP>), photon fluence-based rate constants (<I>k</I>′) (210 –2730 m<SUP>2</SUP> einstein<SUP>–1</SUP>), and quantum yields (Φ) (0.0 3–0.95 mol einstein<SUP>–1</SUP>). During ozonation of CBDs in a natural groundwater, appreciable abatements (>50% at specific ozone doses of 0.5 gO <SUB>3</SUB>/gDOC to ∼100% at ≥1.0 gO<SUB>3</SUB>/gDOC) were achieved fo r tetra-CBDs followed by (<I>Z</I>)-1,1,2,3,4-penta-CBD and hexa-CBD. This i s consistent with the magnitude of the determined <I>k</I><SUB>O<SUB>3</SUB> </SUB> and <I>k</I><B>·</B><SUB>OH</SUB>. The formation of bromate, a poten tially carcinogenic ozonation byproduct, could be significantly reduced by a ddition of H<SUB>2</SUB>O<SUB>2</SUB>. For a typical UV disinfection dose (4 00 J/m<SUP>2</SUP>), various extents of phototransformations (10–90%) coul d be achieved. However, the efficient formation of photoisomers from CBDs wi th <I>E/Z</I> configuration must be taken into account because of their pote ntial residual toxicity. Under UV–C(254 nm) photolysis conditions, no sign ificant effect of H<SUB>2</SUB>O<SUB>2</SUB> addition on CBDs abatement was observed due to an efficient direct phototransformation of CBDs.' (1812 chars)
serialnumber => protected'0013-936X' (9 chars)
doi => protected'10.1021/acs.est.6b04506' (23 chars)
uid => protected14086 (integer)
_localizedUid => protected14086 (integer)modified_languageUid => protectedNULL
_versionedUid => protected14086 (integer)modifiedpid => protected124 (integer)5 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=14074, pid=124)originalId => protected14074 (integer)
authors => protected'Rosario-Ortiz, F. L.; Canonica, S.' (49 chars)
title => protected'Probe compounds to assess the photochemical activity of dissolved organic ma tter' (80 chars)
journal => protected'Environmental Science and Technology' (36 chars)
year => protected2016 (integer)
volume => protected50 (integer)
issue => protected'23' (2 chars)
startpage => protected'12532' (5 chars)
otherpage => protected'12547' (5 chars)
categories => protected'' (0 chars)
description => protected'The photochemical properties of dissolved organic matter (DOM) have been of interest to scientists and engineers since the 1970s. Upon light absorption, chromophoric DOM (CDOM) can sensitize the formation of different short-live d reactive intermediates (RIs), including hydroxyl radical (<SUP><B>·</B></ SUP>OH), singlet oxygen (<SUP>1</SUP>O<SUB>2</SUB>) and superoxide radical a nion (O<SUB>2</SUB><SUP><B>·</B>–</SUP>). In addition, a fraction of the excited singlet states in CDOM decays into excited triplet states (<SUP>3</S UP>CDOM*), which are also important photochemical transients in environmenta l systems. These RIs have a significant impact on different processes in sun lit waters, including degradation of organic contaminants and the inactivati on of pathogens. Due to their transient nature and low steady-state concentr ations, the use of common analytical techniques for the direct measurement o f these species is impractical. Therefore, specific probe compounds (PCs) ar e used. PCs include furfuryl alcohol for <SUP>1</SUP>O<SUB>2</SUB>, and tere phthalic acid for <SUP><B>·</B></SUP>OH. In this publication, we present a critical review of the use of PCs for the assessment of the formation of pho tochemically generated RIs. We first introduce the concept of a PC, includin g the kinetic treatment and necessary assumptions needed to conduct a specif ic measurement. Afterward, we present short overviews of the most studied RI s and review relevant issues regarding the use of specific PCs for their mea surement. We finalize by offering recommendations regarding the use of PCs i n environmental photochemistry.' (1627 chars)
serialnumber => protected'0013-936X' (9 chars)
doi => protected'10.1021/acs.est.6b02776' (23 chars)
uid => protected14074 (integer)
_localizedUid => protected14074 (integer)modified_languageUid => protectedNULL
_versionedUid => protected14074 (integer)modifiedpid => protected124 (integer)6 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=14047, pid=124)originalId => protected14047 (integer)
authors => protected'Yuan, C.; Chakraborty, M.; Canonica, S.; Weavers, L.&nbs p;K.; Hadad, C. M.; Chin, Y.-P.' (122 chars)
title => protected'Isoproturon reappearance after photosensitized degradation in the presence o f triplet ketones or fulvic acids' (109 chars)
journal => protected'Environmental Science and Technology' (36 chars)
year => protected2016 (integer)
volume => protected50 (integer)
issue => protected'22' (2 chars)
startpage => protected'12250' (5 chars)
otherpage => protected'12257' (5 chars)
categories => protected'' (0 chars)
description => protected'Isoproturon (IPU) is a phenylurea herbicide used to control broad-leaf grass es on grain fields. Photosensitized transformation induced by excited triple t states of dissolved organic matter (<SUP>3</SUP>DOM*) has been identified as an important degradation pathway for IPU in sunlit waters, but the reappe arance of IPU in the absence of light is observed after the initial photolys is. In this study, we elucidate the kinetics of this photodegradation and da rk-reappearance cycling of IPU in the presence of DOM proxies (aromatic keto nes and reference fulvic acids). Using mass spectrometry and nuclear magneti c resonance spectroscopic techniques, a semi-stable intermediate (IPU<SUB>in t</SUB>) was found to be responsible for IPU reversion and was identified as a hydroperoxyl derivative of IPU. IPU<SUB>int</SUB> is photogenerated from incorporation of diatomic oxygen to IPU and is subjected to thermolysis whos e rate depends on temperature, pH, the presence of DOM, and inorganic ions. These results are important to understand the overall aquatic fate of IPU an d structurally similar compounds under diurnal conditions.' (1122 chars)
serialnumber => protected'0013-936X' (9 chars)
doi => protected'10.1021/acs.est.6b03655' (23 chars)
uid => protected14047 (integer)
_localizedUid => protected14047 (integer)modified_languageUid => protectedNULL
_versionedUid => protected14047 (integer)modifiedpid => protected124 (integer)7 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=14122, pid=124)originalId => protected14122 (integer)
authors => protected'McNeill, K.; Canonica, S.' (35 chars)
title => protected'Triplet state dissolved organic matter in aquatic photochemistry: reaction m echanisms, substrate scope, and photophysical properties' (132 chars)
journal => protected'Environmental Science: Processes and Impacts' (44 chars)
year => protected2016 (integer)
volume => protected18 (integer)
issue => protected'11' (2 chars)
startpage => protected'1381' (4 chars)
otherpage => protected'1399' (4 chars)
categories => protected'' (0 chars)
description => protected'Excited triplet states of chromophoric dissolved organic matter (<SUP>3</SUP >CDOM*) play a major role among the reactive intermediates produced upon abs orption of sunlight by surface waters. After more than two decades of resear ch on the aquatic photochemistry of <SUP>3</SUP>CDOM*, the need for improvin g the knowledge about the photophysical and photochemical properties of thes e elusive reactive species remains considerable. This critical review examin es the efforts to date to characterize <SUP>3</SUP>CDOM*. Information on <SU P>3</SUP>CDOM* relies mainly on the use of probe compounds because of the di fficulties associated with directly observing <SUP>3</SUP>CDOM* using transi ent spectroscopic methods. Singlet molecular oxygen (<SUP>1</SUP>O<SUB>2</SU B>), which is a product of the reaction between <SUP>3</SUP>CDOM* and dissol ved oxygen, is probably the simplest indicator that can be used to estimate steady-state concentrations of <SUP>3</SUP>CDOM*. There are two major modes of reaction of <SUP>3</SUP>CDOM* with substrates, namely triplet energy tran sfer or oxidation (<I>via</I> electron transfer, proton-coupled electron tra nsfer or related mechanisms). Organic molecules, including several environme ntal contaminants, that are susceptible to degradation by these two differen t reaction modes are reviewed. It is proposed that through the use of approp riate sets of probe compounds and model photosensitizers an improved estimat ion of the distribution of triplet energies and one-electron reduction poten tials of <SUP>3</SUP>CDOM* can be achieved.' (1563 chars)
serialnumber => protected'2050-7887' (9 chars)
doi => protected'10.1039/c6em00408c' (18 chars)
uid => protected14122 (integer)
_localizedUid => protected14122 (integer)modified_languageUid => protectedNULL
_versionedUid => protected14122 (integer)modifiedpid => protected124 (integer)8 => Snowflake\Publications\Domain\Model\Publicationprototypepersistent entity (uid=14034, pid=124)originalId => protected14034 (integer)
authors => protected'Leresche, F.; Von Gunten, U.; Canonica, S.' (57 chars)
title => protected'Probing the photosensitizing and inhibitory effects of dissolved organic mat ter by using <I>N,N</I>-dimethyl-4-cyanoaniline (DMABN)' (131 chars)
journal => protected'Environmental Science and Technology' (36 chars)
year => protected2016 (integer)
volume => protected50 (integer)
issue => protected'20' (2 chars)
startpage => protected'10997' (5 chars)
otherpage => protected'11007' (5 chars)
categories => protected'' (0 chars)
description => protected'Dissolved organic matter (DOM) can act as a photosensitizer and an inhibitor in the phototransformation of several nitrogen-containing organic contamina nts in surface waters. The present study was performed to select a probe mol ecule that is suitable to measure these antagonistic properties of DOM. Out of nine studied nitrogen-containing aromatic compounds, 4-cyanoaniline, <I>N , N</I>-dimethyl-4-cyanoaniline (DMABN), sotalol (a β-blocker) and sulfadia zine (a sulfonamide antibiotic) exhibited a marked photosensitized transform ation that could be substantially inhibited by addition of phenol as a model antioxidant. The photosensitized transformation of DMABN, the selected prob e compound, was characterized in detail under UV-A and visible irradiation ( λ > 320 nm) to avoid direct phototransformation. Low reactivity of DMABN wi th singlet oxygen was found (second-order rate constant <2 × 10<SUP>7</SUP> M<SUP>–1</SUP> s<SUP>–1</SUP>). Typically at least 85% of the reactivit y of DMABN could be inhibited by DOM or the model antioxidant phenol. The ph otosensitized transformation of DMABN mainly proceeded (>72%) through demeth ylation yielding <I>N</I>-methyl-4-cyanoaniline and formaldehyde as primary products. In solutions of standard DOM extracts and their mixtures the photo transformation rate constant of DMABN was shown to vary nonlinearly with the DOM concentration. Model equations describing the dependence of such rate c onstants on DOM and model antioxidant concentrations were successfully used to fit experimental data.' (1545 chars)
serialnumber => protected'0013-936X' (9 chars)
doi => protected'10.1021/acs.est.6b02868' (23 chars)
uid => protected14034 (integer)
_localizedUid => protected14034 (integer)modified_languageUid => protectedNULL
_versionedUid => protected14034 (integer)modifiedpid => protected124 (integer)
Enhanced transformation of aquatic organic compounds by long-lived photooxidants (LLPO) produced from dissolved organic matter
Dissolved organic matter (DOM) plays a crucial role in the photochemical transformation of organic contaminants in natural aquatic systems. The present study focuses on the characterization of a specific effect previously observed for electron-rich phenols, consisting in an acceleration of the DOM-photosensitized transformation of target compounds at low concentrations (< 1 µM). This effect was hypothesized to be caused by DOM-derived "long-lived" photooxidants (LLPO). Pseudo-first-order rate constants for the transformation of several phenols, anilines, sulfonamide antibiotics and phenylureas photosensitized by Suwannee River fulvic acid were determined under steady−state irradiation using the UVA and visible wavelengths from a medium-pressure mercury lamp. A significant enhancement (by a factor of 2.4 − 16) of the first-order transformation rate constant of various electron-rich target compounds was observed for an initial concentration of 0.1 μM compared to 5 μM . This effect points to a relevant reactivity of these compounds with LLPO. For phenols and anilines the enhancement effect occurred only above certain standard one-electron oxidation potentials. From these data series the standard one-electron reduction potential of LLPO was estimated to be in the range of 1.0 − 1.3 V versus the standard hydrogen electrode. LLPO are proposed to mainly consist of phenoxyl radicals formed by photooxidation of electron-poor phenolic moieties of the DOM. The plausibility of this hypothesis was successfully tested by studying the photosensitized transformation kinetics of 3,4-dimethoxyphenol in aqueous solutions containing a model photosensitizer (2-acetonaphthone) and a model electron-poor phenol (4-cyanophenol) as DOM surrogates.
Remke, S. C.; von Gunten, U.; Canonica, S. (2021) Enhanced transformation of aquatic organic compounds by long-lived photooxidants (LLPO) produced from dissolved organic matter, Water Research, 190, 116707 (10 pp.), doi:10.1016/j.watres.2020.116707, Institutional Repository
Inhibitory effect of dissolved organic matter on the transformation of selected anilines and sulfonamide antibiotics induced by the sulfate radical
Dissolved organic matter (DOM) has been shown to inhibit the oxidation of aromatic amines initiated by excited triplet states, an effect that was attributed to the reduction of oxidation intermediates back to their parent compounds. The present study focuses on the quantification of an analogous inhibitory effect of DOM on aqueous oxidations induced by the sulfate radical (SO4·–). Second-order rate constants for the SO4·–-induced transformation of selected anilines and sulfonamide antibiotics were determined by competition kinetics in the presence and absence of DOM from three different isolates at pH 8. In the presence of 1 mgC L–1 of DOM, a significant reduction in the rate constant was observed for most of the compounds compared to DOM-free solutions, but for two electron-rich anilines, increases in the rate constant were measured. For 4-cyanoaniline and sulfamethoxazole, the DOM concentration dependence of the rate constant consisted of a sharp decrease up to ∼1.0 mgC L–1 of DOM followed by a region of slight changes or even increases for higher DOM concentrations (up to 5 mgC L–1). This behavior was attributed to the occurrence of the aforementioned inhibitory effect and a counteracting accelerated transformation of the contaminants due to reactions with secondary radical oxidants resulting from DOM oxidation by SO4·–. Both effects of inhibition and secondary oxidants should be considered when assessing the abatement of aromatic amines in SO4·–-based advanced oxidation processes.
Canonica, S.; Schönenberger, U. (2019) Inhibitory effect of dissolved organic matter on the transformation of selected anilines and sulfonamide antibiotics induced by the sulfate radical, Environmental Science and Technology, 53(20), 11783-11791, doi:10.1021/acs.est.9b04105, Institutional Repository
Laser flash photolysis study of the photoinduced oxidation of 4-(dimethylamino)benzonitrile (DMABN)
Aromatic amines are aquatic contaminants for which phototransformation in surface waters can be induced by excited triplet states of dissolved organic matter (3DOM*). The first reaction step is assumed to consist of a one-electron oxidation process of the amine to produce its radical cation. In this paper, we present laser flash photolysis investigations aimed at characterizing the photoinduced, aqueous phase one-electron oxidation of 4-(dimethylamino)benzonitrile (DMABN) as a representative of this contaminant class. The production of the radical cation of DMABN (DMABN•+) after direct photoexcitation of DMABN at 266 nm was confirmed in accord with previous experimental results. Moreover, DMABN•+ was shown to be produced from the reactions of several excited triplet photosensitizers (carbonyl compounds) with DMABN. Second-order rate constants for the quenching of the excited triplet states by DMABN were determined to fall in the range of 3 × 107–5 × 109 M−1 s−1, and their variation was interpreted in terms of electron transfer theory using a Rehm–Weller relationship. The decay kinetics of DMABN•+ in the presence of oxygen was dominated by a second-order component attributed to its reaction with the superoxide radical anion (O2•−). The first-order rate constant for the transformation of DMABN•+ leading to photodegradation of DMABN was estimated not to exceed ≈5 × 103 s−1.
Leresche, F.; Ludvíková, L.; Heger, D.; Klán, P.; von Gunten, U.; Canonica, S. (2019) Laser flash photolysis study of the photoinduced oxidation of 4-(dimethylamino)benzonitrile (DMABN), Photochemical and Photobiological Sciences, 18(2), 534-545, doi:10.1039/C8PP00519B, Institutional Repository
Effects of the antioxidant moieties of dissolved organic matter on triplet-sensitized phototransformation processes: implications for the photochemical modeling of sulfadiazine
Previous studies have shown that the photodegradation of some pollutants, induced by the excited triplet states of chromophoric dissolved organic matter (3CDOM*), can be inhibited by back-reduction processes carried out by phenolic antioxidants occurring in dissolved organic matter (DOM). Here, for the first time to our knowledge, we included such an inhibition effect into a photochemical model and applied the model predictions to sulfadiazine (SDZ), a sulfonamide antibiotic that occurs in surface waters in two forms, neutral HSDZ and anionic SDZ− (pKa = 6.5). The input parameters of the photochemical model were obtained by means of dedicated experiments, which showed that the inhibition effect was more marked for SDZ− than for HSDZ. Compared to the behavior of 2,4,6-trimethylphenol, which does not undergo antioxidant inhibition when irradiated in natural water samples, the back-reduction effect on the degradation of SDZ was proportional to the electron-donating capacity of the DOM. According to the model results, direct photolysis and ·OH reaction would account for the majority of both HSDZ and SDZ− photodegradation in waters having low dissolved organic carbon (DOC < 1 mgC L−/1). With higher DOC values (>3–4 mgC L−1) and despite the back-reduction processes, the 3CDOM* reactions are expected to account for the majority of HSDZ phototransformation. In the case of SDZ− at high DOC, most of the photodegradation would be accounted for by direct photolysis. The relative importance of the triplet-sensitized phototransformation of both SDZ− and (most importantly) HSDZ is expected to increase with increasing DOC, even in the presence of back reduction. An increase in water pH, favoring the occurrence of SDZ− with respect to HSDZ, would enhance direct photolysis at the expense of triplet sensitization. SDZ should be fairly photolabile under summertime sunlight, with predicted half-lives ranging from a few days to a couple of months depending on water conditions.
Vione, D.; Fabbri, D.; Minella, M.; Canonica, S. (2018) Effects of the antioxidant moieties of dissolved organic matter on triplet-sensitized phototransformation processes: implications for the photochemical modeling of sulfadiazine, Water Research, 128, 38-48, doi:10.1016/j.watres.2017.10.020, Institutional Repository
Abatement of polychoro-1,3-butadienes in aqueous solution by ozone, UV photolysis, and advanced oxidation processes (O3/H2O2 and UV/H2O2)
The abatement of 9 polychloro-1,3-butadienes (CBDs) in aqueous solution by ozone, UV–C(254 nm) photolysis, and the corresponding advanced oxidation processes (AOPs) (i.e., O3/H2O2 and UV/H2O2) was investigated. The following parameters were determined for 9 CBDs: second-order rate constants for the reactions of CBDs with ozone (kO3) (<0.1–7.9 × 103 M–1 s–1) or with hydroxyl radicals (k·OH) (0.9 × 109 – 6.5 × 109 M–1 s–1), photon fluence-based rate constants (k′) (210–2730 m2 einstein–1), and quantum yields (Φ) (0.03–0.95 mol einstein–1). During ozonation of CBDs in a natural groundwater, appreciable abatements (>50% at specific ozone doses of 0.5 gO3/gDOC to ∼100% at ≥1.0 gO3/gDOC) were achieved for tetra-CBDs followed by (Z)-1,1,2,3,4-penta-CBD and hexa-CBD. This is consistent with the magnitude of the determined kO3 and k·OH. The formation of bromate, a potentially carcinogenic ozonation byproduct, could be significantly reduced by addition of H2O2. For a typical UV disinfection dose (400 J/m2), various extents of phototransformations (10–90%) could be achieved. However, the efficient formation of photoisomers from CBDs with E/Z configuration must be taken into account because of their potential residual toxicity. Under UV–C(254 nm) photolysis conditions, no significant effect of H2O2 addition on CBDs abatement was observed due to an efficient direct phototransformation of CBDs.
Lee, M.; Merle, T.; Rentsch, D.; Canonica, S.; von Gunten, U. (2017) Abatement of polychoro-1,3-butadienes in aqueous solution by ozone, UV photolysis, and advanced oxidation processes (O3/H2O2 and UV/H2O2), Environmental Science and Technology, 51(1), 497-505, doi:10.1021/acs.est.6b04506, Institutional Repository
Probe compounds to assess the photochemical activity of dissolved organic matter
The photochemical properties of dissolved organic matter (DOM) have been of interest to scientists and engineers since the 1970s. Upon light absorption, chromophoric DOM (CDOM) can sensitize the formation of different short-lived reactive intermediates (RIs), including hydroxyl radical (·OH), singlet oxygen (1O2) and superoxide radical anion (O2·–). In addition, a fraction of the excited singlet states in CDOM decays into excited triplet states (3CDOM*), which are also important photochemical transients in environmental systems. These RIs have a significant impact on different processes in sunlit waters, including degradation of organic contaminants and the inactivation of pathogens. Due to their transient nature and low steady-state concentrations, the use of common analytical techniques for the direct measurement of these species is impractical. Therefore, specific probe compounds (PCs) are used. PCs include furfuryl alcohol for 1O2, and terephthalic acid for ·OH. In this publication, we present a critical review of the use of PCs for the assessment of the formation of photochemically generated RIs. We first introduce the concept of a PC, including the kinetic treatment and necessary assumptions needed to conduct a specific measurement. Afterward, we present short overviews of the most studied RIs and review relevant issues regarding the use of specific PCs for their measurement. We finalize by offering recommendations regarding the use of PCs in environmental photochemistry.
Rosario-Ortiz, F. L.; Canonica, S. (2016) Probe compounds to assess the photochemical activity of dissolved organic matter, Environmental Science and Technology, 50(23), 12532-12547, doi:10.1021/acs.est.6b02776, Institutional Repository
Isoproturon reappearance after photosensitized degradation in the presence of triplet ketones or fulvic acids
Isoproturon (IPU) is a phenylurea herbicide used to control broad-leaf grasses on grain fields. Photosensitized transformation induced by excited triplet states of dissolved organic matter (3DOM*) has been identified as an important degradation pathway for IPU in sunlit waters, but the reappearance of IPU in the absence of light is observed after the initial photolysis. In this study, we elucidate the kinetics of this photodegradation and dark-reappearance cycling of IPU in the presence of DOM proxies (aromatic ketones and reference fulvic acids). Using mass spectrometry and nuclear magnetic resonance spectroscopic techniques, a semi-stable intermediate (IPUint) was found to be responsible for IPU reversion and was identified as a hydroperoxyl derivative of IPU. IPUint is photogenerated from incorporation of diatomic oxygen to IPU and is subjected to thermolysis whose rate depends on temperature, pH, the presence of DOM, and inorganic ions. These results are important to understand the overall aquatic fate of IPU and structurally similar compounds under diurnal conditions.
Yuan, C.; Chakraborty, M.; Canonica, S.; Weavers, L. K.; Hadad, C. M.; Chin, Y.-P. (2016) Isoproturon reappearance after photosensitized degradation in the presence of triplet ketones or fulvic acids, Environmental Science and Technology, 50(22), 12250-12257, doi:10.1021/acs.est.6b03655, Institutional Repository
Triplet state dissolved organic matter in aquatic photochemistry: reaction mechanisms, substrate scope, and photophysical properties
Excited triplet states of chromophoric dissolved organic matter (3CDOM*) play a major role among the reactive intermediates produced upon absorption of sunlight by surface waters. After more than two decades of research on the aquatic photochemistry of 3CDOM*, the need for improving the knowledge about the photophysical and photochemical properties of these elusive reactive species remains considerable. This critical review examines the efforts to date to characterize 3CDOM*. Information on 3CDOM* relies mainly on the use of probe compounds because of the difficulties associated with directly observing 3CDOM* using transient spectroscopic methods. Singlet molecular oxygen (1O2), which is a product of the reaction between 3CDOM* and dissolved oxygen, is probably the simplest indicator that can be used to estimate steady-state concentrations of 3CDOM*. There are two major modes of reaction of 3CDOM* with substrates, namely triplet energy transfer or oxidation (via electron transfer, proton-coupled electron transfer or related mechanisms). Organic molecules, including several environmental contaminants, that are susceptible to degradation by these two different reaction modes are reviewed. It is proposed that through the use of appropriate sets of probe compounds and model photosensitizers an improved estimation of the distribution of triplet energies and one-electron reduction potentials of 3CDOM* can be achieved.
McNeill, K.; Canonica, S. (2016) Triplet state dissolved organic matter in aquatic photochemistry: reaction mechanisms, substrate scope, and photophysical properties, Environmental Science: Processes and Impacts, 18(11), 1381-1399, doi:10.1039/c6em00408c, Institutional Repository
Probing the photosensitizing and inhibitory effects of dissolved organic matter by using N,N-dimethyl-4-cyanoaniline (DMABN)
Dissolved organic matter (DOM) can act as a photosensitizer and an inhibitor in the phototransformation of several nitrogen-containing organic contaminants in surface waters. The present study was performed to select a probe molecule that is suitable to measure these antagonistic properties of DOM. Out of nine studied nitrogen-containing aromatic compounds, 4-cyanoaniline, N, N-dimethyl-4-cyanoaniline (DMABN), sotalol (a β-blocker) and sulfadiazine (a sulfonamide antibiotic) exhibited a marked photosensitized transformation that could be substantially inhibited by addition of phenol as a model antioxidant. The photosensitized transformation of DMABN, the selected probe compound, was characterized in detail under UV-A and visible irradiation (λ > 320 nm) to avoid direct phototransformation. Low reactivity of DMABN with singlet oxygen was found (second-order rate constant <2 × 107 M–1 s–1). Typically at least 85% of the reactivity of DMABN could be inhibited by DOM or the model antioxidant phenol. The photosensitized transformation of DMABN mainly proceeded (>72%) through demethylation yielding N-methyl-4-cyanoaniline and formaldehyde as primary products. In solutions of standard DOM extracts and their mixtures the phototransformation rate constant of DMABN was shown to vary nonlinearly with the DOM concentration. Model equations describing the dependence of such rate constants on DOM and model antioxidant concentrations were successfully used to fit experimental data.
Leresche, F.; Von Gunten, U.; Canonica, S. (2016) Probing the photosensitizing and inhibitory effects of dissolved organic matter by using N,N-dimethyl-4-cyanoaniline (DMABN), Environmental Science and Technology, 50(20), 10997-11007, doi:10.1021/acs.est.6b02868, Institutional Repository
