Mechanistic Aspects of Photodegradation of Deoxynucleosides Induced by Triplet State of Effluent Organic Matter.

Excited triplet states of wastewater effluent organic matter (3EfOM*) are known as important photo-oxidants in the degradation of extracellular antibiotic resistance genes (eArGs) in sunlit waters. In this work, we further found that 3EfOM* showed highly selective reactivity toward 2'-deoxyguanosine (dG) sites within eArGs in irradiated EfOM solutions at pH 7.0, while it showed no photosensitizing capacity toward 2'-deoxyadenosine, 2'-deoxythymidine, and 2'-deoxycytidine (the basic structures of eArGs). The 3EfOM* contributed to the photooxidation of dG primarily via one-electron transfer mechanism, with second-order reaction rate constants of (1.58-1.74) × 108 M-1 s-1, forming the oxidation intermediates of dG (dG(-H)•). The formed dG(-H)• could play a significant role in hole hopping and damage throughout eArGs. Using the four deoxynucleosides as probes, the upper limit for the reduction potential of 3EfOM* is estimated to be between 1.47 and 1.94 VNHE. Compared to EfOM, the role of the triplet state of terrestrially natural organic matter (3NOM*) in dG photooxidation was minor (∼15%) mainly due to the rapid reverse reactions of dG(-H)• by the antioxidant moieties of NOM. This study advances our understanding of the difference in the photosensitizing capacity and electron donating capacity between NOM and EfOM and the photodegradation mechanism of eArGs induced by 3EfOM*.

Unraveling Multiple Pathways of Electron Donation from Phenolic Moieties in Natural Organic Matter.

Natural organic matter (NOM) exhibits a distinctive electron-donating capacity (EDC) that serves a pivotal role in the redox reactions of contaminants and minerals through the transformation of electron-donating phenolic moieties. However, the ambiguity of the molecular transformation pathways (MTPs) that engender the EDC during NOM oxidation remains a significant issue. Here, MTPs that contribute to EDC were investigated by identifying the oxidized products of phenolic model compounds and NOM samples in direct or mediated electrochemical oxidation (DEO or MEO, respectively) using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). It was found that the oxidation of newly formed phenolic-OH (ArOH) and the oxidative coupling reaction of the phenoxy radical are the main MTPs that directly contribute to EDC, in addition to the transformation of hydroquinones to quinones. Notably, the oxidative coupling reaction of ArOH contributed at least 22-42% to the EDC. Ferulic acid-like structures can also directly contribute to EDC by incorporating H2O into their acrylic substituents. Furthermore, the opening of C rings can indirectly attenuate the EDC through structural alterations in the electron-donating process of NOM. Decarboxylation can either weaken or enhance the EDC depending on the structure of the phenolic moieties in NOM. These findings suggest that the EDC of NOM is a comprehensive result of multiple NOM MTPs, involving not only ArOH oxidation but also the addition of H2O to olefinic bonds and bond-breaking reactions. Our work provides molecular evidence that aids in the comprehension of the multiple EDC-associated transformation pathways of NOM.

Linking Redox Characteristics to Dissolved Organic Matter Derived from Different Biowaste Composts: A Theoretical Modeling Approach Based on FT-ICR MS Analysis.

Compost dissolved organic matter (DOM) is a complex mixture of redox-active organic molecules that impact various biogeochemical processes in soil environments. However, the impact of chemical complexity (heterogeneity and chemodiversity) on the electron accepting capacity (EAC) and electron donating capacity (EDC) of DOM molecules remains unclear, which hinders our ability to predict their environmental behavior and redox properties. In this study, the applicability of Vienna Soil Organic Matter Modeler 2 (VSOMM2) to the composting system based on the FT-ICR MS data has been validated. A molecular modeling approach using VSOMM2 and Schrödinger software was developed to quantitatively assess the redox sites and molecular interactions of compost DOM. Compost DOM molecules are categorized into three distinct groups based on their heterogeneous origins. In addition, we have developed 18 molecular models of compost DOM based on the links of molecules to EAC/EDC. Finally, Ar-OH, quinone, Ar-SH, and Ar-NH2 were identified as the redox sites; noncovalent contacts, H bonds, salt bridges, and aromatic-H bonds might be significant electronic transmission channels of compost DOM. Our findings contribute to the development of precise regulatory methods for functional molecules within compost DOM, providing the fine standards for composts matching specific ecosystem service requirements.

Effects of Microplastics on Soil Carbon Mineralization: The Crucial Role of Oxygen Dynamics and Electron Transfer.

Although our understanding of the effects of microplastics on the dynamics of soil organic matter (SOM) has considerably advanced in recent years, the fundamental mechanisms remain unclear. In this study, we examine the effects of polyethylene and poly(lactic acid) microplastics on SOM processes via mineralization incubation. Accordingly, we evaluated the changes in carbon dioxide (CO2) and methane (CH4) production. An O2 planar optical sensor was used to detect the temporal behavior of dissolved O2 during incubation to determine the microscale oxygen heterogeneity caused by microplastics. Additionally, the changes in soil dissolved organic matter (DOM) were evaluated using a combination of spectroscopic approaches and ultrahigh-resolution mass spectrometry. Microplastics increased cumulative CO2 emissions by 160-613%, whereas CH4 emissions dropped by 45-503%, which may be attributed to the oxygenated porous habitats surrounding microplastics. Conventional and biodegradable microplastics changed the quantities of soil dissolved organic carbon. In the microplastic treatments, DOM with more polar groups was detected, suggesting a higher level of electron transport. In addition, there was a positive correlation between the carbon concentration, electron-donating ability, and CO2 emission. These findings suggest that microplastics may facilitate the mineralization of SOM by modifying O2 microenvironments, DOM concentration, and DOM electron transport capability. Accordingly, this study provides new insights into the impact of microplastics on soil carbon dynamics.

UV absorbance and electron donating capacity as surrogate parameters to indicate the abatement of micropollutants during the oxidation of Fe(II)/PMS and Mn(II)/NTA/PMS.

In this study, the relative residual UV absorbance (UV254) and/or electron donating capacity (EDC) was investigated as a surrogate parameter to evaluate the abatement of micropollutants during the Fe(II)/PMS and Mn(II)/NTA/PMS processes. In the Fe(II)/PMS process, due to the generation of SO4•- and •OH at acidic pH, UV254 and EDC abatement was greater at pH 5. In the Mn(II)/NTA/PMS process, UV254 abatement was greater at pH 7 and 9, while EDC abatement was greater at pH 5 and 7. This was attributed to the fact that MnO2 was formed at alkaline pH to remove UV254 by coagulation, and manganese intermediates (Mn(V)) were formed at acidic pH to remove EDC via electron transfer. Due to the strong oxidation capacity of SO4•-, •OH and Mn(V), the abatement of micropollutants increased with increasing dosages of oxidant in different waters in both processes. In the Fe(II)/PMS and Mn(II)/NTA/PMS processes, except for nitrobenzene (∼23% and 40%, respectively), the removal of other micropollutants was greater than 70% when the oxidant dosages were greater in different waters. The linear relationship between the relative residual UV254, EDC and the removal of micropollutants was established in different waters, showing a one-phase or two-phase linear relationship. The differences of the slopes for one-phase linear correlation in the Fe(II)/PMS process (micropollutant-UV254: 0.36-2.89, micropollutant-EDC: 0.26-1.75) were less than that in the Mn(II)/NTA/PMS process (micropollutant-UV254: 0.40-13.16, micropollutant-EDC: 0.51-8.39). Overall, these results suggest that the relative residual UV254 and EDC could truly reflect the removal of micropollutants during the Fe(II)/PMS and Mn(II)/NTA/PMS processes.

Mechanistic Investigation of Enhanced Photoreactivity of Dissolved Organic Matter after Chlorination.

Chlorine is commonly used in disinfection processes in wastewater treatment plants prior to discharge of the effluents into receiving waters. Effluent organic matter and humic substances constitute up to 90% of dissolved organic matter (DOM) in receiving water, which induces photogeneration of reactive species (RS) such as excited triplet state of DOM (3DOM*), singlet oxygen (1O2), and hydroxyl radical (•OH). The RS plays an important role in the attenuation of trace pollutants. However, the effect of chlorine disinfection on the photoreactivity of the DOM has remained unclear. Here, we investigated the physicochemical properties and subsequent RS variation after chlorination of DOM. Solid-state 13C cross-polarization/magic angle-spinning NMR and Fourier transform ion cyclotron resonance mass spectrometry verified that the aromaticity, electron-donating capacity (EDC), and average molecular weight of DOM decreased markedly after chlorination. It was found for the first time that the photoproduction of 3DOM*, 1O2, and •OH increased markedly after chlorination of DOM upon irradiation of simulated sunlight. The quantum yields of 3DOM*, 1O2, and •OH were positively correlated with E2/E3 (ratio of the absorbance at 254 to 365 nm) while negatively correlated with EDC before and after chlorination. These findings highlight the synergetic effect of chlorine disinfection on the photosensitization of DOM under irradiation of sunlight, which will promote the removal of trace pollutants in surface waters.

Influences of wildfire on the soil dissolved organic matter characteristics and its electron-donating capacity.

Global increases in the intensity and frequency of wildfires are driving major changes in soil organic matter (SOM) characteristics, including soil dissolved organic matter (DOM). As the most crucial component of SOM, soil DOM plays a pivotal role in the carbon cycle and regulates the environmental fate of contaminants through its versatile reactivities, including electron-donating capacity (EDC). However, it is still being determined how wildfire influences key characteristics of soil DOM and subsequent effects on EDC in forest soils. Thus, we conducted our study to fill this gap with the forest soils of Jinyun Mountain Nature Reserve of China, which experienced an unprecedented wildfire event in 2022. The results from optical characterization, high-performance size-exclusion chromatography (HPSEC), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) showed decreasing molecular weight but elevating nitrogen-containing molecular formulas of soil DOM in the burned soils. This could be attributed to the Maillard reaction and microbial re-colonies. Additionally, wildfires increased the condensed aromatics and lignin components in soil DOM. In the burned soils, we observed increasing EDC of soil DOM, which accounts for an increase in lignin-derived phenolic components. Overall, the findings of this study demonstrate that eco-disturbances, such as wildfires, induce alterations in the properties of DOM, leading to variations in its reactivity and potentially influencing the fate of environmental pollutants beyond carbon dynamics alone. Thus, incorporating the dynamic properties of soil DOM, particularly in the context of climate change, can enhance the assessment of risks associated with contaminants in soil and water, providing valuable insights.

Qualitative and quantitative analysis of electrons donated by pollutants in electron transfer-based oxidation system: Electrochemical measurement and theoretical calculations.

In order to gain a profound understanding of the fate of pollutants in advanced oxidation processes (AOPs), this study analyzed the electron contribution of pollutants qualitatively and quantitatively which rarely reported before. The rich electron transfer system was constructed by mesoporous carbon nitride (MCN) coupling with persulfate (PS) driven by visible light and the sulfanilamide antibiotics (SULs) were used as target contaminants. Firstly, the qualitative analysis of electron transfer in the system was confirmed systematically. The electron flow direction tested by i-t curves indicated that PS absorbed electrons, while SULs released electrons. The flow rate of electrons was also accelerated after the addition of SULs. The fitting curve between the kinetics and the peak potential difference tested by CV curve showed that the larger potential difference, the slower rate of oxidative degradation. Secondly, the quantification of electron transfer was achieved through theoretical calculations to simulate the interactions of the 'catalyst-oxidant-antibiotic' system. After the addition of SULs, the adsorption energy of the 'catalyst-oxidant-antibiotic' system was enhanced and the bond length of the peroxide bond was stretched. Notably, the electron transfer analysis results showed that the charge of SULs was around 0.032-0.056e, indicating that SULs pollutants played the role of electron contributors in the system. The oxidative degradation pathway included the direct cracking of S-N bond, shedding of marginal groups, ring-opening and hydroxyl addition reaction. This study clarified the electronic contribution of SULs in the oxidation system, providing necessary theoretical supplement for the analysis of the transformation of pollutants in AOPs.

Adsorption of oxidized humic acid onto redox-inert mineral surfaces induces formation of hydroxyl radicals and carbon dynamics.

The dark formation of hydroxyl radicals (·OH) from O2 activation by reduced humic substances at oxic-anoxic interfaces has been extensively documented. However, their generation in oxic subsurface environments is typically overlooked due to the scarcity of electron donors, especially in the presence of minerals. In this study, the formation of ·OH during the adsorption of oxidized humic acids (HA) onto redox-inert minerals was investigated under oxic and pH-neutral conditions. Batch experiment results demonstrated that the adsorption of oxidized HA onto aluminum (hydr)oxide and Fe-free clay minerals induces the formation of ·OH (e.g., 16/28 µmol/g C) without the addition of exogenous electron donors. In contrast, the interaction of oxidized HA alone with O2 did not result in measurable ·OH production. The enhanced electron-donating capacity (EDC) and humification of the whole HA (mainly in adsorbed state) were measured after adsorption. The surface-catalyzed polymerization of oxidizable polyphenols in HA is proposed as the plausible mechanism for the observed EDC enhancement, which in turn triggers O2 activation for ·OH production. Furthermore, substantial chemical alterations of lignins and condensed aromatics within HA were observed, producing more compounds exhibiting higher molecular weight, aromaticity, O/C ratio, and nominal oxidation state of carbon. It is indicated that the contribution of oxidative polymerization outweighs ·OH oxidation in the molecular transformation of adsorbed HA. Overall, our findings extend the understanding of HA-induced ·OH production from oxic-anoxic interfaces to the oxic zone and present a novel pathway for the abiotic transformation of recalcitrant organic matter in subsurface environments with extensive surface water-groundwater interactions.

Differential responses of the electron transfer capacities of soil humic acid and fulvic acid to long-term wastewater irrigation.

Wastewater irrigation is used to supplement agricultural irrigation because of its benefits and freshwater resource scarcity. However, whether wastewater irrigation for many years affects the electron transfer capacity (ETC) of natural organic matter in soil remains unclear, and organic matter could influence the decomposition and mineralization of substances with redox characteristics in soil through electron transfer, ultimately affecting the soil environment. The composition of soil humic substances (HS) is highly complex, and the effects of soil humic acid (HA) and fulvic acid (FA) on ETC is poorly understood. In this study, we separately evaluated the responses of the electron-accepting capacity (EAC) and electron-donating capacity (EDC) of soil HA and FA in agricultural fields to various durations of wastewater irrigation. Results showed that the EAC of HA and FA increased significantly with increasing the duration of wastewater irrigation. When wastewater irrigation lasted for 56 years, the EAC of HA showed a higher increment (590 %) than that of FA (223 %). The EDC of soil HA and FA, conversely, decreased compared to the control, with the highest reduction of 35.6 % for HA and 65.9 % for FA. Specifically, the EDC of HA gradually decreased starting from 29 years of wastewater irrigation, whereas the decrease in the EDC of FA exhibited no clear pattern in relation to the duration of wastewater irrigation. Increased soil organic matter and total nitrogen content under long-term wastewater irrigation led to an increase in sucrase and phosphatase activities, along with an increase in EAC and a decrease in EDC of HS. This suggests that soil enzyme activities may ultimately lead to changes in ETC. The results of this research provide practical insights into the redox system in soil and its driving role in soil organic matter transformation and nutrient cycling under wastewater irrigation.

A general way to realize the bi-directional promotion effects on the photocatalytic removal of heavy metals and organic pollutants in real water by a novel S-scheme heterojunction: Experimental investigations, QSAR and DFT calculations.

Heavy metals (HMs) often coexist with organic pollutants (OPs) in real surface water. Is it possible to find a general way that the removal of one from these two pollutants will promote the elimination of another pollutant? Herein, the bi-directional promotion effects (BPEs) on synchronous removal of Cr(VI) (i.e., hexavalent chromium) and OPs were achieved by a SnNb2O6/CuInS2 S-scheme heterojunction. Specifically, the apparent rate constants are 0.161 min-1 [(Cr(VI)] and 0.019 min-1 [Tetracycline hydrochloride (TCH)] in coexisting Cr(VI)/TCH system (which are 3.74 and 1.58 times, respectively, compared to the mono-pollutant system), indicating OPs indeed can act as hole scavengers (electron donors) to consume plenty of photoinduced holes and enable more photoexcited electrons to attend to Cr(VI) photoreduction. More significantly, OPs (i.e., TCH, atrazine and 4-chlorophenol) with different molecular structures possess different adiabatic ionization potentials (AIPs), in an inversely linear relationship with BPEs, i.e., the lower AIP value is, the higher electron-donating ability is, the better BPEs present. Finally, TCH and its degradation intermediates toxicity was forecasted via quantitative structure-activity relationship, demonstrating the toxicity decrease of TCH during the photocatalytic process. This work provides a general strategy for simultaneous removal of contaminants, contributing to wastewater purification.

The degradation of p-nitrophenol by biochar is dominated by its electron donating capacity.

The typical aromatic and phenolic pollutant, p-nitrophenol (PNP), is extensively used in the industry and can seriously threaten the environmental health. Biochar, as a solid carbon-rich material, can directly degrade PNP. It has been reported that the PNP degradation by biochar is closely related to the electron exchange capacity of biochar (the sum of electron donating and accepting capacities). However, the roles of electron donating and accepting capacity of biochar in PNP degradation have not been distinguished before. In this study, the biochar samples were chemically modified to manipulate the electron donating and accepting capacities of biochar samples. Compared with pristine biochar (3.67 %), modified biochar had higher degradation efficiencies of PNP (>7.81 %). The strictly positive correlation between the electron donating capacities and the PNP degradation rates of biochar samples (r = 0.98, p < 0.05) indicated that the PNP degradation process by biochar is dominated by the reduction process. Although both the oxidation and reduction degradation products were found in the degradation system, the quenching experiment of OH, a key radical in the process of oxidation degradation, further proved that the oxidation process just played a minor role (<10 %) in the PNP degradation by biochar. This study shed light on the degradation mechanism of PNP by biochar and could promote the application of biochar in the pollution remediation.

Sulfurization alters phenol-formaldehyde resin microplastics redox property and their efficiency in mediating arsenite oxidation.

Microplastics weathering by various types of oxidants in the oxic environment and their interaction with environmental contaminants have drawn numerous scientific attention. However, the environmental fate of microplastics under a reducing environment has been largely unresolved. Herein, the change of physicochemical and redox properties of microplastics during the weathering under a sulfate-reducing environment and the interaction with arsenite were addressed. The sulfurization of phenol-formaldehyde resin microplastics under a sulfate-reducing environment generated smooth and porous particles with the induction of organic S species. Multiple spectroscopic results demonstrated thioether and thiophene groups formed by the substitute removal of O-containing functional groups. Moreover, the sulfurization process induced the reduction of carbonyl groups and oxidation of phenolic hydroxyl groups and resulted in the formation of semiquinone radicals. The O-containing functional groups contributed to microplastics redox property and As(III) oxidation while S-containing functional groups showed no obvious effect. The sulfurized microplastics had lower efficiency in mediating arsenite oxidation than the unsulfurized counterparts due to the decreased electron donating capacity. Producing hydrogen peroxides by electron-donating phenol groups and semiquinone radicals and the direct semiquinone radicals oxidation could mediate arsenite oxidation. The findings of this study help us understand the fate of microplastics in redox fluctuation interfaces.

Role of trace TEMPO as electron shuttle in enhancing chloroquine phosphate elimination in UV-LED-driven persulfate activation process.

Chloroquine Phosphate (CP) is an antiviral drug used for treatment of COVID-19. It is released into wastewater and eventually contaminates natural water. This study reports an effective homogeneous catalysis way for CP degradation by the 2,2,6,6-Tetramethylpiperidine-N-oxyl (TEMPO) enhanced persulfate (PDS) activation under UVB-LEDs irradiation at 305 nm. TEMPO at a low concentration (0.1 µM) enhanced CP degradation in UV305/PDS process in deionized water at different pHs, in different anions and different molecular weight dissolved organic matter solutions and in real surface water. The enhancement was verified to be attributed to the electron shuttle role of TEMPO, which promoted the yield of SO4 •- by enhancing electron donating capacity of the reacting system. The degradation products of CP and their acute toxicities suggested that UV305/PDS/TEMPO process has better performance on CP detoxification than UV305/PDS process. This study provides a new way to tackle the challenge of pharmaceutical pollutions in homogeneous photocatalysis process for natural water and sewage restoration.

Preparation of phosphoric acid modified antibiotic mycelial residues biochar: Loading of nano zero-valent iron and promotion on biogas production.

Antibiotic mycelial residues (AMRs), as recyclable hazardous waste, can realize efficient utilization by reasonable treatment. To solve the problems of undeveloped pore structure and low specific surface area existed in AMR biochar, this study first modified biochar by phosphoric acid (H3PO4) to prepare PBC (H3PO4-modified biochar). Then, PBC was used as carrier to load nano zero-valent iron (nZVI) for preparation of nZVI/PBC. Finally, the biochar materials were used to promote anaerobic digestion (AD) of corn straw. The results showed that H3PO4-modification can effectively improve the specific surface area, pore structure, and electron donating capacity of AMRs biochar. The using of PBC as carrier to load nZVI attenuated the agglomeration of nZVI particles. Both PBC and nZVI/PBC improved the AD process, with biogas yield enhanced by 29.63% and 29.26%, respectively. The nZVI/PBC exhibited higher ability in maintaining the stability of AD system and promotion of fiber degradation than PBC.

Estimation of the biogeochemical reactivities of dissolved organic matter from modified biochars using color.

Modified biochar is widely used as a soil amendment in agricultural systems to improve crop yields and remove environmental pollutants. The water-soluble fraction of biochar, called biochar-derived dissolved organic matter (DOMBC), is the most active biochar component. However, the correlation between the optical properties of DOMBC and its biogeochemical activity remain unclear. In this study, one biochar and six modified derivatives were used to extract DOMBC and characterize its optical properties. The biogeochemical reactivities of DOMBC were determined using biodegradation, photodegradation, and electron-donating capacity assays. The results show that modification changes the biochar characteristics, leading to a variety of DOMBC properties. The DOMBC from modified biochars degrades more rapidly than the original biochar. On the other hand, modification reduces the redox functional groups in DOMBC, resulting in a lower electron-donating capacity of DOM samples. However, the modifications did not seem to affect photodegradation. Not all spectral parameters provide information about the correlations between the DOMBC properties and biogeochemical reactivity. However, two fundamental properties, that is, the specific UV absorbance at 254 nm (SUVA254, showing aromaticity) and spectral slopes over the ranges of 275-295 nm of the UV absorbance (S275-295, showing molecular weight), are the dominant factors affecting the biodegradation and electron-donating capacities of DOMBC. In this study, a rapid and straightforward method is presented, which can be used to characterize DOMBC and predict the reactivity of biochar that is used as an environmental amendment to minimize toxic organic compounds.

Application of UV absorbance and electron-donating capacity as surrogates for micropollutant abatement during full-scale ozonation of secondary-treated wastewater.

Ozonation of secondary-treated wastewater for the abatement of micropollutants requires a reliable control of ozone doses. Changes in the UV absorbance of dissolved organic matter (DOM) during ozonation allow to estimate micropollutant abatement on-line and were therefore identified as feed-back control parameter. In this study, the suitability of the electron-donating capacity (EDC) as an additional surrogate parameter which is independent of optical DOM properties was evaluated during full-scale ozonation. For this purpose, a recently developed EDC analyzer was enhanced to enable continuous on-line EDC and UV absorbance measurements. During a multi-week monitoring campaign at the wastewater treatment plant of Zurich, Switzerland, specific ozone doses were varied from 0.13 to 0.91 mgO3⋅mgDOC-1 and selected micropollutants with different ozone reactivities were analyzed by LC-MS in conjunction with bromate analysis by IC-MS. In agreement with previous laboratory studies, the relative residual UV absorbance and EDC both decreased exponentially as a function of the specific ozone dose and, in comparison to the residual UV absorbance, residual EDC values showed a more pronounced decrease at low specific ozone doses ≤0.34 mgO3⋅mgDOC-1. Logistic regression models allowed to estimate relative residual micropollutant concentrations in the ozonation effluent using either the residual UV absorbance or EDC as explanatory variable. Averaging those models along the explanatory variables allowed to estimate target values in relative residual UV absorbances and EDC for specific micropollutant abatement targets. In addition, both parameters allowed to identify conditions with elevated conversions of bromide to bromate. Taken together, these findings show that the integration of relative residual EDC values as a second control parameter can improve existing absorbance-based ozonation control systems to meet micropollutant abatement targets, particularly for treatment systems where low ozone doses are applied.

Oxidant-reactive carbonous moieties in dissolved organic matter: Selective quantification by oxidative titration using chlorine dioxide and ozone.

The application of oxidants for disinfection or micropollutant abatement during drinking water and wastewater treatment is accompanied by oxidation of matrix components such as dissolved organic matter (DOM). To improve predictions of the efficiency of oxidation processes and the formation of oxidation products, methods to determine concentrations of oxidant-reactive phenolic, olefinic or amine-type DOM moieties are critical. Here, a novel selective oxidative titration approach is presented, which is based on reaction kinetics of oxidation reactions towards certain DOM moieties. Phenolic moieties were determined by oxidative titration with ClO2 and O3 for five DOM isolates and two secondary wastewater effluent samples. The determined concentrations of phenolic moieties correlated with the electron-donating capacity (EDC) and the formation of inorganic ClO2-byproducts (HOCl, ClO2-, ClO3-). ClO2-byproduct yields from phenol and DOM isolates and changes due to the application of molecular tagging for phenols revealed a better understanding of oxidant-reactive structures within DOM. Overall, oxidative titrations with ClO2 and O3 provide a novel and promising tool to quantify oxidant-reactive moieties in complex mixtures such as DOM and can be expanded to other matrices or oxidants.

Dual roles of biochar redox property in mediating 2,4-dichlorophenol degradation in the presence of Fe3+ and persulfate.

Recent studies suggested that biochars could mediate the degradation of organic contaminants. The role of biochars in mediating organic contaminant degradation could be amplified in a Fenton-like reaction, and comparing biochars with varied properties may provide insightful information to understand the reaction mechanisms. In this study, biochar was applied in a Fenton-like reaction system with Fe3+ and persulfate (PS) to degrade 2,4-dichlorophenel (2,4-DCP). Biochars with different intensities of persistent free radicals (PFRs), oxygen-containing functional groups (OFGs), and redox properties were investigated regarding their roles in 2,4-DCP removal. Compared to biochar system, PS addition increased 2,4-DCP degradation and Fe3+ addition increased its sorption. The combination of PS and Fe3+ promoted 2,4-DCP degradation over 2 times higher. Various reactive oxygen species (ROS), including SO4•-, HO•, and O2•-, were involved in 2,4-DCP degradation, contributing to around 50% of the overall 2,4-DCP degradation. The direct electron transfer between biochar particles and 2,4-DCP contributed to the rest of 2,4-DCP degradation. A significant positive correlation was observed between 2,4-DCP degradation and electron donating capacity (EDC) or Fe2+. We thus concluded that EDC-involved structures in biochars could either directly donate electron to 2,4-DCP, or reduce Fe3+ to Fe2+, which activated PS to generate ROS. This dual roles of biochar should be well considered in biochar application and production. This study provided a useful theoretical basis for manipulating biochar redox properties to enhance their application potential in pollution control.

Use of Ore-Derived Humic Acids With Diverse Chemistries to Elucidate Structure-Activity Relationships (SAR) of Humic Acids in Plant Phenotypic Expression.

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