Reactivity of unactivated peroxymonosulfate and peroxyacetic acid with thioether micropollutants: Mechanisms and rate prediction.

Thioether compounds, prevalent in pharmaceuticals, are of growing environmental concern due to their prevalence and potential toxicity. Peroxy chemicals, including peroxymonosulfate (PMS) and peroxyacetic acid (PAA), hold promise for selectively attacking specific thioether moieties. Still, it has been unclear how chemical structures affect the interactions between thioethers and peroxy chemicals. This study addresses this knowledge gap by quantitatively assessing the relationship between the structure of thioethers and intrinsic reaction rates. First, the results highlighted the adverse impact of electron-withdrawing groups on reactivity. Theoretical calculations were employed to locate reactive sites and investigate structural characteristics, indicating a close relationship between thioether charge and reaction rate. Additionally, we established a SMILES-based model for rapidly predicting PMS reactivity with thioether compounds. With this model, we identified 147 thioether chemicals within the high production volume (HPV) and Food and Drug Administration (FDA) approved drug lists that PMS could effectively eliminate with the toxicity (-lg LC50) decreasing. These findings underscore the environmental significance of thioether compounds and the potential for their selective removal by peroxides.

Molecular and optical signatures of photochemical transformation of dissolved organic matter: Nonnegligible role of suspended particulate matter in urban river.

Natural dissolved organic matter (DOM) is one of the Earth's dynamic carbon pools and a key intermediate in the global carbon cycle. Photochemical processes potentially affect DOM composition and activity in surface water. Suspended particulate matter (SPM) is the integral component of slow-moving rivers, and holds the potential for photochemical reactivity. To further investigate the influence of SPM on DOM photochemical transformation, this study conducted experiments comparing samples with and without SPM irradiated under simulated sunlight. Surface water samples from slow-moving urban rivers were collected. DOM optical characteristics and molecular features obtained by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were investigated. Photolabile DOM was enriched in unsaturated and highly aromatic terrestrial substances. Photoproduced DOM had low aromaticity and was dominated by saturated aliphatics, protein-like substances, and carbohydrates. Study results indicated that the presence of SPM had a nonnegligible impact on the molecular traits of DOM, such as composition, molecular diversity, photolability, and bioavailability during photochemical reactions. In the environment affected by SPM, molecules containing heteroatoms exhibit higher photosensitivity. SPM promotes the photochemical transformation of a wider range of chemical types of photolabile DOM, particularly nitrogen-containing compounds. This study provides an essential insight into the more precise simulation of photochemical reactions of DOM influenced by SPM occurring in natural rivers, contributing to our understanding of the global carbon cycle from new theoretical perspectives.

Impact of aqueous environments on hydrogen peroxide activation by manganese oxides: Kinetics and the critical role of bicarbonate.

MnO2 activating H2O2 is a promising way in the field of advanced oxidation processes (AOPs) and in situ chemical oxidation (ISCO) to remove contaminants. However, few studies have focused on the influence of various environmental conditions on the performance of MnO2-H2O2 process, which restricts the application in real world. In this study, the effect of essential environmental factors (ionic strength, pH, specific anions and cations, dissolved organic matter (DOM), SiO2) on the decomposition of H2O2 by MnO2 (ε-MnO2 and ß-MnO2) were investigated. The results suggested that H2O2 degradation was negatively correlated with ionic strength and strongly inhibited under low pH conditions and with phosphate existence. DOM had a slight inhibitory effect while Br-, Ca2+, Mn2+ and SiO2 placed negligible impact on this process. Interestingly, HCO3- inhibited the reaction at low concentrations but promoted H2O2 decomposition at high concentrations, possibly due to the formation of peroxymonocarbonate. This study may provide a more comprehensive reference for potential application of H2O2 activation by MnO2 in different water systems.

Simultaneous removal of phosphate and antibiotic from hydrolyzed urine by novel spherical particles.

Phosphate recovery from wastewater is regarded as promising strategy to achieve sustainable supply of non-renewable natural resources. In this study, a novel technique for spherical materials preparation was developed to achieve both phosphate recovery and antibiotic removal from urine. Phosphate removal and sulfamethoxazole (SMX) degradation performance of the synthesized spherical materials was studied in synthesized urine and real urine. MgB, made from magnesium oxide (10%) and biochar (10%), was the most effective in phosphate removal and SMX degradation. Struvite formation and radical production were the mechanisms of phosphate removal and SMX degradation, respectively. The phosphate removal capacity of MgB was 0.181 g/g and the removal cost was around 0.245 RMB/g phosphate. Meanwhile, the combination of MgB and persulfate could achieve a 98% degradation efficiency of SMX, which could eliminate the hazardous impurity in final product. Furthermore, this technique has also been validated useful in treating real hydrolyzed urine.

Transformation of tetracycline antibiotics with goethite: Mechanism, kinetic modeling and toxicity evaluation.

Tetracycline antibiotics (TCs) are a group of the top selling and widely used antibiotics that have been frequently detected in various environments. The interaction between TCs and goethite (α-FeOOH), one of the most common crystalline oxide minerals in aqueous environment and soil, is unclear. Apart from adsorption, this study firstly demonstrated that transformation of tetracycline (TTC) occurred in the presence of goethite. The transformation kinetics and mechanism of TTC with goethite were investigated to gain a better understanding of the fate of TCs in the natural environment. The results showed that the transformation of TCs by goethite explicitly exhibited two-stage kinetics, wherein an initial period of fast transformation was followed by a continuous slow transformation. Hydroxyl groups on goethite were identified as major reactive sites, among which singly coordinated hydroxyls (FeOH) were more reactive than doubly coordinated hydroxyls (Fe2OH) towards the transformation of TTC. On the basis of transformation rates, speciation of TTC and functional groups on goethite surface, a kinetic model was established successfully describing the transformation of TTC by goethite under conditions of varying reactant concentration and pH. The transformation of TTC by goethite mainly resulted in a N,N-dedimethylation product that did not show antimicrobial properties towards Escherichia coli. This study indicates that Fe(III)-(hydro)oxides in soils and sediments may play an important role in the natural attenuation of tetracycline antibiotics and their bioactivity.

Characterization of Lignin Compounds at the Molecular Level: Mass Spectrometry Analysis and Raw Data Processing.

Lignin is the second most abundant natural biopolymer, which is a potential alternative to conventional fossil fuels. It is also a promising material for the recovery of valuable chemicals such as aromatic compounds as well as an important biomarker for terrestrial organic matter. Lignin is currently produced in large quantities as a by-product of chemical pulping and cellulosic ethanol processes. Consequently, analytical methods are required to assess the content of valuable chemicals contained in these complex lignin wastes. This review is devoted to the application of mass spectrometry, including data analysis strategies, for the elemental and structural elucidation of lignin products. We describe and critically evaluate how these methods have contributed to progress and trends in the utilization of lignin in chemical synthesis, materials, energy, and geochemistry.

Photo-ammonification in surface water samples: Mechanism and influencing factors.

Dissolved organic nitrogen (DON) accounts for a large proportion of the total aquatic nitrogen. Compared with dissolved inorganic nitrogen (DIN), the reactivity of DON has received limited attention. Photo-ammonification contributes significantly to the transformation of DON to DIN. However, information on the mechanism of this process is limited. This study investigated the photo-ammonification process of different natural surface water samples. The effects of seasons and rainfall on this process were explored, and the contributing factors were identified. Results showed that the seasonal effect on photo-ammonification differed for different water samples, whereas rainfall increased the rates of photo-ammonification for most of the lakes. The concentrations of reactive species, including triplet states of chromophoric dissolved organic matter (3CDOM*) and singlet oxygen (1O2), were found to be significantly correlated with water optical-parameters. Multivariable linear regression analysis (R2 = 0.617) revealed that the photo-ammonification of DON was mainly facilitated by 3CDOM* whereas 1O2 competed with 3CDOM* and showed an inhibiting effect. The components of dissolved organic matter (DOM) were identified by fluorescence excitation emission matrices coupled with parallel factor analysis and were found to be greatly influenced by the location. Allochthonous humic-like components were found to promote the production of reactive species while tryptophan-like component was found to be a reactive species consumer. This study revealed that the composition of DOM and the reactive species governed the rates of photo-ammonification.

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

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

Biochar-activated peroxydisulfate as an effective process to eliminate pharmaceutical and metabolite in hydrolyzed urine.

Eliminating pharmaceutical active compounds from source-separated urine is essential for nutrient recovery and reducing the contaminant load to wastewater treatment plants. However, limited oxidation treatment processes have shown satisfactory performance due to strong scavenging effect of urine components. This study proposed a heterogeneous catalytic system by combining biochar with peroxydisulfate (PDS), which effectively removed sulfamethoxazole (SMX) and its major human metabolite, N4-acetyl-sulfamethoxazole (NSMX) in urine. The performance of biochar/PDS was investigated in both a complete-mixing reactor and a biochar-packed column. Interestingly, urine components slightly inhibited the degradation of sulfonamides in biochar suspension but significantly improved their removal in biochar-packed column. Further investigation elucidated the PDS activation process and the effects of the main urine components, which explained the different results in biochar suspension and biochar-packed column. The biochar/PDS system mainly produced ·OH radical, singlet oxygen and surface-bound radicals (SBR), which transformed SMX to products of no apprarent antimicrobial properities. A cost-effective two-stage process was designed utilizing SBR as the major reactive species. This study may help to improve the understanding of the catalytic role of biochar and provide cost-effective treatment options for urine.

Significant Effect of Evaporation Process on the Reaction of Sulfamethoxazole with Manganese Oxide.

Soil in the vadose zone is an important sink for antibiotics. However, previous studies have examined only the degradation of antibiotics in soil slurry systems, which were largely different from real-world unsaturated soil environments. Whether the same transformation mechanisms apply to unsaturated soil systems has been a question. Here, the degradation of sulfamethoxazole (SMX) by manganese dioxide (γ-MnO2) in both suspension systems and evaporation processes were examined. Results show that the slow degradation of SMX in the suspension system can be significantly promoted as the water gradually evaporates. SMX degraded differently in evaporation as compared to suspension systems because of the quenching effect of generated Mn2+. Transformation products of SMX in both systems also showed different toxicity toward Escherichia coli because of different evolutions of intermediates. This study has strong implications for the assessment and prediction of the transformation and fate of antibiotics in natural soil environments.

A novel magnesium-based oxygen releasing compound for eutrophic water remediation.

Eutrophication of surface water bodies is a global problem in recent years. Dosing polluted water with oxygen releasing compounds (ORCs), especially those that can remove excessive nutrients simultaneously is regarded as one of the most economical and eco-friendly methods of treating eutrophic waters. In this study, a novel Mg-based ORC was synthesized and characterized as a magnesium hydroxide and hydrogen peroxide complex (MHHPC) with Mg to H2O2 ratio of 2:1. Oxygen-releasing, pH-adjusting and nutrient-removal potentials of MHHPC were evaluated in nano-pure and eutrophic water. The overall performance of MHHPC in preventing the eutrophic water from turning black and odorous was compared with the performance of other ORCs namely, MgO2, CaO2 and the combination of MgCl2 and H2O2. The results showed that MHHPC was capable of constantly releasing oxygen to aqueous phase over a period of one week. Phosphate and ammonia nitrogen in synthetic buffered water can were removed as struvite and other precipitates from the aqueous phase. In the synthetic eutrophic water, all the ORCs tested were able to reduce aqueous ammonia nitrogen below 0.5 mM, while only CaO2 and MHHPC successfully removed the aqueous phosphate. However, CaO2 and MgCl2+H2O2 significantly inhibited microbial activity.

Reactive Nitrogen Species Mediated Degradation of Estrogenic Disrupting Chemicals by Biochar/Monochloramine in Buffered Water and Synthetic Hydrolyzed Urine.

There is increasing concern about the severe endocrine-related health problems because of the discharge of estrogenic disrupting chemicals (EDCs) into the natural environment. In this study, we investigated the activation of monochloramine (NH2Cl) by biochar [pyrolyzed by cotton straw at 350 °C (Cot350), wheat straw at 350 and 700 °C (WS350 and WS700), and corn straw at 350 and 700 °C (CS350 and CS700)] for the degradation of estradiol (E2) and ethinylestradiol (EE2). Approximately 95% of parent E2 and EE2 was removed by Cot350/NH2Cl in buffered solution, and 87% of E2 and 75% of EE2 were removed in urine within 24 h. Electronic paramagnetic resonance analysis and radical-quenching experiments showed that biochar activated NH2Cl and primarily generated •NO radicals for the degradation of the EDCs. The nitrogen and silicon elements of Cot350 served as primary catalytic sites for NH2Cl activation, whereas the sp2-hybridized carbon on WS700 and CS700 played a major role. The effect of major urine components (i.e., ammonia species, chloride, and bicarbonate) on the reaction pathways of biochar/NH2Cl was also elucidated. This study provides new insights into the reaction pathways of NH2Cl activation by biochar and suggests potential applications for other carbonaceous materials for NH2Cl activation.

Degradation of Organic Micropollutants in UV/NH2Cl Advanced Oxidation Process.

Monochloramine (NH2Cl) can be irradiated by UV to create an advanced oxidation condition (i.e., UV/NH2Cl) for the elimination of organic micropollutants (OMPs) from source water. However, information in retrospective studies was scarce on how UV/NH2Cl performance would be affected by the water matrix and OMP molecular structures. In this study, the degradation of five representative OMPs, including triclosan, carbamazepine, sulfamethoxazole, estradiol (E2), and ethinylestradiol (EE2), was examined in different water matrices. All OMPs were rapidly removed by UV/NH2Cl but exhibited different degradation mechanisms. Although •OH, •Cl, and direct photolysis mainly contributed to the overall degradation of OMPs in buffered nanopure water, the contribution of reactive nitrogen species (RNS) generated from the photolysis of NH2Cl was not negligible in the degradation of E2 and EE2. A phenolic group was identified as the moiety reactive toward RNS. Based on quantitative analysis of the impact on OMP degradation from cosolutes (including Cl-, HCO3-, NOM) as well as pH and NH2Cl doses, we developed a kinetic model for the prediction of OMP degradation in complex water matrices. In environmental water matrices, the performance and radical contributions in UV/NH2Cl and UV/H2O2 systems were taken into comparison, which showed faster degradation of OMPs and a more significant contribution of CO3•- in the UV/NH2Cl process.

Identification of sources and transformations of nitrate in the Xijiang River using nitrate isotopes and Bayesian model.

Coupled nitrogen and oxygen isotopes of nitrate have proven useful in identifying nitrate sources and transformation in rivers. However, isotopic fractionation and low-resolution monitoring limit the accurate estimation of nitrate dynamics. In the present study, the spatio-temporal variations of nitrate isotopes (15N and 18O) and hydrochemical compositions (NO3- and Cl-) of river water were examined to understand nitrate sources in the Xijiang River, China. High-frequency sampling campaigns and isotopic analysis were performed at the mouth of the Xijiang River to capture temporal nitrate variabilities. The overall values of δ15N-NO3- and δ18O-NO3- ranged from +4.4‰ to +14.1‰ and from -0.3‰ to +6.8‰, respectively. The results of nitrate isotopes indicated that NO3- mainly originated from soil organic nitrogen (SON), chemical fertilizer (CF), and manure and sewage wastes (M&S). The negative correlation of nitrate isotopic values with NO3-/Cl- ratios suggested the importance of denitrification in NO3- loss. The results of Bayesian model with incorporation of isotopic fractionation during the denitrification showed that SON and CF contributed to the most (72-73%) nitrate in the wet season; whereas approximately 58% of nitrate was derived from anthropogenic inputs (M&S and CF) in the dry season. The nitrate flux was 2.08 × 105 tons N yr-1 during one hydrologic year between 2013 and 2014, with 86% occurring in the wet season. Long-term fluctuations in nitrate flux indicated that nitrate export increased significantly over the past 35 years, and was significantly correlated with nitrate concentrations. The seasonal pattern of nitrate dynamics indicated the mixing of nitrified NO3- and denitrified NO3- between surface flow and groundwater flow under different hydrological conditions. Overall, the present study quantitatively evaluates the spatio-temporal variations in nitrate sources in a subtropical watershed, and the high-frequency monitoring gives a better estimate of nitrate exports and proportional contributions of nitrate sources.

Removal of sulfonamide antibiotics and human metabolite by biochar and biochar/H2O2 in synthetic urine.

Source-separated urine has been increasingly regarded as a promising alternative waste-stream for effectively removing pharmaceuticals and human metabolites. This study investigated the removal of sulfonamide antibiotics, one category among the most frequently detected antibiotics in the environment, by biochar and biochar/H2O2 in synthetic urine matrix. The adsorption and degradation of four parent sulfonamide antibiotics, including sulfamethoxazole, sulfadiazine, sulfamethazine, sulfadimethoxine, and one human metabolite, N4-acetyl-sulfamethoxazole (together referred as SAs) were investigated. Biochar derived from cotton straw was applied as adsorbent for SAs and catalyst for H2O2. Results showed that the adsorption of SAs was inhibited in urine compared with that in phosphate buffer solution. Bicarbonate in urine placed major influence. Langmuir isotherm model well described the adsorption process in both buffer and urine matrices. Adsorption and desorption rates were estimated by a kinetic model, which well fitted the removal of SAs from aqueous phase at various biochar doses. The adsorption of SAs on biochar was due to multiple forces, in which van der Waals forces and hydrophobicity played major roles in distinguishing the sorption behavior of different SAs. To destruct the SAs, H2O2 was added with biochar. Except for N4-acetyl-sulfamethoxazole, all the parent SAs can be degraded in urine matrix. Carbonate radical, produced from the activation of peroxymonocarbonate by biochar, was proposed to be the major contributing reactive species in biochar/H2O2 system in urine matrix.

PPCP Degradation by Chlorine-UV Processes in Ammoniacal Water: New Reaction Insights, Kinetic Modeling, and DBP Formation.

The combination of chlorine and UV (i.e., chlorine-UV process) has been attracting more attention in recent years due to its ready incorporation into existing water treatment facilities to remove PPCPs. However, limited information is available on the impact of total ammonia nitrogen (TAN). This study investigated two model PPCPs, N,N-diethyl-3-toluamide (DEET) and caffeine (CAF), in the two stages of the chlorine-UV process (i.e., chlorination and UV/chlor(am)ine) to elucidate the impact of TAN. During chlorination, the degradation of DEET and CAF was positively correlated with the overall consumption of total chlorine by TAN. Reactive nitrogen intermediates, including HNO/NO- and ONOOH/ONOO-, along with •OH were identified as major contributors to the removal of DEET and CAF. During UV irradiation, DEET and CAF were degraded under UV/chlorine or UV/NH2Cl conditions. •OH and •Cl were the major reactive species to degrade DEET and CAF under UV/NH2Cl conditions, whereas •OCl played a major role for degrading CAF under UV/chlorine conditions. Numerical models were developed to predict the removal of DEET and CAF under chlorination-UV process. Chlorinated disinfection byproducts were detected. Overall, this study presented kinetic features and mechanistic insights on the degradation of PPCPs under the chlorine-UV process in ammoniacal water.

Degradation of DEET and Caffeine under UV/Chlorine and Simulated Sunlight/Chlorine Conditions.

Photoactivation of aqueous chlorine could promote degradation of chlorine-resistant and photochemically stable chemicals accumulated in swimming pools. This study investigated the degradation of two such chemicals, N,N-diethyl-3-methylbenzamide (DEET) and caffeine, by low pressure ultraviolet (UV) light and simulated sunlight (SS) activated free chlorine (FC) in different water matrices. Both DEET and caffeine were rapidly degraded by UV/FC and SS/FC but exhibited different kinetic behaviors. The degradation of DEET followed pseudo-first-order kinetics, whereas the degradation of caffeine accelerated with reaction. Mechanistic study revealed that, under UV/FC, ·OH and Cl· were responsible for degradation of DEET, whereas ClO· related reactive species (ClOrrs), generated by the reaction between FC and ·OH/Cl·, played a major role in addition to ·OH and Cl· in degrading caffeine. Reaction rate constants of DEET and caffeine with the respective radical species were estimated. The imidazole moiety of caffeine was critical for the special reactivity with ClOrrs. Water matrix such as pH had a stronger impact on the UV/FC process than the SS/FC process. In saltwater matrix under UV/FC and SS/FC, the degradation of DEET was significantly inhibited, but the degradation of caffeine was much faster than that in nonsalty solutions. The interaction between Br- and Cl- may play an important role in the degradation of caffeine by UV/FC in saltwater. Reaction product analysis showed similar product patterns by UV/FC and SS/FC and minimal formation of chlorinated intermediates and disinfection byproducts.

Interaction between common antibiotics and a Shewanella strain isolated from an enhanced biological phosphorus removal activated sludge system.

With increasing production and consumption, more antibiotics are discharged into wastewater treatment plants and generally cannot be sufficiently removed. Because of the complexities of biological treatment processes, the fates of antibiotics and their effects on microorganisms, particularly those involved in the phosphorus removal system, are still unclear. Here, a Shewanella strain was isolated from an enhanced biological phosphorus removal (EBPR) system and was found to have the ability to remove phosphorus (P) and chemical oxygen demand (CODcr). Antibiotics affected the Shewanella strain through metabolism of the three main intracellular polymers, altering the ability of the strain to remove P and CODcr. These effects varied with the structure and concentration of the antibiotics. The Shewanella strain removed cefalexin and amoxicillin by degradation or adsorption, producing 2-hydroxy-3-phenyl pyrazine from cefalexin. This study enabled the recognition of the effect and removal of antibiotics during wastewater treatment.

Kinetics and modeling of sulfonamide antibiotic degradation in wastewater and human urine by UV/H2O2 and UV/PDS.

Sulfonamide antibiotics have been frequently detected in the aquatic environment and are of emerging concern due to their adverse bio-effect and potential of inducing antibiotic resistance. This study investigated the degradation kinetics of sulfonamide antibiotics in synthetic wastewater and hydrolyzed human urine by low pressure (LP) UV, UV/H2O2 and UV/peroxydisulfate (PDS). Direct photolysis rates of sulfonamide antibiotics varied and depended on the structures. Sulfonamides with a five-membered heterocyclic group underwent faster direct photolysis. For indirect photolysis processes, second-order rate constants of sulfonamide antibiotics with hydroxyl radical, sulfate radical and carbonate radical were determined, which were (6.21-9.26) × 10(9), (0.77-16.1) × 10(10) and (1.25-8.71) × 10(8) M(-1) s(-1), respectively. A dynamic model was applied and successfully predicted the degradation kinetics of sulfonamides in different water matrices. In synthetic wastewater, carbonate radical contributed to approximately 10% of the overall removal, whereas in synthetic hydrolyzed urine, carbonate radical was the dominant reactive species to degrade sulfonamides. Sulfonamide antibiotics were eliminated more efficiently in synthetic hydrolyzed urine than in synthetic wastewater and UV/PDS was more efficient than UV/H2O2 to degrade most sulfonamides. Energy evaluation showed that UV/PDS costs less energy than LPUV and UV/H2O2 under the experimental conditions applied in this study, particularly for sulfonamides whose indirect photolysis overweighed direct photolysis. By varying UV dose and oxidant dose, the UV/H2O2 process can be optimized to achieve higher efficiency than the UV/PDS process in synthetic wastewater.