Mechanism of Fuel Gas Denitration on the KOH-Activated Biochar Surface.

Previous experimental studies have found that biochar after KOH activation can significantly improve the efficiency of NO removal, but its mechanism is still unclear. To investigate the reaction mechanism of this denitration reaction, in this study, the aromatic benzene ring structure was used to simulate the surface of biochar, and the reaction process was calculated by density functional theory (DFT). The reaction process on the pristine biochar was simulated for comparison. The results indicated that there were two potential mechanisms for NO removal and had the identical rate-determining step, with an activation energy of 161.5 kJ/mol. Second, the influence by K coadsorbates on the NO reduction mechanism was studied. The adsorption by K atoms does not alter the last reaction step, but it was found to reduce the activation energy of this rate-determining step (to 129.3 kJ/mol). A third type of reaction mechanism was theoretically studied for the situation with both K and OH coadsorbates on the biochar surface. The reaction mechanism changed with an increase in the overall reaction rate by increasing the pre-exponential factor. In summary, the rate-determining activation energy for the heterogeneous NO reduction was found to decrease in the following order: 161.5 kJ/mol (pristine biochar) → 129.3 kJ/mol (activation by K adsorbates) → 125.8 kJ/mol (activation by both K and OH adsorbates); the pre-exponential factor was found to change in the following order: 6.23 × 1014 s-1 (pristine biochar) → 4.86 × 1014 s-1 (activation by K adsorbates) → 8.89 × 1014 s-1 (activation by K and OH adsorbates). Hence, the role by K adsorbates is primarily to reduce the rate-determining activation energy, while the OH group adsorbate increases the number of active sites on the surface of biochar.

Diatomic Pd-Cu Metal-Phosphorus Sites for Complete N≡N Bond Formation in Photoelectrochemical Nitrate Reduction.

The synergistic effect of bimetallic heterogeneous catalysis in the reaction of nitrate reduction to nitrogen has been widely discussed, but it is still not clear how this effect works at the atomic scale, hindering the rational design of high-performance catalysts. Here, for the first time, 2D phosphorene was used as a giant P ligand to confine high-density PdCu dual-atom to form a unique PdCuP4 coordination structure, and this catalyst achieves 96.3 % NO3 - removal rate and 95.2 % N2 selectivity. In situ characterization combined with density functional theory (DFT) calculations show that the PdCu dual-atom form covalent-like bonds with adjacent P atoms, reducing the adsorption energy of the reactants. The synergistic effect of PdCu dual-atom promotes the breaking of N-O bond, and the short bond length of ≈3 Šbetween PdCu atoms accelerates the transfer of NO2 - , and eventually the two Pd-N adjacent to the surface of Pd rapidly combine to form N2 .

Recognition and Selectivity Analysis Monitoring of Multicomponent Steroid Estrogen Mixtures in Complex Systems Using a Group-Targeting Environmental Sensor.

The same class of steroid estrogen mixtures, coexisting in the environment of 17ß-estradiol, estrone (E1), and ethinyl estradiol (EE2), have strong ability to disrupt the human endocrine system and are seriously prejudicial to the health of the organism and environmental safety. Herein, a highly sensitive and group-targeting environmental monitoring sensor was fabricated for a comprehensive analysis of multicomponent steroid estrogens (multi-SEs) in complex systems. This breakthrough was based on the highly sensitive photoelectrochemical response composite material CdSe NPs-TiO2 nanotube and highly group-specific aptamers. The optimized procedure exhibited not only high sensitivity in a wide range of concentrations from 0.1 to 50 nM, indeed, the minimum detection limit was 33 pM, but also strong resistance to interference. The affinity and consistent action pockets of this sensor enable selective detection of multi-SEs in complex systems. It subsequently was applied for the analysis of multi-SEs from three real samples in the environment including medical wastewater, river water, and tap water to provide a means to clarify the fate of multi-SEs in the process of migration and transformation. This monitoring sensor has a brilliant application prospect for the identification and monitoring of the same class of endocrine-disrupting chemical mixtures in environmental complex systems.

Insights into the Oxidation of Organic Cocontaminants during Cr(VI) Reduction by Sulfite: The Overlooked Significance of Cr(V).

Literature works reported that organic cocontaminants could be degraded during Cr(VI), a contaminant, reduction by sulfite (Cr(VI)/sulfite process). However, the role of Cr(V) and Cr(IV) intermediates in the Cr(VI)/sulfite process has been overlooked. In this study, we confirmed the generation of Cr(V) and proposed a new mechanism for the decomposition of coexisting organic contaminants during Cr(VI)/sulfite reactions occurring in oxygenated solutions at pHini 4.0 with the molar ratio of sulfite to Cr(VI) of 10.0. UV-visible and electron paramagnetic resonance (EPR) spectra indicate that Cr(V) was the predominant Cr intermediates in oxygenated solutions, while Cr(IV) accumulated in deoxygenated solutions. The contribution of Cr(V) to the degradation of organic contaminants was verified by the EPR spectra collected at 2 K and using methyl phenyl sulfoxide as a probe compound. Both Cr(V) and SO4•- contributed to the decomposition of organic contaminants in oxygenated solutions, with the relative contributions from each species being strongly dependent on properties of the target organic cocontaminants. The key mechanisms responsible for Cr(V) accumulation were supported by DFT calculations, and the degradation kinetics of organic cocontaminants was simulated with the program Kintecus 6.51. This work advances the fundamental understanding of the oxidative transformation of coexisting organic contaminants in this process.

Overlooked Role of Fe(IV) and Fe(V) in Organic Contaminant Oxidation by Fe(VI).

Fe(VI) has received increasing attention since it can decompose a wide range of trace organic contaminants (TrOCs) in water treatment. However, the role of short-lived Fe(IV) and Fe(V) in TrOC decomposition by Fe(VI) has been overlooked. Using methyl phenyl sulfoxide (PMSO), carbamazepine, and caffeine as probe TrOCs, we observed that the apparent second-order rate constants (kapp) between TrOCs and Fe(VI) determined with the initial kinetics data were strongly dependent on the initial molar ratios of TrOCs to Fe(VI). Furthermore, the kapp value increases gradually as the reaction proceeds. Several lines of evidence suggested that these phenomena were ascribed to the accumulation of Fe(IV) and Fe(V) arising from Fe(VI) decay. Kinetic models were built and employed to simulate the kinetics of Fe(VI) self-decay and the kinetics of PMSO degradation by Fe(VI). The modeling results revealed that PMSO was mainly degraded by Fe(IV) and Fe(V) rather than by Fe(VI) per se and Fe(V) played a dominant role, which was also supported by the density functional theory calculation results. Given that Fe(IV) and Fe(V) have much greater oxidizing reactivity than Fe(VI), this work urges the development of Fe(V)/Fe(IV)-based oxidation technology for efficient degradation of TrOCs.

Monitoring 2,3',5,5'-tetrachlorobiphenyl with a rapid and sensitive environmental aptamer sensor.

Polychlorinated biphenyl (PCB) detection in the environment is significant for both environmental protection and human health. Herein, a highly sensitive aptamer sensor has been established by employing a 2,3',5,5'-tetrachlorobiphenyl (PCB72) targeting aptamer as a highly specific recognition element and a gold/silver (Au@Ag) nanocomposite as the surface-enhanced Raman spectroscopy (SERS) substrate for detecting environmental PCB72. The Au@Ag nanoparticles (NPs) exhibit a strong SERS enhancement and provide an efficient substrate for immobilizing the PCB72 aptamer and Raman signal labelled molecule, 4-mercaptobenzoic acid (4-MBA). The targeted PCB72 could competitively bind with the PCB72 aptamer, resulting in a few aptamers sticking to the Au@Ag NPs and the "hot spot" strengthening effect of the substrate. Under optimal conditions, this aptamer sensor exhibits great performance with high sensitivity, excellent selectivity and stability for the monitoring of PCB72, which shows an excellent linear correlation ranging from 1 to 1000 pg mL-1 with a limit of detection of 0.3 pg mL-1. Furthermore, this aptamer assay exhibits high specificity and selectivity for PCB72 with the detection error of less than 0.27 for other PCBs and 0.21 for other interfering species, even if the coexisting interferents are 100-fold concentration in the system. Additionally, the recognition mechanism of the binding of aptamers to PCB72 is analyzed via UV-vis spectroscopy and molecular docking simulations, which suggest that PCB72 could insert into the aptamers. Furthermore, this method is successfully utilized for PCB72 detection in real water samples with a simple pre-treatment. In general, this work provides a new and effective method using an environmental aptamer sensor for rapid and sensitive PCB72 detection.

Wavelength dependency and photosensitizer effects in UV-LED photodegradation of iohexol.

Iodinated X-ray contrast media (ICM) are ubiquitously present in water sources and challenging to eliminate using conventional processes, posing a significant risk to aquatic ecosystems. Ultraviolet light-emitting diodes (UV-LED) emerge as a promising technology for transforming micropollutants in water, boasting advantages such as diverse wavelengths, elimination of chemical additives, and no induction of microorganisms' resistance to disinfectants. The research reveals that iohexol (IOX) degradation escalates as UV wavelength decreases, attributed to enhanced photon utilization efficiency. Pseudo-first-order rate constants (kobs) were determined as 3.70, 2.60, 1.31 and 0.65 cm2 J-1 at UV-LED wavelengths of 255, 265, 275 and 285 nm, respectively. The optical properties of dissolved organic matter (DOM) and anions undeniably influence the UV-LED photolysis process through photon competition and the generation of reactive substances. The influence of Cl- on IOX degradation was insignificant at UV-LED 255, but it promoted IOX degradation at 265, 275 and 285 nm. IOX degradation was accelerated by ClO2-, NO3-and HA due to the formation of various reactive species. In the presence of NO3-, the kobs of IOX followed the order: 265 > 255 > 275 > 285 nm. Photosensitizers altered the spectral dependence of IOX, and the intermediate photoactivity products were detected using electron spin resonance. The transformation pathways of IOX were determined through density functional theory calculations and experiments. Disinfection by-products (DBPs) yields of IOX during UV-LED irradiation decreased as the wavelength increased: 255 > 265 > 275 > 285 nm. The cytotoxicity index value decreased as the UV-LED wavelength increased from 255 to 285 nm. These findings are crucial for selecting the most efficient wavelength for UV-LED degradation of ICM and will benefit future water purification design.

Destroying pathogen-tumor symbionts synergizing with catalytic therapy of colorectal cancer by biomimetic protein-supported single-atom nanozyme.

The crucial role of intratumoral bacteria in the progression of cancer has been gradually recognized with the development of sequencing technology. Several intratumoral bacteria which have been identified as pathogens of cancer that induce progression, metastasis, and poor outcome of cancer, while tumor vascular networks and immunosuppressive microenvironment provide shelters for pathogens localization. Thus, the mutually-beneficial interplay between pathogens and tumors, named "pathogen-tumor symbionts", is probably a potential therapeutic site for tumor treatment. Herein, we proposed a destroying pathogen-tumor symbionts strategy that kills intratumoral pathogens, F. nucleatum, to break the symbiont and synergize to kill colorectal cancer (CRC) cells. This strategy was achieved by a groundbreaking protein-supported copper single-atom nanozyme (BSA-Cu SAN) which was inspired by the structures of native enzymes that are based on protein, with metal elements as the active center. BSA-Cu SAN can exert catalytic therapy by generating reactive oxygen species (ROS) and depleting GSH. The in vitro and in vivo experiments demonstrate that BSA-Cu SAN passively targets tumor sites and efficiently scavenges F. nucleatum in situ to destroy pathogen-tumor symbionts. As a result, ROS resistance of CRC through elevated autophagy mediated by F. nucleatum was relieved, contributing to apoptosis of cancer cells induced by intracellular redox imbalance generated by BSA-Cu SAN. Particularly, BSA-Cu SAN experiences renal clearance, avoiding long-term systemic toxicity. This work provides a feasible paradigm for destroying pathogen-tumor symbionts to block intratumoral pathogens interplay with CRC for antitumor therapy and an optimized trail for the SAN catalytic therapy by the clearable protein-supported SAN.

Interfacial Super-Assembly of Intertwined Nanofibers toward Hybrid Nanochannels for Synergistic Salinity Gradient Power Conversion.

Capturing the abundant salinity gradient power into electric power by nanofluidic systems has attracted increasing attention and has shown huge potential to alleviate the energy crisis and environmental pollution problems. However, not only the imbalance between permeability and selectivity but also the poor stability and high cost of traditional membranes limit their scale-up realistic applications. Here, intertwined "soft-hard" nanofibers/tubes are densely super-assembled on the surface of anodic aluminum oxide (AAO) to construct a heterogeneous nanochannel membrane, which exhibits smart ion transport and improved salinity gradient power conversion. In this process, one-dimensional (1D) "soft" TEMPO-oxidized cellulose nanofibers (CNFs) are wrapped around "hard" carbon nanotubes (CNTs) to form three-dimensional (3D) dense nanochannel networks, subsequently forming a CNF-CNT/AAO hybrid membrane. The 3D nanochannel networks constructed by this intertwined "soft-hard" nanofiber/tube method can significantly enhance the membrane stability while maintaining the ion selectivity and permeability. Furthermore, benefiting from the asymmetric structure and charge polarity, the hybrid nanofluidic membrane displays a low membrane inner resistance, directional ionic rectification characteristics, outstanding cation selectivity, and excellent salinity gradient power conversion performance with an output power density of 3.3 W/m2. Besides, a pH sensitive property of the hybrid membrane is exhibited, and a higher power density of 4.2 W/m2 can be achieved at a pH of 11, which is approximately 2 times more compared to that of pure 1D nanomaterial based homogeneous membranes. These results indicate that this interfacial super-assembly strategy can provide a way for large-scale production of nanofluidic devices for various fields including salinity gradient energy harvesting.

Highly sensitive and group-targeting detection of steroid estrogens in water environment using a valid oligonucleotide class-specific editing technique.

Steroid environmental estrogens (SEEs) are often coexist in water, require complex analytical techniques for separation and monitoring. However, aptamer-based chemical detection often only recognizes one of them, and the detection of SEEs is still a huge challenge. Herein, a group-targeting aptamer with the ability to recognize SEEs was constructed using efficient oligonucleotide class-specific editing technology, and a photoelectrochemical aptasensor capable of detecting the class of SEEs was established. A quantitative analysis of highly toxic SEEs in the environment and carrying similar core carbon skeleton, including 17ß-estradiol, esterone, estriol and ethinylestradiol, was performed. The detection limit was as low as 0.1 nM with a response time of only 15 min. Specifically, this method exhibited high anti-interference with different complex media existing. Combining the theoretical calculations with a variety of spectral experiments, the Π-Π stacking and hydrogen bond synergistic interactions between the photoelectric interface and the three ring structures on SEEs and the hydroxyl group of ring 1 were analyzed in depth. Besides, the conformational changes of loose base helix structure and the free rotation limitation of oligonucleotides after the recognition of SEEs at the molecular level were also elucidated, facilitating the transfer of electrons on the surface of the photoelectrode.

Enhanced formation of iodinated trihalomethanes in a mixed chlorine/chloramine system and attenuation by UV-activated process.

Iodinated trihalomethanes (I-THMs) have drawn increasing concerns due to their higher toxicity than those of their chlorinated and brominated analogues. In this study, I-THM formation was firstly evaluated for three treatment scenarios - (i) chlorine alone, (ii) chloramine alone, and (iii) mixed chlorine/chloramine - in the presence and absence of UV irradiation for the iodide-containing humic acid solution or natural water. The results indicated that I-THM formation decreased in the order of mixed chlorination/chloramination > chloramination > > chlorination, which fitted the trend of toxicity evaluation results using Chinese hamster ovary cells. Conversely, total organic halide concentration decreased in the order of chlorination > > chloramination ≈ mixed chlorination/chloramination. Besides, I-THM formation can be efficiently controlled in a UV-activated mixed chlorine/chloramine system. Influencing factors including pH values and Br-/I- molar ratios were also systematically investigated in a mixed chlorine/chloramine system. Enhanced I-THM formation was observed with increasing pH values (6.0-8.0) and Br-/I- molar ratios (1: 1-10: 1). The results obtained in this study can provide new insights into the increasing risk of I-THM formation in a mixed chlorine/chloramine system and the effective control of I-THMs in the iodide-containing water using UV irradiation.

Photodegradation pathway of iodate and formation of I-THMs during subsequent chloramination in iodate-iodide-containing water.

This study investigated the mechanisms of mixed IO3-/I- system under UV irradiation in drinking water and compared the iodinated trihalomethanes (I-THMs) formation of a mixed IO3-/I- system to that of single I- and IO3- systems during subsequent chloramination. The effects of initial I-/IO3- molar ratio, pH, and UV intensity on a mixed IO3-/I- system were studied. The introduction of I- enhanced the conversion rate of IO3- to reactive iodine species (RIS). Besides, IO3- degradation rate increased with the increase of initial I- concentration and UV intensity and the decrease of pH value. In a mixed IO3-/I- system, IO3- could undergo direct photolysis and photoreduction by hydrated electron (eaq-). Moreover, the enhancement of I-THM formation in a mixed IO3-/I- system during subsequent chloramination was observed. The I-THM yields in a mixed IO3-/I- system were higher than the sum of I-THMs produced in a single IO3- and I- systems at all the evaluated initial I- concentrations and pH values. The difference between I-THM formation in a mixed IO3-/I- system and the sum of I-THMs in a single IO3- and I- systems increased with the increase of initial I- concentration. As the initial pH decreased from 9 to 5, the difference of I-THM yields enhanced, while the total I-THM yield of a mixed IO3-/I- system and single I- and IO3- systems decreased slightly. Besides, IO3--I--containing water with DOC concentration of 2.5-4.5 mg-C/L, which mainly contained humic-acid substances, had a higher risk in I-THMs formation than individual I--containing and IO3--containing water.

Formation of disinfection by-products in a UV-activated mixed chlorine/chloramine system.

In recent years, ultraviolet (UV) irradiation coupled with chlor(am)ination process is ubiquitous in secondary water supply systems in many cities of China. However, the disinfection by-products (DBPs) formation in a UV-activated mixed chlorine/chloramine system (MCCS) still remains unclear. In this study, the DBPs formation in a UV-activated MCCS was systematically investigated, considering influencing factors including the mass ratios of free chlorine to NH2Cl, UV irradiation, pH values, NOM types, Br- concentration and toxicity of the DBPs. Results indicated that DBPs formation decreased remarkably as mass ratio of free chlorine to NH2Cl changed from 5:0 to 0:5. The DBPs formation in humic acid (HA)-containing water was the highest, followed by those in fulvic acid (FA) and algal organic matter (AOM). Besides, better control of the DBP-related calculated toxicity can be achieved in acidic conditions regardless of the UV irradiation. Furthermore, in the presence of Br-, a significant reduction of DBPs formation could be achieved in a UV-activated MCCS. The findings also demonstrated that DBPs formation in real water can be effectively reduced at high UV fluence in a MCCS.

Degradation of diiodoacetamide in water by UV/chlorination: Kinetics, efficiency, influence factors and toxicity evaluation.

The formation and control of haloacetamides (HAcAms) in drinking water have raised high attention due to their high genotoxicity and cytotoxicity, especially the most cytotoxic one, diiodoacetamide (DIAcAm). In this study, the degradation of DIAcAm by UV/chlorination was investigated in terms of degradation kinetics, efficiency, influencing factors, oxidation products and toxicity evaluation. Results revealed that the degradation of DIAcAm by UV/chlorine process followed pseudo-first-order kinetics, and the rate constant between DIAcAm and OH radicals was determined as 2.8 × 109 M-1 s-1. The contribution of Cl to DIAcAm degradation by UV/chlorine oxidation was negligible. Increasing chlorine dosage and decreasing pH significantly promoted the DIAcAm degradation during UV/chlorine oxidation, but the presence of bicarbonate (HCO3-) and natural organic matter (NOM) inhibited it. The mass balance analysis of iodine species was also evaluated during UV/chlorine oxidation of DIAcAm. In this process, with DIAcAm decreasing from 16.0 to 0.8 µM-I in 20 min, IO3-, I- and HOI/I2 increased from 0 to 6.3, 6.1 and 0.5 µM-I, respectively. The increase of CHO cell viability during DIAcAm degradation indicated that the toxicity of DIAcAm could be decreased by chlorination, UV irradiation and UV/chlorine oxidation treatments, in which UV/chlorine oxidation was more effective on toxicity reduction than chlorination and UV irradiation alone.

Comparison of different disinfection processes for controlling disinfection by-product formation in rainwater.

With increasing shortage of clean water, rainwater has been considered as a precious alternative drinking water source. The processes applied to rainwater treatment are responsible for the safety of drinking water. Therefore, we systematically compared different disinfection processes to evaluate the control of disinfection by-product (DBP) formation and integrated cyto- and genotoxicity of the treated rainwater for the first time. The evaluated disinfection processes included chlorination and chloramination, pre-oxidation by potassium permanganate (KMnO4) and potassium ferrate (K2FeO4), ultraviolet/hydrogen peroxide (UV/H2O2), and ultraviolet/persulfate (UV/PS) processes. The results revealed that chloramination was effective for controlling the formation of carbonaceous DBPs (C-DBPs), but not nitrogenous DBPs (N-DBPs). Compared to KMnO4 pre-oxidation, better reduction of almost all DBPs was observed during K2FeO4 pre-oxidation. According to the calculation of cytotoxicity index (CTI) and genotoxicity index (GTI), cyto- and genotoxicity of the samples decreased obviously at the dosage of ≥ 2.0 mg/L KMnO4 and K2FeO4. The control of the cyto- and genotoxicity of the formed DBPs from the two UV-related AOPs was more effective at the dosage of ≥ 1.0 mM PS and ≥ 5.0 mM H2O2. Moreover, UV/PS was much more powerful to alter the structure of DBP precursors in rainwater.

A comparison of dissolved organic matter transformation in low pressure ultraviolet (LPUV) and ultraviolet light-emitting diode (UV-LED)/chlorine processes.

This study compared the degradation of dissolved organic matter (DOM) by UV/chlorine advanced oxidation processes (AOPs) with emerging ultraviolet light-emitting diode (UV-LED, 275 nm) and traditional low pressure UV (LPUV, 254 nm) as UV sources. Excitation emission matrix-parallel factor (EEM-PARAFAC) analysis and two-dimensional (2D) correlation gel permeation chromatograph were applied to explore the evolutions of DOM during oxidation processes. The degradation behaviors of DOM indicated by UV absorbance at 254 nm (UV254), dissolved organic carbon (DOC), and fluorophores fitted the pseudo-first-order kinetics well. The removal efficiency of DOM was similar under UV-LED and LPUV irradiation alone. However, UV-LED exhibited much higher degradation rates (increased by 29-160%) than LPUV regardless of the tracking variables during UV/chlorine processes. For three PARAFAC components, humic-like fluorescences were preferentially degraded by UV/chlorine oxidation compared with protein-like fluorescence potentially due to the differences of electronic moieties and molecular weight (MW). The decline in UV254, DOC, and fluorophores increased with increasing chlorine dosage; linear correlations between those indicators were observed during the two AOPs. Moreover, UV-LED/chlorine could achieve greater extents of MW change. Our study demonstrated that UV-LED could be a superior alternative for the future selection of UV source in the UV/chlorine process.

Mechanistic study on chlorine/nitrogen transformation and disinfection by-product generation in a UV-activated mixed chlorine/chloramines system.

The conversion mechanisms of chlorine species (including free chlorine, monochloramine (NH2Cl), dichloramine, and total chlorine), nitrogen species (including ammonium (NH4+), nitrate (NO3-), and nitrite (NO2-)) as well as the formation of disinfection by-products (DBPs) in a UV-activated mixed chlorine/chloramines system in water were investigated in this work. The consumption rates of free chlorine and NH2Cl were significantly promoted in a HOCl/NH2Cl coexisting system, especially in the presence of UV irradiation. Moreover, the transformation forms of nitrogen in both ultrapure and HA-containing waters were considerably affected by UV irradiation and the mass ratio of free chlorine to NH2Cl. NO3- and NO2- can be easily produced under UV irradiation, and the removal efficiency of total nitrogen with UV was obvious higher than that without UV when the initial ratio of HOCl/NH2Cl was less than 1. The roles of different radicals in the degradation of free chlorine, NH2Cl and NH4+ were also considered in such a UV-activated mixed chlorine/chloramines system. The results indicated that OH• was important to the consumption of free chlorine and NH2Cl, and showed negligible influence on the consumption of NH4+. Besides, the changes of DOC and UV254 in HA-containing water in UV-activated mixed chlorine/chloramines system indicated that the removal efficiency of DOC (24%) was much lower than that of UV254 (94%). The formation of DBPs in a mixed chlorine/chloramines system was also evaluated. The yields of DBPs decreased significantly as the mass ratio of HOCl/NH2Cl varied from 1 : 0 to 0 : 1. Moreover, compared to the conditions without UV irradiation, higher DBPs yields and DBP-associated calculated toxicity were observed during the UV-activated mixed chlorine/chloramine process.

Effect of bromide and iodide on halogenated by-product formation from different organic precursors during UV/chlorine processes.

The effect of bromide and iodide on the transformation of humic acid (HA) and algal organic matter (AOM), and the formation of disinfection by-products (DBPs) during UV/chlorination were investigated. Experimental results indicated that the halides effectively inhibited mineralization, with multiple changes in organic molecule transformation due to differences in formation and speciation of reactive halogen species and free halogen. As a consequence, bromide and iodide also played important roles in DBP formation. The DBP yields in HA-containing water during UV/chlorination decreased in the order of iodide loaded > freshwater â‰« bromide loaded, whereas DBP formation in AOM-containing water decreased remarkably with halides added (freshwater > bromide loaded â‰« iodide loaded) at high UV fluence. Moreover, Pearson correlation analysis exhibited weaker correlation between DBPs and water parameters in AOM-containing water, while DBPs in HA-containing water exhibited better correlation with water parameters. For both simulated waters, the theoretical toxicity was calculated and peaked in bromide-containing water, whereas the calculated toxicity in iodide-containing water was comparable or slightly higher than that in freshwater. Therefore, UV/chlorine treatment may achieve good quality water with reduced DBP-associated toxicity in freshwater or iodide-containing water (iodide only), but careful consideration is needed when purifying source waters containing bromide (bromide only), especially for AOM/bromide-containing water.

Bisulfite triggers fast oxidation of organic pollutants by colloidal MnO2.

Colloidal MnO2 is the most reactive phase of Mn(IV) while HSO3- is a common reductant in water treatment. This study shows that the presence of HSO3- resulted in significant increase in the decomposition rate of organic contaminants by colloidal MnO2. The degradation rate of contaminants in the MnO2/HSO3- process dropped with elevating pH and a proper MnO2/HSO3- molar ratio was critical for efficient decomposition of contaminants. The time-resolved spectroscopy of manganese species, the influence of pyrophosphate on UV absorbance spectra, and the relative rate constants of contaminants oxidation in MnO2/HSO3- process suggested that the synergetic effect of HSO3- and colloidal MnO2 arose from the generation of Mn(III)aq, which could oxidize contaminants rapidly. The presence of pyrophosphate, ethylenediaminetetraacetic acid, and humic acid depressed the degradation of contaminants in MnO2/HSO3- process by complexing with Mn(III)aq, buffering the solution or competing with contaminants for Mn(III)aq, and/or inhibiting the consumption of bisulfite. However, Ca2+ and Mg2+ accelerated the oxidation of contaminants in MnO2/HSO3- process by enhancing the reduction of MnO2 by HSO3-. The good negative correlation of the O/N or H Mulliken charges of organic contaminants with their removal in MnO2/HSO3- process suggested that organic contaminants were oxidized by Mn(III)aq via electrophilic attack.

Enhanced inactivation of E. coli by pulsed UV-LED irradiation during water disinfection.

Pulsed ultraviolet (UV) irradiation has presented enhanced inactivation efficiency in water disinfection and food decontamination. As an emerging UV source, UV light-emitting diodes (UV-LEDs) are an attractive alternative for pulsed irradiation because they can be turned on and off with a high and adjustable frequency. In this study, disinfection efficiencies of pulsed and continuous UV-LED irradiation were compared for Escherichia coli (E. coli) inactivation in water using a high power 285 nm LED and low power 265 and 280 nm LEDs. Factors including various duty cycles, pulse frequencies and UV irradiances were evaluated. The log-inactivation of E. coli increased substantially as the duty cycle decreased from 100% to 5% at the same UV dose. For 265 and 280 nm LEDs, the log-inactivation enhancements of pulsed UV irradiation were similar. When a higher irradiance was applied, the energy efficiency enhancement of pulsed UV irradiation became more obvious. The log-inactivation of E. coli enhanced remarkably using high current pulsed irradiation of 280 nm LEDs. Compared to continuous UV irradiation, pulsed UV-LED irradiation is an attractive alternative for E. coli inactivation in water considering energy efficiency.