Three-dimensional Excitation-emission Matrix Fluorescence Spectroscopy Research Articles

A new view into three-dimensional excitation-emission matrix fluorescence spectroscopy for dissolved organic matter

Three-dimensional excitation-emission matrix fluorescence spectroscopy (3D EEMs) has been extensively used for dissolved organic matter (DOM) characterization. However, the application of 3D EEMs is constantly limited by issues such as contradictory component identification, confusing interpretation of spectral indicators, and inability to establish biodegradability. In this study, some improvements were proposed by investigating the 3D EEMs, spectral indicators, and degradability of the standard and representative DOM. To overcome the unclear identification of DOM components, it was recommended to partition 3D EEMs into three subareas: aromatic protein (New-I), humic-like (New-II), and soluble microbial by-product-like (New-III). Significant strong positive correlations (ρ = 0.727, P < 0.001) were observed between fluorescence index (FI) and biological index (BIX), and (R = 0.809, P < 0.001) humification index (HIX) and specific ultraviolet absorbance of 254 nm (SUVA254). Except for FI (R = -0.483, P = 0.023), no other spectral indicators (P > 0.05) were found to be significantly correlated with molecular weight. As thence results, the FI and HIX were the most suitable indicators for evaluating DOM. The half-life (20 < 21 < 26 < 29 < 46 days) revealed that the degradability of individual DOM components was in the order of tyrosine > tryptophan > fulvic acid > protein > humic acid. The degradation dynamics were governed by first-order decay kinetics (R2 = 0.91–0.99). This study clarified the fluorescence properties and degradability of DOM, as well as the reliability of spectral indicators. The degradation performance of individual DOM components engaged in the carbon cycling process was revealed, paving the path for further applications of 3D EEMs in DOM research.

Association between greenhouse gases and dissolved organic matter composition in the main rivers around Taihu Lake

River ecosystems receive a large amount of organic matter, which will increase the production of greenhouse gases (GHGs), including carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Despite extensive research on the distribution of greenhouse gases and dissolved organic matter (DOM), little is known about the associations between greenhouse gases and DOM compositions. In this study, the distributions of GHGs (CO2, CH4 and N2O) and DOM in the overlying water of the main rivers around Taihu Lake were investigated. The results showed that the concentration of GHGs was positively correlated with dissolved organic carbon concentrations. Three-dimensional excitation-emission matrix fluorescence spectroscopy techniques were employed to identify the source of the DOM, which was related to protein-like and humic-like components. The DOM was a combination of terrigenous and endogenous origins. The GHGs (except CO2) were significantly associated with DOM composition. These results emphasize the importance of the relationship between GHGs (CO2, CH4 and N2O) and DOM compositions in river ecosystems.

Characteristics of dissolved organic matter in urban road runoff under different traffic densities in Beijing, China.

The characteristics of dissolved organic matter (DOM) in road runoff under different traffic densities were compared using resin fractionation, molecular weight distribution analysis, three-dimensional excitation-emission matrix fluorescence spectroscopy, and UV-visible spectroscopy. Heavy traffic density strongly increased the concentration of DOM in road runoff, resulting in higher dissolved organic carbon. The distribution of molecular weights in DOM was not influenced by the traffic. DOM was dominated by colloidal organic matter with molecular weight in the 1kDa to 0.45μm size range. Hydrophobic fractions accounted for a large proportion than hydrophilic fractions in DOM, and hydrophobic acids increased with higher traffic density. Traffic density did not alter the fluorescent substances in DOM, including fulvic-like UV fluorescent substances and protein-like substances. However, more tryptophan-like protein substances were found in DOM from road runoff with heavy traffic. Moreover, the aromatization degree of DOM was not affected by heavy traffic, while the degree of humification decreased.

The use of a self-generated current in a coupled MFC-AnMBR system to alleviate membrane fouling

In this study, we developed a coupled microbial fuel cell-anaerobic membrane bioreactor (MFC-AnMBR) system to degrade and remove membrane foulants, rather than preventing foulants from reaching the membrane surface through electrostatic repulsion. The MFC-AnMBR system consists of a conductive membrane as the MFC anode and an MBR filter membrane. The operating time of an experimental group with a 0.38-mA current was extended to 89 days longer than that of a control group (no cleaning during the operating period). Fourier-transform infrared spectroscopy indicated that the main membrane foulants were polysaccharides, proteins, and lipids. The concentrations of polysaccharides and proteins were significantly lower in the experimental group than in the control group. In confocal laser scanning microscopy, membrane surface proteins, α-polysaccharides, and β-polysaccharides decreased in the experimental group by 45.34%, 57.19%, and 26.46% compared to the control group. Three-dimensional excitation–emission matrix fluorescence spectroscopy and molecular weight (MW) analysis revealed that foulants deposited on the anode film surface were degraded into substances with low MW more effectively in the experimental group than in the control group. Two-dimensional heterogeneous correlation spectroscopy and high-throughput sequencing revealed that protein-like substances were degraded in both the control and experimental groups, but degradation of polysaccharide-like substances was more efficient in the experimental group. The degradation of polysaccharide-like and protein-like substances can be attributed to bacteria involved in anaerobic fermentation and electrogenic bacteria. Therefore, in the presence of electrons, polysaccharide-like substances with high MW can be converted into hydroxy-containing compounds with low MW, which are more readily degraded and utilized by microorganisms, thereby preventing membrane fouling.

Three-dimensional excitation-emission matrix (EEM) fluorescence approach to probing the binding interactions of polystyrene microplastics to bisphenol A

Microplastics (MPs) are readily to bind with contaminants, hence becoming the mobile composite pollutions with the migration of MPs in the environment. However, the binding mechanisms between MPs and various contaminants are still unclear due to the scarcity of investigation methods. In this work, three-dimensional excitation-emission matrix fluorescence spectroscopy approach is developed to probe the binding interactions between polystyrene MPs and a typical hydrophobic comtaminant bisphenol A (BPA). The binding affinity and thermodynamic parameters of the binding interactions are accurately and rapidly determined. Roles of environmental conditions in the binding interactions of MPs and BPA are discriminated. Results show that the binding strength of MPs to BPA is relatively higher under neutral (logK=4.96, pH 7) and weak acidic (logK=4.63, pH 6) conditions. The binding strength significantly grows with the increasing temperature from 4 to 35 °C. The binding process is barely influenced by ionic strength, but being promoted in the presence of divalent ions (Ca2+ and Mg2+). The binding process of MPs to BPA is solely driven by entropy. Under neutral condition, hydrophobic forces dominate the binding interactions between MPs and BPA, with the assistance of weak hydrogen bonds. The predominant hydrophobic interactions are weakened under acidic conditions, resulting in lower binding strength. Under alkaline conditions, both hydrophobic forces and hydrogen bonds are weakened, while electrostatic repulsions are magnified, leading to the obviously decreased binding strength. The results benefit to a better understanding of the composition pollutions of MPs and hydrophobic pollutants in aquatic environments.

Enhanced phosphorus mobility in a calcareous soil with organic amendments additions: Insights from a long term study with equal phosphorus input

The agricultural practice of replacing chemical fertilizers with organic amendments (manure and/or straw) may have consequences for phosphorus (P) loss to the environment. Such a knowledge gap was examined using a ten-year field trial in calcareous soil containing four treatments with the equal annual P input but varied organic amendment combinations as follows: mineral fertilizer only as control (MF), mineral fertilizer coupled with manure (MM), mineral fertilizer coupled with manure and straw (MMS) and mineral fertilizer coupled with straw (MS). The soil P distribution, P fractions and speciation, Fe(III) reduction and P sorption kinetics were investigated using the chemical extraction, K edge X-ray absorption near-edge structure and Langmuir equations. The electronic shuttle capacity of soils and speciation of soil dissolved organic matter (DOM) were also evaluated using electrochemical methods, three-dimensional excitation-emission matrix fluorescence spectroscopy and Fourier transform infrared spectra methods. Results showed that soil Olsen-P and total P increased at depths of 20–40 cm in MM, MMS and MS treatments, suggesting that manure and/or straw addition significantly mobilized P in the soil profile. Manure and/or straw addition also decreased soil maximum P sorption capacity (Smax) and increased the desorption rate at depths of 0–20 cm in soil across treatments. At a depth of 0–20 cm in soil of the MS treatment, the enhanced Fe(Ⅲ) reduction coupled with a decrease of Fe-bound P supports that Fe reduction dominates the mobilization of P. The transformation of Ca bound-P to Al/Fe bound-P in a depth of 0–20 cm in soil of the MM treatment may be due to the high proportion of humic-like substances in the DOM at a depth of 0–20 cm in soil of the MM treatment, which may have caused a slight/microsite acidification. These results can help to develop optimized fertilization practices to effectively mitigate P loss from calcareous soils with manure and/or straw addition.

Preliminary evaluation of the operation variables and degradation pathway in the alkali-catalyzed hydrothermal oxidation of triclosan

Due to the lack of green treatment technologies for chlorinated organic contaminant detoxification, in this study, the effect of non-hazardous alkali-catalyzed hydrothermal oxidation (HTO) on triclosan (TCS) was investigated. The optimal parameters determined by single-factor experiments were: a H2O2/TCS (H/T) ratio of 2.5 mL/mg, a temperature of 180 °C, a residence time of 120 min. Using these parameters, the final dechlorination efficiency (DE) of 99.69% was obtained. Response surface methodology (RSM) was employed to further determine the optimal conditions under multi-factor interactions. The optimal parameters were an H/T ratio of 2.5 mL/mg, a temperature of 187 °C, and a residence time of 150 min. The determined DE was 99.47%. The results of three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy showed that the degradation of TCS generated humic acid-like organics with aromatic ring and phenolic hydroxyl functional groups. Furthermore, fluorescence spectroscopy analysis showed that the residence time increased from 30 to 120 min, and the fluorescence intensity difference increased from 100.5 to 218 au, which confirmed that •OH participated in the alkali-catalyzed HTO process. There were two different reaction pathways: (1) Cleavage of the C–O bond between the two benzene rings, followed by the opening and dechlorination of the benzene ring via oxidation; (2) The benzene rings were directly hydroxylated, opened, and dechlorinated through oxidation. The intermediate products were further oxidized to non-Cl-containing organics, achieving the harmless degradation of TCS. Further analysis showed that the total organic carbon (TOC) removal efficiency was about 80% at a residence time of 140 min, indicating that TCS was almost completely mineralized. This study provides a green and environmentally benign approach for the detoxification of chlorinated organic contaminants.

Fast identification of fluorescent components in three-dimensional excitation-emission matrix fluorescence spectra via deep learning

Three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy has been widely applied to detect the fluorescent components in samples from natural water bodies to wastewater treatment processes. Data interpretation methods such as parallel factor analysis (PARAFAC) are required to decompose the overlapped fluorescent signals in the 3D-EEM spectra. However, strict requirements of data and complicated procedures of the PARAFAC limit the online monitoring and analysis of samples. Here we develop a fast fluorescent identification network (FFI-Net) model based on the deep learning approach to fast predict the numbers and maps of fluorescent components by simply inputting a single 3D-EEM spectrum. Two types of convolutional neural networks (CNN) are trained to classify the numbers of fluorescent components with an accuracy of 0.956 and predict the maps of fluorescent components with the min mean absolute error of 8.9 × 10-4. We demonstrate that the accuracy of the FFI-Net model will be further improved when more 3D-EEM data are available as a training dataset. Meanwhile, a user-friendly interface is designed to facilitate practical applications. Our approach gives a robust way to overcome the shortage of the PARAFAC and provides a new platform for online analysis of the fluorescent components in water samples.

Mechanistic study of antimonate reduction by Escherichia coli W3110

Microbial-assisted antimonate [Sb(V)] reduction immobilizes this redox-sensitive metalloid in the subsurface. Most indigenous aerobes in antimony (Sb)-contaminated areas do not contain Sb(V)-reducing genes but can resist high levels of Sb(V) threat. Herein, to unravel the mechanisms of Sb(V) resistance by aerobes, we used Escherichia coli W3110 as a model aerobe and incubated it with 10 μM Sb(V). We found that strain W3110, without known Sb(V)-reducing genes, was able to reduce Sb(V) to Sb(III). Our transcriptome analysis and reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) results show that the Sb(V) threat at the 10 μM level had a negligible effect on the gene expression of strain W3110. In vitro incubation experiments further indicate that Sb(V) reduction was attributable to extracellular polymeric substances (EPS). Moreover, the three-dimensional excitation-emission matrix fluorescence spectroscopy reveals that the tryptophan-like components in EPS were involved in Sb(V) binding as evidenced by its weakened fluorescence intensity upon Sb(V) addition. The FTIR and XPS analyses indicate that hemiacetal and amide groups in EPS contributed to the reduction of Sb(V). Preculture with 10 μM Sb(V) did not exhibit a significant difference in Sb(V)-reducing capacity, suggesting that Sb(V) stress probably did not stimulate EPS secretion of W3110. Our results highlight the importance of EPS as the first line of defense against toxins, especially for those bacteria without such functional genes.

Probing changes in humus chemical characteristics in response to biochar addition and varying bulking agents during composting: A holistic multi-evidence-based approach

Despite the various benefits of humus, the changes in its chemical characteristics during composting in response to biochar addition and varying bulking agents remain to be further explored. In this study, three treatments were conducted, in which swine manure, bulking agent, and biochar were mixed at ratios of 4:1:0, 8:1:0, and 8:1:1. Fourier transform infrared spectroscopy (FTIR), carbon nuclear magnetic resonance spectroscopy (13C-NMR), three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM), and near-edge X-ray absorption fine structure (NEXAFS) were employed to characterize the chemical and structural properties of humus from multiple perspectives. The 3D-EEM spectra in this study showed a larger increase in humic acids (HAs) content (56%) and HAs to fulvic acids ratio (128%) during composting, indicating stronger humification in biochar-amended treatment. FTIR, 13C-NMR, and NEXAFS all confirmed the essential properties of HA as the core agronomic functional substance with rich aromatic and carboxyl groups, and that its aromaticity increased gradually during composting. In addition, 13C-NMR demonstrated that biochar addition and a relatively higher bulking agent ratio aided an increase in the carboxyl C proportion in HA after composting. In particular, NEXAFS revealed that biochar addition promoted the diversification of C, N, and O species in HA, with the emergence of quinone C and O-alkyl C as the main representatives. This work suggests that biochar addition and a relatively high bulking agent ratio could enhance humification and improve the agronomic function of humus.

The partitioning behavior of PAHs between settled dust and its extracted water phase: Coefficients and effects of the fluorescent organic matter

The occurrence and distribution of polycyclic aromatic hydrocarbons (PAHs) in a city of Central China were determined in the settled dust and its extracted water phase from different land use types and bus stops in Nanchang City. The physicochemical properties of its water extracted dissolved organic matter (WEOM) were characterized to investigate the effect of fluorescence organic matter on the dust-water partitioning coefficients (Kd) using three-dimensional excitation-emission matrix fluorescence spectroscopy combined parallel factor analysis. Results showed that the range of ∑PAHs in settled dust and the extracted water phase was 0.05–15.92 μg·g−1 and 2–211 ng·L−1, respectively. These PAHs mostly came from the combustion of biomass. The risk assessment showed that PAHs in dust had no obvious health risk (less than the magnitude of 10−6). Additionally, the high molecular weight (HMW) PAHs and the low molecular weight (LMW) PAHs were preferentially adsorbed by dust and the dissolved portion, respectively. It was confirmed by the relatively high logKd values of 4.23 for the HMW-PAHs. Pearson correlation analysis suggested that the higher concentration of dissolved organic carbon and humic-like substance were in favor of PAHs in dust released into waters. This study can provide information on pollution control when considering the impact of fluorescent organic matter on the fate and transport of PAHs.

Construction of nano-flower MIL-125(Mo)-In2Se3 Z-scheme heterojunctions by one-step solvothermal method for removal of tetracycline from wastewater in the synergy of adsorption and photocatalysis way

The synergy of adsorption and photocatalysis has received considerable attention in the field of environmental remediation. In this work, a novel nano-flower MIL-125(Mo)-In2Se3 (M-In) adsorbent photocatalyst was firstly prepared by one-step solvothermal method. Benefiting from the 3D nano-flower structure, tightness 2D/2D heterojunction interface, highly exposed active site of MIL-125(Mo) and the spontaneous polarization of lamellar In2Se3, M-In exhibited an excellent adsorption and photodegradation performance in removal of tetracycline (TC) pollutants. The results of adsorption kinetic and adsorption equilibrium were well fitted by Pseudo-second-order model and Freundlich isotherm model, indicating that the adsorption progress was non-uniform and multilayer. In addition, the degradation rate of TC reached 94.14% within 120 min under visible light exposure in the presence of optimumratioM-In-1. The results of trapping experiments, three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy and liquid chromatograph-mass spectrometer showed that h+ played a significant role and O2– also played a role in the photo-degradation process. Hence, the novel adsorbent photocatalyst can be used to treat TC wastewater and the study gives some inspiration for the design and construction of efficient photocatalysts.

Algal Organic Matter Drives Methanogen-Mediated Methylmercury Production in Water from Eutrophic Shallow Lakes.

Algal blooms bring massive amounts of algal organic matter (AOM) into eutrophic lakes, which influences microbial methylmercury (MeHg) production. However, because of the complexity of AOM and its dynamic changes during algal decomposition, the relationship between AOM and microbial Hg methylators remains poorly understood, which hinders predicting MeHg production and its bioaccumulation in eutrophic shallow lakes. To address that, we explored the impacts of AOM on microbial Hg methylators and MeHg production by characterizing dissolved organic matter with Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy and quantifying the microbial Hg methylation gene hgcA. We first reveal that the predominance of methanogens, facilitated by eutrophication-induced carbon input, could drive MeHg production in lake water. Specifically, bioavailable components of AOM (i.e., CHONs such as aromatic proteins and soluble microbial byproduct-like materials) increased the abundances (Archaea-hgcA gene: 438-2240% higher) and activities (net CH4 production: 16.0-44.4% higher) of Archaea (e.g., methanogens). These in turn led to enhanced dissolved MeHg levels (24.3-15,918% higher) for three major eutrophic shallow lakes in China. Nevertheless, our model results indicate that AOM-facilitated MeHg production could be offset by AOM-induced MeHg biodilution under eutrophication. Our study would help reduce uncertainties in predicting MeHg production, providing a basis for mitigating the MeHg risk in eutrophic lakes.

Enhanced in-situ electro-generation of H2O2 using PTFE and NH4HCO3 modified C/PTFE electrode for treatment of landfill leachate

In this study, the carbon black/polytetrafluoroethylene (C/PTFE) electrode was prepared under the best conditions, and then it was modified by PTFE and NH4HCO3 to make a PTFE-C/PTFE electrode. PTFE-C/PTFE electrode was used to enhance H2O2 in-situ electro-generation and the electro-peroxone process (EPP) treatment of leachate. Various analytical methods results were applied to prove that the PTFE-C/PTFE electrode greatly improved the performance of H2O2 generation and electrode stability. The effects of initial pH, current intensity, ozone flow and Cl− concentration on the removal of NH4+ and chemical oxygen demand (COD) from landfill leachate were studied in the EPP with PTFE-C/PTFE as cathode (MEPP) by one factor at a time (OFAT) method. The initial pH value 7.5, current intensity 300 mA, ozone flow 875 mg/h and Cl− concentration value 4198 mg/L were selected as the best operating parameters. A response surface methodology based on box-behnken design (BBD) was employed to optimize running conditions of the MEPP of leachate. After optimization, Mineralization efficiency of the NH4+ and COD was obtained to be 79.83% and 52.14%, and biochemical oxygen demand (BOD5)/COD ratio increased to 0.38 after 4 h. The removal curves of NH4+ and COD in the MEPP conforms to the zero-order and first-order reaction kinetics, respectively. Three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM) analysis shows that MEPP has a good removal effect on organics in leachate. Energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis were carried out for the cathode sediment, which was mainly magnesium ion silicate precipitation and NaCl.

Adsorption characteristics of methylene blue by a dye-degrading and extracellular polymeric substance -producing strain

Biosorption of dye by microbes and the extracellular polymeric substances (EPS) were of great environmental significance, especially for the dye-degrading and EPS-producing strain. Previous studies were mainly focused on the adsorption capacities and regeneration properties of pure culture, few were on the biosorption of dyes by the dye-degraders and the contributions of EPS on adsorption. In this study, a dye-degrading and EPS-producing strain i.e., Klebsiella oxytoca was used to evaluate its removal capacity to methylene blue. The maximum adsorption capacity (qe) by the strain was calculated as 145 mg g−1, which is superior to many reported bio-adsorbents and some synthetic materials. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy results suggested that CO, –NH2 and P-OH groups were involved in the adsorption. High pressure steam sterilization (HPSS) increased the hydrophilicity of cell wall but did not significantly change the cell structure. Compared with the dead resting cell (DRC), the relative higher qe obtained by live resting cell (LRC) possibly due to the loss of some cell structure during the HPSS process. Adsorption experiments by EPS-free LRC, confocal laser microscope and three-dimensional excitation-emission matrix fluorescence spectroscopy results confirmed that the EPS played a role in the adsorption of MB dye. The adsorption characteristics of the dye-degrader and the contributions of EPS on adsorption were investigated in detail in this study. The results were benefit for better understanding of the interaction mechanisms between the dye molecules and cells that before the biodegradation process, which were of great significance for the practical usage of residual sludge on removal of dyes.

Variation in Extracellular Polymeric Substances from Enterobacter sp. and Their Pb2+ Adsorption Behaviors.

The objective of this study was to investigate the effects of the cultivation time, temperature, and pH value on the yield and composition of extracellular polymeric substances (EPS) from Enterobacter sp. FM-1 (FM-1) and to analyze the Pb2+ adsorption behavior of soluble EPS (S-EPS), loosely bound EPS (LB-EPS), and tightly bound EPS (TB-EPS). Maximum EPS production was obtained when the cultivation time, temperature, and pH value were 24 h, 30 °C, and 8.0, respectively. The main components of EPS were proteins, polysaccharides, and nucleic acids, but the different EPS types contained different proportions and specific components. The Pb2+ adsorption capacity of LB-EPS was 2.23 and 1.50 times higher than that of S-EPS and TB-EPS, respectively. After Pb2+ adsorption by LB-EPS, the pH value of the reaction system decreased to the lowest of 5.23, which indicated that LB-EPS contained more functional groups that could release H+, which will help to better adsorb Pb2+ through ion exchange. The three-dimensional excitation–emission matrix fluorescence spectroscopy (3D-EEM) analysis showed that the fluorescence intensity of tryptophan-containing substances decreased by 85.5% after Pb2+ adsorption by LB-EPS, which indicated the complexation of tryptophan-containing substances with Pb2+. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) O spectra indicated that the C=O peak from protein amide I of tryptophan-containing substances in LB-EPS was mainly responsible for the complexation of Pb2+. After the adsorption of Pb2+, the proportion of the C=O peak in LB-EPS increased by 33.89%, indicating that the complexation of LB-EPS with Pb2+ was mainly attributed to the O atom in the C=O terminus of protein amide I.

Interactions between cerium dioxide nanoparticles and humic acid: Influence of light intensities and molecular weight fractions

Cerium dioxide nanoparticles (CeO2 NPs) are ubiquitous in the water environment due to the extensive commercial applications. The complexity of heterogeneous humic acid (HA) plays a significant role in affecting the physicochemical properties of CeO2 NPs in aqueous environments. However, the effects of light intensities and HA fractions on the interaction mechanism between CeO2 NPs and HA are poorly understood. Here, we provided the evidence that both light intensities (>3 E L−1 s−1) and molecular weights (>10 kDa) can effectively affect the interactions between CeO2 NPs and HA. The absolute content of reactive oxygen species (ROS) and quantum yield (Φ) of 3HA* were inhibited when HA (10 mg of C L−1) interacts with CeO2 NPs. However, they were positively correlated with the increasing irradiation time and simulated sunlight intensities. High molecular weights of HA fraction (>100 kDa) restrained the ROS generation and Φ of 3HA* due to surface adsorption between HA and CeO2 NPs blocking reactive sites, competitive absorption for simulated sunlight. Fourier transform infrared and three-dimensional excitation-emission matrix fluorescence spectroscopy confirmed that the carboxylic groups of HA have high complexation capacity with CeO2 NPs. These findings are essential for us to improve the understanding of the impacts of HA on CeO2 NPs under different conditions in natural waters.

Optimized pre-treatment of high strength food waste digestate by high content aluminum-nanocluster based magnetic coagulation

Coagulation-based pre-treatment efficiency of high strength digestate of food waste (HSDFW) anaerobic digestion is negated by organic ligand-catalyzed decomposition of coagulants. In this study, an efficient HSDFW pre-treatment method, magnetic seeds (MS) coagulation, was employed by using highly stable Keggin Al30 nanocluster (PAC30), MS and polyacrylamide (PAM), and its operation was optimized by evaluating the performance of removing turbidity, total suspended solids (TSS), chemical oxygen demand (COD), and total phosphorous (TP) phosphate. Results showed that at the optimum dosage of 4.82 g/L, PAC30 demonstrated excellent removals as high as 98.93% ± 0.1% of turbidity, 98.04% ± 0.1% of TSS, 58.28% ± 0.3% of total COD, 99.98% ± 0.01% of TP and 99.50% ± 0.01% of dissolved phosphate, respectively. Apparent molecular weight (AMW) and three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy analyses demonstrated more efficient removal of dissolved organic matter (DOM), particularly non-biodegradable and hydrophobic components by PAC30 than commercial coagulant. The sedimentation was much improved from 40 min by coagulation/flocculation to about 5 min settling by MS coagulation. The PAC30 based magnetic coagulation (MC) presents theoretical guidance on a cost-effective and much less footprint pre-treatment alternative for high strength wastewater.

Enhanced photocatalytic degradation of gaseous toluene and liquidus tetracycline by anatase/rutile titanium dioxide with heterophase junction derived from materials of Institut Lavoisier-125(Ti): Degradation pathway and mechanism studies

Anatase/rutile titanium dioxide (TiO2) with heterophase junction and large Brunauer-Emmett-Teller (BET) specific surface area (50.1 m2 g−1) is successfully synthesized by calcinating Materials of Institut Lavoisier-125(Ti) (MIL-125(Ti)) with 30% O2/Ar at the temperature of 600 °C (M−O−600). Several techniques are used to examine the physicochemical, photoelectrochemical and optical properties of samples, and their photocatalytic performances are evaluated by photodegradation of gaseous toluene and liquidus tetracycline (TC) under visible light illumination. It is found that the calcination temperature has significant influence on the crystal structure and physicochemical parameters of TiO2. The weight fractions of rutile and anatase TiO2 of M−O−600 are approximately 0.7 and 0.3, which displays outstanding photocatalytic activity. Through the construction of heterophase junction, M−O−600 has better oxygen adsorption and higher density of localized states, which effectively promotes the generation of superoxide radical (·O2–) and hydroxyl radical (·OH) species. In-situ infrared spectra indicate that toluene is oxidized to benzyl alcohol, benzaldehyde and benzoic acid in turn and then oxidized to formic acid and acetic acid before eventually degraded into H2O and CO2. Gas chromatography-mass spectrometry (GC–MS) is also used to further investigate the degradation pathway of toluene. Degradation pathway and mechanism of TC are studied by liquid chromatography-tandem mass spectrometry (LC-MS). Moreover, three-dimensional excitation-emission matrix fluorescence spectroscopy (3D EEMs) and total organic carbon (TOC) show that TC can be effectively mineralized through a series of reactions by M−O−600 during photocatalysis.

Weak electricity stimulates biological nitrate removal of wastewater: Hypothesis and first evidences

Nitrate pollution in water is a worldwide health and environmental concern. Biological nitrate removal of wastewater is widely used countering eutrophication of water bodies; however it could be troublesome and expensive when influent carbon source is insufficient. Here we present a novel process, the microbial fuel cell (MFC)-resistance-type electrical stimulation denitrification process (RtESD) using microbial weak electricity originated from the wastewater, to enhance nitrate removal. Results show that the optimal nitrate dependent denitrification rate (0.027 mg N/L·h) and nitrate removal efficiency (98.1%) can be achieved; partial autotrophic denitrification was enhanced in RtESD under stimulation of 0.2 V of microbial weak electricity (MWE). Aromatic proteins also increased in the presence of 0.2 V MWE stimulation according to three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy profiles, indicating that electron transfer could be improved in the case of MWE stimulation. Furthermore, the microbial community structure and diversity analysis results demonstrated that MWE stimulation inhibited the heterotrophic denitrifying bacteria and activated the autotrophic denitrifying bacteria in RtESD. Two hypotheses, enhancement of electron transfer and improvement of microorganism activity, were proposed regarding to the MWE stimulated pathways. This study provided a promising method utilizing MWE derived from wastewater to improve the denitrification rate and removal efficiency of nitrate-containing wastewater treatment processes.