Three-dimensional Excitation-emission Matrix Fluorescence Spectroscopy Research Articles

Effect of nitrogen retention composite additives Ca(H2PO4)2 and MgSO4 on the degradation of lignocellulose, compost maturation, and fungal communities in compost.

This study investigated the effects of the nitrogen retention composite additives Ca(H2PO4)2 and MgSO4 on lignocellulose degradation, maturation, and fungal communities in composts. The study included control (C, without Ca(H2PO4)2 and MgSO4), 1% Ca(H2PO4)2 + 2% MgSO4 (CaPM1), 1.5% Ca(H2PO4)2 + 3% MgSO4 (CaPM2). The results showed that Ca(H2PO4)2 and MgSO4 enhanced the degradation of total organic carbon (TOC) and promoted the degradation of lignocellulose in compost, with CaPM2 showing the highest TOC and lignocellulose degradation. Changes in the three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM) of dissolved organic matter (DOM) components in compost indicated that the treatment group with the addition of Ca(H2PO4)2 and MgSO4 promoted the production of humic acids (HAs) and increased the degree of compost decomposition, with CaPM2 demonstrating the highest degree of decomposition. The addition of Ca(H2PO4)2 and MgSO4 modified the composition of the fungal community. Ca(H2PO4)2 and MgSO4 increased the relative abundance of Ascomycota, decreased unclassified_Fungi, and Glomeromycota, and activated the fungal genera Thermomyces and Aspergillus, which can degrade lignin and cellulose during the thermophilic stage of composting. Ca(H2PO4)2 and MgSO4 also increased the abundance of Saprotroph, particularly undefined Saprotroph. In conclusion, the addition of Ca(H2PO4)2 and MgSO4 in composting activated fungal communities involved in lignocellulose degradation, promoted the degradation of lignocellulose, and enhanced the maturation degree of compost.

Research on enhancing sewage sludge lysis and bioreactor initiation through composite thermophilic strains

Returning lysed sludge to biochemical tanks to achieve in-situ sludge reduction is promising. A novel approach for regulating and initiating the sludge lysis process utilizing thermophilic strains is proposed. In this study, three strains were isolated from sludge, and sequencing of the 16 S rDNA amplicon revealed that the three thermophilic strains were the closest relatives to the genus Geobacillus, and they were designated as Geobacillus sp. DX5, Geobacillus sp. DX8 and Geobacillus sp. DX11. Sludge lysis experiments demonstrated that composite thermophilic strains (CTS) were dosed at 65°C, and the sludge VSS removal efficiency after 24 h was 37.8%, significantly surpassing individual strains. Moreover, 65.8% of proteins and 52.0% of polysaccharides in Extracellular polymeric substances (EPS) of sludge were degraded. Furthermore, Three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy results revealed a substantial release of dissolved organic matter during sludge lysis. Inoculation of CTS under optimal conditions (65°C, pH 7, 4 × 1010cfu/L) resulted in VSS removal efficiency and protease activity of 42.7% and 2584 U/L, respectively. After 20 days of inoculation with CTS to initiate sludge lysis reactor, VSS removal efficiency reached 46%. Additionally, it stimulated the growth of the thermophilic bacterial community, engaging indigenous thermophilic strains in the sludge lysis process.

Selenium bio-nanocomposite based on extracellular polymeric substances (EPS): Synthesis, characterization and application in alleviating cadmium toxicity in rice (Oryza sativa L.)

Selenium nanoparticles (SeNPs) have gained significant attention owing to their favorable bioavailability and low toxicity, making them widely applications in the fields of medicine, food and agriculture. In this study, bacterial extracellular polymeric substances (EPS) were used as a novel stabilizer and capping agent to prepare dispersed SeNPs. Results show that EPS-SeNPs presented negative potential (−38 mV), spherical morphologies with average particle size about 100–200 nm and kept stable at room temperature for a long time. X-ray diffraction (XRD) analysis demonstrated that the synthesized nanoparticles were pure amorphous nanoparticles, and X-ray photoelectron spectroscopy (XPS) spectrum showed a spike at 55.6 eV, indicating the presence of zero-valent nano‑selenium. Fourier-transform infrared spectroscopy (FTIR) and three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy analysis confirmed proteins and polysaccharides in EPS played a crucial role in the synthesis of EPS-SeNPs. Compared to EPS or sodium selenite (Na2SeO3), EPS-SeNPs showed a relatively moderate result in terms of scavenging free radicals in vitro. In contrast, EPS-SeNPs demonstrated lower toxicity to rice seeds than Na2SeO3. Notably, the exogenous application of EPS-SeNPs effectively alleviated the growth inhibition and oxidative damaged caused by cadmium (Cd), and significantly reduced Cd accumulation in rice plants.

Humification levels of dissolved organic matter in the eastern plain lakes of China based on long-term satellite observations

Under the influence of intensive human activities and global climate change, the sources and compositions of dissolved organic matter (DOM) in the eastern plain lake (EPL) region in China have fluctuated sharply. It has been successfully proven that the humification index (HIX), which can be derived from three-dimensional excitation-emission matrix fluorescence spectroscopy, can be an effective proxy for the sources and compositions of DOM. Therefore, combined with remote sensing technology, the sources and compositions of DOM can be tracked on a large scale by associating the HIX with optically active components. Here, we proposed a novel HIX remote sensing retrieval (IRHIX) model suitable for Landsat series sensors based on the comprehensive analysis of the covariation mechanism between HIX and optically active components in different water types. The validation results showed that the model runs well on the independent validation dataset and the satellite-ground synchronous sampling dataset, with an uncertainty ranging from 30.85 % to 36.92 % (average ± standard deviation = 33.6 % ± 3.07 %). The image-derived HIX revealed substantial spatiotemporal variations in the sources and compositions of DOM in 474 lakes in the EPL during 1986–2021. Subsequently, we obtained three long-term change modes of the HIX trend, namely, significant decline, gentle change, and significant rise, accounting for 74.68 %, 17.09 %, and 8.23 % of the lake number, respectively. The driving factor analysis showed that human activities had the most extensive influence on the DOM humification level. In addition, we also found that the HIX increased slightly with increasing lake area (R2 = 0.07, P < 0.05) or significantly with decreasing trophic state (R2 = 0.83, P < 0.05). Our results provide a new exploration for the effective acquisition of long-term dynamic information about the sources and compositions of DOM in inland lakes and provide important support for lake water quality management and restoration.

Spatial variation of dissolved organic matter in the Tuojiang River Basin in Chengdu, China: insights based on EEMs-PARAFAC analysis.

Three-dimensional excitation-emission matrix fluorescence spectroscopy coupled with parallel factor analysis was adopted to investigate the characteristics of dissolved organic matter (DOM) components in water samples collected from the Tuojiang River Basin in Chengdu, including its main stream and tributaries. Four DOM components that matched with three fluorescence peaks were identified in the whole river basin and tributaries; while three components corresponding to four fluorescence peaks were identified in the main stream. In all cases, humic-like components accounted for high proportions of the DOM. Correlation analysis revealed the same sources for four components in the whole river basin and its tributaries, whereas two components had different sources in the main stream. Ultraviolet absorbance parameters (SUVA254, SR) and fluorescence parameters (BIX, HIX, FI, β:α) indicated the dominant autochthonous sources of DOM in the whole river basin. Higher terrestrial inputs of DOM were observed in the tributaries than in the main stream. In the areas influenced by human activities (6#, 17#, 18#), the sources of DOM showed strong terrestrial characteristics and high degrees of humification and aromatization, as well as serious pollution. The results of this study have potentially far-reaching implications for environmental water management in the area.

Diurnal and seasonal variations of pCO2 and fluorescent dissolved organic matter (FDOM) in different polluted lakes.

This study aimed to assess pollution and daily-to-seasonal dynamics of the partial pressure of CO2 (pCO2) and CO2 degassing flux concerning the fluorescent dissolved organic matter (FDOM) from tropical lakes. A membrane-enclosed pCO2 sensor and water quality multimeter analyzer was deployed to continuously record daily and seasonal variations in pCO2 and CO2 degassing flux in three lakes in Savar, Dhaka. During both wet and dry seasons, all lake water was supersaturated with CO2 in contrast to the atmospheric equilibrium (~400 μatm). The pCO2 values in the lake water during the dry season were relatively low in comparison, and the pCO2 levels in the wet season were much higher due to external inputs of organic matter from watersheds and direct inputs of CO2 from soils or wetlands. The estimated water-to-air CO2 degassing flux in the different levels of polluted lakes varies with the pollution context. Study areas calculated the carbon flux and three lakes released respectively 86.75×107g CO2 year-1, 13.8×107g CO2 year-1, and 9.17×107g CO2 year-1. Three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy combined with parallel factor (PARAFAC) analysis was used to investigate the distributions of fluorescent components in DOM. EEM-PARAFAC analysis identified humic-like, fulvic-like, protein-like, and more tyrosine-like FDOM components and their environmental dynamics. Terrestrial DOM may provide inputs to the terrestrial humic-like component in the lake water. In contrast, the biological activity of plankton-derived FDOM is the most likely source for the autochthonous humic-like component. FDOM and DO concentrations have negative correlations with pCO2, indicating that when the FDOM and DO level is decreased, the amount of pCO2 values increases.

Remote sensing identification of urban water pollution source types using hyperspectral data

Owing to accelerated urbanisation, increased pollutants have degraded urban water quality. Timely identification and control of pollution sources enable relevant departments to effectively perform water treatment and restoration. To achieve this goal, a remote sensing identification method for urban water pollution sources applicable to unmanned aerial vehicle (UAV) hyperspectral images was established. First, seven fluorescent components were obtained through three-dimensional excitation-emission matrix fluorescence spectroscopy of dissolved organic matter (DOM) combined with parallel factor analysis. Based on the hierarchical cluster analysis of the seven fluorescence components and three spectral indices, four pollution source (PS) types were determined, namely, domestic sewage, terrestrial input, agricultural and algal, and industrial wastewater sources. Second, several water colour and optical parameters, including the absorption coefficient of chromophoric DOM at 254 nm, humification index, chlorophyll-a concentration, and hue angle, were utilised to develop an identification method with a recognition accuracy exceeding 70% for the four PSs that is suitable for UAV hyperspectral data. This study demonstrated the potential of identifying PSs by combining the fluorescence characteristics of DOM with the optical properties of water, thus expanding the application of remote sensing technologies and providing more comprehensive and reliable information for urban water quality management.

DOM accumulation in the hyporheic zone promotes geogenic Fe mobility: A laboratory column study

Hyporheic zone (HZ) systems have a natural purification capacity, and they are commonly used to provide high quality drinking water. However, the presence of organic contaminants in HZ systems in anaerobic environments causes the aquifer sediments to release metals (e.g., Fe) at levels above drinking water standards, which affects the quality of groundwater. In this study, the effects of typical organic pollutants (dissolved organic matter (DOM)) on Fe release from anaerobic HZ sediments were investigated. Ultraviolet fluorescence spectroscopy, three-dimensional excitation-emission matrix fluorescence spectroscopy, excitation–emission matrix spectroscopy coupled with parallel factor analysis and Illumina MiSeq high-throughput sequencing were used to determine the effects of the system conditions on Fe release from HZ sediments. Compared with the control conditions (low traffic and low DOM as a baseline), the Fe release capacity was enhanced by 26.7 % and 64.4 % at low flow rate (85.8 m/d) and high organic matter concentration (1200 mg/L), which was consistent with the residence-time effect. The transport of heavy metals under different system conditions varied with the influent organic composition. The influent organic matter composition and fluorescence parameters (the humification index, biological index and fluorescence index) were closely related to the release of the Fe effluent, while these factors had less influence on Mn and As. From 16S rRNA analysis of the aquifer media at different depths at the end of the experiment, under low flow rate and high influent concentration conditions, reduction of Fe minerals by Proteobacteria, Actinobacteriota, Bacillus, and Acidobacteria promoted the release of Fe. These functional microbes play an active role in the Fe biogeochemical cycle in addition to reducing Fe minerals to promote Fe release. In summary, this study reveals the effects of the flow rate and influent DOM concentration on the release and biogeochemistry of Fe in the HZ. The results presented herein will contribute to a better understanding of the release and transport of common groundwater contaminants in the HZ and other groundwater recharge environments.

The spectral resolution of DOM in urban rivers affected by different non-point source intensities using self-organizing maps.

UV-Vis, three-dimensional excitation-emission matrix fluorescence spectroscopy (EEMs) and a self-organizing map (SOM) were used to study changes in the composition and constituent concentrations of dissolved organic matter (DOM) in the water column of two urban rivers with different non-point source inputs during spring and summer. The level of humification and the relative molecular mass of DOM were remarkably higher in the summer than in the spring (P < 0.01) in both rivers. The SOM model showed that the fluorescence intensity of the spring component was lower than in summer in water bodies with higher levels of non-point source inputs, while the opposite was true for water bodies with lower levels of non-point source inputs. Principal component analysis (PCA) showed that nutrients like nitrogen and phosphorus promoted autogenous processes in these water bodies. Seasonal variations and differing intensities of non-point source inputs had remarkable effects on urban river waters (R2 = 0.775, P < 0.001). Non-point source inputs increased the concentrations of humus-like fractions and promoted autogenesis in the water bodies.

Spatial heterogeneity and compositional profiles of dissolved organic matter in farmland soils across mainland China

Dissolved organic matter (DOM) plays an essential role in many geochemical processes, however its complexity, chemical diversity, and molecular composition are poorly understood. Soil samples were collected from 500 vegetable fields in administrative regions of mainland China, of which 122 were selected for further investigation. DOM properties were characterized by three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) (field intensity is 15 Tesla). Our results indicated that the main constituents were UVA humic-like substances, humic-like substances, fulvic acid-like substances, and tyrosine-like substances. A total of 10,989 molecular formulae with a mass range of 100.04 to 799.59 Da were detected, covering the mass spectrometric information of the soil samples from 27 different regions. CHO and CHON molecules were dominant in DOM, whereas lignin, tannins, and aromatic substances served as the main components. The results of cluster analysis revealed that the soil properties in Jiangxi Province were considerably different from those in other regions. The key backgrounds of the DOM molecular characteristics in the vegetable-field soil samples across mainland China were provided at the molecular level, with large abundance and great variability.

Identify the Virus-like Models for COVID-19 as Bio-Threats: Combining Phage Display, Spectral Detection and Algorithms Analysis.

The rapid identification and recognition of COVID-19 have been challenging since its outbreak. Multiple methods were developed to realize fast monitoring early to prevent and control the pandemic. In addition, it is difficult and unrealistic to apply the actual virus to study and research because of the highly infectious and pathogenic SARS-CoV-2. In this study, the virus-like models were designed and produced to replace the original virus as bio-threats. Three-dimensional excitation-emission matrix fluorescence and Raman spectroscopy were employed for differentiation and recognition among the produced bio-threats and other viruses, proteins, and bacteria. Combined with PCA and LDA analysis, the identification of the models for SARS-CoV-2 was achieved, reaching a correction of 88.9% and 96.3% after cross-validation, respectively. This idea might provide a possible pattern for detecting and controlling SARS-CoV-2 from the perspective of combining optics and algorithms, which could be applied in the early-warning system against COVID-19 or other bio-threats in the future.

The Z-scheme photocatalyst S-BiOBr/Bi2Sn2O7 with 3D/0D interfacial structure for the efficient degradation of organic pollutants

The establishment of heterojunction photocatalysts with significant degradation ability is identified as an effective strategy to address refractory pollutants. S-BiOBr nano-flowers were successfully synthesized by the isomorphous replacement combined self-assembly methods, and then Bi2Sn2O7 was deposited in-situ on the surface to construct a 3D/0D interfacial Z-scheme S-BiOBr/Bi2Sn2O7 heterojunction. The S-BiOBr/Bi2Sn2O7 maintained high activity on the degradation of rhodamine B, tetracycline and the inactivation of Spirulina, and three-dimensional excitation-emission matrix fluorescence spectroscopy was used to track the dynamic degradation process of pollutants. Mechanism analysis revealed that the h+ and O2− radicals played a leading role in the photocatalytic process, and OH played an assisting role. This enhanced activity can be attributed to the formation of oxygen vacancies at the interface when BiOBr is doped with S, which not only promoted the upward shift of the conduction band and thus improving the oxidation ability, but also narrowed the bandgap and thus boosting the visible light harvesting of BiOBr. Semiconductor produced photogenerated electron-hole pairs are effectively separated, and the redox ability of photogenerated carriers is maintained. These results provide a reasonable design method of high-efficiency heterojunction photocatalysis for refractory pollutants’ removal from wastewater.

Spatiotemporal Variation of Riverine Dissolved Organic Matter Degradation Based on EEMs-PARAFAC: A Case Study of Shili River in Jiujiang, Jiangxi Province, China, as a Typical Demonstration City of the Yangtze River protection Strategy

This study investigated the spatio-temporal distribution of dissolved organic matter (DOM) composition and its sources before and after degradation in the Shili River watershed in Jiujiang (China). Spatio-temporal variation of riverine DOM water samples before and after five days of degradation in a simulated channel was characterized by spectral feature analysis using three-dimensional excitation-emission matrix fluorescence spectroscopy coupled with parallel factor analysis. Across all water samples (#1,#2 and #3) before and after degradation, a total of four fluorescent components in DOM were identified: C1, C2, C3, and C4. The aromaticity index (SUVA254) was negatively correlated with the C2 and C3 components and biological index (BIX) and freshness index (β:α), but it had little correlation with the humification index (HIX). The greater the aromaticity of DOM in water, the lower the proportion of recently produced DOM and its biological activity. The C3 component had a strong positive correlation with BIX, β:α, and C2. The results suggested that C2 and C3 were derived from the same substances. According to the fluorescence parameters, DOM was dominated by autochthonous contributions. The fluorescence intensity of DOM increased gradually along the direction of water flow. The increase of water temperature in spring and autumn enhanced the endogenous level of DOM. The levels and fluctuations of BIX and β:α in different seasons and different sampling points were basically consistent. DOC concentration does not fully represent the localized nature of the DOM. The analysis of some fluorescence parameters and light absorption parameters showed that the DOM source was more internal than terrestrial. This study reveals the composition, source and temporal and spatial characteristics of DOM in the Shili River Basin, which has theoretical guiding significance for water environment management.

Impact of emerging pollutant florfenicol on enhanced biological phosphorus removal process: Focus on reactor performance and related mechanisms

Florfenicol (FF), an emerging pollutant antibiotic that is difficult to biodegrade, inevitably enters sewage treatment facilities with high level. To date, however, the performance and related mechanism of FF on enhanced biological phosphorus removal (EBPR) have not been reported. In order to fill this gap, this work investigated the potential impacts of FF on EBPR and revealed the relevant mechanisms. The effect of FF on EBPR was dose-dependent, that was, low dose had no effect on EBPR, while high FF concentration inhibited EBPR. Mechanism investigation showed that FF had no effect on anaerobic phosphate release, but reduced oxic phosphorus uptake. Three-dimensional Excitation-emission Matrix fluorescence spectroscopy and X-ray photoelectron spectroscopy analysis showed that FF affected the structure and components of activated sludge extracellular polymers (EPS). High content of FF stimulated sludge to secrete more EPS. High level of FF reduced the relative abundance of microorganisms responsible for biological phosphorus removal. Microbiological community structure analysis indicated 2.0 mg FF/L increased the relative abundance of Candidatus_Competibacter and Terrimonas from 9.22 % and 12.49 % to 19.00 % and 16.28 %, respectively, but significantly reduced the relative abundance of Chinophagaceae from 11.32 % to 0.38 %, compared with the blank.

Effect of Colloids in Sediment and Soil on Their Sorption Behavior of Chloramphenicol

Natural colloids (NCs) are ubiquitous in sediments and soils, which could affect the environmental fate of antibiotics. Focusing on chloramphenicol (CAP), different sources of the sediments and soil samples were selected to research the sorption capacity of NCs with different relative molecular weights towards CAP, as well as the impactors, combined with a multi-method approach including cross-flow ultrafiltration, dynamic light scattering, UV-visible absorption spectroscopy, and three-dimensional excitation-emission matrix fluorescence spectroscopy. The results revealed that the low molecular weight (LMW) of NCs was associated with a low autochthonous origin and a higher humification degree. The high molecular weight (HMW) of NCs were mainly terrestrial sources, and the aromatic rings contained more oxygen-containing functional groups such as carboxyl, hydroxyl, and carbonyl groups. Four fluorescence components were identified using the parallel factor analysis model, and the humic-like substances were the primary fluorescent components. Moreover, based on batch experiments, the study investigated the sorption behavior of CAP by the different fractions of the solid samples. The results showed that the sorption processes of CAP were well fitted by the linear model and Freundlich model. The average sorption rate of CAP by the original solid samples and the solid samples with removed organic and inorganic carbon were 4.46%, 3.93%, and 6.61%, respectively, indicating that organic carbon played an important role in the sorption behavior of CAP. The results of the sorption experiments indicated that CAP was more easily adsorbed on the LMW NCs that had a high degree of humification and a more aliphatic chain on the aromatic rings. In addition, tryptophan-like protein substances in NCs showed the inhibiting effect on the sorption progress of CAP. Redundancy analysis indicated that the sorption of CAP by NCs in sediment and soil was mainly related to the source, aromatics, oxygen functional groups on aromatic rings, humification degree, and humic-like substances of NCs.

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.