Excitation-emission Matrix Fluorescence Research Articles

Front-face excitation-emission matrix fluorescence spectroscopy combined with interpretable deep learning for the rapid identification of the storage year of Ningxia wolfberry

Ningxia wolfberry stored for many years may be disguised as fresh wolfberry by unscrupulous traders and sold for huge profits. In this work, the front-face excitation-emission matrix (FF-EEM) fluorescence spectroscopy coupled with interpretable deep learning was proposed to identify the storage year of Ningxia wolfberry in a lossless, fast and accurate way. Alternating trilinear decomposition (ATLD) algorithm was used to decompose the three-way data array obtained by Ningxia wolfberry samples, extracting the chemically meaningful information. Meanwhile, a convolutional neural network (CNN) model for the identification of the storage year of Ningxia wolfberry, called EEMnet, was proposed. The model successfully classified wolfberry samples from different storage years by extracting the subtle feature differences of the spectra, and the correct classification rate of the training set, test set and prediction set was more than 98%. In addition, a series of interpretability analyses were implemented to break the “black box” of the deep learning model. These results indicated that the method based on FF-EEM fluorescence spectroscopy combined with EEMnet could quickly and accurately identify the year of Ningxia wolfberry in a green way, providing a new idea for the identification of the storage years of Chinese medicinal materials.

Insight into micropollutant abatement during ultraviolet light-emitting diode combined electrochemical process: Reaction mechanism, contributions of reactive species and degradation routes

Electrochemical process coupling with ultraviolet light-emitting diode for micropollutant abatement was evaluated in the treatment of wastewater containing Cl−. Four representative micropollutants, atrazine, primidone, ibuprofen and carbamazepine, were selected as target compounds. The impacts of operating conditions and water matrix on micropollutant degradation were investigated. Fluorescence excitation-emission matrix spectroscopy spectra and high performance size exclusion chromatography were employed to characterize the transformation of effluent organic matter in treatment. The degradation efficiencies of atrazine, primidone, ibuprofen and carbamazepine are 83.6 %, 80.6 %, 68.7 % and 99.8 % after 15 min treatment, respectively. The increment of current, Cl− concentration and ultraviolet irradiance promote the micropollutant degradation. However, the presence of bicarbonate and humic acid inhibit micropollutant degradation. The mechanism of micropollutant abatement was elaborated based on reactive species contributions, density functional theory calculation and degradation routes. Free radicals (HO•, Cl•, ClO• and Cl2•-) could be generated by chlorine photolysis and subsequent propagation reactions. The concentrations of HO• and Cl• are 1.14 × 10−13 M and 2.0 × 10−14 M in optimal condition, respectively, and the total contributions of HO• and Cl• for the degradation of atrazine, primidone, ibuprofen and carbamazepine are 24 %, 48 %, 70 % and 43 %, respectively. The degradation routes of four micropollutants are elucidated based on intermediate identification, Fukui function and frontier orbital theory. Micropollutants can be effectively degraded in actual wastewater effluent, and the small molecule compound proportion increases during effluent organic matter evolution. Compared with photolysis and electrolysis, the coupling of the two processes has potential for energy saving in micropollutant degradation, which shed light on the prospects of ultraviolet light-emitting diode coupling with electrochemical process for effluent treatment.

Performances and mechanisms of ferrate(VI) oxidation process for shale gas flowback water treatment

The aim of this study was to determine effective and green methods for the removal of organic matter from shale gas flowback water (SGFW). The effects of ferrate (Fe(VI)), initial pH, and reaction time on the removal efficiency of Fe(VI) were investigated. A chemical oxygen demand removal efficiency of 57 % was achieved under the optimal conditions of Fe(VI)= 1500 mg/L, pH= 8.0, T = 25 °C, 60 min. Combined with the results of the chemical probe method, competitive kinetic experiments, electron spin resonance spectra, and radical quenching studies, hydroxyl radicals (∙OH) were demonstrated as the dominant reactive species responsible for oxidation. Furthermore, the fluorescence intensity of soluble microbial by-product-like matter and acid-like components were found to be reduced by 64 % and 43 %, respectively, using fluorescence excitation-emission matrix spectroscopy tests. The results of gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry indicated that electron-rich organic compounds were easily removed by Fe(VI) oxidation. Bacterial culture and coagulation experiments showed that Fe(VI) had both disinfection and coagulation effects in the SGFW. Furthermore, considering H2O2 as a precursor for ∙OH generation, the combined H2O2-Fe(VI) process was investigated in this study, and the results showed that the process has a synergistic effect and can increase the Chemical Oxygen Demand (COD) removal up to 68 % (Fe=1500 mg/L, pH=8.0, H2O2 =0.05 mol/L, T = 25 °C). Finally, an ultrafiltration membrane fouling experiment proved that the oxidation processes can increase the membrane-specific flux and alleviate fouling resistance. This study provides a reference for the design and operation of organic removal process in the SGFW treatment.

Dissolved organic matter composition and fluorescence characteristics of the river affected by coal mine drainage

Coal mine drainage (CMD) discharged into surface waters results in serious environmental pollution risk to rivers, lakes, and reservoirs. Coal mine drainage generally contains a variety of organic matter and heavy metals due to coal mining activities. Dissolved organic matter (DOM) plays an important role in the physicochemical and biological processes of many aquatic ecosystems. In this study, the investigations were carried out in the dry and wet seasons in 2021 to assess the characteristics of DOM compounds in coal mine drainage and the CMD-affected river. The results indicated that the pH of CMD-affected river pressed close to coal mine drainage. Besides, coal mine drainage lowered DO by 36% and increased total dissolved solids by 19% in the CMD-affected river. Coal mine drainage decreased absorption coefficient a(350) and absorption spectral slope S275-295 of DOM in the CMD-affected river; hence, DOM molecular size increased with decreasing S275-295. Three-dimensional fluorescence excitation-emission matrix spectroscopy and parallel factor analysis identified humic-like C1, tryptophan-like C2, and tyrosine-like C3 in the CMD-affected river and coal mine drainage. DOM in the CMD-affected river mainly originated from microbial and terrestrial sources, with strong endogenous characteristics. The ultra-high-resolution Fourier transform ion cyclotron resonance mass spectrometry analysis revealed that coal mine drainage had a higher relative abundance of CHO (44.79%), with a higher unsaturation degree of DOM. Coal mine drainage decreased the AImod,wa, DBEwa (double bond equivalents), Owa, Nwa, and Swa values and increased the relative abundance of the O3S1 species with DBE of 3 and carbons number range of 15-17 at the CMD inlet to the river channel. Moreover, coal mine drainage with the higher protein content increased the protein content of water at the CMD inlet to the river channel and the downstream river. DOM compositions and proprieties in coal mine drainage were investigated to further understand the influence of organic matter on heavy metals in future study.

Water-soluble brown carbon in atmospheric aerosols from the resource-dependent cities: Optical properties, chemical compositions and sources

As a vital type of light-absorbing aerosol, brown carbon (BrC) presents inherent associations with atmospheric photochemistry and climate change. However, the understanding of the chemical and optical properties of BrC is limited, especially in some resource-dependent cities with long heating periods in northwest China. This study showed that the annual average abundances of Water-soluble BrC (WS-BrC) were 9.33±7.42 and 8.69±6.29 µg/m3 in Baotou and Wuhai and the concentrations, absorption coefficient (Abs365), and mass absorption efficiency (MAE365) of WS-BrC presented significant seasonal patterns, with high values in the heating season and low values in the non-heating season; while showing opposite seasonal trends for the Absorption Ångström exponent (AAE300-400). Comparatively, the levels of WS-BrC in developing regions (such as cities in Asia) were higher than those in developed regions (such as cities in Europe and Australia), indicating the significant differences in energy consumption in these regions. By combining fluorescence excitation-emission matrix (EEM) spectra with the parallel factor (PARAFAC) model, humic-like (C1 and C2) and protein-like (C3) substances were identified, and accounted for 61.40%±4.66% and 38.6%±3.78% at Baotou, and 60.33%±6.29% and 39.67%±4.17% at Wuhai, respectively. The results of source apportionment suggested that the potential source regions of WS-BrC varied in heating vs. non-heating seasons and that the properties of WS-BrC significantly depended on primary emissions (e.g., combustion emissions) and secondary formation.

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.

Indirect photodegradation of ofloxacin in simulated seawater: Important roles of DOM and environmental factors

Dissolved organic matter (DOM) plays a non-negligible role in the indirect photodegradation of organic contaminants. This research investigated the roles of DOM and the environmental factors (salinity, pH, NO3−, and HCO3−) in the indirect photodegradation of ofloxacin (OFX) in simulated seawater. Results showed that DOM can significantly accelerate the indirect photodegradation of OFX, and 1O2 and 3DOM* were the main reactive intermediates (RIs) that could promote the indirect photodegradation of OFX. Fluorescence excitation–emission matrix spectroscopy–parallel factor analysis (EEMs-PARAFAC) was used to divide DOM into four fluorescence components. The indirect photodegradation rate of OFX was affected by DOM structure, and terrigenous DOM usually produced more RIs to promote the indirect photodegradation of OFX. Increased salinity significantly promotes the indirect photodegradation of OFX, while increased NO3− concentration had no effect on the OFX indirect photodegradation. pH affected the formation of RIs and the structure of OFX, thereby affecting the indirect photodegradation of OFX. The indirect photodegradation rate of OFX increased in the HCO3− solution, which is due to the formation of carbonate radical (CO3−). This study is essential in understanding the role of DOM in OFX indirect photodegradation and providing a novel insight into the fate, removal, and transformation of OFX.

Implementation of Line Search for Parafac Analysis of Fluorescence Excitation–Emission Matrix

Implementation of Line Search for Parafac Analysis of Fluorescence Excitation–Emission Matrix

Characterizing the effects of stormwater runoff on dissolved organic matter in an urban river (Jiujiang, Jiangxi province, China) using spectral analysis.

The effect of stormwater runoff on dissolved organic matter (DOM) in rivers is one of the central topics in water environment research. Jiujiang is one of the first cities established in the green development demonstration zone of the Yangtze River Economic Belt (Jiangxi Province, China). Three-dimensional excitation-emission matrix fluorescence with parallel factor analysis (3DEEM-PARAFAC) and ultraviolet-visible (UV-Vis) spectroscopy were used to explore the effects of runoff on organic matter in Shili River (Jiujiang, Jiangxi Province, China). The results show that the runoff led to an increase of some critical pollutants and DOM concentrations, especially in the middle reaches of the river. The concentration and relative molecular weight of DOM in water increased as a result of runoff. Three humic-like (C1-C3) and two protein-like (C4 and C5) components of DOM were identified using the PARAFAC model. The sources of the three humic-like components (C1, C2, C3) were consistent, unlike those of the protein-like component C4. Compared with the pre-rainfall period, the content of humus compounds flowing into the river through the early rainwater runoff was lower, which caused the relative content and proportion of humic substances little change and protein-like species increasing. The DOM mainly derived from autochthonous sources, and runoff had limited effect on its characteristics. Jiujiang is a key demonstration city for Yangtze River conservation. Rainwater runoff is one of the pollution sources of urban rivers, which leads to the deterioration of water quality and influences the distribution characteristics of DOM in water bodies. The PARAFAC components could adequately represent different indicators and sources of DOM in urban rivers, providing an important reference for urban river management.

Unveiling Molecular Transformations of Soil Organic Matter after Remediation by Chemical Oxidation Based on ESI-FT-ICR-MS analysis

Remediation of soils contaminated with organic pollutants is often accomplished by chemical oxidation processes using oxidants such as persulfate or H2O2. However, it is unclear how different oxidants transform soil organic matter (SOM) and affect soil ecosystem services. Herein, two chemical oxidation technologies, Fenton reaction (FT) and base-activation of sodium persulfate (BP), were investigated to remediate diesel-polluted soils. The molecular transformation of SOM was analyzed using excitation–emission matrix fluorescence spectroscopy (EEM FS) and electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS). Fulvic acid-like substances and lipids were consumed in both treatments, while the contents of lignin-like and tannin-like substances increased after BP treatment. The oxygen to carbon ratios (O/C), modified aromaticity index (AImod), and double bond equivalent (DBE) of SOM increased significantly in BP-treated soil, while these parameters decreased in FT-treated soil (FTS), suggesting the oxygen-containing, unsaturated and aromatic compounds were produced in BPS but removed in FTS. The increased cation exchange capacity (CEC) value (81.47 cmol/kg) and germination index of wheat seed (97%) for the SOM in BPS indicate the possible favorable effect of persulfate-based treatment on soil quality. Overall, this study advances mechanistic understanding of the effects of H2O2- and persulfate-based soil remediation technologies based on the molecular compositions of SOM and soil quality.

Composition of organic matter‑iron‑phosphorus associations in sediments of algae- and macrophyte-dominated zones in Lake Taihu

The biogeochemical cycles of phosphorus (P) and organic matter (OM) are significantly influenced by iron (Fe) through forming OM-Fe-P associations. The sources and compositions of organic matter in the two typical states (algae-dominated and macrophyte-dominated) of shallow lakes are different, which could modulate the formation of OM-Fe-P associations and influence the internal loadings of P in lakes. In this study, OM and P bound with Fe were extracted from the sediments of algae-dominated zone (A-zone) and macrophyte-dominated zone (M-zone) in Lake Taihu via the citrate-bicarbonate-dithionite (CBD) reduction method, and were analyzed to elucidate the differences in OM-Fe-P associations between the two zones. The results showed that OM-Fe-P associations in the sediments of M-zone had higher a molar C/Fe ratio but a lower molar P/Fe ratio. Four components identified by excitation-emission matrix fluorescence coupled with parallel factor analysis (EEM-PARAFAC) in OM-Fe-P associations in the two zones were all humic-like substances and the relative abundance of the corresponding PARAFAC components had no significant difference between the two zones. However, the total fluorescence intensity of the humic-like components was higher in M-zone than those in A-zone. This could be attributed to the higher aromaticity of OM produced from macrophyte than that from algae, as evidenced by the difference in the easily-desorbed OM between two zones. In M-zone, high aromatic compounds which are preferentially associated with Fe, could be more produced from macrophyte plants than from algae and resulted in the higher C/Fe molar ratio. The higher C/Fe molar ratio (2.1 ± 0.9) of OM-Fe-P associations in M-zone reflected that more OM originated from macrophyte could be involved in the coprecipitation with Fe (III) and OM-Fe-P associations in M-zone were probably more resistant to the microbial and chemical reduction. Our results from the real situation confirmed the mechanism related to the role of OM composition in the reduction of OM-Fe-P associations to explain the lower internal loading of P in M-zone than that in A-zone.

Greenhouse gas emission during swine manure aerobic composting: Insight from the dissolved organic matter associated microbial community succession

Greenhouse gas emissions during aerobic composting is unavoidable, but good practices can minimize emission. Therefore, to explore the key factors influencing the release of greenhouse gas emissions during composting, the inaction of organic matter conversion, greenhouse gas emissions and bacterial community structure during co-composting with different ratio (pig manure and corn straw) over a 6-week period was studied. The excitation-emission matrix fluorescence spectroscopy with the parallel factor was used to identify that dissolved organic matter associated microbial community succession mainly influenced greenhouse gas emissions. Protein-like fractions of dissolved organic matter were more likely to decompose and promote CH4 and CO2 emissions, while the humic-like fractions of dissolved organic matter positively affected N2O emissions. The largest of greenhouse gas emissions was appeared in MR2 with 12.7 kg CO2-eq, and the MR3 and MR4 reduced greenhouse gas emissions by 26.8 % and 11.4 %, respectively.

Pd nanoparticles decorated BiVO4 pine architectures for photocatalytic degradation of sulfamethoxazole

Sulfamethoxazole (SMX) has been extensively detected in wastewater treatment plant effluents and surface water. Because of its potential risks to ecology and health, treatment for eliminating SMX is urgently required. In this study, we report the application of Pd nanoparticles decorated on BiVO4 pine architecture for the photocatalytic degradation of SMX. The results showed that the barer BiVO4 and Pd–BiVO4 eliminated SMX under visible-light irradiation. After 210 min of irradiation, 98.8% of SMX was substantially eliminated by Pd–BiVO4, whereas bare BiVO4 can degraded approximately 36.3% of SMX. Pd–BiVO4 also exhibited a high mineralization rate (84% of total organic carbon (TOC) removal) compared to bare BiVO4 (51% of TOC removal). Through three-dimensional excitation-emission matrix fluorescence spectra, SMX with high fluorescence intensity can be degraded to non-fluorescence intermediate products, further confirming the high mineralization of SMX over Pd–BiVO4 catalyst. Well-dispersed Pd nanoparticles on the {040} facet of BiVO4 pine architecture can support the recombination of photogenerated charge carriers because of the formation of the Schottky junction at the Pd–BiVO4 interface. Besides, the active species trapping tests indicated that •O2− and h+ radicals dominate SMX photodegradation over Pd–BiVO4. The main degradation intermediates of SMX in the reaction solution was also identified through ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry analysis. This investigation can provide insight into designing metallic/semiconductor junctions for antibiotic elimination in water media.

Use of Machine Learning with Fused Spectral Data for Prediction of Product Sensory Characteristics: The Case of Grape to Wine

Generations of sensors have been developed for predicting food sensory profiles to circumvent the use of a human sensory panel, but a technology that can rapidly predict a suite of sensory attributes from one spectral measurement remains unavailable. Using spectra from grape extracts, this novel study aimed to address this challenge by exploring the use of a machine learning algorithm, extreme gradient boosting (XGBoost), to predict twenty-two wine sensory attribute scores from five sensory stimuli: aroma, colour, taste, flavour, and mouthfeel. Two datasets were obtained from absorbance-transmission and fluorescence excitation-emission matrix (A-TEEM) spectroscopy with different fusion methods: variable-level data fusion of absorbance and fluorescence spectral fingerprints, and feature-level data fusion of A-TEEM and CIELAB datasets. The results for externally validated models showed slightly better performance using only A-TEEM data, predicting five out of twenty-two wine sensory attributes with R2 values above 0.7 and fifteen with R2 values above 0.5. Considering the complex biotransformation involved in processing grapes to wine, the ability to predict sensory properties based on underlying chemical composition in this way suggests that the approach could be more broadly applicable to the agri-food sector and other transformed foodstuffs to predict a product's sensory characteristics from raw material spectral attributes.

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.

Treatment of micro-polluted water with low C/N ratio by immobilized bioreactor using PVA/sintered ores@sponge cube: Performance effects and potential removal pathways

The widespread use of industrial products containing lead (Pb2+) and tetracycline (TC) medications led to the combined pollution of nitrate, Pb2+, and TC in water. A novel biomaterial containing polyvinyl alcohol (PVA) and sponge cube with sintered ores (PVA/sintered ores@sponge cube) was prepared to ensure the maximum NO3−-N removal efficiency (96.21 %) of the bioreactor under the hydraulic retention time (HRT) of 7.0 h, pH of 6.0, and the carbon to nitrogen (C/N) of 1.5 that had the ability to remove TC and Pb2+ synergistically. Composite pollutants slightly decreased denitrification performance in the combined pollution system on account of the addition of sintered ores. Results of scanning electron microscopy (SEM) showed that the sintered ores in the biocarrier induced denitrification and the adsorption of bio‑iron oxides were involved in the removal of TC and Pb2+. The simultaneous removal of composite pollutants during denitrification was facilitated by extracellular polymeric substances (EPS) as revealed by Fourier transform infrared spectroscopy (FTIR) and fluorescence excitation-emission matrix (EEM). In addition, high-throughput sequencing results showed that Zoogloea had the highest proportion in the bioreactor.

Spectroscopic Tracking of the Characteristics of Microplastic-Derived Dissolved Organic Matter

Microplastic-derived dissolved organic matter (MP-DOM) has received increasing attention in recent years. In this study, the fluorescence excitation-emission matrix (EEM) combined with parallel factor analysis (PARAFAC) was used to track the leaching behavior of polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), polyethylene terephthalate (PET), and polystyrene (PS) MP-DOM. After seven days of leaching, PVC reached a leaching concentration of 7.59 mg/L, and the other four microplastics reached approximately 4.5~4.7 mg/L. The leaching activity of PVC was considerably more active in an alkaline environment and under UV irradiation. All the fluorescence signals of MP-DOM components were located in the protein/phenol-like fluorescence region. The fact that C1 and C2 were found in every microplastic revealed that these substances took up quite a large proportion of MP-DOM. Protein/phenolic substances in MP-DOM showed different binding ability with different heavy metals, which can be realized from the log K values calculated for Cr3+ (3.99–5.51), Cu2+ (3.06–4.83), Cd2+ (3.76–4.41), and Fe3+ (3.11–5.03). This work introduced more MP-DOM samples, and offered spectroscopic insight into the characteristics and environmental fate of MP-DOM at a molecular level. Furthermore, this study displayed the potential applicability of using the integrated methods to track the MP-DOM formation process and environmental behavior in natural aquatic systems.

Characterization of DOM and disinfection by-products precursors in biological activated carbon filter backwash water from drinking water treatments

Abstract Biological activated carbon filter backwash water (BAC FBW) removes pollutants from BAC filters in drinking water treatment plants. Characterizing the dissolved organic matter (DOM) in BAC FBW is of great significance for the recycling and treatment of backwash water. DOM pollution was monitored over a year using three-dimensional excitation–emission matrix fluorescence spectra. The dissolved organic carbon (DOC) concentration and fluorescence results showed that the DOC concentration reached the lowest value of 1.95 mg/L in the summer. The relative abundances of fluorescence components had a direct relationship with temperature variations. The soluble microbial products were enhanced greatly during cold seasons, while fulvic-acid-like and humic-acid-like compounds remained constant. Disinfection by-products (DBPs) formation potential and cytotoxicity were evaluated. The total haloacetonitriles (HANs), trihalomethanes (THMs), halonitromethanes (HNMs), and haloacetaldehyde (HALs) formation potentials ranged from 35.5 to 47.3 μg/L, 95.1 to 126 μg/L, 4.95 to 8.06 μg/L, and 43.4 to 53.0 μg/L in BAC FBW, respectively. Among all DBPs included in the calculation, the order of contribution to cytotoxicity was HANs > HALs > THMs > HNMs, respectively. Especially, HANs were much higher than the other DBPs, which should be controlled to avoid the biological risk of effluent quality.

Effect of freezing-air thawing pretreatment of cutting fluid wastewater on the organics' distribution, transfer and transformation

The cutting fluid wastewater was treated by freezing-air thawing method. After thawing, stable stratification occurred in the thawing wastewater, and the froth floated on the liquid surface, and the liquid from top to bottom was divided into the first layer, the second layer, the third layer and the fourth layer. The molecular weight (MW) distribution and organics characteristics of the froth layer and each layer wastewater were analyzed by ultrafiltration membrane filtration combined with mass balance, three-dimensional fluorescence excitation-emission matrix spectroscopy, ultraviolet absorption spectroscopy, flourier transform infrared spectroscopy and droplet size analysis. The results showed that the cutting fluid wastewater contained 66.74 % organics with MW > 100 kDa and 17.04 % organics with MW < 1 kDa, and the organics might contain aromatic and heterocyclic compounds. After three times of freezing-air thawing: 27.53 % of organic matter was volatilized into the air; the froth layer was mainly macromolecular organic matter with MW > 100 kDa, accounting for 94.59 %; from the froth layer to the fourth layer wastewater, the content of macromolecules with MW > 100 kDa gradually decreased, while the content of small molecules with MW < 1 kDa gradually increased. The results of molecular weight distribution analysis, spectroscopy analysis and droplet size analysis indicated that during the freezing-air thawing process, there was not only the demulsification maybe but also the destruction of molecular structure. The molecular weight distribution of the mixture of the froth layer and the fourth layer wastewater were close to that of the raw cutting fluid wastewater, so the mixture of the froth layer and the fourth layer wastewater could be reused in metal process. The wastewater in the first, second and third layers had better biodegradability, which could be treated by biological method.

Insights into surface circulation and mixing in James Bay and Hudson Bay from dissolved organic matter optical properties

Hudson Bay and James Bay are fed by numerous rivers, which also deliver large amounts of dissolved organic matter (DOM). The objective of this study is to assess Hudson Bay wide DOM spatial distribution using ultraviolet-visible light absorption and excitation-emission matrix fluorescence spectroscopies. Overall, a five-component PARAFAC model was validated using 1060 discrete samples collected over nine field campaigns between 2009 and 2018 and including the first samples from James Bay ( n = 112). Regional and seasonal variations were observed. Particularly striking was a 9-fold difference in concentration between coastal and marine zones of these bays, which implies limited mixing between those regions. Seasonal variations in absorption coefficient at 355 nm and terrestrial humic-like components were found only in east Hudson Bay, revealing a regional disparity in seasonal DOM behaviour. The summer intensities and relative abundances of DOM revealed that cyclonic circulation transports terrestrial DOM around James Bay following its eastern shores before being transported northward along the western coast of Belcher Islands. The vertical distribution of DOM indicated that fluorescent DOM is delivered to the deeper layer by winter convective mixing in northern Hudson Bay. • Limited mixing between the coastal and marine regions of the bay is observed. • The strong terrestrial signal of east James Bay is found in northern Belcher Island. • DOM is delivered to the deeper layer by winter convection in northern Hudson Bay.