Characterizing treated wastewaters of different industries using clustered fluorescence EEM-PARAFAC and FT-IR spectroscopy: implications for downstream impact and source identification

Riverine seasonal rainfall event tracing of organic pollution sources using fluorescence fingerprint difference spectrum

Elucidating the dynamics of dissolved organic matter (DOM) transport and transformation under seasonal rainfall events is essential for the conservation of riverine ecosystems, for mitigating the effects of climate change, and for crafting informed water management strategies. Therefore, this study aimed to investigate the evolutionary characteristics of organic pollution sources during consecutive rainfall events in early spring and to quantify their relative contributions to the process of surface water pollution. The results showed seasonal rainfall induces water quality exceedances in rivers due to the combined impacts of terrestrial inputs and endogenous releases. Humic acid (HA) (region V) and fulvic acid (FA) (region III) emerged as the predominant organic matter in the water column, with their fluorescence intensity altering as rainwater flushed the riverbed. Sources of pollution include agricultural and urban domestic sources (AS + DS) (72.29 %), industrial and urban domestic and microbial sources (IS + DS + MS) (37.71 %), and agricultural and industrial sources (AS + IS) (63.32 %), indicating that agricultural surface pollution discharges contribute significantly. The gas-chromatography-mass spectrometry (GC-MS) further confirmed that exogenous inputs were predominantly comprised of particulate pollutants. This study underscores the efficacy of fluorescence difference spectrometry in delineating the migration and transformation of river pollution sources during seasonal rainfall and facilitating the implementation of targeted management strategies for river ecosystems.

Research on a harmless treatment method for oily sludge in coal chemical wastewater and the pollutant transformation mechanism of oily sludge during the treatment process

This study developed an ultrasound synergistic subcritical hydrothermal treatment method (U-SHT) to address the challenges posed by the high oil and water content, complex composition, and hazardous nature of oily sludge (OS) generated during the pretreatment of coal chemical wastewater. The study investigated the efficiency of this method for the harmless disposal and resource recovery of OS, and the migration-transformation mechanism of hazardous organic pollutants in OS. The findings revealed that U-SHT achieved a removal efficiency of chemical oxygen demand in OS of 91.16 %, an oil resource recovery efficiency of 96.60 %, and a residual oil rate of 0.28 %, meeting API emission standards. Further research indicated that the solubilizing effect of the surfactant on the oil enhanced the demulsifying effect of ultrasonic cavitation on the emulsified structure of OS, enabling ultrasound to efficiently release and disperse pollutants within OS. This promoted the decomposition and transformation of pollutants under subcritical hydrothermal conditions, with synergistic removal efficiencies for typical pollutants such as long-chain alkanes, polycyclic aromatic hydrocarbons, and phenols reaching 96.61 %, 97.63 %, and 97.76 %, respectively. Economic evaluation indicated that the cost of OS treatment was $29.66/m3, significantly lower than existing methods, demonstrating promising practical application prospects.

Green manuring reduces cadmium accumulation in rice: Roles of iron plaque and dissolved organic matter

In southern China, winter green manure is widely used in rice cropping systems for improving grain yields and soil fertility. Cd pollution has recently been reported in some of these paddy fields. Research on the in-depth understanding of how green manuring affects Cd absorption in rice is limited. This study aimed to investigate the impacts of different green manures, including single plantation and mixed plantation on the absorption of Cd by rice and explore the underlying mechanisms. Pot experiments demonstrated that compared with winter fallow-rice, green manuring treatments considerably decreased rice Cd content, promoted the conversion of bioavailable Cd fraction into a more stable form, induced the formation of iron plaque, and increased the content of humic-like fraction (HF) in soil dissolved organic matter (DOM). Treatment with mixed plantation resulted in a greater decrease in rice Cd content and an increase in HF and iron plaque contents than single plantation. Hydroponic experiments confirmed that both iron plaque and green manure-derived DOM significantly reduced the Cd content in rice seedlings. In conclusion, green manure incorporation is an efficient measure for the safe utilization of Cd-contaminated soil, and mixed plantation of different green manures exerts stronger effects.

Source apportionment based on EEM-PARAFAC combined with microbial tracing model and its implication in complex pollution area, Wujin District, China

Further improving the quality of surface water is becoming more difficult after the control of main point-sources, especially in the complex pollution area with mixed industrial and agricultural productions, whereas the pollution source apportionment might be the key to quantify different pollution sources and developing some effective measures. In this study, a technical framework for source apportionment based on three-dimensional fluorescence and microbial traceability model is developed. Based on screening of the main environmental factors and their spatiotemporal characteristics, potential pollution sources have been tentatively identified. Then, the pollution sources are further tested based on the analysis of fluorescence excitation-emission matrix (EEM) and the similarity of fluorescence components in surface water and potential pollution sources. At the same time, the correlation between microbial species and pollution sources is constructed by analyzing the spatiotemporal characteristics of microbial composition and the response of main species to environmental factors. Therefore, pollution source apportionment is quantified using PCA-APCS-MLR, Fast Expectation-maximization for Microbial Source Tracking (FEAST), and Bayesian community-wide culture-independent microbial source tracking (SourceTracker). PCA-APCS-MLR could not effectively distinguish the contributions of different industrial sources in the complex environment of this study, and the contribution of unknown sources was high (average 39.60%). In contrast, the microbial traceability model can accurately identify the contribution of 7 pollution sources and natural sources, effectively reduce the proportion of unknown sources (average of FEAST is 19.81%, SourceTracker is 16.72%), and show better pollution identification and distribution capabilities. FEAST exhibits a more sensitive potential in source apportionment and shorter calculation time than SourceTracker, thus might be used to guide the precise regional pollution control, especially in the complex pollution environments.

Characteristics of DOM and Their Relationships with Potentially Toxic Elements in the Inner Mongolia Section of the Yellow River, China

The characterization of dissolved organic matter (DOM) is important for better understanding of the migration and transformation mechanisms of DOM in water bodies and its interaction with other contaminants. In this work, fluorescence characteristics and molecular compositions of the DOM samples collected from the mainstream, tributary, and sewage outfall of the Inner Mongolia section of the Yellow River (IMYR) were determined by using fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). In addition, concentrations of potentially toxic elements (PTEs) in the relevant surface water and their potential relationships with DOM were investigated. The results showed that the abundance of tyrosine-like components increased significantly in downstream waters impacted by outfall effluents and was negatively correlated with the humification index (HIX). Compared to the mainstream, outfall and tributaries have a high number of molecular formulas and a higher proportion of CHOS molecular formulas. In particular, the O5S class has a relative intensity of 41.6% and the O5-7S class has more than 70%. Thirty-eight PTEs were measured in the surface water samples, and 12 found above their detective levels at all sampling sites. Protein-like components are positively correlated with Cu, which is likely indicating the source of Cu in the aquatic environment of the IMYR. Our results demonstrated that urban wastewater discharges significantly alter characteristics and compositions of DOM in the mainstream of IMYR with strongly anthropogenic features. These results and conclusions are important for understanding the role and sources of DOM in the Yellow River aquatic environment.

Analysing N-nitrosamine occurrence and sources in karst reservoirs, Southwest China

N-nitrosamines in reservoir water have drawn significant attention because of their carcinogenic properties. Karst reservoirs containing dissolved organic matter (DOM) are important drinking water sources and are susceptible to contamination because of the fast flow of various contaminants. However, it remains unclear whether N-nitrosamines and their precursor, DOM, spread in karst reservoirs. Therefore, this study quantitatively investigated the occurrence and sources of N-nitrosamines based on DOM properties in three typical karst reservoirs and their corresponding tap water. The results showed that N-nitrosamines were widely spread, with detection frequencies > 85%. Similar dominant compounds, including N-nitrosodimethylamine, N-nitrosomethylethylamine, N-nitrosopyrrolidine, and N-nitrosodibutylamine, were observed in reservoirs and tap water, with average concentrations of 4.7-8.9 and 2.8-6.7 ng/L, respectively. The average carcinogenic risks caused by these N-nitrosamines were higher than the risk level of 10-6. Three-dimensional fluorescence excitation-emission matrix modeling revealed that DOM was composed of humus-like component 1 (C1) and protein-like component 2 (C2). Fluorescence indicators showed that DOM in reservoir water was mainly affected by exogenous pollution and algal growth, whereas in tap water, DOM was mainly affected by microbial growth with strong autopoietic properties. In the reservoir water, N-nitrosodiethylamine and N-nitrosopiperidine were significantly correlated with C2 and biological indicators, indicating their endogenously generated sources. Based on the principal component analysis and multiple linear regression methods, five sources of N-nitrosamines were identified: agricultural pollution, microbial sources, humus sources, degradation processes, and other factors, accounting for 46.8%, 36.1%, 7.82%, 8.26%, and 0.96%, respectively. For tap water, two sources, biological reaction processes, and water distribution systems, were identified, accounting for 75.7% and 24.3%, respectively. Overall, this study presents quantitative information on N-nitrosamines' sources based on DOM properties in typical karst reservoirs and tap water, providing a basis for the safety of drinking water for consumers.

Enhanced Cr(VI) stabilization by terrestrial-derived soil protein: Photoelectrochemical properties and reduction mechanisms

Glomalin-related soil protein (GRSP) is a stable iron-organic carbon mixture that can enhance heavy metal sequestration in soils. However, the roles of GRSP in the transformation and fate of Cr(VI) have been rarely reported. Herein, we investigated the electrochemical and photocatalytic properties of GRSP and its mechanisms in Cr(VI) adsorption and reduction. Results showed that GRSP had a stronger ability for Cr(VI) adsorption and reduction than other biomaterials, with the highest adsorption amount of up to 0.126 mmol/g. The removal efficiency of Cr(VI) by GRSP was enhanced (4-7%) by ultraviolet irradiation due to the hydrated electrons produced by GRSP. Fe(II) ions, persistent free radicals, and oxygen-containing functional groups on the GRSP surface as electron donors participated in the reduction of Cr(VI) under dark condition. Moreover, Cr(III) was mainly adsorbed on the -COOH groups of GRSP via electrostatic interactions. Based on 2D correlation spectroscopy, the preferential adsorption occurred on the GRSP surface for Cr(VI) in the sequential order of CO → COO- → O-H → C-O. This work provides new insights into the Cr(VI) adsorption and reduction mechanism by GRSP. Overall, GRSP can serve as a natural iron-organic carbon for the photo-reduction of Cr(VI) pollution in environments.

Significant contribution of different sources of particulate organic matter to the photoaging of microplastics

Particulate organic matter (POM), as an important component of organic matter, can act as a redox mediator and thus intervene in the environmental behavior of microplastics (MPs). However, quantitative information on the role of POM in the photoaging of MPs under ultraviolet (UV) light is still lacking. To raise the knowledge gap, through environmental simulation experiments and qualitative/quantitative experiments of active substances, we found that POM from peat soil has stronger oxidation capacity than POM from sediment, and the involvement of POM at high water content makes the aging of MPs more obvious. This is because the persistent radicals and electron-absorbing groups on the surface of POM indirectly generate reactive oxygen species (ROS) by promoting electron transfer, and the dissolved organic matter (DOM) released from POM under UV light (POM-DOM) is further excited to generate triplet-state photochemistry of DOM (3DOM*) to promote the aging of MPs. Theoretical calculations revealed that the benzene ring, mainly C = C, and C = O in the main chain in the plastic macromolecule structure are more susceptible to ROS attack, and the differences in the vulnerable sites contained in different plastic structures as well as the differences in the energy band gaps lead to differences in their aging processes. This study firstly elucidates the key role and intrinsic mechanism of POM in the photoaging of MPs, providing a theoretical basis for a comprehensive assessment of the effect of POM on MPs in the environment.

Harnessing the composition of dissolved organic matter in lagoon sediment in association with rare earth elements using fluorescence and UV-visible absorption spectroscopy

Dissolved Organic Matter (DOM) plays a pivotal role in influencing metal binding and mobility within lagoon sediments. However, there exists a gap in understanding the compositional alterations of DOM concerning Rare Earth Elements (REEs) across varying pollution gradients. This study aimed to characterize DOM and examine its relationship with REEs in sediment cores from different pollution levels in Yundang Lagoon, China using excitation-emission matrix-parallel factor analysis (EEM-PARAFAC). The results raveled four distinct fluorescent components. Among these, two correspond to humic-like substances, while the remaining two are attributed to protein-like substances. Remarkably, the prevalence of protein-like compounds was observed to exceed 58% of the total fluorescence intensity across all the investigated sites. Furthermore, a substantial discrepancy in total fluorescence intensity was detected between the Songbai Lake and the Inner and Outer Lagoon, indicating a variance in DOM content. In terms of REEs, the average concentration of total REEs was notably elevated within the Songbai Lake sediments (318.36 mg/kg) as compared to the Inner and Outer Lagoon sediments (296.36 and 278.05 mg/kg, respectively). Of significance is the enrichment of Light Rare Earth Elements (LREEs), particularly Ce, La, Pr, and Nd, over Heavy REEs (HREEs) across all surveyed locations. Intriguingly, a coherent trend emerged wherein the fluorescence intensity and LREE concentrations exhibited a synchronized increase from Outer to Inner to Songbai Lake core sediments. This observation substantiates a strong correlation between DOM content and pollution levels (p < 0.05). By shedding light on the intricate interplay between DOM and REEs within urban aquatic sediments, this study imparts novel insights which enrich our comprehension of urban environmental dynamics.

UV/persulfate processes for the removal of total organic carbon from coagulation-treated industrial wastewaters

Sulfate radical-based oxidation processes were investigated to understand the relationship between persulfate (PS) consumption and total organic carbon (TOC) removal from industrial wastewater under various PS concentrations. First, the degradation and mineralization of Bisphenol A (BPA) (initial concentration: 11 mg/L) were investigated in ultraviolet (UV)/PS systems. Complete degradation was achieved within 30 min of UV irradiation, and 41%-72% TOC removal was achieved at PS concentrations of 200 and 400 mg/L. The consumed concentration of S2O82- and generated concentration of SO42- increased gradually to similar levels. The ratio of the PS consumption to TOC removal based on the mass concentration (mg/L) was 14.5 and 23.2 at 180 min for 200 and 400 mg/L of S2O82-, respectively. Three types of coagulation-treated industrial wastewater from metal-processing, food-processing, and adhesive-producing plants were obtained, and TOC removal was analyzed using the same UV/PS systems (initial TOC concentration: 100 mg/L). The TOC removal rates ranged from 16.9% to 94.4% after 180 min of UV irradiation at PS concentrations of 1,000, 2,000, 4,000, and 8,000 mg S2O82-/L. Despite the higher TOC removal at higher PS concentrations, the PS activation efficiency decreased significantly as the PS concentration increased. Only approximately 30%-40% activation efficiency was achieved at a PS concentration of 8,000 mg/L. In this study, the ratio of PS consumption to TOC removal ranged from 20.6 to 43.9.

Effect of the molecular weight of DOM on the indirect photodegradation of fluoroquinolone antibiotics

Dissolved organic matter (DOM) is ubiquitous and widespread in natural water and influences the transformation and removal of antibiotics. Nevertheless, the influence of DOM molecular weight (MW) on the indirect photodegradation of antibiotics has rarely been reported. This study attempted to explore the influence of the molecular weight of DOM on the indirect photodegradation of two fluoroquinolone antibiotics (FQs), ofloxacin (OFL) and norfloxacin (NOR), by using UV-vis absorption and fluorescence spectroscopy. The results showed that indirect photodegradation was considered the main photodegradation pathway of FQs in DOM fractions. Triplet-state excited organic matter (3DOM*) and singlet oxygen (1O2) were the main reactive intermediates (RIs) that affected the indirect photodegradation of FQs. The indirect photodegradation rate of FQs was significantly promoted in DOM fractions, especially in the low molecular weight DOM fractions (L-MW DOM, MW < 10 kDa). The results of excitation-emission matrix spectroscopy combined with parallel factor analysis (EEM-PARAFAC) showed that terrestrial humic-like substances had a higher humification degree and fluorophore content in L- MW DOM fractions, which could produce more 3DOM* and 1O2 to promote the indirect photodegradation of FQs. This study provided new insight into the effects of DOM at the molecular weight level on the indirect photodegradation of antibiotics in natural water.

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.

A Comprehensive Review on the Excitation-Emission Matrix Fluorescence Spectroscopic Characterization of Petroleum-Containing Substances: Principles, Methods, and Applications

Petroleum-containing substance (PCS) is a general term used for petroleum and its derivatives. A comprehensive characterization of PCSs is crucial for resource exploitation, economic development and environmental protection. Fluorescence spectroscopy, especially excitation-emission matrix fluorescence (EEMF) spectroscopy, has been proved to be a powerful tool to characterize PCSs since its remarkable sensitivity, selectivity, simplicity and high efficiency. However, there is a lack of systematic review focusing on this field in the literature. This paper reviews the fundamental principles and measurements of EEMF for characterizing PCSs, and makes a systematic introduction to various information mining methods including basic peak information extraction, spectral parameterization and some commonly used chemometric methods. In addition, recent advances in applying EEMF to characterize PCSs during the whole life-cycle process of petroleum are also revisited. Furthermore, the current limitations of EEMF in the measurement and characterization of PCSs are discussed and corresponding solutions are provided. For promoting the future development of this field, the urgent need to build a relatively complete EEMF fingerprint library to trace PCSs, not only pollutants but also crude oil and petroleum products, is proposed. Finally, the extensions of EEMF to high-dimensional chemometrics and deep learning are prospected, with the expectation of solving more complex systems and problems.

How does anthropogenic activity influence the spatial distribution of dissolved organic matter in rivers of a typical basin located in the Loess Plateau, China

River ecosystems interact strongly with adjacent terrestrial environments and receive dissolved organic matter (DOM) from a variety of sources, all of which are vulnerable to human activities and natural processes. However, it is unclear how and to what extent human and natural factors drive DOM quantity and quality changes in river ecosystems. Here, three fluorescence components were identified via optical techniques, including two humic-like substances and one protein-like component. The protein-like DOM was mainly accumulated in anthropogenically impacted regions, while humic-like components exhibit the opposite trend. Furthermore, the driving mechanisms of both natural and anthropogenic factors on the variations in DOM composition were investigated using partial least squares structural equation modelling (PLS-SEM). Human activities, especially agriculture, positively influence the protein-like DOM directly by enhancing anthropogenic discharge with protein signals and also indirectly by affecting water quality. Water quality directly influences the DOM composition by stimulating in-situ production through a high nutrient load from anthropogenic discharge and inhibiting the microbial humification processes of DOM due to higher salinity levels. The microbial humification processes can also be restricted directly by a shorter water residence time during the DOM transport processes. Furthermore, protein-like DOM was more sensitive to direct anthropogenic discharge than indirect in-situ production (0.34 vs. 0.25), especially from non-point source input (39.1%), implying that agricultural industry optimization may be an efficient way to improve water quality and reduce protein-like DOM accumulation.

Molecular characteristics and biological effects of dissolved organic matter leached from microplastics during sludge hydrothermal treatment

Previous knowledge of dissolved organic matter leached from microplastics (MP-DOM) was mainly based on the aquatic environment. The molecular characteristics and biological effects of MP-DOM in other environments have rarely been examined. In this work, FT-ICR-MS was applied to identify MP-DOM leached from sludge hydrothermal treatment (HTT) at different temperatures, and the plant effects and acute toxicity were investigated. The results showed that the molecular richness and diversity of MP-DOM increased with rising temperature, accompanied by molecular transformation in the meantime. The oxidation was crucial whereas the amide reactions mainly occurred at 180-220 ^oC. MP-DOM promoted root development of Brassica rapa (field mustard) by affecting the expression of genes and the effect was enhanced with rising temperature. Specifically, the lignin-like compounds in MP-DOM down-regulated Phenylpropanoids biosynthesis, while CHNO compounds up-regulated the nitrogen metabolism. Correlation analysis presented that alcohols/esters leached at 120-160 ^oC were responsible for the promotion of root, while glucopyranoside leached at 180-220 ^oC was vital for root development. However, MP-DOM produced at 220 ^oC showed the acute toxicity to luminous bacteria. Considering the further-treatment of sludge, the optimum HTT temperature could be controlled at 180 ^oC. This work provides novel insight into the environmental fate and eco-environmental effects of MP-DOM in sewage sludge.

Fate of Naturally Dissolved Organic Matter and Synthetic Organic Compounds Subjected to Drinking Water Treatment Using Membrane, Activated Carbon, and UV/H2O2 Technologies

Organic pollutants are toxic and are present in drinking water. The conventional processes of most water plants can basically meet the discharge standard. However, based on the improvement of the objective of organic pollutants control and the constant change of water characteristics, the results may not be ideal. This study evaluates the effectiveness of different treatments such as microfiltration, nanofiltration, reverse osmosis, activated carbon, and ultraviolet irradiation/H₂O₂ in terms of the removal of organic pollutants. Among the DOM results, nanofiltration, reverse osmosis, and activated carbon showed optimal performance due to the characteristics of processes and the compound properties. However, the risks of low-molecular-weight organic residue and byproduct formation are still present. Thirty-nine species of synthetic organic compounds (SOC) were qualitatively and semiquantitatively analyzed. Different technologies showed varying removal capabilities for SOC based on their properties and many substances coexisted leading to abnormal removal performances. These residual organics showed the characteristics of lower molecular weight, more hydrophilicity, further unknown impacts, and with risk of DBPs. Based on the above insights, possible methods can be rationally chosen for on-demand decontamination of organics in unconfined aquatic environment and long-time impact on water characteristics and human health also should be considered.

Temperature effects on microbial dissolved organic matter metabolisms: Linking size fractions, fluorescent compositions, and functional groups

This study elucidated the compositional and structural variations of size fractions of microbially-induced dissolved organic matter (DOM) caused by short-term temperature changes (5 to 35 °C), taking riverine DOM as an example. A simple and efficient method combining fractionation-[parallel factor analysis and two-dimensional Fourier-transform infrared correlation spectroscopy (PARAFAC-2D FTIR COS)]-correlation was introduced to link fluorescent DOM components and their structures in terms of surface functional groups. Results indicated that the higher temperature stimulated the decomposition of aromatics (sizes decreased from 10 kDa-0.22 μm to <10 kDa) and the transformation of proteins to humics (with sizes <0.22 μm); while both the higher and lower temperatures inhibited the utilization of larger-sized DOM (>0.22 μm, especially the non-fluorescence part) and synthesis of larger-sized microbial-derived proteins and humics (>0.22 μm), which may result in more smaller-sized (<10 kDa) and refractory aromatics transported from rivers to oceans in the warming future. However, the structure-determined DOM behaviors could be less affected by temperature since the fluorescent proteins and humics revealed similar functional group compositions, such as carboxyl, hydroxyl, carbonyl/aldehyde, carboxylic anhydride, and carboxamide groups. These findings have strong implications for DOM biogeochemistry in future temperature-shock scenarios. The proposed method will support in-depth analyses of structure-regulated processes from a mechanistic perspective.

Pyrolysis Atmospheres and Temperatures Co-Mediated Spectral Variations of Biochar-Derived Dissolved Organic Carbon: Quantitative Prediction and Self-Organizing Maps Analysis

Biochar-derived dissolved organic carbon (BDOC), as a highly activated carbonaceous fraction of biochar, significantly affects the environmental effect of biochar. This study systematically investigated the differences in the properties of BDOC produced at 300-750 °C in three atmosphere types (including N₂ and CO₂ flows and air limitation) as well as their quantitative relationship with biochar properties. The results showed that BDOC in biochar pyrolyzed in air limitation (0.19-2.88 mg/g) was more than that pyrolyzed in N₂ (0.06-1.63 mg/g) and CO₂ flows (0.07-1.74 mg/g) at 450-750 °C. The aliphaticity, humification, molecular weight, and polarity of BDOC strongly depended on the atmosphere types as well as the pyrolysis temperatures. BDOC produced in air limitation contained more humic-like substances (0.65-0.89) and less fulvic-like substances (0.11-0.35) than that produced in N₂ and CO₂ flows. The multiple linear regression of the exponential form of biochar properties (H and O contents, H/C and (O+N)/C) could be used to quantitatively predict the bulk content and organic component contents of BDOC. Additionally, self-organizing maps could effectively visualize the categories of fluorescence intensity and components of BDOC from different pyrolysis atmospheres and temperatures. This study highlights that pyrolysis atmosphere types are a crucial factor controlling the BDOC properties, and some characteristics of BDOC can be quantitatively evaluated based on the properties of biochar.

Intermittent energization improves microbial electrolysis cell-assisted thermophilic anaerobic co-digestion of food waste and spent mushroom substance

Microbial electrolysis cell-assisted thermophilic anaerobic digestion (MEC-TAD) is a promising method to improve anaerobic co-digestion efficiency; however, its application is restricted by high energy consumption. To improve the energy use efficiency of MEC-TAD, this study investigated the effect of different intermittent energization strategies on thermophilic co-digestion performance. Results revealed that an 18 h-ON/6h-OFF energization schedule resulted in the fastest electron transfer rate and the highest methane yield (364.3 mL/g VS). Mechanistic analysis revealed that 18 h-ON/6h-OFF resulted in the enrichment of electroactive microorganisms and increased abundance of enzyme-coding genes associated with energy metabolism (ntp, nuo, atp), electron transfer (pilA, nfrA2, ssuE), and the hydrogenotrophic methanogenic pathway. Finally, energy balance analysis revealed that 18 h-ON/6h-OFF had the highest net energy benefit (2.52 kJ) and energy conversion efficiency (110.76 %). Therefore, intermittent energization of MEC-TAD using an 18 h-ON/6h-OFF schedule can provide improved performance and more energy savings.

Properties of river organic carbon affected by wastewater treatment plants

Tracking the sources of organic carbon (OC) is critical not only for understanding riverine carbon dynamics but also for providing management options to improve water quality. We collected water samples from upland forest streams to the mainstream Geumho River (GHR) of South Korea, which included a variety of wastewater treatment plants (WWTP) effluents. We analyzed the concentrations, optical properties, and dual carbon isotope ratios of these samples to identify the sources of OC. Dissolved organic carbon (DOC) was the dominant form of OC in the GHR compared to particulate organic carbon (POC), as the former accounted for 87 % of OC. The concentrations of DOC and POC ranged from 1.2 to 11.2 mg L^-1 and from 0 and 3.6 mg L^-1, respectively, aside from the livestock WWTP effluent. Dominant fluorescence components were terrestrial humic substances in upper reaches whereas protein-like materials in lower reaches of the GHR whose watershed includes a large city with many WWTPs. Significantly lower Δ¹⁴C-DOC and Δ¹⁴C-POC were observed in industrial WWTP effluents than the other sites due to the contribution of fossil OC. Livestock WWTP effluents had higher δ¹³C-DOC and δ¹³C-POC than most of the sites, possibly due to the animal feed derived from C4 plants such as corn. Fossil OC contributed 29-52 % of [DOC] and 36-56 % of [POC] from industrial WWTP effluents, whereas C4-plants derived OC contributed about half of [DOC] and [POC] from a livestock WWTP effluent. The results suggest that anthropogenic sources of organic carbon could alter river carbon dynamics, and that caution is needed when we interpret isotope ratios of riverine organic carbon, particularly when the river passes through highly populated areas wherein WWTP effluents are large.

Calibration-free PAT: Locating selective crystallization or precipitation sweet spot in screenings with multi-way PARAFAC models

When developping selective crystallization or precipitation processes, biopharmaceutical modalities require empirical screenings and analytics tailored to the specific needs of the target molecule. The multi-way chemometric approach called parallel factor analysis (PARAFAC) coupled with ultraviolet visible light (UV/Vis) spectroscopy is able to predict specific concentrations and spectra from highly structured data sets without the need for calibration samples and reference analytics. These calculated models can provide exploratory information on pure species spectra and concentrations in all analyzed samples by representing one model component with one species. In this work, protein mixtures, monoclonal antibodies, and virus-like particles in chemically defined and complex solutions were investigated in three high-throughput crystallization or precipitation screenings with the aim to construct one PARAFAC model per case. Spectroscopic data sets of samples after the selective crystallization or precipitation, washing, and redissolution were recorded and arranged into a four-dimensional data set per case study. Different reference analytics and pure species spectra served as validation. Appropriate spectral preprocessing parameters were found for all case studies allowing even the application of this approach to the third case study in which quantitative concentration analytics are missing. Regardless of the modality or the number of species present in complex solutions, all models were able to estimate the specific concentration and find the optimal process condition regarding yield and product purity. It was shown that in complex solutions, species demonstrating similar phase behavior can be clustered as one component and described in the model. PARAFAC as a calibration-free approach coupled with UV/Vis spectroscopy provides a fast overview of species present in complex solution and of their concentration during selective crystallization or precipitation, washing, and redissolution.

Biogeochemical dynamics of particulate organic phosphorus and its potential environmental implication in a typical "algae-type" eutrophic lake

Organic phosphorus (P_o) plays a very important role in the process of lake eutrophication, but there is still a lack of knowledge about the internal cycle of P_o in suspended particulate matter (SPM) dominated by algal debris. In this study, the characterization of bioavailable P_o by sequential extraction and enzymatic hydrolysis showed that 45% of extracted TP was P_o in SPM of Lake Dianchi, and 43-98% of total P_o in H₂O, NaHCO₃ and NaOH fractions was enzymatically hydrolyzable P_o (EHP, H₂O-EHP: 31-53%). Importantly, labile monoester P was the main organic form (68%) of EHP, and its potential bioavailability was higher than that of diester P and phytate-like P. According to the estimation of P pools in SPM of the whole lake, the total load of P_i plus EHP in the H₂O extract of SPM was 74.9 t and had great potential risk to enhance eutrophication in the lake water environment. Accordingly, reducing the amount of SPM in the water during the algal blooming period is likely to be a necessary measure that can successfully interfere with or block the continuous stress of unhealthy levels of P on the aquatic ecosystem.

Interactions between lead(II) ions and dissolved organic matter derived from organic fertilizers incubated in the field

This work was to study composition characteristics and the subsequent effect on the lead (Pb) binding properties of dissolved organic matter (DOM) derived from seaweed-based (SWOF) and chicken manure organic fertilizers (CMOF) during a one-year field incubation experiment using the excitation-emission matrix-parallel factor (EEM-PARAFAC) and two-dimensional correlation spectroscopy (2DCOS) analysis. Results showed that high aromatic and hydrophobic fluorescent substances were enriched in CMOF-derived DOM and SWOF-derived DOM and enhanced over time. And phenolic groups in the fulvic-like substances for SWOF-derived DOM and carboxyl groups in the humic-like substances for CMOF-derived DOM had the fastest responses over time, respectively. Moreover, both non-fluorescent polysaccharides and fluorescent humic-like substances or fulvic-like substances with aromatic (C=C) groups first participated in the binding process of Pb to SWOF-derived DOM on day 0 and 180 during the lead binding process. In contrast, humic-like substances associated with aromatic (C=C) and phenolic groups gave a faster response to Pb binding on day 360. Regarding CMOF-derived DOM, the fulvic-like substances associated with aromatic (C=C) and carboxylic groups displayed a faster response to Pb ions on day 0. Nonetheless, polysaccharides and humic-like associated with phenolic groups had a faster response on days 180 and 360. It is noteworthy that the polysaccharides, which participated in Pb binding to CMOF-derived DOM, posed a higher risk of Pb in the environment after 360 days. Therefore, these findings gave new insights into the long-term applications of commercial organic fertilizers for the amendment of soil.

Using EEM-PARAFAC to identify and trace the pollution sources of surface water with receptor models in Taihu Lake Basin, China

The identification and apportionment of the multiple pollution sources are essential and crucial for improving the effectiveness of surface water resources management. In this study, the surface water samples were collected from Taihu Lake Basin, and the optimal water quality parameters for the receptor models were selected firstly with multivariate statistical analyses. In order to identify the potential pollution sources in surface water, dissolved organic matter (DOM) was analyzed with the excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC). Through the Pearson correlation analysis of water quality parameters and DOM components, the pollution sources were further verified, i.e., agricultural activities, domestic sewage, phytoplankton growth/terrestrial input and industrial sources. In addition, principal component analysis (PCA) combined with the absolute principal component score-multiple linear regression (APCS-MLR) and positive matrix factorization (PMF) models were employed to quantify pollution sources. Compared with PCA-APCS-MLR model, PMF model resulted in higher performance on evaluation statistics and lower proportion of unexplained variability, thus showed more realistic and robust representation. The results of PMF showed that agricultural activities (42.08%) and domestic sewage (21.16%) were identified as the dominant pollution sources of surface water in the study area. This study highlights the effectiveness of EEM-PARAFAC in identifying the pollution sources, and the applicability of PMF in apportioning the contributions of each potential pollution source in surface water.

DOM tracking and prediction of rural domestic sewage with UV-vis and EEM in the Yangtze River Delta, China

Compared with the urban sewage treatment plants, the operation of rural decentralized sewage facilities is trapped by the absence of professionals, thus having to be run dependently on the self-adaptive operation of the facilities, which makes timely monitoring particularly important. In this study, organic pollutants in rural domestic sewage and urban domestic sewage are analyzed using ultraviolet-visible (UV-vis) absorption spectroscopy, fluorescence excitation-emission matrix (EEM) and Fourier transform infrared reflectance (FTIR). Compared with the UV-vis absorption spectrum, EEM can not only make up the deficiency in the detection of some easily degradable organics in sewage, but also reveal the transformation of different components, thus indicating timely the treatment progress of rural sewage. Linear fitting of COD and spectrum shows that UV₂₅₄ combined with fluorescence excitation-emission at Ex/Em = 250/330 nm might be more suitable for the prediction of COD in rural water than the UV₂₅₄ alone. This is of great significance for guiding the self-adaptive operation of rural domestic sewage facilities, improving their stability and efficiency, so as to improve the rural living environment.

Cognizing and characterizing the organic phosphorus in lake sediments: Advances and challenges

Organic phosphorus (OP) is one of the main forms of phosphorus in lake ecosystems. Mounting evidence has shown that sediment OP has become a major but underestimated issue in addressing lake eutrophication and algal bloom. However, a holistic view of sediment OP remains missing. This review aims to provide an overview of progress on the studies of OP in lake sediments, focusing on the contribution of OP to internal P loading, its potential role in algal bloom, and the migration and transformation. In addition, this work systematically summarized current methods for characterizing OP content, chemical fraction, composition, bioavailability, and assessment of OP release in sediment, with the pros and cons of each method being discussed. In the end, this work pointed out following efforts needed to deepen the understanding of sediment OP, namely: (1) In-depth literature review from a global perspective regarding the contribution of sediment OP to internal P loading with further summary about its pattern of distribution, accumulation and historical changes; (2) better mathematical models for describing drivers and the linkages between the biological pump of algal bloom and the replenishment of sediment OP; (3) fully accounting the composition and molecular size of OP for better understanding its transformation process and mechanism; ; (4) developing direct, high-sensitivity and combined techniques to improve the precision for identifying OP in sediments; (5) establishing the response of OP molecular properties and chemical reactivity to OP biodegradability and designing a comprehensive and accurate composite index to deepen the understanding for the bioavailability of OP; and (6) integrating fundamental processes of OP in current models to better describe the release and exchange of P in sediment-water interface (SWI). This work is expected to provide critical information about OP properties and deliver perspectives of novel characterization methods.

Interactions between dissolved organic matter and perfluoroalkyl acids in natural rivers and lakes: A case study of the northwest of Taihu Lake Basin, China

Understanding the interactions between dissolved organic matter (DOM) and perfluoroalkyl acids (PFAAs) is essential for predicting the distribution, transport, and fate of PFAAs in aquatic environments. Based on field investigations in the northwest of Taihu Lake Basin combined with laboratory experiments, we obtained DOM and PFAA concentrations as well as compositions and investigated key factors of DOM affecting PFAA variability and capture of PFAAs by DOM. Results indicated that the total concentrations of PFAAs were 73.4-689 ng/L in surface water and that PFAAs were dominated by C3-7 perfluoroalkyl carboxylic acids and perfluorooctane sulfonic acid. The main components of DOM included tyrosine-, fulvic-, and tryptophan-like substances. The Mantel test revealed a significant positive correlation between DOM and PFAAs (P = 0.0001). Fulvic-like substances were identified as the most crucial factors affecting PFAA variability. The laboratory experiments revealed that DOM can spontaneously aggregate into a microgel. Furthermore, 19.1-50.9% of PFAAs, DOM characteristic peaks, and several metals (Ca, Mg, Cu, and Fe) can be removed during aggregation, indicating the capacity of DOM binding organic/inorganic substances. The fulvic-like substances were more effectively removed than the protein-like substances. The distribution coefficients of all PFAAs except perfluorohexanoic acid significantly correlated with their perfluorinated carbon numbers (r = 0.975, p<0.001). Our results provided insights into the interactions between DOM and PFAAs, improving the understanding of the distribution, transport, and fate of PFAAs in aquatic environments.

A shift from chemical oxygen demand to total organic carbon for stringent industrial wastewater regulations: Utilization of organic matter characteristics

From 2022, industrial wastewater discharge regulations in South Korea will replace chemical oxygen demand (COD_Mn) with total organic carbon (TOC). A shift from COD_Mn to TOC is a pioneering change in protecting water bodies from organic contaminants. However, several industries are struggling to meet these TOC requirements even though their effluents met the COD_Mn limits. Effluent COD_Mn/TOC ratios (1.28 ± 0.64) found in our study were lower than the COD_Mn/TOC coefficients (1.33-1.80) suggested by the Ministry of Environment in South Korea. Aliphatic and particulate organic matter contents in effluents likely influenced the COD_Mn/TOC ratio. Regardless of the industrial category, dissolved organic carbon often consists of low molecular weight neutrals, hydrophobic organic carbon, and protein-like substances in raw and treated industrial wastewaters. The present study also revealed that TOC and COD_Mn represented different organic matter fractions in the paper mill and oil refinery wastewater, whereas the industrial park wastewater showed similar dissolved organic matter characteristics. Specifically, COD_Mn was effective in the determination of humic content in paper mill wastewater but was underestimated in oil refinery wastewater. Additionally, only paper mill effluents exceeded the TOC requirements (4 of 6 samples) and required an additional post-treatment process owing to higher organic loads.

Exploring the fate of dissolved organic matter at the molecular level in the reactive electrochemical ceramic membrane system using fluorescence spectroscopy and FT-ICR MS

This research evaluated the performance of reactive electrochemical ceramic membrane (REM) in treating secondary effluent and investigated the fate of dissolved organic matter (DOM) at the molecular level. The role of adsorption, electrosorption, and oxidation in DOM removal was comprehensively elucidated based on fluorescence spectroscopy and high-resolution mass spectrometry (FT-ICR MS). Among the fluorescence components (C1-C3) in secondary effluent, microbial humic-like C2 showed fewer adsorption on the REM surface without applying an electrical potential. The electrosorption helped an enhanced uptake of all DOM components and transformed them onto the electrode surface. The fluorescence components and all three fractions (hydrophilic, transphilic, and hydrophobic) were rapidly degraded, and finished water with stable DOM was obtained. The leading degradation phenomena were the change of the unsaturated compounds to the aliphatic and transformation of large-sized molecules to medium and small-sized ones. Above 70% of the compounds in the secondary effluent acted as precursors, which were mineralized/degraded and transformed products were found on the REM surface and in the finished water. The compounds containing sulfur (CHOS) were easily and preferably degraded/mineralized, followed by the compounds containing nitrogen (CHON) and CHO. The oxidation of DOM led to the extensive formation of organo-chlorinated compounds, which contributed above 80% in products. Overall, the combination of fluorescence spectroscopy and FT-ICR MS provided unique behavior of DOM in the secondary effluent toward electro-oxidation in the REM system. These findings could help explore the potential of REM for different water matrices to project the possible composition of DOM in the finished water.

Elevated temperature altered the binding sequence of Cd with DOM in arable soils

Dissolved organic matter (DOM) is one of the most active soil components, which plays pivotal roles in the migration and fate of heavy metals in soils. The interactions of heavy metals with DOM are controlled by the structure and properties of DOM. The changes of temperature have a significant effect on the content and composition of DOM and thus may affect the binding nature of heavy metals with DOM. In the current study, we conducted a 180-d incubation experiment with an arable soil at temperatures of 15, 30 and 45 °C. Fluorescence spectroscopy was used to examine the composition of DOM and two-dimensional correlation spectroscopy was applied to determine the binding intensity and sequence between cadmium (Cd) with DOM. Two humic-like substances (C1, C3) and a protein-like substance (C2) were identified from soil DOM. Elevated temperature changed the characteristic and structure of DOM. The humification degree and aromaticity of DOM increased from 15 °C to 30 °C but decreased at high temperature (45 °C). The alterations in temperature exert no impact on the type of organic functional groups in DOM binding with Cd. However, elevated temperature changed the binding sequence of Cd with DOM fractions. Polysaccharide, phenolic, and aromatic groups exhibited the fastest response to Cd at 15, 30, and 45 °C, respectively. These observations would provide a better understanding on the environmental behavior of Cd in arable soils under the context of global warming.

Comprehensive characterization of industrial wastewaters using EEM fluorescence, FT-IR and 1H NMR techniques

The organic matter present in six industrial wastewaters (pulp and paper mill, brewery, textile, dairy, slaughterhouse effluents and a municipal landfill leachate) has been studied in this work using three analytical techniques: excitation-emission matrix fluorescence (EEMF), proton nuclear magnetic resonance spectroscopy (¹H NMR) and Fourier transform infrared spectroscopy (FTIR). The pulp and paper mill effluent shows characteristic signals of the presence of lignins, carbohydrates and carboxylic acids, as well as sulfate, carbonate and sulfonates (coming from surfactants used in the cleaning of tanks). The main constituents of the brewery effluent are peptides and proteins coming mainly from spent yeast and diatomite filters (the presence of the latter was confirmed by SiO bands in the FTIR spectrum). The municipal landfill leachate is characterized by the majority presence of humic substances (typical of an old landfill) and a residual presence of small peptides, amino acids and carboxylic acids. Additionally, several inorganic compounds were identified by FTIR, such as nitrate, sulfate, phosphate and cyanide ions. The textile effluent from a cotton-based industry contains carbohydrates, carboxylic acids and sulfonates, which can act as auxochromes in the textile industry. The dairy effluent comprises amino acids and small peptides coming from the biodegradation of milk and whey in addition to carbohydrates (lactose) and carboxylic acids (mainly lactic acid). The presence of tyrosine-like peaks B in the EEMF spectrum of the slaughterhouse effluent indicates the existence of small peptides and amino acids coming from the biodegradation of blood proteins. Additionally, residual glucose, fatty acids, phosphate and sulfate were also identified in this effluent.

Improving the outcomes from electroactive constructed wetlands by mixing wastewaters from different beverage-processing industries

Denitrification in electroactive constructed wetland (EW) systems is constrained by the carbon source and the carbon/nitrogen (C/N) ratio (the COD/TN ratio). In this study, wastewater with a high C/N from a brewery was added to wastewater with a low C/N (dairy wastewater) in an EW system, and the pollutant removal, bioelectricity generation, transformations of dissolved organic matter, and microbial community structures were evaluated. The results showed that the average removal rates of ammonium nitrogen, total nitrogen, and chemical oxygen demand from the wastewater mixture were 6.40%, 46.44%, and 23.85% higher than those from the wastewater with a low C/N, respectively. Dissimilatory nitrate reduction to ammonium was effectively inhibited, and the NH₄⁺-N removal was 25.52% higher, when the wastewater mixture was used instead of the high C/N wastewater. Similarly, the output voltage was significantly increased, and the internal resistance of the device was reduced, for the wastewater mixture. The structure of the microbial community improved, the relative abundance of electrochemically active bacteria was higher, and the protein-like and humic-like components were lower, in the mixture treatment than in the individual treatment. The results show that the nitrogen removal and biopower generation improved in an EW system when high C/N wastewater was used as the carbon source.

Optimization of Ultrasound-Assisted Extraction of Bioactive Compounds from Acacia Seyal Gum Using Response Surface Methodology and Their Chemical Content Identification by Raman, FTIR, and GC-TOFMS

Acacia Seyal gum (ASG), also known as gum Arabic, is an antioxidant-rich soluble fiber. ASG has been reported to have many biological activities, including anticancer, antidiabetic, antiulcer, and immunomodulatory activity. Extraction of bioactive compounds from ASG is commonly performed using conventional extraction methods. However, these techniques have certain limitation in terms of extraction time, energy, and solvent requirements. Ultrasound-assisted extraction (UAE) could be used as an alternative technique to extract bioactive compounds in less time, at low temperature, and with less energy and solvent requirements. In this study, the UAE extraction of ASG was optimized using response surface methodology (RSM). A face-centered central composite design (FCCCD) was used to monitor the effect of different independent factors of ultrasound operation (sonication time, temperature, and solvent ratio) on ASG extraction yield. In addition, screening and characterization of phytochemicals in 60% ethanol ASG extract was carried out using Raman microscopy, Fourier transform infrared spectroscopy (FTIR), and gas chromatography time-of-flight mass spectroscopy (GC-TOFMS) analysis. The results indicated that, under optimal conditions (extraction time 45 min, extraction temperature 40 °C, and solid–liquid ratio of 1:25 g/mL), the yield of ASG was 75.87% ± 0.10. This yield was reasonably close to the predicted yield of 75.39% suggested by the design of experiment. The ANOVA revealed that the model was highly significant due to the low probability value (p < 0.0001). Raman spectrum fingerprint detected polysaccharides, such as galactose and glucose, and protein like lysine and proline, while FTIR spectrum revealed the presence of functional groups peaks value of alkanes, aldehydes, aliphatic amines, and phenol. GC-TOFMS spectroscopic detected the presence of strong d-galactopyranose, carotenoid, and lycopene antioxidant compounds. In conclusion, this study demonstrated that the UAE technique is an efficient method to achieve a high yield of ASG extracts. The selected model is adequate to optimize the extraction of several chemical compounds reported in this study.

Catalytic degradation of acetaminophen by Fe and N Co-doped multi-walled carbon nanotubes

An Fe and N co-doped carbon nanotube (CNT) (Fe/N-CNT) was successfully prepared using a simple hydrothermal method. CNT, Fe doped CNTs (Fe-CNT), N doped CNTs (N-CNT), and Fe/N-CNT were characterized using scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and zeta potential analysis. The catalytic activities of the materials were investigated via pharmaceutical (acetaminophen, ACT) degradation using persulfate (PS). The ACT removal rate was in the order: Fe-CNT > N-CNT > Fe-CNT > CNT, for 30 min with 10 mg/L ACT, 0.05 g/L materials, and 0.08 mM PS. The doped N existed as pyridinic-N, pyrrolic-N/N-Fe, graphitic-N, and oxidized-N, while the doped Fe existed as Fe-N, FeO/Fe₃O₄, and Fe₂O₃/FeOOH at the edge. The rates of ACT removal and PS decomposition were well correlated with pyrrolic-N/N-Fe. The ACT removal in the Fe/N-CNT + PS system was as high as >98.4% and was not significantly affected by the initial pH of 2.0-8.2 and ten consecutive uses. However, natural organic matter (NOM) inhibited ACT removal by the accumulation on Fe/N-CNT. The results of ACT removal in the presence of radical scavengers, PS decomposition, and cyclic voltammetry showed that the ACT removal was dominantly attributed to a non-radical pathway with the accelerated electron transfer from ACT to PS through the Fe/N-CNT. The results in this study strongly suggest that the Fe/N-CNT + PS system is an excellent process for the degradation of refractory organic pollutants in various water matrices with improved performance and stability attributed by non-radical pathway.

Characterization and biogeochemical implications of dissolved organic matter in aquatic environments

Dissolved organic matter (DOM) is viewed as one of the most chemically active organic substances on earth. It plays vital roles in the fate, bioavailability and toxicity of aquatic exogenous chemical species (e.g., heavy metals, organic pollutants, and nanomaterials). The characteristics of DOM such low concentrations, salt interference and complexity in aquatic environments and limitations of pretreatment for sample preparation and application of characterization techniques severely limit understanding of its nature and environmental roles. This review provides a characterization continuum of aquatic DOM, and demonstrate its biogeochemical implications, enabling in-depth insight into its nature and environmental roles. A synthesis of the effective DOM pretreatment strategies, comprising extraction and fractionation methods, and characterization techniques is presented. Additionally, the biogeochemical dynamics of aquatic DOM and its environmental implications are discussed. The findings indicate the collection of representative DOM samples from water as the first and critical step for characterizing its properties, dynamics, and environmental implications. However, various pretreatment procedures may alter DOM composition and structure, producing highly variable recoveries and even influencing its subsequent characterization. Therefore, complimentary use of various characterization techniques is highly recommended to obtain as much information on DOM as possible, as each characterization technique exhibits various advantages and limitations. Moreover, DOM could markedly change the physical and chemical properties of exogenous chemical species, influencing their transformation and mobility, and finally altering their potential bioavailability and toxicity. Several research gaps to be addressed include the impact of pretreatment on the composition and structure of aquatic DOM, molecular-level structural elucidation for DOM, and assessment of the effects of DOM dynamics on the fate, bioavailability and toxicity of exogenous chemical species.

Road-deposited sediments mediating the transfer of anthropogenic organic matter to stormwater runoff

It has been regarded that road-deposited sediment (RDS) is one of the important sinks of anthropogenic pollutants as well as the major source of pollutants in stormwater runoff. However, the role of RDS, as a mediator of pollutants to the stormwater runoff, has not yet been investigated so far. Therefore, in this study, the leaching of dissolved pollutants, especially dissolved organic matter (DOM) from RDS, in synthetic precipitation was investigated. A significant amount of metals, nutrients, dissolved compounds, and DOM was leached. The leaching of DOM during 10 sequential leachings was 1811.3 and 2301.7 mg C/kg for larger (63 μm-2 mm) and smaller (< 63 μm) RDS, respectively. The results of UV/Vis spectroscopy, fluorescence spectroscopy, and size exclusion chromatography showed that the leached DOM was of anthropogenic/abiotic origins with lower molecular weight and humification degree. It is ubiquitous in stormwater runoff and industrial discharges and differs from natural organic matter. The results strongly suggest that RDS is an important mediator transferring anthropogenic pollutants to stormwater runoff. In addition, the removal of RDS, such as sweeping, would significantly reduce the pollutants input to the runoff.

Monitoring the influence of wastewater effluent on a small drinking water system using EEM fluorescence spectroscopy coupled with a PARAFAC and PCA statistical approach

The potential use of a statistical approach for the investigation of complex dissolved organic matter (DOM) sources in surface water within a recycled water system monitored by excitation-emission matrix (EEM) fluorescence spectroscopy is shown. The work in this manuscript utilize information extracted from EEM spectroscopy to characterize DOM in collected surface water samples along with a wastewater treatment plant to drinking water treatment plant, discussing that humic-like and protein-like DOM sources predominate in the investigated water samples. Five different fluorescent components were resolved, describing several different types of DOM with different excitation and emission spectra that were distinct among the watershed sampling sites and indicating the influences of anthropogenic impacts. In addition, these novel fluorescence parameters have potential to improve resolution to direct more targeted water quality monitoring approaches.

Determining the leading sources of N-nitrosamines and dissolved organic matter in four reservoirs in Southern China

The presence of carcinogenic N-nitrosamines and dissolved organic matter (DOM) in freshwater is a significant concern from the perspective of public health and drinking water treatment plant operation. This study investigated the N-nitrosamines concentration and their precursors' distributions, and DOM composition in four reservoirs located in a southern city of China. A total of 22 renowned precursors were identified. Precursors from industrial and pharmaceutical origins were found to be dominant in all reservoirs; however, traces of pesticide-based precursors, i.e. pirimicarb and cycluron were also found. The distribution of nine N-nitrosamines was substantially different among the reservoirs. N-Nitrosodibutylamine (NDBA), N-Nitrosopiperidine (NPIP), N-Nitrosodimethylamine (NDMA), and N-Nitrosopyrrolidine (NPYR) were abundantly present in all reservoirs. Most of N-nitrosamines except NDMA and N-nitrosodiethylamine (NDEA) were far below the generally accepted cancer risk of 10^-6, and NDMA/NDEA were found close to the risk level (10^-6). Anthropogenic DOM was dominant in three reservoirs as depicted by a higher biological index (BIX) than the humification index (HIX). By the principle component analysis, BIX appeared as an indicator of N-nitrosamines (except NDEA and NPIP). A strong and direct relationship was observed between the NDMA-formation potential (FP) and concentration of total N-nitrosamines (∑NA), and BIX. These results confirmed that the anthropogenic activities were the leading source of DOM and N-nitrosamines in this city based on land-use.

Molecular insights into the effects of pyrolysis temperature on composition and copper binding properties of biochar-derived dissolved organic matter

Biochar-derived dissolved organic matter (BDOM), which has a substantial impact on the environmental behavior of heavy metals, is critical for understanding the environmental efficacy of biochar. Here, we used a suite of advanced spectroscopic and mass spectroscopic methods to investigate the relationship among the pyrolysis temperature of biochar, composition of BDOM, and interactions of BDOM with Cu. The binding affinity of BDOM and Cu showed incredibly increase, with the increasing pyrolysis temperature (300-500 °C) which promoted the release of condensed aromatic compounds and oxygen-containing functional groups from biochar into dissolved phase. A notable difference in the sequences binding with Cu was occurred during the changing pyrolysis temperature. The amide only involved in the binding process between Cu and BDOM at low-temperature (300 and 400 °C), whereas phenolic only associated with the such binding process at high-temperature (500 °C). Apart from this, the carboxyl and polysaccharides took part in the binding process of Cu with BDOM, no matter how higher the temperature is. A further analysis by X-ray absorption spectroscopy revealed that bidentate carboxylic-Cu complexes appear to be the predominant binding pattern for Cu to BDOM. Our results might contribute to provide novel information for the environment applications of biochar.

A multi-responsive pyranone based Schiff base for the selective, sensitive and competent recognition of copper metal ions

Exploring a new multi-responsive pyranone chemosensor capable of sensing copper ions specifically and selectively through colorimetric, UV-Vis absorption and fluorescence methods is of great importance. In this piece of work, a novel pyranone based Schiff base ligand 4-Hydroxy-6-methyl-3-[1-(2-morpholin-4-yl-ethylimino)-ethyl]-pyran-2-one (DM) was synthesized by the condensation of dehydroacetic acid and 4-(2-aminoethyl) morpholine. The structural determination of ligand DM was executed using distinct spectral techniques i.e.,¹H NMR, ¹³C NMR, FT-IR and HR-MS techniques. The reported Schiff base DM showed an immediate colorimetric change from pale yellow to colorless accompanied by a strong change in the UV-Vis absorption band onto the addition of Cu (II) ions. This metal ligand chelation leads a decrease in ICT process. Also the decrease in fluorescence emission intensity of Schiff base DM with Cu (II) ions addition showed its turn-off behavior towards copper ions. Further absorption/ emission titration studies, Job's plot, HR-MS and ¹H NMR titration data designated 2:1 stoichiometric ratio between DM and Cu (II) ions respectively. Density functional theory studies were also performed to authenticate the binding mechanism theoretically. The sensitivity of Schiff base DM towards Cu (II) ions was applicable at every pH conditions and at the same time DM exhibited selectivity towards Cu (II) ions with a negligible interference of other metal ions. DM showed a detection limit of 7.7 nM towards copper ions via fluorescence emission studies. The best part about DM is that it has good stability but showed an instant chemical reversibility when titrated with EDTA solution.

Copper-binding properties of microplastic-derived dissolved organic matter revealed by fluorescence spectroscopy and two-dimensional correlation spectroscopy

Despite numerous studies on microplastics (MPs), little attention has been paid to the dissolved organic substances leached from MPs and their environmental fate. In this study, we explored the copper-binding characteristics of MP-derived dissolved organic matter (MP-DOM) leached from several MP types, including commercial polypropylene, polyvinylchloride, and expanded polystyrene, under dark and UV irradiation conditions. The copper-binding affinity of MP-DOM was examined using fluorescence quenching method based on different fluorophores identified via the excitation emission matrix-parallel factor analysis (EEM-PARAFAC). The heterogeneous distribution of binding sites across the functional groups of MP-DOM was further elucidated by utilizing two-dimensional correlation spectroscopy (2D-COS) based on Fourier transform infrared spectroscopy (FTIR). Phenol/protein-like fluorescence prevailed in all MP-DOM samples, whereas humic-like fluorescence was more pronounced in the irradiated MP-DOM. For all tested plastic types, two plastic-derived fluorescent components (C2 and C3) exhibited substantial fluorescence quenching with increasing copper concentrations. The calculated stability constants showed larger differences between the two leaching conditions than between the three MP types with higher log K_M values for the UV-irradiated (4.08-5.36) than dark-treated MP-DOM (1.05-3.60). The binding constants were comparable to those of natural organic matter with aquatic/terrestrial origins. The 2D-COS results further revealed that the oxygen-containing structures in MP-DOM generated by UV irradiation might be responsible for the higher binding affinity of the irradiated MP-DOM. This is the first study demonstrating the environmental reactivity of MP-DOM towards metal binding, highlighting the importance of leaching conditions for the metal-binding behavior of MP-DOM.

Influences of coagulation pretreatment on the characteristics of crude oil electric desalting wastewaters

Highly polluted crude oil electric desalting wastewaters (EDWs) severely affect the efficiency of refinery wastewater treatment plants (WWTPs). Coagulation is an efficient pretreatment to reduce the impacts of EDWs. In the present study, the influences of coagulation pretreatment on the characteristics of EDWs of three typical Chinese crude oils, Liaohe heavy oil (LHO), Karamay heavy oil (KHO) and Daqing light oil (DLO), were investigated. The stability of three raw EDWs was broken and the contents of organic pollutants were significantly reduced by aluminum sulfate coagulation. More soluble COD and polar oils were removed from LHO-EDW (1241 and 98 mg L^-1) and KHO-EDW (779 and 57 mg L^-1) compared to DLO-EDW (417 and 11 mg L^-1). Coagulation significantly changed the compositions of the organic pollutants of two heavy oil EDWs; however, slightly influenced DLO-EDW, particularly the polar organic pollutants. Most types of aromatic compounds, aliphatic acids and O_x polar compounds were removed from two heavy oil EDWs, but mainly alkanes were removed from DLO-EDW. As such, the differences in the types of dominant polar compounds became insignificant among treated heavy oil and light oil EDWs. Coagulation notably decreased the acute biotoxicity and improved the biodegradability of all treated EDWs. The residual organic nitrogen compounds in treated KHO-EDW contributed to a higher residual biotoxicity compared to treated LHO-EDW. The results demonstrate that coagulation can effectively improve the qualities of heavy oil EDWs by lowering the contents of organic pollutants and removing recalcitrant compounds, thus guaranteeing the efficiency of refinery WWTPs.

Direct versus indirect effects of human activities on dissolved organic matter in highly impacted lakes

Human activities can alter dissolved organic matter (DOM) in lakes through both direct (i.e., exporting DOM of anthropogenic sources) and indirect effects (i.e., enhancing the autochthonous production of DOM via nutrient loading). Distinguishing between the direct and indirect effects is important to better understand human impacts on aquatic systems, but it remains highly challenging due to the interdependence of associated environmental variables. Here, we demonstrated that disentangling the direct and indirect effects can be achieved through combining large-scale environmental monitoring with the Partial Least Squares Path Modeling (PLS-PM). We presented DOM data from 61 lakes within the floodplain of the Yangtze River (Lakes-YR), China, a region that has been subjected to intense anthropogenic disturbances. We analyzed the amount and composition of DOM through dissolved organic carbon (DOC), chromophoric DOM (CDOM), and fluorescent DOM (FDOM). Four fluorescence components were identified, including one tyrosine-like component, one tryptophan-like component, and two humic-like components. Most of the lakes were dominated by freshly produced DOM with small molecular weights and low humification. Results from the PLS-PM models showed that the autochthonous production was more important than anthropogenic inputs in mediating DOC and CDOM. In contrast, FDOM parameters in lakes were more sensitive to the direct, anthropogenic sources, including treated domestic, industrial wastewater, and the effluents of aquaculture. These sources can be identified by elevated FDOM content per DOC (FDOM: DOC ratio) relative to autochthonous DOM, suggesting the potential of using FDOM as a tracer to identify and monitor the contribution of anthropogenic organic matter to inland waters.

Monitoring dissolved organic matter in wastewater and drinking water treatments using spectroscopic analysis and ultra-high resolution mass spectrometry

Dissolved organic matter (DOM) plays a critical role in determining the quality of wastewater and the safety of drinking water. This is the first review to compare two types of popular DOM monitoring techniques, including absorption spectroscopy and fluorescence excitation-emission matrices (EEMs) coupled with parallel factor analysis (PARAFAC) vs. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), for the applications in wastewater and drinking water treatments. The optical techniques provide a series of indices for tracking the quantity and quality of chromophoric and fluorescent DOM, while FT-ICR-MS is capable of identifying thousands of DOM compounds in wastewater and drinking water at the molecule level. Both types of monitoring techniques are increasingly used in studying DOM in wastewater and drinking water treatments. They provide valuable insights into the variability of DOM composition in wastewater and drinking water. The complexity and diversity of DOM highlight the challenges for effective water treatments. Different effects of various treatment processes on DOM are also assessed, which indicates that the information on DOM composition and its removal is key to optimize the treatment processes. Considering notable progress in advanced treatment processes and novel materials for removing DOM, it is important to continuously utilize these powerful monitoring tools for assessing the responses of different DOM constituents to a series of treatment processes, which can achieve an effective removal of DOM and the quality of treated water.

Adsorption of microplastic-derived organic matter onto minerals

Microplastic (MP) pollution is an increasing global problem due to the ubiquity of these particles in the environment and the uncertainty surrounding their fate. Most MPs undergo extensive weathering in the environment, which may result in the release of dissolved organic matter (DOM) into the aqueous phase. In this study, for the first time, we examined the adsorptive behavior of MP-derived DOM (MP-DOM) on minerals (kaolinite and goethite) using DOM samples leached from commercial plastics including polyvinylchloride (PVC) and polystyrene (PS) under dark and ultraviolet (UV) irradiation conditions. MP-DOM was characterized by a higher distribution of relatively smaller-sized molecules than natural organic matter (NOM). The PS-derived DOM (PS-DOM) leached under UV treatment exhibited more oxygen-containing groups than their counterparts in the dark. MP-DOM also exhibited net negative charges at neutral pH ranges. Adsorption isotherm experiments revealed that the mineral surfaces had high adsorption affinities for both types of MP-DOM, which is likely associated with both electrostatic attraction and ligand exchange. The extent of adsorption was greater for the UV-irradiated than the dark-treated DOM, and on goethite compared to kaolinite. The Fourier-transform infrared (FTIR) spectra of the residual PS-DOM after adsorption revealed differences in the adsorption affinities between its functional groups. Two-dimensional correlation spectroscopy for the irradiated PS-DOM showed that preferential adsorption occurred on minerals in the sequential order of oxidized structures → (PS monomers) → carboxylates in additives → carbonyl groups. The adsorption isotherm model parameters for MP-DOM were comparable to those obtained from aquatic/terrestrial NOM, which suggests that plastic-derived DOM can interact with minerals as strongly as NOM. This study highlights the overlooked role played by plastic-derived DOM in mineral-enriched environments, opening new opportunities for improving our understanding of the fate and environmental impacts of MPs.

A Review of Current and Emerging Approaches for Water Pollution Monitoring

The aquatic ecosystem is continuously threatened by the infiltration and discharge of anthropogenic wastewaters. This issue requires the unending improvement of monitoring systems to become more comprehensive and specific to targeted pollutants. This review intended to elucidate the overall aspects explored by researchers in developing better water pollution monitoring tools in recent years. The discussion is encircled around three main elements that have been extensively used as the basis for the development of monitoring methods, namely the dissolved compounds, bacterial indicator, and nucleic acids. The latest technologies applied in wastewater and surface water mapped from these key players were reviewed and categorized into physicochemical and compound characterizations, biomonitoring, and molecular approaches in taxonomical and functional analyses. Overall, researchers are continuously rallying to enhance the detection of causal source for water pollution through either conventional or mostly advanced approaches focusing on spectrometry, high-throughput sequencing, and flow cytometry technology among others. From this review’s perspective, each pollution evaluation technology has its own advantages and it would be beneficial for several aspects of pollutants assessments to be combined and established as a complementary package for better aquatic environmental management in the long run.

Molecular investigation into the transformation of dissolved organic matter in mature landfill leachate during treatment in a combined membrane bioreactor-reverse osmosis process

This study investigated the effectiveness of a combined membrane bioreactor (MBR) and reverse osmosis (RO) process for treating leachate produced by a large-scale anaerobic landfill. The MBR process had limited treatment efficiency for removing organic pollutants, but when combined with RO, the integrated system completely removed macromolecular compounds (i.e., humic- and fulvic-like substances) and produced effluent that satisfied the applicable discharge standard. The landfill leachate contained many types of DOM that had high molecular weight and were highly unsaturated. Although the MBR process removed some DOM that had a relatively low saturated degree (mainly aliphatic compounds (2.0 ≥ H/C ≥ 1.5) with relatively high bioavailability), many bio-refractory compounds were not removed. The RO system greatly reduced the content of residual DOM in MBR effluent and was effective for removing heteroatom DOM, especially polycyclic aromatics (AI > 0.66) and polyphenols (0.66 ≥ AI > 0.50). The effluent from the combined process of MBR and RO treatment mainly contained a small number of aliphatic compounds and phenolic compounds (AI ≤ 0.50 and H/C < 1.5) that had higher bioavailability than DOM in the raw leachate and posed little environmental risk.