Excitation-emission Matrix Research Articles

Responses of partial denitrification process to long-term perfluorooctane sulfonic acid stress: Performance, microbial community and functional genes

This study investigated the changes in reactor performances, microbial communities and functional genes in partial denitrification (PD) process under elevated perfluorooctane sulfonic acid (PFOS) stress. The results showed that PFOS significantly (P ≤ 0.001) decreased NO-2-N accumulation rate from 71.15 ± 1.83 % to 65.96 ± 3.97 % and increased total nitrogen removal efficiency from 25.49 ± 1.67 % to 30.90 ± 4.97 %, which indicated that PFOS addition hindered the PD process but promoted the total nitrogen removal. Excitation emission matrix fluorescence spectroscopy and fourier transform infrared spectroscopy suggested significant changes in fluorescence characteristics and functional groups of extracellular polymeric substances, especially, PFOS induced the considerable synthesis of protein-like substances. In addition, high-throughput sequencing revealed that the abundance of genus Thauera, which is responsible for the NO-2-N accumulation, was significantly decreased from 35.98 % to 26.00 % under PFOS stress. While the abundances of common denitrifying bacteria, such as genus Denitratisoma, SM1A02 and OLB8, increased after PFOS exposure, which was consistent with the changes of nitrogen transition. Moreover, PICRUSt showed that the abundance of NO-3-N reductase genes (napA) significantly (P ≤ 0.001) downregulated from 0.02 % to 0.01 %, while NO-2-N reductase genes (nirK) significantly (P ≤ 0.001) upregulated by 1.97 folds after PFOS addition. These results showed that PFOS stress had a profound influence on microbial structure and the functional genes. Overall, this study demonstrated the response mechanism of PD system to long-term PFOS stress and made some contributions to the improvement in the control strategy of wastewater treatment plants (WWTPs).

Rapid identification of high-temperature Daqu Baijiu with the same aroma type through the excitation emission matrix fluorescence of maillard reaction products

The flavor of high-temperature Daqu Baijiu with the same aroma type is similar but the quality and price are very different, so that the high-quality Baijiu is often pretended as low-quality Baijiu. In this study, excitation-emission matrix fluorescence spectrometry combined with chemometrics was proposed for rapid identification of high temperature Daqu Baijiu with the same aroma type. The method was based on seven components screened by alternating trilinear decomposition (ATLD), and the discriminant model was established by data-driven-soft independent modeling of class analogy (DD-SIMCA), with the discriminant rate of 100%. Some Maillard reaction products, such as pyrazine and furfural compounds, with correlation >0.8 were obtained by GC-MS combined with Pearson analysis, and the prediction accuracy between 90.32% and 96.77%. This method has the characteristics of high sensitivity, fast detection and no pre-treatment, which provides a new strategy for rapid discrimination of high-temperature Daqu Baijiu with the same aroma type.

Fraction analysis of soil phosphorus and dissolved organic matter reveals the release potential of phosphorus and its influencing factors in the submerged area of the Sanhekou Reservoir, China

Abstract Different forms of inorganic phosphorus in surface soils can be released into water or adsorbed into sediment in response to various environmental factors. Although the Sanhekou Reservoir is still under construction, the periodic wetting-drying events may result in the release of inorganic phosphorus from the soil into the water once it is completed. Therefore, this study aimed to investigate the background soil values and estimate the phosphorus release fluxes of the Puhe River, Wenshuihe River, and Jiaoxihe River of the reservoir. We would like to provide a theoretical basis for the subsequent management and ecological protection of the reservoir based on this study. The Chang–Jackson chemical continuous extraction method was used to determine the forms of inorganic phosphorus in the soil, and fluorescence data were obtained by excitation–emission matrix combined with parallel factor (EEM-PARAFAC). The results showed that there were four types of phosphorus in the soil of the reservoir, including calcium-bound phosphate, aluminium-bound phosphate, iron-bound phosphate, and occluded phosphate. The total quantities of these phosphorus types were measured to be 6.71 × 104, 1.14 × 104, 0.91 × 104, and 0.49 × 104t, respectively. Additionally, it was observed that there was 2.12 × 104 t of bioavailable phosphorus present in the soil.

Dynamics of chromophoric dissolved organic matter in a highly productive Amundsen Sea polynya

Dissolved organic carbon (DOC) is the largest organic carbon pool in the ocean, and is the most active component in respect to the ocean carbon cycling. However, its study in Antarctica has been limited due to challenges associated with sample collection. In this study, we conduct an investigation on the chromophoric dissolved organic matter (CDOM) in a highly productive Amundsen Sea Polynya (ASP), where phytoplankton blooms occur annually during the austral summer, serving as the primary source of DOC and CDOM. The relative abundances of CDOM, as indicated by the absorption coefficient at 254 nm (a254), exhibit significant variability, reaching up to 6.34 m−1. Four fluorescent components, including two humic-like components (C1 and C4) and two protein-like components (C2 and C3), are identified by excitation emission matrix coupled with parallel factor analysis (EEM-PARAFAC). Our findings suggest that heterotrophic metabolism primarily contributes to the formation of humic-like fluorescent components and DOC removal. Water mass, solar radiation, primary productivity as well as microbial degradation are identified as the main factors influencing CDOM dynamics in ASP. This study bears significant implications for advancing our understandings of the CDOM and DOC dynamics in the coastal polynyas of Antarctica, thus facilitating improved evaluation of carbon cycle in the Antarctica.

3D excitation-emission matrix fluorescence spectroscopy of Biluochun before and after Tomb-Sweeping Day

<p class="Abstract">Tea is an important public drink and its value is in accordance with the time of picking, for example, tea picked before Tomb-Sweeping Day is more expensive than that after Tomb-Sweeping Day. To avoid buying shoddy tea, it is necessary to identify the picking time of the tea. Considering the fact that the chemical components are related to the picking time, in this work, fluorescence spectroscopy is proposed to find the difference between these two kinds of Biluochun. The intensity of the excitation and emission wavelengths for the Biluochun was measured at the same to obtain 3D fluorescence spectra. The contour maps of Biluochun picked before and after Tomb-Sweeping Day were drawn and compared. The results shown that fluorescent intensity at the region from 660 nm to 680 nm, which is corresponding to chlorophyll, is obviously different for both kinds. The different fluorescent intensity demonstrated that the chlorophyll contained in Biluochun after Tomb-Sweeping Day was higher than that before Tomb-Sweeping Day, which can be used to classify these two kinds.</p>

Corrosion analysis of unearthed jade from Daye Zhen Tomb of Northern Zhou Dynasty

X-ray fluorescence spectroscopy, scanning electron microscopy energy spectrum, excitation-emission matrix spectroscopy, and Fourier transform infrared spectroscopy was applied to the unearthed jade with multilayered corrosion, to reveal the microstructure, composition structure, and distribution of organic matters. Our results showed that the interior of the jade was mainly composed of layered serpentine with a regular structure, while the white layer structure on the surface is scattered and irregular, and the content of calcite formed by elements Ca and C increases significantly; between the green matrix and the white layer on the surface, there are brown corrosion zones with obvious fluorescence effect and mainly composed of humic acid, which continuously extends inward along the corrosion cracks for accelerating the internal corrosion. This article, for the first time, argued for the corrosive and fluorescent humic acid bands that appear inside serpentine jade and cautions its role in investigating the corrosion of jade.

Application of vibrational and fluorescence spectroscopy to the compositional analysis of colored-flesh potatoes.

Determination of composition and physicochemical parameters of natural products requires dedicated, often laborious and expensive, analytical protocols. Different spectroscopic techniques, in conjunction with chemometrics, seem to have a considerable potential in direct analysis of raw plant material and foods, without any chemical treatment. Fluorescence spectroscopy and three vibrational spectroscopy techniques were applied to determine total polyphenol content, antioxidant activity and macronutrient levels in red- and purple-fleshed potato varieties. Excitation-emission matrix fluorescence, Fourier transform Raman, attenuated total reflection Fourier transform infrared and near-infrared spectra were recorded for the freeze-dried samples. Combining spectral data and the results of reference analyses, partial least squares regression models were constructed for each parameter studied. For polyphenols and antioxidant activity, quantification errors found for validation samples amounted to 3.74-5.04% and 4.75-6.35%, respectively, whereas macronutrient analysis gave errors in the 3.45-4.55%, 3.09-5.30% and 5.10-8.58% ranges for starch, protein and sugar determinations, respectively. The obtained results demonstrate that different spectroscopic techniques in combination with multivariate modeling allow simultaneous determination of various parameters of plant samples based on a single sample spectrum. They can effectively replace commonly used protocols of food product analysis requiring sample dissolving and extraction of the compounds of interest. © 2023 Society of Chemical Industry.

Rapid detection and quantification of adulteration in saffron by excitation-emission matrix fluorescence combined with multi-way chemometrics.

Saffron has gained people's attention and love for its unique flavor and valuable edible value, but the problem of saffron adulteration in the market is serious. It is urgent for us to find a simple and rapid identification and quantitative estimation of adulteration in saffron. Therefore, excitation-emission matrix (EEM) fluorescence combined with multi-way chemometrics was proposed for the detection and quantification of adulteration in saffron. The fluorescence composition analysis of saffron and saffron adulterants (safflower, marigold and madder) were accomplished by alternating trilinear decomposition (ATLD) algorithm. ATLD and two-dimensional principal component analysis combined with k-nearest neighbor (ATLD-kNN and 2DPCA-kNN) and ATLD combined with data-driven soft independent modeling of class analogies (ATLD-DD-SIMCA) were applied to rapid detection of adulteration in saffron. 2DPCA-kNN and ATLD-DD-SIMCA methods were adopted for the classification of chemical EEM data, first with 100% correct classification rate. The content of adulteration of adulterated saffron was predicted by the N-way partial least squares regression (N-PLS) algorithm. In addition, new samples were correctly classified and the adulteration level in adulterated saffron was estimated semi-quantitatively, which verifies the reliability of these models. ATLD-DD-SIMCA and 2DPCA-kNN are recommended methods for the classification of pure saffron and adulterated saffron. The N-PLS algorithm shows potential in prediction of adulteration levels. These methods are expected to solve more complex problems in food authenticity. © 2023 Society of Chemical Industry.

Characteristics and phytotoxicity of hydrochar-derived dissolved organic matter: Effects of feedstock type and hydrothermal temperature

The dissolved organic matter (DOM) with high mobility and reactivity plays a crucial role in soil. In this study, the characteristics and phytotoxicity of DOM released from the hydrochars prepared from different feedstocks (cow manure, corn stalk and Myriophyllum aquaticum) under three hydrothermal carbonization (HTC) temperatures (180, 200 and 220°C) were evaluated. The results showed that the hydrochars had high dissolved organic carbon content (20.15 to 37.65 mg/g) and its content showed a gradual reduction as HTC temperature increased. Three fluorescent components including mixed substance of fulvic acid-like and humic acid-like substances (C1, 30.92%-58.32%), UVA humic acid-like substance (C2, 25.27%-29.94%) and protein-like substance (C3, 11.74%-41.92%) were identified in hydrochar DOM by excitation emission matrix spectra coupled with parallel factor analysis. High HTC temperature increased the relative proportion of aromatic substances (C1+C2) and humification degree of hydrochar DOM from cow manure, while it presented adverse effects on the hydrochar DOM from corn stalk and Myriophyllum. aquaticum. The principal component analysis suggested that feedstock type and HTC temperature posed significant effects on the characteristics of hydrochar DOM. Additionally, seed germination test of all hydrochar DOM demonstrated that the root length was reduced by 8.88%-26.43% in contrast with control, and the germination index values were 73.57%-91.12%. These findings provided new insights into the potential environmental effects for hydrochar application in soil.

Unraveling heterogeneity of dissolved organic matter in highly connected natural water bodies at molecular level

The exploring of molecular-level heterogeneity of dissolved organic matter (DOM) in highly connected water bodies is of great importance for pollution tracing and lake management, and provides new perspectives on the transformations and fate of DOM in aquatic systems. However, the inherent homogeneity of DOM in connected water bodies poses challenges for its heterogeneity analysis. In this work, an innovative method combining fluorescence spectroscopy, high-resolution mass spectrometry (HRMS), and cluster analysis was developed to reveal the heterogeneity of DOM in highly connected water bodies at the molecular level. We detected 4538 molecules across 36 sampling sites in Chaohu Lake using HRMS. Cluster analysis based on excitation-emission matrix (EEM) data effectively divided the sampling sites into four clusters, representing the water bodies from West Chaohu Lake, East Chaohu Lake, agricultural land, and urban areas. Analysis of DOM in the western and eastern parts of the lake revealed that aerobic degradation led to a decrease in CHOS and aliphatic compounds, alongside an increase in CHO and highly unsaturated and phenolic compounds. Furthermore, we unveiled the characteristics and sources of heterogeneity in DOM from agricultural land and urban areas. Our method accurately captured the heterogeneous distribution of DOM in the lake and revealed the heterogeneous composition of DOM at molecular level. This work underscores the importance of integrating complementary spectroscopic analyses with HRMS in DOM research with similar compositions.

Geographical origin traceability and authenticity detection of Chinese red wines based on excitation-emission matrix fluorescence spectroscopy and chemometric methods

Excitation–emission matrix fluorescence (EEMF) spectroscopy combined with chemometrics was developed for the geographical origin traceability and authenticity detection of Chinese red wines. Parallel factor analysis coupled with partial least squares-discriminant analysis (PARAFAC-PLS-DA), N-way partial least squares-discriminant analysis (N-PLS-DA) and unfolded partial least squares-discriminant analysis (U-PLS-DA) were used to identify the geographical origins and adulteration of red wines. Accuracy, sensitivity, specificity and precision were used to evaluate the performances of the discriminant models. The accuracy of PARAFAC-PLS-DA for training samples and prediction samples from different origins was 0.88 and 0.83, respectively. N-PLS-DA and U-PLS-DA, which used full EEMF data as model inputs, had the same excellent performance and both provided an accuracy of 1. With regard to the identification of adulterated samples, the accuracy of PARAFAC-PLS-DA for training samples and prediction samples was 0.71 and 0.83, respectively. By comparison, in both N-PLS-DA and U-PLS-DA models, only one prediction sample with the lowest adulteration level was misclassified. N-way partial least squares regression (N-PLSR) was successfully used to quantify adulteration levels for the first time, with Rc2 > 0.98, both RMSEC and RMSEP < 6%. This study showed that EEMF combined with chemometrics is an effective method for the geographical origin traceability and authenticity detection of Chinese red wines.

Fluorescence spectroscopic characterization of dissolved organic matter in the wastewater treatment plant and hybrid constructed wetlands coupling system in winter: A case study in eastern China

Dissolved organic matter (DOM) in municipal wastewater can have a detrimental effect on aquatic ecosystems, as DOM can participate in the global carbon cycle and change the transport of other pollutants. The characteristics of DOM can also affect the utilization efficiency of dissolved organic carbon by microorganisms in water. In this study, variations in DOM quantity and quality in a full-scale wastewater treatment plant (WWTP) coupled with a hybrid constructed wetland (CW) system during cold periods were characterized by using excitation-emission matrix spectroscopy combined with parallel factor analysis (EEM-PARAFAC). The results showed that the DOM concentration significantly decreased after exiting the WWTP, while a slight increase was found in the CW. The coupled system could significantly eliminate influent DOM with a removal efficiency of 92.1%. The CW system could still remove DOM even in winter. Five fluorescent components, including three humic-like components, one protein-like component and one tyrosine-like component, were identified. Although the biological treatment process in the WWTP contributed a large number of protein-like substances, the optical indices showed that the bioavailability of wastewater was gradually reduced, indicating that DOM was selectively removed by the integrated system. Moreover, there were significant correlations between water quality parameters and DOM indices. This study could contribute to a better understanding of the elimination process of dissolved organic carbon in coupled systems of WWTPs and CWs and offer novel ideas for organic carbon resource recovery and water quality monitoring in watershed environments.

Rational regulation of 3D N-doped carbon macro-architectures toward low-temperature plasma catalysis: The roles of nitrogen content and hierarchical porous structure

The application of low-temperature plasma technology with optimized catalysts in water treatment has shown a good application prospect. However, the relationships between catalytic performance and composition (N atom-doping) and structure (hierarchical porous) of catalysts is still unclear. Here, 3D N-doped carbon macro-architectures is designed by thermolysis of energetic Zn-MOF, where triazole ligand with ultra-high nitrogen content provided the possibility for effective nitrogen doping and creation of hierarchical porous structure. In the DBD system, a series of energetic MOF-derived carbon (EMC-x) catalysts with different pyrolysis temperatures (from 700 to 1000 °C) were prepared, and the composition/structure-effective relationship was investigated in detail. Degradation mechanisms and pathways were analyzed by bursting experiments, quantitative detection of H2O2 and O3, three-dimensional excitation-emission matrix spectroscopy (3D-EEM), LC-MS. The results confirmed that EMC-10 with high nitrogen content and hierarchical porous structure has a wide range of applications in synergistic plasma removal of TTCH from water bodies.

The influence of micro-flocculation on membrane fouling during ultrafiltration of dissolved organic matter

This study investigated the mitigating effect of micro-flocculation as an ultrafiltration (UF) membrane pretreatment process on membrane fouling caused by organic matter in urban micro-polluted river water. The removal characteristics of organic matter by micro-flocculation were analyzed using three-dimensional fluorescence excitation emission matrix (3D-FEEM) and liquid chromatography organic carbon detector (LC-OCD). Furthermore, the variation of floc properties such as flocculation index and fractal dimension of micro-flocs formed under different flocculant dosages and their effects on UF membrane flux were investigated. The experimental results show that micro-flocculation using ferric chloride (FeCl3) can effectively remove large molecular weight organics. The features of flocs, which are influenced by the amount of FeCl3, affect the formation of the cake layer. Micro-flocculation can control the formation of a floc cake layer with a larger size and lower fractal dimension. It is helpful to effectively delay the attenuation rate of membrane flux by reducing membrane pore blockage and forming a filter cake layer with high porosity, which is of great significance for improving membrane technology. After the FeCl3 micro-flocculation treatment, the final specific flux of the membrane increased by 57.0 %. The combination of FeCl3 micro-flocculation and UF is a superior technical and economical treatment scheme for micro-polluted river water.

Unveiling the molecular responses of dissolved organic matter in landfill leachate to activated carbon adsorption

Powdered activated carbon (PAC) is an effective method for removing dissolved organic matter (DOM) in membrane bioreactor effluent of landfill leachate (MBR effluent). Among commercially available PACs, wood-based PAC (WoAC) and coal-based PAC (CoAC) are two most common ones. However, the interactions between two PACs and DOM in MBR effluent at the molecular level as well as the effect of PACs properties on the adsorption of DOM compounds are not fully understood. To address the gap, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), three-dimensional fluorescence excitation-emission matrix (EEM) spectroscopy and other spectroscopic techniques were employed to study the change of DOM in MBR effluent when adsorbed by WoAC and CoAC. The results showed that CoAC had a better removal performance of DOM (89.2% for UV254 and 78.4% for DOC) than WoAC (80.9% for UV254 and 70.8% for DOC), which was likely due to the Fe component in CoAC playing an important role in the DOM adsorption process. Both WoAC and CoAC exhibited preferential adsorption for compounds with high unsaturation or poor oxygen. Moreover, the Fe component in CoAC may bind with some functional groups (e.g., carboxyl groups) in unsaturated compounds, which may enhance the adsorption of unsaturated compounds. These findings deepen our understanding of PAC-DOM interactions at the molecular level and provide guidance for designing cost-effective PACs for landfill leachate treatment.

Characterizing water-soluble brown carbon in fine particles in four typical cities in northwestern China during wintertime: integrating optical properties with chemical processes

Abstract. Brown carbon (BrC) aerosol could impact atmospheric radiative forcing and play a crucial role in atmospheric photochemistry. In this study, fine particulate matter (PM2.5) filter samples were collected synchronously in four major cities in northwestern China during the winter season (December 2019–January 2020): Lanzhou (LZ), Xining (XN), Yinchuan (YC), and Ürümqi (UR), which are represented as energy-producing and heavy manufacturing cities in China. The primary aim of the study is to explore the optical properties, sources, and chemical processes of water-soluble BrC (WS-BrC). The average mass absorption efficiency at 365 nm (MAE365) of WS-BrC at these four cities was 1.24 ± 0.19 m2 g−1 (XN), 1.19 ± 0.12 m2 g−1 (LZ), 1.07 ± 0.23 m2 g−1 (YC), and 0.78 ± 0.16 m2 g−1 (UR). The properties of WS-BrC were further investigated by an acid–base titration experiment. The results showed that the MAE365 values in all cities increased with higher pH values (2–11), while the fluorescence intensities of water extracts fluctuated with pH values, being stronger under both highly acidic and basic conditions. The sensitivity to pH variation was most pronounced in the WS-BrC samples from YC and LZ, indicating the important contribution of acid or base functional group compounds in these locations. Additionally, the study revealed significant photo-enhancement (LZ) or photo-bleaching (YC and UR) phenomena of WS-BrC in different cities. These results suggest that the sources and/or chemical processes of WS-BrC varied among the cities. The sources and chemical processes of WS-BrC were further explored by a combination of parallel factor analysis (PARAFAC) on excitation–emission matrix (EEM) spectra of WS-BrC and positive matrix factorization analysis (PMF) on high-resolution mass spectra of water-soluble organic aerosol (WSOA). Six PARAFAC components were identified, including three humic-like substances (HULIS; two less oxygenated (LO) HULIS and one highly oxygenated (HO) HULIS), two protein-like or phenol-like substances (PLS), and one undefined substance. Four PMF factors were identified, including a water-soluble primary OA (WS-POA), a less oxidized oxygenated OA associated with coal combustion-induced WSOA (LO-OOA), and two highly oxidized oxygenated OAs resulting from photochemical oxidation and aqueous-phase oxidation transformations (HO-OOA1 and HO-OOA2). WS-POA was determined to be the most significant source of light absorption, accounting for 30 %–60 % based on multiple linear regression models, and it showed a significant correlation with PLS and LO-HULIS components. The loss of light absorption of WS-POA was found to occur through its conversion to LO-OOA and HO-OOAs through photochemical or aqueous reactions, with HO-OOAs being significantly correlated with the HO-HULIS component. These processes can be clearly illustrated by integrating optical properties and chemical composition using a Van Krevelen diagram and an EEM plot.

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.

Direct and Indirect Effects of Land Use on Dissolved Organic Matter in a Typical Karst River

Land use can directly affect the abundance of riverine dissolved organic matter (DOM) by transporting terrestrial organic matter to rivers and can also indirectly enhance local production of DOM by increasing riverine nutrient loading. This study investigated the characteristics and spatial distribution of DOM components in the Furong River during the rainy season (July) using ultraviolet-visible light absorption spectroscopy (UV-VIS) and three-dimensional excitation emission matrix fluorescence spectroscopy-parallel factor analysis (EEM-PARAFAC) techniques. Furthermore, correlation analysis and the partial least squares path model (PLS-PM) were used to identify and quantify the direct and indirect impacts of land use on DOM at multiple scales. The results revealed that:① the direct effects of land use on DOM were generally stronger than the indirect effects. ② The responses of different DOM components to riverine nutrient status and land use varied, with dissolved organic carbon (DOC) and colored dissolved organic matter (CDOM) components being more susceptible to riverine nutrient status and fluorescent dissolved organic matter (FDOM) being more sensitive to land use. ③ The direct impact intensity of land use on DOC and CDOM fluctuated slightly with the spatial scale, but the total impact intensity had no visible spatial scale difference, and the direct impact intensity on the FDOM component decreased with the increase in spatial scale. ④ Dryland, urban and other construction land, patch density (PD), edge density (ED), and Shannon's diversity index (SHDI) were typical land use metrics that exacerbated DOM abundance, whereas paddy field, shrubland, largest patch index (LPI), and aggregation index (AI) were typical land use metrics that effectively mitigated DOM abundance. Total nitrogen (TN), nitrate nitrogen (NO3--N), and dissolved total phosphorus (DTP) were water quality parameters that were significantly affected by land use and were closely related to DOM components, that is, nitrogen and phosphorus played an important "intermediary" role in "land use-riverine DOM." FDOM could be used as indicators to measure the strength of terrestrial organic matter directly input to rivers by land use.

Stabilization of hydrophobic organic compounds in sediment using alkali-activated rice husk biochar: Enhancement of sorption by dissolved organic matter

Polycyclic aromatic hydrocarbons and phthalate esters are hydrophobic organic compounds (HOCs) that pose strong risks to aquatic and sediment ecosystems. The aim of this study was to develop a material for stabilizing (sorbing) HOCs in contaminated sediment. Activated biochar with a high surface area (called RH–NaOH) was successfully synthesized by activating rice husk biochar with an alkali (NaOH). The kinetics of HOC sorption to the RH–NaOH were described well by a three-stage intraparticle diffusion model. The sorption isotherms were adequately described by the Sips sorption model. The presence of dissolved organic matter (DOM) at environmentally relevant concentrations enhanced HOC sorption to the RH–NaOH by as much as a factor of 10, and this was mainly caused by the fulvic-acid- and humic-acid-like fractions of the DOM. The degree of sorption enhancement was predicted by the integrated volume of the fulvic-acid- and humic-acid-like fraction regions of the excitation–emission matrix that was used to characterize the DOM. The polycyclic aromatic hydrocarbon and phthalate ester stabilization efficiencies when 150 d was allowed for equilibration between the sediment and RH–NaOH to be reached were 96.5% and 94.6%, respectively. The stabilization tests indicated that HOC sorption proceeded via multiple stages with different kinetics. These stages were attributed to complex processes involving HOC and DOM sorption and desorption, HOC–DOM interactions, and HOC and HOC–DOM mixture diffusion into pores. The RH–NaOH has great potential for use as a sorbent for stabilizing HOCs in contaminated sediment.

Learning from fluorescence: A tool for online multiparameter monitoring of a microalgae culture

We propose a systematic approach for monitoring important productivity parameters in a Dunaliella salina culture using 2D fluorescence data. For this purpose, a methodology based on Machine Learning algorithm Projection to Latent Structures Regression (PLSR) coupled with variable selection strategies was used. Additionally, a robustness analysis is proposed to support the validation of the yielded models and provide a measure of their reliability. Robust (i.e., Q2≥ 0.5) and parsimonious (i.e., selecting down to 3 % of the fluorescence variables present in a 250–700 nm wavelength excitation-emission matrix) models were obtained for monitoring cell count, chlorophyll b, total carotenoids and β-carotene culture concentration, and the ratio between total carotenoids and total chlorophylls, all of which were validated with a left-out batch performing with R2 higher than 0.7 except for β-carotene (R2 = 0.54).