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

Comprehensive chemical analysis and characterization of heavy oil electric desalting wastewaters in petroleum refineries

Large quantities of highly polluted point-source wastewaters (EDWs) are generated from electric desalting process of heavy oils (HOs), resulting in severe impacts on the efficiency of wastewater treatment plants in petroleum refineries. In the present study, a comprehensive chemical analysis and characterization of EDWs of two typical Chinese heavy oils, Liaohe heavy oil (LHO) and Karamy heavy oil (KHO), were investigated using Daqing light oil (DLO) as a control. The HO-EDWs (LHO-EDW and KHO-EDW) show high pollutants contents with complicated compositions, more polar dissolved organic pollutants (DOPs), strong emulsion stability and high acute biotoxicity towards Vibrio fischeri, compared to DLO-EDW. LHO-EDW and KHO-EDW have nearly equal pollutants contents but different compositions and distributions, where more types of DOPs exist in KHO-EDW. Large amounts of biologically recalcitrant aromatic compounds, as well as heteroatomic compounds such as CHO, CHOS and CHON species, extensively distribute in HO-EDWs. The organic nitrogen compounds (e.g., anilines and N_2-3O_x, N₁O_xS₁) in KHO-EDW most probably contribute to and thus leading to elevated levels of acute biotoxicity. Additionally, highly dispersed colloidal, micron-sized particles and polar compounds promote the emulsification and stabilization of HO-EDWs. These results can guide the development of pretreatment technologies for HO-EDWs, thus improving the treatment and management of heavy oil refineries' wastewater streams.

Distribution and removal of fluorescent dissolved organic matter in 15 municipal wastewater treatment plants in China

Fluorescent dissolved organic matter (FDOM), having complex structures like aromatic structure and double bond structure, is able to represent relatively refractory parts of dissolved organic matter (DOM). This study investigated the distribution of FDOM in the influents and the removal in the secondary effluents of 15 municipal wastewater treatment plants (WWTPs) in 15 provincial capitals of China. Eight components have been identified using excitation emission matrix combined with parallel factor analysis (EEM-PARAFAC). Tryptophan-like (C1 or C4), terrestrial humic-like (C2) and microbial humic-like (C3) fluorescent components were major FDOM components in municipal wastewater, appearing in 11 WWTPs simultaneously. The removal of total fluorescence was generally about 30%-40%, while hydrophobic humic-like compounds (C5 and C8) were the most refractory components with 4%-16% removal and C3 was the second most refractory with -11%-41% removal. The compositions of FDOM in municipal wastewater were different in northeast/west and middle/east regions according to the self-organized map (SOM) analysis. Wastewater sources had more important influence on fluorescent characteristics of secondary effluents than biological treatment processes. Besides, this study found that humification index (HIX) was the most suitable index to describe the bulk fluorescent character of wastewater since it had a good correlation with abundance, removal and ratios of main fluorescent components either in the influents or in the secondary effluents.

Characterization of urban and industrial wastewaters using excitation-emission matrix (EEM) fluorescence: Searching for specific fingerprints

Excitation-emission matrix (EEM) fluorescence spectroscopy has been applied to characterize several urban and industrial wastewaters (effluents from different types of industries: brewery, winery, dairy, biscuit, tinned fish industry, slaughterhouse, pulp mill, textile dyeing and landfill leachates), searching for specific fluorescence fingerprints. Tryptophan protein-like peaks (T₁ and T₂) are the predominant fluorescence in urban and food industry wastewaters (brewery, winery, dairy/milk, biscuit and fish farm industries) but no special fingerprint has been found to discriminate among them. Protein-like fluorescence also dominates the spectra of meat/fish industries (effluents from a tinned fish industry and a slaughterhouse), but in this case tyrosine protein-like peaks (B₁ and B2) also appear in the spectra in addition to tryptophan-like peaks. This fact might constitute a specific feature to differentiate these wastewaters from others, since the appearance of peaks B is quite uncommon in wastewaters. The textile dyeing effluent shows a characteristic triple humic-like fluorescence (peaks A, C₁ and C₂) that may represent a specific fingerprint for this kind of effluent. Leachates from medium-aged and old landfills might also show a specific fingerprint in their EEM spectra: the sole presence of the humic-like peak C with very high fluorescence intensity. This feature also allows differentiating them from young landfill leachates, which show predominance of protein-like peaks. The fluorescence index (FI) does not seem to be very appropriate to characterize wastewaters and its usefulness might be limited to the study of humic substances in natural waters, although further studies are needed on this topic. However, the humification index (HIX) and the biological index (BIX) do seem to be useful for studying wastewaters, since they have provided consistent results in the present work. This study shows the potential of EEM fluorescence to identify the origin of some industrial effluents, although more research is needed to check these preliminary results.

Characteristics of microplastic polymer-derived dissolved organic matter and its potential as a disinfection byproduct precursor

Although there are numerous studies concerning the occurrence of microplastics (MP) in the environment and its impact on the ecosystem, dissolved organic matter (DOM) leached from MP (MP-DOM) has received little attention, and its characteristics have been rarely examined. It is presumed that the DOM leaching from plastics could be accelerated when plastics lost their protective additives during their transport and weathering processes in aquatic systems. In this study, two additive-free MPs (or micro-sized plastic polymers) were leached in artificial freshwater under UV irradiation and dark conditions. The leached DOM was characterized by typical analyses for naturally occurring DOM (N-DOM) such as dissolved organic carbon (DOC), size exclusion chromatography (SEC), and Fourier-transform infrared spectroscopy (FTIR). The potential to generate trihalomethanes (THMs), a well-known environmental impact of N-DOM, was also explored for the DOM with plastic origins for the first time. The leaching results demonstrated that UV irradiation promoted the leaching of DOM from the plastic polymers with an amount corresponding to ∼3% of the total mass of the polymers. The leached amounts were much greater than those previously reported using commercial plastics which presumably contained protective additives. The SEC results revealed that, different from typical aquatic N-DOM, MP-DOM is mostly composed of low molecular weight fractions <350 Da. For the two polymer types (polyethylene and polypropylene), the MP-DOM exhibited a high potential to form THMs upon chlorination, which was comparable to those of typical aquatic N-DOM. This study highlighted an overlooked contribution of UV irradiation to the DOM leaching from additive-free plastics and the potential risk of MP-DOM to produce toxic disinfection byproducts (DBPs) upon chlorination.

Characterization of fluorescent dissolved organic matters in metalworking fluid by fluorescence excitation-emission matrix and high-performance liquid chromatography

In recent years, precise environment supervision has gradually become vital in water pollution control, which requires the clear identification of dissolved organic matters (DOM) in wastewater. Metalworking fluid (MWF) is a type of wastewater with high toxicity. Over ten million m³ of MWF is discharged per year. However, its DOM characteristics have not yet been systematically investigated. Therefore, in this study, the fluorescent DOM (FDOM) of MWF was firstly characterized by excitation-emission matrix-parallel factor analysis (EEM-PARAFAC) and high-performance liquid chromatography (HPLC). Three fluorescent components (C1-C3) of the MWF from three metalworking plants (BO, TH, and YD) were identified. The peaks measured for C1 and C3 were attributed to tryptophan-like (Peak T) and humic/fulvic acid-like (Peak A + C) peaks, respectively, and the peaks at C2 were identified as humic-like (Peak A + M) or tryptophan-like (Peak T) peaks. There were differences in the C2 and C3 components of MWF from the three metalworking plants. The FDOM of MWF from the three metalworking plants exhibited similar polarity, but different apparent molecular weight distributions. In addition, the highest intensities of the three fluorescent peaks were sensitive to variations in the pH, humic acid (HA) concentrations, and metal ion levels (Cu²⁺, Fe³⁺, and Ni²⁺). The findings of this study not only indicate the FDOM characteristics of MWF, but also provide a promising method and valuable guidance for the practical monitoring of MWF in natural water bodies.

Effects of fish culture on particulate organic matter in a reservoir-type river as revealed by absorption spectroscopy and fluorescence EEM-PARAFAC

Dam construction and fish culture can change the biogeochemical processes in river, yet their impact on the spectral properties of particulate organic matter (POM) remains to be studied. This was investigated in a reservoir-type river (Minjiang river, SE China) using absorption spectroscopy and fluorescence excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). Five fluorescent components were identified from POM with PARAFAC. Four components C1-C4 were affected by the seasonal variations of rainfall and runoff, indicating the influences of hydrological condition and terrestrial inputs. The Chlorophyll a concentration (Chl a) correlated significantly with the humic-like C3 (p < 0.05) and the protein-like C4 (p < 0.01), indicating phytoplankton was an important source of C3 and C4. The Chl a and fluorescence intensities of C3-C4 were higher in the fish culture zones than in other areas, and the absorption coefficient a₃₀₀ and C1-C4 were lower downstream the dam. These results indicated that fish farming in the reservoir probably promoted the production of POM. The a₃₀₀ and C1 per unit mass of suspended particulate matter (a₃₀₀/TSM and C1/TSM) correlated significantly with the median particle size (p < 0.01), which might be related to the contribution of micro-phytoplankton. The absorption spectra of POM showed a shoulder peak at ∼280 nm, and its intensity correlated significantly and positively with Chl a (p < 0.01). These results indicated that the peak was probably derived from phytoplankton production. Our results have implications for better understanding the influences of human activities on the dynamics of river POM.

Role of extracellular polymeric substances in biofilm formation by Pseudomonas stutzeri strain XL-2

Pseudomonas stutzeri strain XL-2 exhibited significant performance on biofilm formation. Extracellular polymeric substances (EPS) secreted by strain XL-2 were characterized by colorimetry and Fourier transform infrared (FT-IR) spectroscopy. The biofilm growth showed a strong positive correlation (r_P=0.96, P<0.01) to extracellular protein content, but no correlation to exopolysaccharide content. Hydrolyzing the biofilm with proteinase K caused a significant decrease in biofilm growth (t=3.7, P<0.05), whereas the changes in biofilm growth were not significant when the biofilm was hydrolyzed by α-amylase and β-amylase, implying that proteins rather than polysaccharides played the dominant role in biofilm formation. More specifically, confocal laser scanning microscopy (CLSM) revealed that the extracellular proteins were tightly bound to the cells, resulting in the cells with EPS presenting more biofilm promotion protein secondary structures, such as three-turn helices, β-sheet, and α-helices, than cells without EPS. Both bio-assays and quantitative analysis demonstrated that strain XL-2 produced signal molecules of N-acylhomoserine lactones (AHLs) during biofilm formation process. The concentrations of C₆-HLS and C₆-oxo-HLS were both significantly positively correlated with protein contents (P<0.05). Dosing exogenous C₆-HLS and C₆-oxo-HLS also resulted in the increase in protein content. Therefore, it was speculated that C₆-HLS and C₆-oxo-HLS released by strain XL-2 could up-regulate the secretion of proteins in EPS, and thus promote the formation of biofilm.

Identification of oxidative stress and estrogenic activity induced by polarity fractions of effluent organic matter

This study evaluated oxidative stress and estrogenic activity induced by hydrophobic (HP), transphilic (TP), and hydrophilic (HL) fractions of effluent organic matter (EfOM) from municipal and industrial wastewater treatment plants. Fluorescence regional integration (FRI) analysis indicated that EfOM showed higher FRI distribution in regions II (aromatic protein-like) and IV (soluble microbial products, SMPs) than Suwannee River natural organic matter (SRNOM), which was primarily in regions III (fulvic acid-like) and V (humic acid-like). The HP and HL fractions of industrial EfOMs significantly increased catalase (CAT) and glutathione S-transferase (GST) activity and lipid peroxidation compared with those of the control (p <  0.05). Estrogenic activity was the highest in industrial EfOM followed by municipal EfOM, and both were significantly higher than that of SRNOM and the control (p <  0.05). FRI distribution in region II was significantly related to CAT, GST, and estrogenic activity (r = 0.7142, 0.7786, and 0.8107, respectively) for the HL fraction of EfOM. For the HP fraction of EfOM, regions II and IV were significantly related to estrogenic activity (r = 0.7221 and 0.6707, respectively). These findings suggest that aromatic protein-like substances and SMPs in EfOM were responsible for the observed oxidative stress and estrogenic activity.

Improved dewaterability of anaerobically digested sludge and compositional changes in extracellular polymeric substances by indigenous persulfate activation

In this study, an indigenous activation of persulfate by iron-bearing minerals was examined using peroxymonosulfate (PMS) and peroxydisulfate (PDS) for the dewaterability and extracellular polymeric substances (EPS) composition of anaerobically digested sludge (ADS). Iron minerals originally present in the ADS seemed to operate as an initiator of the persulfate activation, which was indicated by an increase in the total dissolved iron in the supernatant. The PMS showed higher performance in improving the ADS dewaterability compared to the PDS, with more reduction in the average microbial flocs size. The extracted EPS consisted of three different fluorescent components of tryptophan-like (C1), humic-like (C2), and fulvic-like (C3) components. In the tightly bound (TB)-EPS, two humic-like components (C2 and C3), which were resistant to degradation, exhibited a strong linkage with dewaterability; whereas, in both the PMS and the PDS systems, the C1 was preferentially degraded by the radical-based oxidation, with a greater extent for the PMS-based treatments. The results showed that prior to the actual EPS degradation, the produced radicals were initially involved in cell disruption. The SEC results during the oxidation clearly demonstrated the degradation of a large-sized biopolymer fraction, followed by the production of relatively small sized molecules. They also revealed in the TB-EPS a close association between the ADS dewaterability and the degradation of humic substances.

A combined heterotrophic and sulfur-based autotrophic process to reduce high concentration perchlorate via anaerobic baffled reactors: Performance advantages of a step-feeding strategy

The combined anaerobic baffled reactors (ABRs) of heterotrophic and sulfur-based autotrophic processes were first investigated for the removal of high perchlorate concentration under different feeding strategies. The removal efficiency of the step-feeding ABR (SF-ABR) reached 97.56% at 800 mg/L perchlorate, which was significantly superior to the normal-feeding ABR (NF-ABR). In three components of the extracellular polymeric substances (EPS), the fluorescence intensity of the tryptophan-like component were identified by fluorescence excitation-emission matrix (EEM) spectra with parallel factor (PARAFAC) analysis, and exhibited a positive relationship with the perchlorate removal rate in the heterotrophic perchlorate reduction unit (HPR unit) of the SF-ABR (R² = 0.9791) and NF-ABR (R² = 0.9860). Bacterial community analysis suggested the dominating perchlorate reducing bacteria and the diversity in two ABRs. Principal component analysis indicated that the electron donor affected the microbial community structures. The study confirms that the SF-ABR is a powerful bioreactor for the combined heterotrophic and sulfur-based autotrophic process.

Effect of gasification biochar application on soil quality: Trace metal behavior, microbial community, and soil dissolved organic matter

Compared to pyrolysis biochar (PBC), gasification biochar (GBC) differs in both composition and surface functionalities due to the use of an oxidizing purging gas. This work compares the effect of using PBC and GBC as soil amendments on the soil properties, trace metal bioavailability, soil microbial activity, and soil dissolved organic matter (DOM). Biochar-driven reduction of bioavailable metals does not necessarily result in a positive impact on the soil microbial growth. The DOM in the soil was strongly related to the soil microbial activity, as revealed by the strong correlation between the soil dehydrogenase activity (DHA) and soil dissolved organic carbon (r = 0.957, p <  0.01). Three identified fluorescent components (C1, C2, C3) in the soil DOM were closely associated with the soil microbial activity, for instance, with a clear positive correlation between the soil DHA and C1 (r = 0.718, p <  0.05) and a significant negative correlation between the total bacterial fatty acid methyl ester content and C3 (r = -0.768, p <  0.05). The bioavailability of Cd and Zn is not only related to the pH and surface functionalities of the biochar, but also to its aromatic carbon and inorganic mineral composition. This study further demonstrates that a fluorescence excitation-emission matrix coupled with parallel factor analysis is a useful tool to monitor changes in the soil quality after application of biochar, which is greatly relevant to the soil biota.

Combination of self-organizing map and parallel factor analysis to characterize the evolution of fluorescent dissolved organic matter in a full-scale landfill leachate treatment plant

The dissolved organic matter (DOM) characterization in a full-scale landfill leachate treatment plant is of great importance for the design and operation of treatment processes. In this study, the long-term removal behaviors of DOM during landfill leachate treatment were explored using excitation emission matrix fluorescence spectroscopy (EEMs) coupled with parallel factor analysis (PARAFAC) and self-organizing map (SOM). Results indicated that the application of combining PARAFAC and SOM on EEMs analysis effectively characterized long-term removal behaviors of DOM during leachate treatment. The DOM in raw leachate was dominated by humic substances, while its composition exhibited significant seasonal differences. A large proportion of protein-like fluorescent dissolved organic matter (FDOM) and bulk DOM were removed within membrane bioreactor (MBR) system. Meanwhile the humic-like FDOM removal capacity in nanofiltration (NF) process was well comparable with those in the MBR system owing to the bio-recalcitrant nature of humic substances. The protein-like FDOM and bulk DOM were removed synchronously in both the process of MBR and NF. Moreover, samples distribution exhibited obvious differences among NF concentrate samples. In general, the performance of MBR-NF treatment for landfill leachate displayed reasonable stability in DOM removal irrespective of seasonal variations. This study enhanced our understanding of EEMs application in characterizing leachate-derived DOM composition and has potential implications for the associated monitoring investigations in engineered systems.

Response of sediment organic phosphorus composition to lake trophic status in China

Organic phosphorus (P_o) constitutes the most important fraction of P in lake sediments, and the compositional properties of P_o affect its behavior in lake ecosystems. In this study, ³¹P NMR, FT-IR spectroscopy, and UV-visible absorbance spectroscopy were combined to identify the dynamic composition of sediment P_o across two sets of lakes in China ranging from oligotrophic to eutrophic, and their possible effects on lake eutrophication were evaluated. The results showed that sediment P_o content (accounting for 24-75% of TP) was positively correlated with trophic status in both Eastern Plain and Yun-Gui Plateau lakes of China, and the linear relationship was more stable compared to total P (TP), implying that sediment P_o may be a superior indicator of trophic status than TP. The P_o component, phosphonate accounted for only 0.4% or less of P_o, while the monoester P and diester P, accounted for 2-24% and 0.5-5% of P_o, respectively, and were the main factors causing P_o to increase with the increasing trophic status. The factors were closely related to the enhanced organic sewage load and intensification of contemporary sedimentation of phytoplankton. As trophic status increased, sediment P_o might integrate into larger amounts of aromatic substances and functional groups, which could enhance the stability of P_o in sediments. Furthermore, sediments from lakes with higher trophic status exhibited a higher degree of humification and molecular weights, which impart resistance to biodegradation, and therefore, reduced the risk of sediment P_o release. However, the massive accumulation of bioavailable P_o (monoester and diester P) allows possible degradation, supporting algal growth and maintains eutrophic status because there is abundant alkaline phosphatase in eutrophic lakes. Thus, to control lake eutrophication more effectively, targeted actions are urgently required to reduce the accumulation and degradation of P_o in lake sediment.

Insight into removal of dissolved organic matter in post pharmaceutical wastewater by coagulation-UV/H2O2

The removal of four dissolved organic matter (DOM) fractions, non-acid hydrophobics, hydrophobic acids, hydrophilics and transphilics, was achieved by coagulation-UV/H₂O₂ oxidation in post-pharmaceutical wastewater (PhWW). Coagulation with Polyferric chloride (PFC), Polymeric ferric sulfate (PFS) and Polymeric aluminum ferric chloride (PAFC) was studied separately to evaluate the effects of the initial pH and coagulant dosage. The coagulation-UV/H₂O₂ oxidation method resulted in much higher reduction rates for dissolved organic carbon (DOC) (by 75%) and UV₂₅₄ (by 92%) than coagulation or UV/H₂O₂ oxidation alone. The proportion of non-acid hydrophobics, hydrophobic acids, transphilics and hydrophilics removed by coagulation was 54%, 49%, 27% and 12 %, while the combined treatment removed 92%, 87%, 70% and 39%, respectively. Parallel factor analysis (PARAFAC) of fluorescence measurements revealed that the humic-like fluorescent component C4 showed the highest removal (by 44%) during the coagulation stage. After coagulation-UV/H₂O₂ treatment, the humic-like fluorescent component C3 had the highest removal (by 72%), whereas xenobiotic organic fluorescent components C1 and C4 remained recalcitrant to decomposition. Significant correlations (R² > 0.8) between C1 and the hydrophobic acids and non-acid hydrophobics suggested the possibility of using fluorescence spectroscopy as an effective tool to assess variations in DOM fraction treatment efficacy in coagulation-UV/H₂O₂ systems. After the combined treatment, toxic inhibition of cellular activity by post PhWW decreased from 88% to 47% and biodegradability increased from 0.1 to 0.52.

Insight into transformation of dissolved organic matter in the Heilongjiang River

Heilongjiang is a "browning" river that receives substantial terrestrial organic matter, where reactivity of dissolved organic matter (DOM) may have important effect on ecosystem function and carbon biogeochemical cycle. However, little is known about microbial transformations of different DOM components, which could provide valuable insight into biogeochemical reactivity of DOM. In this study, bioavailability experiments were conducted for 55 days to determine changes of different DOM components by microbial transformations. Labile matter (C1) was detected only in initial DOM, and tryptophan-like substances (C4) were observed from day 5 onwards. Thus, three individual components were identified at each sampling time of the bioavailability experiment. The increase of F_max in DOM components revealed that microbial humic-like substances (C2), terrestrial humic-like substances (C3), and C4 were produced by microbial transformation, especially in the spring samples. Further, two-dimensional correlation spectroscopy (2D-COS) indicated that shorter wavelength tryptophan-like and microbial humic-like substances can be degraded by microbes or transformed into longer wavelength complex substances. Relatively simple microbial humic-like substances were preferentially produced compared to complex terrestrial humic-like substances. The results make sense to understand the biogeochemical cycling and environmental effects of DOM in the Heilongjiang River.

Identification of textile wastewater in water bodies by fluorescence excitation emission matrix-parallel factor analysis and high-performance size exclusion chromatography

Identifying the causes of water body pollution is critical because of the serious water contamination in developing countries. The textile industry is a major contributor to severe water pollution due to its high discharge of wastewater with high concentrations of organic and inorganic pollutants. In this study, fluorescence excitation emission matrix-parallel factor (EEM-PARAFAC) analysis was applied to characterize textile industry wastewater and trace its presence in water bodies. The EEM spectra of textile wastewater samples collected from 12 wastewater treatment plants (WWTPs) revealed two characteristic peaks: Peak T1 (tryptophan-like region) and Peak B (tyrosine-like region). Two protein-like components (C1 and C2) were identified in the textile wastewater by PARAFAC analysis. The components identified from different textile WWTPs were considered identical (similarity >0.95). C1 and C2 were not sensitive to changes in pH, ionic strength, or low humic acid concentration (TOC < 4 mg/L). Therefore, C1 combined with C2 was proposed as a source-specific indicator of textile wastewater, which was further demonstrated by conducting high-performance size exclusion chromatography analysis. These results suggested that EEM-PARAFAC analysis is a reliable means of identifying textile wastewater pollution in water bodies and may also enable the identification of other industrial wastewater.

Application potential of biochar in environment: Insight from degradation of biochar-derived DOM and complexation of DOM with heavy metals

Biochar-derived dissolved organic matter (DOM) is important for determining the application potential of biochar in soil remediation. However, little is known about the degradation behavior of biochar-derived DOM and its interaction with heavy metals. Here, incubation experiments combined with quenching titration experiments, which analyzed by spectroscopic technology and chemometric method, were conducted to reveal such behaviors and mechanisms. Ultraviolet-visible (UV-Vis) spectra showed that high aromatic and hydrophobic fractions were enriched in biochar-derived DOM and enhanced during the cultivation process, thus the biochar-derived DOM may retain a high aromaticity, stability, and resistance. However, the environmental risk of Cu caused by the increase of DOM hydrophobicity cannot be overlooked while applying biochar to polluted soil. One fulvic-like (C1), one protein-like (C2) and two humic-like (C3, C4) substances were identified from biochar-derived DOM by using parallel factor analysis of excitation-emission matrix. Additionally, the fluorescence intensity variations of these components in DOM offered an additional interpretation for the observations from UV-Vis spectra. Two-dimensional correlation spectroscopy revealed that Cd binding to biochar-derived DOM first occurred in the protein- and fulvic-like fraction while protein- and humic-like substances had a stronger affinity for Cu. Furthermore, both phenolic and carboxyl groups firstly participated in the binding process of Cd with biochar-derived DOM, while polysaccharide gave the fastest response to Cu binding. These results clearly demonstrated the differences in specific heavy metal binding features of individual fluorescent substances and functional groups in biochar-derived DOM and contribute to improving the application effect of biochar in a multi-heavy metal polluted soil system.

Dynamics of dissolved organic matter in a wastewater effluent-impacted Japanese urban stream: characteristics, occurrence and photoreactivity of fluorescent components

We report the results of using the excitation-emission matrix (EEM) method combined with parallel factor analysis (PARAFAC) to investigate the characteristics and occurrence of dissolved organic matter (DOM) in an urban stream impacted by effluent from a wastewater treatment plant (WWTP). The PARAFAC model divides the bulk EEM spectra into six individual fluorescent components with three humic-like components (C1-C3), two protein-like components (C4 and C5) and a wastewater-derived component (C6). In general, intensities of fluorescent components are abundant in WWTP effluent impacted samples, thus showing that such an effluent is a major source of DOM in urban rivers, but C5 is considered to have autochthonous sources within the stream. In areas where the effluent is released, the fluorescent intensity from components (except C5) gradually decreases as these components are transported downstream. However, concentrations of dissolved organic carbon remain almost constant downstream of the release area. These results would be attributed to degradation and/or modification of fluorophore. Photolysis experiments confirmed that fluorescent intensities can decrease with increase of irradiation times. C6 particularly showed a rapid photodegradation, remaining only 24.1% after 48 h photolysis. These findings would be important when assessing DOM source and water quality in aquatic environments by EEM-PARAFAC.

Novel insights into variation of fluorescent dissolved organic matters during antibiotic wastewater treatment by excitation emission matrix coupled with parallel factor analysis and cosine similarity assessment

In this work, the variation of fluorescent dissolved organic matters (FDOM) of antibiotic wastewater in a full-scale treatment plant was studied. Fluorescent components of anaerobic, aerobic, Fenton stages were separately figured out by parallel factor analysis (PARAFAC) based on excitation emission matrix (EEM) dataset. Then, these components were pairwise quantitatively compared according to cosine similarity (CS). It was found that, after the anaerobic treatment, the major components showed remarkable similarity (CS > 0.97) to those of raw wastewater, although their maximum fluorescence intensity (F_max) decreased slightly or moderately (7% ∼ 54%). However, the aerobic treatment dramatically changed both the composition and content of fluorescent components, as all the protein-like components completely disappeared and only the humic-like components with much lower intensity were observed. After Fenton oxidation, all these humic-like components were remained (CS > 0.97) with fairly reduced F_max (51% ∼ 61%). For both aerobically treated and Fenton-oxidized wastewater, F_max correlated well with dissolved organic carbon (DOC). This suggested a dominant proportion of humic-like substances. The combination of PARAFAC based on separate EEM dataset of each treatment stage and CS assessment is a good approach to better understand FDOM variation and can be of much practical significance to monitor wastewater quality.

Spectroscopic study on transformations of dissolved organic matter in coal-to-liquids wastewater under integrated chemical oxidation and biological treatment process

A large amount of wastewater containing various toxic organic contaminants is produced during coal-to-liquids process. In this study, several spectroscopic methods were used to monitor the transformation of organic pollutants during an integrated chemical oxidation and biological process. The results showed that the hydrophobic acid fraction increased after Fenton oxidation, which was likely due to the production of small-molecule organic acids. Soluble microbial products were generated during biological treatment processes, which were degraded after ozonation; meanwhile, the hydrophilic base and acid components increased. Ultraviolet-visible spectroscopic analysis indicated that peaks at the absorption wavelengths of 280 and 254nm, which are associated with aromatic substances, were detected in the raw water. The aromatic substances were gradually removed, becoming undetectable after biological aeration filter (BAF) treatment. Fourier transform infrared spectroscopy analysis revealed that the functional groups of phenols; benzene, toluene, ethylbenzene, and xylene (BTEX); aromatic hydrocarbons; aliphatic acids; aldehydes; and esters were present in raw wastewater. The organic substances were oxidized into small molecules after Fenton treatment. Aromatic hydrocarbons were effectively removed through bioadsorption and biodegradation after BAF process. Biodegradable organic matter was reduced and finally became undetectable after anoxic-oxic treatment in combination with a membrane bioreactor. Four fluorescent components were fractionated and obtained via excitation-emission matrix parallel factor analysis (EEM-PARAFAC). Dissolved organic matter fractionation in conjunction with EEM-PARAFAC was able to monitor more precisely the evolution of characteristic organic contaminants.

Effects of floodgates operation on nitrogen transformation in a lake based on structural equation modeling analysis

Floodgates operation is one of the primary means of flood control in lake development. However, knowledge on the linkages between floodgates operation and nitrogen transformation during the flood season is limited. In this study, water samples from six sampling sites along Lake Xingkai watershed were collected before and after floodgates operation. The causal relationships between environmental factors, bacterioplankton community composition and nitrogen fractions were determined during flood season. We found that concentrations of nitrogen fractions decreased significantly when the floodgates were opened, while the concentrations of total nitrogen (TN) and NO₃^- increased when the floodgates had been shut for a period. Further, we proposed a possible mechanism that the influence of floodgates operation on nitrogen transformation was largely mediated through changes in dissolved organic matter, dissolved oxygen and bacterioplankton community composition as revealed by structural equation modeling (SEM). We conclude that floodgates operation has a high risk for future eutrophication of downstream watershed, although it can reduce nitrogen content temporarily. Therefore, the environmental impacts of floodgates operation should be carefully evaluated before the floodwaters were discharged into downstream watershed.

Biosensors for wastewater monitoring: A review

Water pollution and habitat degradation are the cause of increasing water scarcity and decline in aquatic biodiversity. While the freshwater availability has been declining through past decades, water demand has continued to increase particularly in areas with arid and semi-arid climate. Monitoring of pollutants in wastewater effluents are critical to identifying water pollution area for treatment. Conventional detection methods are not effective in tracing multiple harmful components in wastewater due to their variability along different times and sources. Currently, the development of biosensing instruments attracted significant attention because of their high sensitivity, selectivity, reliability, simplicity, low-cost and real-time response. This paper provides a general overview on reported biosensors, which have been applied for the recognition of important organic chemicals, heavy metals, and microorganisms in dark waters. The significance and successes of nanotechnology in the field of biomolecular detection are also reviewed. The commercially available biosensors and their main challenges in wastewater monitoring are finally discussed.

Qualitative analysis of activated sludge using FT-IR technique

The ability to measure and control the composition of activated sludge is an important issue, aiming at evaluating the effectiveness of changes occurring in the sludge, what determines its usefulness to treat wastewater. In this research, diffuse reflectance infrared Fourier transform (FTIR–DRIFT) technique was used, which relies on measuring the reflectance of the powdered substance’s surface layer and capturing spectra in range of infrared wave. First, spectra correlation table of the substances mostly occurring in wastewater was developed to assess the main components of the tested samples of activated sludge. The simplest compounds containing functional groups characteristic for particular chemical classes were chosen: peptides (peptone and albumin), fats (glycerin and fatty acids), carbohydrates (glucose and sucrose), nitrogen compounds (NaNO₃ and NH₄SO₄), sulfur compounds (Na₂SO₄ and Na₂S₂O₃), silicate, etc. The spectra of those substances were captured and characteristic absorption bands for respective bonds in the function groups were assigned. Second, samples of activated sludge from lab-scale membrane bioreactors (MBRs), which purifies petroleum wastewater, were taken. Samples were properly prepared (lyophilization and homogenization) and their spectra were captured. During spectra analysis, previously developed correlation table was used. In obtained spectra of activated sludge, absorption bonds characteristic for amides, peptides, carbohydrates, fats, and aliphatic was identified. The spectra profile of the sludge sample from MBR feed with petroleum wastewater was slightly different from the control MBR sample’s spectra. Intensity of bands in the area characteristic for aliphatic compounds and phenols was clearly higher. This study proves the usefulness of FT-IR technique to observe changes in the chemical composition of activated sludge.

Investigating binding characteristics of cadmium and copper to DOM derived from compost and rice straw using EEM-PARAFAC combined with two-dimensional FTIR correlation analyses

The binding of Cd and Cu to dissolved organic matter (DOM) derived from compost (CP) and rice straw (ST) was studied through an approach combining parallel factor (PARAFAC) analysis and two-dimensional correlation spectroscopy (2DCOS). Both humic-like and protein-like substances have been observed in CP and ST. Comparing with the Cu, Cd exhibited a lower affinity to DOM, and the quenching curve of Cd failed to be fitted by the Ryan and Weber Model, indicating that the environmental risk caused by applying CP or ST to Cd-polluted soil should be considered. The stability constants (log K_M) of Cu ranged from 3.87 to 5.03, and a larger value was found in CP than those in ST. Protein-like component also showed obvious fluorescence quenching with heavy metals addition. Besides, in CP, phenol-OH and carboxyl showed the fastest response to Cd and Cu, respectively; however, in ST, amide group and phenol-OH displayed the fastest response to Cd and Cu, respectively. These results provide a more detailed knowledge of the interaction mechanism of heavy metals with DOM at the molecular level, which is of great significance for reasonable application of compost and rice straw and efficient control of heavy metal in farmland soil.

Novel insights into the coagulation process for pharmaceutical wastewater treatment with fluorescence EEMs-PARAFAC

In this study, coagulation process was applied to treat the effluent of pharmaceutical wastewater using polymeric ferric sulfate as a coagulant. Three-dimensional excitation-emission matrix fluorescence spectroscopy coupled with parallel factor analysis (EEMs-PARAFAC) was applied to investigate the fluorescent characteristics of dissolved organic matter (DOM) from pharmaceutical wastewater and the reduction of contaminant and fluorescent variations in the coagulation process. It shows that coagulation was effective to remove contaminants in the effluent of pharmaceutical wastewater, and the optimum coagulate dosage was 0.5 g/L, where the removal efficiency of total organic matter (TOC), UV₂₅₄, turbidity and NH₄⁺-N were achieved 44.2%, 43.3%, 87.0% and 10.27%, respectively. Five fluorescence components were identified by EEMs-PARAFAC, including one fulvic-like component (C1), one xenobiotic-like component (C2), two humic-like components (C3 and C5) and one protein-like component (C4); DOM of pharmaceutical wastewater was dominated by C3, C4 and C2. Under the optimum coagulation condition, the decreasing order of removal efficiencies was C5 (49.92%), C3 (40.95%), C4 (10.58%), C2 (9.68%) and C1 (5.05%). Principal component analysis (PCA) showed C3, C5 had remarkable correlations with TOC and UV₂₅₄, suggesting that C3 and C5 may be a good indicator for the reduction of TOC and UV₂₅₄. PCA indicated that the EEM-PARAFAC could be successfully applied to the evaluation of the coagulation efficiency for pharmaceutical wastewater treatment.

Process model economics of xanthan production from confectionery industry wastewaters

In this research a process and cost model for a xanthan production facility was developed using process simulation software (SuperPro Designer^®). This work represents a novelty in the field for two reasons. One is that xanthan gum has been produced from several wastes but never from wastewaters from confectionery industries. The other more important is that the aforementioned software, which in intended exclusively for bioprocesses, is used for generating a base case, i.e. starting point for transferring the technology to industrial scales. Previously acquired experimental knowledge about using confectionery wastewaters from five different factories as substitutes for commercially used cultivation medium have been incorporated into the process model in order to obtain an economic viability of implementing such substrates. A lower initial sugar content in the medium based on wastewater (28.41 g/L) compared to the synthetic medium (30.00 g/L) gave a lower xanthan content at the end of cultivation (23.98 and 26.27 g/L, respectively). Although this resulted in somewhat poorer economic parameters, they were still in the range of being an investment of interest. Also the possibility of utilizing a cheap resource (waste) and reducing pollution that would result from its disposal has a positive effect on the environment.

Spectroscopic descriptors for dynamic changes of soluble microbial products from activated sludge at different biomass growth phases under prolonged starvation

In this study, the spectroscopic indices of soluble microbial products (SMP) were explored using absorption and fluorescence spectroscopy to identify different distinctive biomass growth phases (i.e., exponential phase, pseudo-endogenous phase, and endogenous phase) and to describe the microbial activity of activated sludge in a batch type bioreactor under prolonged starvation. The optical descriptors, including UV absorption at 254 nm (UVA254), spectral slope, absorbance slope index (ASI), biological index (BIX), humification index (HIX), and the ratio of tryptophan-like to humic-like components (C1/C2), were examined to describe the dynamic changes in SMP. These indices were mostly associated with dissolved organic carbon (DOC) of SMPs and specific oxygen uptake rate (SOUR). Among those, ASI was the most strongly correlated with the SOUR data for the pseudo-endogenous and the endogenous periods. Although the three microbial phases were well discriminated using the spectral slope, BIX, and the C1/C2 ratio, the C1/C2 ratio can be suggested as the most preferable indicator as it can also trace the changes of the relative abundance of proteins to humic-like substances in SMPs. The suggested spectroscopic descriptors were reasonably explained by the general trends of decreased large-sized biopolymer fractions (e.g., proteins) and increased humic substrates (HS) with starvation time, which were detected by size exclusion chromatography. This study provides a novel insight into the strong potential of using optical descriptors to easily probe microbial status in biological treatment systems.

Dynamic changes of dissolved organic matter in membrane bioreactors at different organic loading rates: Evidence from spectroscopic and chromatographic methods

Excitation emission matrix-parallel factor analysis (EEM-PARAFAC) and size exclusion chromatography (SEC) were utilized to explore the dynamics in extracellular polymeric substances (EPS), soluble microbial products (SMP), and effluent for the membrane bioreactors at two different organic loading rates (OLRs). Combination of three different fluorescent components explained the compositional changes of dissolved organic matter. The lower OLR resulted in a higher production of tryptophan-like component (C1) in EPS, while the opposite trends were found for the other two components (humic-like C2 and tyrosine-like C3), signifying the role of C1 in the endogenous condition. Larger sized molecules were more greatly produced in EPS at the lower OLR. Meanwhile, all the size fractions of SMP were more abundant at the higher OLR particular for the early phase of the operation. Irrespective of the OLR, the higher degrees of the membrane retention were found for relatively large sized and protein-like molecules.

Detection of Androgenic-Mutagenic Compounds and Potential Autochthonous Bacterial Communities during In Situ Bioremediation of Post-methanated Distillery Sludge

Sugarcane-molasses-based post-methanated distillery waste is well known for its toxicity, causing adverse effects on aquatic flora and fauna. Here, it has been demonstrated that there is an abundant mixture of androgenic and mutagenic compounds both in distillery sludge and leachate. Gas chromatography-mass spectrometry (GC-MS) analysis showed dodecanoic acid, octadecanoic acid, n-pentadecanoic acid, hexadecanoic acid, β-sitosterol, stigmasterol, β-sitosterol trimethyl ether, heptacosane, dotriacontane, lanosta-8, 24-dien-3-one, 1-methylene-3-methyl butanol, 1-phenyl-1-propanol, 5-methyl-2-(1-methylethyl) cyclohexanol, and 2-ethylthio-10-hydroxy-9-methoxy-1,4 anthraquinone as major organic pollutants along with heavy metals (all mg kg^-1): Fe (2403), Zn (210.15), Mn (126.30, Cu (73.62), Cr (21.825), Pb (16.33) and Ni (13.425). In a simultaneous analysis of bacterial communities using the restriction fragment length polymorphism (RFLP) method the dominance of Bacillus sp. followed by Enterococcus sp. as autochthonous bacterial communities growing in this extremely toxic environment was shown, indicating a primary community for bioremediation. A toxicity evaluation showed a reduction of toxicity in degraded samples of sludge and leachate, confirming the role of autochthonous bacterial communities in the bioremediation of distillery waste in situ.

Lipid biomarkers and spectroscopic indices for identifying organic matter sources in aquatic environments: A review

Understanding the dynamics of organic matter (OM) and the roles in global and local carbon cycles is challenging to the fields of environmental sciences and biogeochemistry. The accurate identification of OM is an essential element to achieve this goal. Lipids, due to their ubiquitous presence and diagenetic and chemical stability, have long and successfully been used as molecular makers in assessing the sources and the fate of OM in natural environments. In parallel, optical properties of dissolved organic matter (DOM) have been suggested as efficient tools in tracing OM sources. In this review, three representative lipid biomarkers and several common spectroscopic indices were compared for their capabilities to identify OM sources in various aquatic environments. Spectroscopic indices present various benefits in term of the high sensitivity, easy and rapid analysis, and a low cost, providing reliable information on major sources (i.e., autochthonous, allochthonous and anthropogenic) of DOM in given systems investigated. However, for further understanding the associated biogeochemistry (e.g., diagenetic changes in sources), using biomarkers is preferable due to their abilities to identify a wide spectrum of different sources simultaneously as well as their high resolution for mixed OM sources. Thus, a complementary use of both tools is highly recommended for accurately tracking OM sources and the dynamics in aquatic systems, particularly in a watershed affected by multiple sources. Nevertheless, future studies need to be carried out (1) to refine the accuracy of the source assignments in a wide range of settings along with the development of an extensive database encompassing various sources, environmental factors, and geographical locations and (2) to understand how biogeochemical processes reflect the biomarkers and the spectroscopic indices used.

PARAFAC analysis of IBIL spectra from silver ion exchanged glasses

In this work we present for the first time an application of PARAllel FACtor (PARAFAC) analysis to the investigation of Ion Beam Induced Luminescence (IBIL) spectra of Ag⁺↔Na⁺ ion exchanged silicate glasses, in order to check the possibility to obtain additional information on the formation of silver aggregates under ion irradiation by a proper statistical rearrangement of experimental spectra. We decomposed the data by PARAFAC taking into account both IBIL emission features and their evolution as a function of the time. Shape and trend under irradiation of the extracted components were correlated to silver concentration and aggregates in the investigated systems. Strength and weakness of this statistical approach applied to IBIL spectra recorded as a function of time were evidenced and discussed.

Fluorescence peak integration ratio IC:IT as a new potential indicator tracing the compositional changes in chromophoric dissolved organic matter

The present study demonstrates that the ratio of fluorescence integration of peak C to peak T (I_C:I_T) can be used as an indicator tracing the compositional dynamics of chromophoric dissolved organic matter (CDOM). CDOM absorption and fluorescence spectroscopy and stable isotope δ¹³C were determined on a seasonal basis in seventeen Chinese inland waters as well as in a series of mixing and photodegradation experiments in the lab. A strong positive linear correlation was recorded between I_C:I_T and the ratio of terrestrial humic-like C1 to tryptophan-like C4 (C1:C4) derived by parallel factor analysis. The r² for the linear fitting between I_C:I_T and C1:C4 (r²=0.80) was notably higher than between C1:C4 and other indices tested, including the ratio of CDOM absorption at 250nm to 365nm, i.e. a(250):a(365) (r²=0.09), spectral slope (S_275-295) (r²=0.26), spectral slope ratio (S_R) (r²=0.31), the humification index (HIX) (r²=0.47), the recent autochthonous biological contribution index (BIX) (r²=0.27), and a fluorescence index (FI₃₇₀) (r²=0.07). I_C:I_T exhibited larger variability than the remaining six indices and a closer correlation with stable isotope δ¹³C than that observed for a(250):a(365), S_275-295, S_R, FI₃₇₀, and BIX during field campaigns. Confirming our field observations, significant correlations were recorded between I_C:I_T and the remaining six indices, and I_C:I_T also demonstrated notably larger variability than the six other indices during our wastewater addition experiment. Compared with HIX, eutrophic water addition and photobleaching substantially decreased I_C:I_T but had no pronounced effect on a(250):a(365), S_275-297, S_R, FI₃₇₀, and BIX, further suggesting that I_C:I_T is the most efficient indicator of the CDOM compositional dynamics.

The partitioning behavior of persistent toxicant organic contaminants in eutrophic sediments: Coefficients and effects of fluorescent organic matter and particle size

In the shallow lakes, the partitioning of organic contaminants into the water phase from the solid phase might pose a potential hazard to both benthic and planktonic organisms, which would further damage aquatic ecosystems. This study determined the concentrations of polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), and phthalate esters (PAEs) in both the sediment and the pore water from Lake Chaohu and calculated the sediment - pore water partition coefficient (K_D) and the organic carbon normalized sediment - pore water partition coefficient (K_OC), and explored the effects of particle size, organic matter content, and parallel factor fluorescent organic matter (PARAFAC-FOM) on K_D. The results showed that log K_D values of PAHs (2.61-3.94) and OCPs (1.75-3.05) were significantly lower than that of PAEs (4.13-5.05) (p < 0.05). The chemicals were ranked by log K_OC as follows: PAEs (6.05-6.94) > PAHs (4.61-5.86) > OCPs (3.62-4.97). A modified MCI model can predict K_OC values in a range of log 1.5 at a higher frequency, especially for PAEs. The significantly positive correlation between K_OC and the octanol - water partition coefficient (K_OW) were observed for PAHs and OCPs. However, significant correlation was found for PAEs only when excluding PAEs with lower K_OW. Sediments with smaller particle sizes (clay and silt) and their organic matter would affect distributions of PAHs and OCPs between the sediment and the pore water. Protein-like fluorescent organic matter (C2) was associated with the K_D of PAEs. Furthermore, the partitioning of PARAFAC-FOM between the sediment and the pore water could potentially affect the distribution of organic pollutants. The partitioning mechanism of PAEs between the sediment and the pore water might be different from that of PAHs and OCPs, as indicated by their associations with influencing factors and K_OW.

Dissolved organic carbon content and characteristics in relation to carbon dioxide partial pressure across Poyang Lake wetlands and adjacent aquatic systems in the Changjiang basin

Dissolved organic carbon (DOC) plays diverse roles in carbon biogeochemical cycles. Here, we explored the link between DOC and pCO₂ using high-performance size-exclusion chromatography (HPSEC) with UV₂₅₄ detection and excitation emission matrix (EEM) fluorescence spectroscopy to determine the molecular weight distribution (MW) and the spectral characteristics of DOC, respectively. The relationship between DOC and pCO₂ was investigated in the Poyang Lake wetlands and their adjacent aquatic systems. The results indicated significant spatial variation in the DOC concentrations, MW distributions, and pCO₂. The DOC concentration was higher in the wetlands than in the rivers and lakes. pCO₂ was high in wetlands in which the dominant vegetation was Phragmites australis, whereas it was low in wetlands in which Carex tristachya was the dominant species. DOC was divided into five fractions according to MW, as follows: super-low MW (SLMW, <1 kDa); low MW (LMW, 1-2.5 kDa); intermediate MW (IMW, 2.5-3.5 kDa); high MW (HMW, 3.5-6 kDa); and super-high MW (SMW, > 40 kDa). Rivers contained high proportions of HMW and extremely low amounts of SLMW, whereas wetlands had relatively high proportions of SLMW. The proportion of SMW (SMW_p) was particularly high in wetlands. We found that pCO₂ significantly positively correlated with the proportion of IMW, and significantly negatively correlated with SMW_p. These data improve our understanding of the MW of bioavailable DOC and its conversion to CO₂. The present results demonstrate that both the content and characteristics of DOC significantly affect pCO₂. pCO₂ and DOC must be studied further to help understanding the role of the wetland on the regional CO₂ budget.

Changes in fluorescent dissolved organic matter upon interaction with anionic surfactant as revealed by EEM-PARAFAC and two dimensional correlation spectroscopy

Surfactants are present in significant amounts in both domestic and industrial wastewater, which may interact with dissolved organic matter (DOM). The present study investigated the interactions of sodium dodecyl sulfate (SDS) with three different DOM solutions, including bovine serum albumin (BSA), humic acid (HA), and the mixture of the two (BSA-HA), based on two advanced spectroscopic tools: excitation emission matrix (EEM) combined with parallel factor analysis (EEM-PARAFAC) and two dimensional correlation spectroscopy (2D-COS). The responses of two protein-like components to the addition of SDS differed depending the presence and the absence of HA. A decreasing and an increasing trend was observed for tryptophan-like (C1) and tyrosine-like (C2) components, respectively, in the BSA solution, while the BSA-HA mixture exhibited increasing fluorescence trends for both protein-like components. The conflicting results suggest that HA plays a secondary role in the protein-SDS interactions. No interaction between the SDS and humic-like component was found. 2D-COS combined with fluorescence spectra demonstrated that the protein-SDS interaction occurred on the order of C2 > C1 for the BSA solution but C1 > C2 for the BSA-HA mixture. Analyses of Scatchard plots confirmed the sequential order interpreted from 2D-COS, showing consistent trends in the binding constants. However, the presence of HA affected the protein-SDS interactions in different manners for C1 and C2, enhancing and reducing the binding constants, respectively. Circular dichroism spectra confirmed the occurrence of conformational changes in BSA with SDS. EEM-PARAFAC and 2D-COS successfully explained different interactions of surfactant with protein-like components in the presence of HA.

Characterizing fluorescent dissolved organic matter in a membrane bioreactor via excitation-emission matrix combined with parallel factor analysis

In this study, we successfully tracked the dynamic changes in different constitutes of bound extracellular polymeric substances (bEPS), soluble microbial products (SMP), and permeate during the operation of bench scale membrane bioreactors (MBRs) via fluorescence excitation-emission matrix (EEM) combined with parallel factor analysis (PARAFAC). Three fluorescent groups were identified, including two protein-like (tryptophan-like C1 and tyrosine-like C2) and one microbial humic-like components (C3). In bEPS, protein-like components were consistently more dominant than C3 during the MBR operation, while their relative abundance in SMP depended on aeration intensities. C1 of bEPS exhibited a linear correlation (R(2)=0.738; p<0.01) with bEPS amounts in sludge, and C2 was closely related to the stability of sludge. The protein-like components were more greatly responsible for membrane fouling. Our study suggests that EEM-PARAFAC can be a promising monitoring tool to provide further insight into process evaluation and membrane fouling during MBR operation.

Fluorescence spectroscopy for wastewater monitoring: A review

Wastewater quality is usually assessed using physical, chemical and microbiological tests, which are not suitable for online monitoring, provide unreliable results, or use hazardous chemicals. Hence, there is an urgent need to find a rapid and effective method for the evaluation of water quality in natural and engineered systems and for providing an early warning of pollution events. Fluorescence spectroscopy has been shown to be a valuable technique to characterize and monitor wastewater in surface waters for tracking sources of pollution, and in treatment works for process control and optimization. This paper reviews the current progress in applying fluorescence to assess wastewater quality. Studies have shown that, in general, wastewater presents higher fluorescence intensity compared to natural waters for the components associated with peak T (living and dead cellular material and their exudates) and peak C (microbially reprocessed organic matter). Furthermore, peak T fluorescence is significantly reduced after the biological treatment process and peak C is almost completely removed after the chlorination and reverse osmosis stages. Thus, simple fluorometers with appropriate wavelength selectivity, particularly for peaks T and C could be used for online monitoring in wastewater treatment works. This review also shows that care should be taken in any attempt to identify wastewater pollution sources due to potential overlapping fluorophores. Correlations between fluorescence intensity and water quality parameters such as biochemical oxygen demand (BOD) and total organic carbon (TOC) have been developed and dilution of samples, typically up to ×10, has been shown to be useful to limit inner filter effect. It has been concluded that the following research gaps need to be filled: lack of studies on the on-line application of fluorescence spectroscopy in wastewater treatment works and lack of data processing tools suitable for rapid correction and extraction of data contained in fluorescence excitation-emission matrices (EEMs) for real-time studies.

Anthropogenic signature of sediment organic matter probed by UV-Visible and fluorescence spectroscopy and the association with heavy metal enrichment

Sediment organic matter (SOM) was extracted in an alkaline solution from 43 stream sediments in order to explore the anthropogenic signatures. The SOM spectroscopic characteristics including excitation-emission matrix (EEM)-parallel factor analysis (PARAFAC) were compared for five sampling site groups classified by the anthropogenic variables of land use, population density, the loadings of organics and nutrients, and metal enrichment. The conventional spectroscopic characteristics including specific UV absorbance, absorbance ratio, and humification index did not properly discriminate among the different cluster groups except in the case of metal enrichment. Of the four decomposed PARAFAC components, humic-like and tryptophan-like fluorescence responded negatively and positively, respectively, to increasing degrees of the anthropogenic variables except for land use. The anthropogenic enrichment of heavy metals was positively associated with the abundance of tryptophan-like component. In contrast, humic-like component, known to be mostly responsible for metal binding, exhibited a decreasing trend corresponding with metal enrichment. These conflicting trends can be attributed to the overwhelmed effects of the coupled discharges of heavy metals and organic pollutants into sediments. Our study suggests that the PARAFAC components can be used as functional signatures to probe the anthropogenic influences on sediments.

Differences in spectroscopic characteristics between dissolved and particulate organic matters in sediments: Insight into distribution behavior of sediment organic matter

In this study, we examined the distribution behavior of sediment organic matter (SOM) between dissolved and particulate phases and the potential influencing factors by comparing the spectroscopic features of pore water organic matter (PWOM) and alkaline-extractable organic matter (AEOM) of river sediments. The characteristics of SOM were described by several selected spectral indicators and fluorescence excitation emission matrix (EEM)-parallel factor analysis (PARAFAC). The spectral indicators showed that larger sized SOM molecules with a higher aromatic content were more enriched in sediment particles than in pore water. The relative ratios of humification index between dissolved and particulate phases revealed that the SOM constituents with a higher degree of structural condensation were preferentially distributed onto sediment particles. EEM-PARAFAC demonstrated different distribution behaviors of protein-like (tyrosine-like and tryptophan-like) and humic-like substances in sediments. The relative abundance of tyrosine-like component was much higher in PWOM than in AEOM, whereas the other three components tended to be more abundant in AEOM. The predominant presence of tyrosine-like component suggests its potential operation as a discriminant indicator between PWOM and AEOM. Spearman correlations and non-metric multidimensional scaling further revealed that distribution of protein-like components onto sediment particles might be associated with reductive environments, aluminum minerals, and anthropogenic activities of upstream watersheds. This study demonstrated a successful application of using EEM-PARAFAC to examine the distribution behavior of different SOM constitutes between dissolved and solid phases.

Using multiple combined analytical techniques to characterize water extractable organic nitrogen from Lake Erhai sediment

In this study, UV-vis absorbance, fluorescence, and FT-IR spectroscopy were combined to characterize the components and structure of the water extractable organic nitrogen (WEON) in Lake Erhai sediment. Lake Erhai sediment WEON comprised predominantly high molecular weight WEON, with the fraction with a molecular weight>1kDa accounting for 87.7% of the total. It was mainly composed of humic acid-like substances, with fewer simple aromatic proteins. Large amounts of aliphatic and amide compounds were detected by IR in the sediments. There were more polymerizable aromatic rings and carbonyl, carboxyl, hydroxyl, and ester compounds in the high molecular weight WEON than in the low molecular weight WEON. Additionally, fluorescence regional integration results implied that the ratio PIII+V,n/PI+II+IV,n can be indirectly taken as an indicator for WEON content in Erhai sediments. Furthermore, the composition and structural characteristics of the WEON were found to be closely related with their properties in the sediment. The large amount of aliphatic compounds in the sediment as well as the relatively high humification and aromatic degree in high molecular weight WEON, stabilizes the WEON in Lake Erhai sediment. Compared with other lake sediments of different trophic statues (such as Lake Dianchi, Lake Poyang, Lake Taihu and Lake Donghu), Erhai sediment exhibited a higher degree of humification, which benefited for reducing sediment WEON releasing risk. And it can be regarded as the reason why the nutrient content in Erhai sediment is very high, but its water quality is still good.