Excitation-emission Matrix Fluorescence Spectroscopy Research Articles

Insight into removals of PARAFAC components from dissolved and particulate organic matter in wastewater treatment process by two-dimensional correlation and structure equation modeling

BackgroundMost particulate organic matter (POM) cannot be directly degraded in the conventional wastewater treatment, which should be transformed into dissolved organic matter (DOM) through a hydrolysis process. However, non-hydrolyzed POM in the biological treatment can limit treated efficiencies for the wastewater treatment plants (WWTPs) facilities. Hence an operational tool is indispensable for insight into removals of DOM and POM factions in the WWTP. In this study, excitation-emission matrix fluorescence spectroscopy (EEM) combined parallel factor analysis (PARAFAC), two-dimensional correlation (2D-COS) and structural equation modeling (SEM) was employed to evaluate removals of DOM and POM in a wastewater treatment plant.ResultsFour fluorescence components were identified in DOM and POM substances from the WWTP by EEM combined with PARAFAC, i.e., tyrosine-like (TYLF), tryptophan-like (TRLF), microbial byproduct-like (MBLF), and fulvic acid-like (FALF). In A2/O process, the TYLF and TRLF of DOM were removed to a larger extent than those of MBLF and FALF in anaerobic tank, while TYLF and MBLF of POM were removed to a great extent than those of TRLF and FALF in primary sedimentation and aerobic tanks. By the 2D-COS, a decreasing variation order of DOM fractions in the wastewater treatment process was UV-FALF → MBLF2 → Vis-FALF → TRLF → TYLF, while the decreasing order of POM fractions was Vis-FALF → UV-FALF → MBLF2 → TYLF → MBLF1 → TRLF. SEM revealed that TRLF and TYLF of DOM were degraded by anaerobic microorganism, and TRLF could be transformed partially into FALF. However, TRFL and TYLF of POM were discomposed by aerobic microorganism.ConclusionsThe 2D-COS and SEM can be practicable tools as EEM-PARAFAC for monitoring DOM and POM in the WWTP. The study could present a theoretical support to improving the retrofit of WWTP and formulating emission standards for organic pollutants.

Fast identification of fluorescent components in three-dimensional excitation-emission matrix fluorescence spectra via deep learning

Three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy has been widely applied to detect the fluorescent components in samples from natural water bodies to wastewater treatment processes. Data interpretation methods such as parallel factor analysis (PARAFAC) are required to decompose the overlapped fluorescent signals in the 3D-EEM spectra. However, strict requirements of data and complicated procedures of the PARAFAC limit the online monitoring and analysis of samples. Here we develop a fast fluorescent identification network (FFI-Net) model based on the deep learning approach to fast predict the numbers and maps of fluorescent components by simply inputting a single 3D-EEM spectrum. Two types of convolutional neural networks (CNN) are trained to classify the numbers of fluorescent components with an accuracy of 0.956 and predict the maps of fluorescent components with the min mean absolute error of 8.9 × 10-4. We demonstrate that the accuracy of the FFI-Net model will be further improved when more 3D-EEM data are available as a training dataset. Meanwhile, a user-friendly interface is designed to facilitate practical applications. Our approach gives a robust way to overcome the shortage of the PARAFAC and provides a new platform for online analysis of the fluorescent components in water samples.

Excitation-emission matrix fluorescence spectroscopy combined with chemometrics methods for rapid identification and quantification of adulteration in Atractylodes macrocephala Koidz

Atractylodes macrocephala Koidz. (AMK) is a perennial herb with various medical functions and has been wildly used in ethno-medical system. It is common that unscrupulous merchants try to make huge profits by adulterating AMK powder with other cheaper or lower quality edible powder substance due to the growing shortage of genuine medicinal materials resources and the rising cost. Therefore, this work proposed excitation-emission matrix fluorescence spectroscopy combined with chemometrics methods for the rapid identification and quantification of AMK adulteration with other types of powder. Partial least squares discriminant analysis (PLS-DA), k-nearest neighbor (kNN) and random forest (RF) model were used for the classification of pure AMK and specific type powder adulterated AMK. The correct classification rates for test sample were 93.0%, 95.0% and 100% for kNN, PLS-DA and RF, respectively. And RF could accurately classify 11 holdout adulterated AMK samples, even when the adulteration level was only 10%. Furthermore, the PLS regression model was used for the prediction of adulteration level in AMK. The results proved that the classification and regression models were reliable.

Mechanistic study of antimonate reduction by Escherichia coli W3110

Microbial-assisted antimonate [Sb(V)] reduction immobilizes this redox-sensitive metalloid in the subsurface. Most indigenous aerobes in antimony (Sb)-contaminated areas do not contain Sb(V)-reducing genes but can resist high levels of Sb(V) threat. Herein, to unravel the mechanisms of Sb(V) resistance by aerobes, we used Escherichia coli W3110 as a model aerobe and incubated it with 10 μM Sb(V). We found that strain W3110, without known Sb(V)-reducing genes, was able to reduce Sb(V) to Sb(III). Our transcriptome analysis and reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) results show that the Sb(V) threat at the 10 μM level had a negligible effect on the gene expression of strain W3110. In vitro incubation experiments further indicate that Sb(V) reduction was attributable to extracellular polymeric substances (EPS). Moreover, the three-dimensional excitation-emission matrix fluorescence spectroscopy reveals that the tryptophan-like components in EPS were involved in Sb(V) binding as evidenced by its weakened fluorescence intensity upon Sb(V) addition. The FTIR and XPS analyses indicate that hemiacetal and amide groups in EPS contributed to the reduction of Sb(V). Preculture with 10 μM Sb(V) did not exhibit a significant difference in Sb(V)-reducing capacity, suggesting that Sb(V) stress probably did not stimulate EPS secretion of W3110. Our results highlight the importance of EPS as the first line of defense against toxins, especially for those bacteria without such functional genes.

Resolving the Tribo-catalytic reaction mechanism for biochar regulated Zinc Oxide and its application in protein transformation

The utilization of mechanical energy to control water pollutants under dark conditions is currently a point of study focus. Herein, biochar -zinc oxide (BC-ZnO) composites with various structures were synthesized by co-pyrolysis of cotton and ZnO at different temperature and used for tribo-catalytic reaction. The introduction of BC can improve charge transmission and separation efficiency. Ultraviolet photoelectron spectra (UPS) and density functional theory (DFT) calculation prove the addition of BC can reduce work function of ZnO, and enhance its electron-donating ability. Specially, suitable adsorption amount is the key factor to improve the tribo-catalytic performance. When the pyrolysis temperature is 600 °C, BC-ZnO has the best degradation efficiency, which can degrade 90% Rhodamine B (RhB) in 75 min, while ZnO can degrade only 38%. On this basis, using bovine serum albumin (BSA) as a model, the effect of tribo-catalytic reaction on controlling proteins in water was studied by fluorescence excitation-emission matrix spectroscopy (3D EEM) and infrared microscope, and the transformation of proteins was further analyzed. This study provides a new strategy to improve the tribo-catalytic performance of ZnO, and explores its application prospects of biological wastewater control.

Determination of four pesticides in honeysuckle by Echo State Network based on excitation-emission matrix fluorescence spectroscopy technique

Determination of four pesticides in honeysuckle by Echo State Network based on excitation-emission matrix fluorescence spectroscopy technique

Removal of natural organic matter in full-scale conventional and advanced water treatment plants: Assimilable organic carbon and its precursors

This study aimed to investigate the performance of three full-scale long-time water treatment plants with influent from Taihu Lake for the removal of natural organic matter (NOM) and assimilable organic carbon (AOC), emphasizing on the processes of pre- and post-ozonation and biological activated carbon filtration (BACF). High-performance size exclusion chromatography (HPSEC) separation, hydrophilicity/hydrophobicity resin fractionation and excitation-emission matrix (EEM) fluorescence spectroscopy were applied to determine NOM fraction variation in purification processes and their relationships with AOC. The results indicated that NOM fractions with high hydrophilicity (NHPI) and lower molecular weight (1 kDa - 10 kDa) likely contributed to the majority of AOC. The advanced water treatment processes behaved negative removals of AOC since the BACF with long-time operation introduced large amounts of AOC precursors and could cause drastic rebound of AOC upon chlorination disinfection. Finally, during exposure to ozone, the formation rate of AOC showed a linear relationship with UV254 and total fluorescence intensity (TFI) and each regional fluorescence intensity (RFI) with slight interference by the presence of particulate organic matter (POM). This study provides useful information for variation of NOM and its associated bio-availability during conventional and advanced processes in full-scale water treatment plants.

Highly efficient degradation of bisphenol A with persulfate activated by vacuum-ultraviolet/ultraviolet light (VUV/UV): Experiments and theoretical calculations

Enhanced degradation and mineralization of bisphenol A (BPA) known as a typical endocrine disrupting chemical (EDC) in VUV/UV-activated persulfate process (VUV/UV/PS) were investigated. The pseudo-first-order reaction rate constant and total organic carbon (TOC) removal ratio of BPA in this process were 1.75 and 1.70 times of those in UV-activated PS process (UV/PS), respectively. The excitation-emission matrix (EEM) fluorescence spectroscopy of reaction solution at different time clearly indicated the change of BPA and its intermediates during the reaction process. The significant interactive effects of three important operating parameters including the initial concentration of BPA, the initial concentration of PS and the initial pH of solution on BPA degradation efficiency were evaluated and optimized by using central composite design (CCD) of response surface methodology (RSM). At the optimum experimental conditions (i.e., 30 mg/L BPA, 1.25 mM PS and at pH 9), the maximum degradation efficiency of BPA at 2 min was up to 92.2%. Sulfate radicals (SO4•-) were the dominant reaction activate species for BPA degradation. Based on the analysis of liquid chromatograph-mass spectrometry (LC/MS), gas chromatograph-mass spectrometry (GC/MS) and Fourier transform infrared spectroscopy (FTIR) of the reaction mixture and density function theory (DFT) calculation, it was proposed that BPA degradation was mainly caused by SO4•--induced hydroxylation reaction, HO• addition and β-scission of C–C bond. Moreover, the electrical energy consumption of BPA degradation in VUV/UV/PS process was less. Additionally, BPA in real water samples could also be effectively degraded at lower treatment costs in this process. Hence, the present study demonstrates that VUV/UV activation of PS is a highly efficient and economical alternative to remove BPA in real water matrices..

Spectroscopic characterization of dissolved organic matter from macroalgae Ulva pertusa decomposition and its binding behaviors with Cu(II)

Dissolved organic matter (DOM) from macroalgae is regarded a crucial source of autochthonous DOM in coastal ocean. In the present study, the characteristics of DOM from the macroalgae Ulva pertusa decomposition (U. pertusa-DOM) and its binding behaviors with Cu(II) using multiple spectroscopic techniques and chemometric analyses. The labile U. pertusa-DOM could be consumed and transformed by microorganisms. The absorption spectroscopic descriptors indicate that the hydrophobicity, aromaticity, and molecular weight of the U. pertusa-DOM increase during the 27-day incubation period. Fluorescence excitation–emission matrix spectroscopy combined with parallel factor analysis suggests that the relative abundance of the protein-like component (C1) (96.10–84.96%) sequentially decreases, whereas the humic-like components (C2) (2.16–9.73%) and (C3) (1.75–5.31%) in the U. pertusa-DOM increase with the U. pertusa decomposition. The Cu(II) binding properties of the U. pertusa-DOM are dependent on the decomposition time. The order of the conditional stability constant (logKM) is C2 > C1 > C3. The complexation capacity (f) of C1 is higher than those of C2 and C3 at a specific time. Synchronous fluorescence spectroscopy coupled with two-dimensional correlation spectroscopy reveals that the microbial degradation could accelerate the Cu(II) binding to humic-like fractions in the U. pertusa-DOM. These findings will help us better understand the biogeochemical behaviors of macroalgal DOM and heavy metal in coastal ecosystems.

Deciphering dissolved organic matter from freshwater aquaculture ponds in Eastern China based on optical and molecular signatures

Aquaculture makes great contribution to global food production. The aquaculture capture scale of China was far ahead of other countries in the world. Despite the potential role of dissolved organic matter (DOM) to affect fish growth and ecological cycle, the characterization of DOM in aquaculture industry was poorly understood. In this study, fluorescence excitation-emission matrix (EEM) spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) were conducted to decipher the optical and molecular signatures of DOM in freshwater aquaculture ponds in Eastern China. The EEM dataset was decomposed by parallel factor analysis (PARAFAC). Three main components including humic/fulvic acid-like (C1 and C3), tryptophan-like (C2) and tyrosine-like substances (C3) were obtained. FT-ICR-MS identified DOM composition at molecular level. In terms of formula classes, the dominant CHO species were followed by CHON and CHOS groups. According to compound classification criteria, the key components of lignins, tannins, proteins and lipids illustrated the primary source from terrestrial sediment, feeding doses and stocked creatures, implying the great influence by the land-based aquaculture ponds. Typical spectral indexes such as humification index (HIX), biological index (BIX) and fluorescence index (FI) consistently reflected the lower humification degree of DOM and greater contribution from protein-like sources. Furthermore, to utilize readily available spectral indexes to predict the time-consuming molecular properties, redundancy analysis and the pairwise correlation analysis was carried out to prove that two spectral indexes (E2:E3 and BIX) were negatively associated with four molecular formula derived parameters (O/Cwa, AImodwa, DBEwa and NOSCwa). The findings expanded our understanding of aquaculture DOM evolved in environmental chemistry.

Accelerated humification and alteration of microbial communities by distillers' grains addition during rice straw composting

This research explored the influence of distillers' grains amendment on the humification performance and microbial communities during rice straw composting. The composition of dissolved organic matter and maturity index were analyzed by the fluorescence excitation emission matrix spectroscopy and parallel factor analysis. High-throughput sequencing and redundancy analysis were employed for revealing the structure dynamics for microbial community and their shaping factors, respectively. Results indicated that addition of distillers' grains effectively increased the microbial activity, which was beneficial to the organic matter degradation and nitrogen conservation. Microbial community structures were significantly changed with different amendment strategies. Nitrate, water soluble carbon, organic matter, ammonium were the key parameters influencing the variation of bacterial community in different treatments. Water soluble carbon significantly affected the dominant fungal community dynamics. These results showed that addition of distillers' grains effectively improved the nutritional status and changed the microbial communities during rice straw composting.

Probing changes in humus chemical characteristics in response to biochar addition and varying bulking agents during composting: A holistic multi-evidence-based approach

Despite the various benefits of humus, the changes in its chemical characteristics during composting in response to biochar addition and varying bulking agents remain to be further explored. In this study, three treatments were conducted, in which swine manure, bulking agent, and biochar were mixed at ratios of 4:1:0, 8:1:0, and 8:1:1. Fourier transform infrared spectroscopy (FTIR), carbon nuclear magnetic resonance spectroscopy (13C-NMR), three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM), and near-edge X-ray absorption fine structure (NEXAFS) were employed to characterize the chemical and structural properties of humus from multiple perspectives. The 3D-EEM spectra in this study showed a larger increase in humic acids (HAs) content (56%) and HAs to fulvic acids ratio (128%) during composting, indicating stronger humification in biochar-amended treatment. FTIR, 13C-NMR, and NEXAFS all confirmed the essential properties of HA as the core agronomic functional substance with rich aromatic and carboxyl groups, and that its aromaticity increased gradually during composting. In addition, 13C-NMR demonstrated that biochar addition and a relatively higher bulking agent ratio aided an increase in the carboxyl C proportion in HA after composting. In particular, NEXAFS revealed that biochar addition promoted the diversification of C, N, and O species in HA, with the emergence of quinone C and O-alkyl C as the main representatives. This work suggests that biochar addition and a relatively high bulking agent ratio could enhance humification and improve the agronomic function of humus.

Performance and microbial characteristics of a novel pilot-scale tubing biological contact oxidation reactor for rural drinking water

Drinking water treatment under rural conditions often require compactness and portability. To address this, the present study developed a pilot-scale helical tubular biological contact oxidation (BCO) reactor filled with annular porous biofilm carriers (fillers). To determine the drinking water treatment efficiency and microbial characteristics, the system was investigated for 212 days at (24.1 ± 3.4) °C under different flow rates (1.86 L · h−1, 3.72 L · h−1, and 7.2 L · h−1) to treat simulated rural drinking water. The results show that (62.7 ± 9.3) % of ammonium (NH4+-N) and (19.5 ± 5.4) % of UV254 absorbance were removed by the BCO reactor after entering the stable operation period. It is shown that shorter hydraulic retention time (HRT) weakened the removals of tryptophan-like substances and fulvic acid according to the three-dimension fluorescence excitation emission matrix spectroscopy, with the removal ratios decreased from 90% to 0% when the HRT declined from 16.8 h to 4.2 h. Despite operating at regular room temperature ((24.1 ± 3.4) °C), the drinking water BCO reactor underwent a long start-up period (5.5 months) to reach a steady state in terms of biofilm concentration and pollutant removal performance. Genus Xanthobacter and Methylobacterium might significantly contribute to the removal of NOM in the BCO reactor, while genus Pedomicrobium and Bradyrhizobium were speculated to be responsible for nitrogen conversion. The present study provides new insights into the application of BCO reactors for ammonium and NOM removal from rural drinking water.

Effect of bamboo sphere amendment on the organic matter decomposition and humification of food waste composting

The aim of this study is to examine the effect of bamboo sphere on the organic matter decomposition and humification of food waste composting. Food waste composting were carried out on four treatments, namely control (CK), 3% (T1), 6% (T2) and 9% (T3) (w/w) bamboo sphere treatments. Results showed that adding bamboo sphere facilitated the organic matter decomposition and increased the seed germination index. The number of cells in T2 treatment was always the highest during the composting process. Furthermore, the final humic substances and humic acid contents increased by 41.08% and 68.3%, respectively, in 6% bamboo sphere treatment. Fourier transform infrared and excitation-emission matrix fluorescence spectroscopy analysis revealed that adding bamboo sphere accelerated the humification of composting with more aromatic structures and humic acid-like substances. GC-MS studies revealed that the compost products of 6% bamboo sphere treatment had more ring structures, and thus enhanced the humification.

Characterization of dissolved organic matter at urban and industrial rainwater of Bangladesh by fluorescence spectroscopy and EEM-PARAFAC modeling

Fluorescent dissolved organic matter (fDOM) was characterized seasonally in urban and industrial rainwater in one of the most polluted countries in the world, Bangladesh, using excitation-emission matrix (EEM) fluorescence spectroscopy and Parallel factor analysis (PARAFAC). EEM and PARAFAC modeling enabled identification of six fluorophores (peaks: A, C, M, T, Tuv, Wuv) and five fDOM components (humic-like, protein-like, fulvic acid (C)-like, humic (M)-like, and detergent-like), in both urban and industrial rain. The concentration of dissolved organic carbon (DOC) varied between 0.2–37.9 mg/L and 0.3–39.4 mg/L in urban and industrial rainwater, respectively. DOC concentration and fDOM component intensity were higher in the dry than in the wet season. DOC concentration was higher in urban than industrial rain in maximum months of the year. However, the higher intensity of fDOM components in industrial rainwater than in urban indicated that the industrial atmosphere might contain more nitrogenous organic compounds besides carbonaceous. The anthropogenic detergent-like component was present throughout the year with high intensity both at urban and industrial rain. fDOM indices and principal component analysis (PCA) described that organic components were not fresh, and originated from both allochthonous and autochthonous sources, and affected by microbial decomposition. fDOM components had strong positive correlations with gases (SO2, NOX, CO, and O3) and particulate matters (PM2.5 and PM10), indicating that they originated from similar local and distant sources. The Hybrid Single-Particle Lagrangian Integrated (HYSPLIT) back trajectory model described the local and distant air mass flow direction around sampling stations and interpreted their role in fDOM intensity fluctuations.

Efficacy and cytotoxicity of engineered ferromanganese-bearing sludge-derived biochar for percarbonate-induced phthalate ester degradation

Phthalate esters (PAEs) are a group of ubiquitous organic environmental contaminants. Engineered ferromanganese-bearing sludge-derived biochar (SDB), synthesized using one-step pyrolysis in the temperature range between 300 and 900 °C, was used to enable Fenton-like processes that decontaminated PAE-laden sediments. SDB was thoroughly characterized using scanning electron microscopyenergy-dispersive spectroscopy, transmission electron microscopy, Brunauer–Emmett–Teller surface area, thermogravimetric analysis, Raman spectroscopy, Fourier-transform infrared spectroscopy, electron paramagnetic resonance, X-ray photoelectron spectroscopy, and fluorescence excitation–emission matrix spectroscopy coupled with parallel factor analysis. The maximum PAE degradation was remarkable at 90% in 12 h at pH 6.0 in the presence of 1.7 g L−1 of SDB 900. The highly-effective PAE degradation was mainly attributed to the synergism between FeOx and MnOx, which strengthened the activation of percarbonate (PC) via electron transfer, hydroxy addition, and hydrogen abstraction through radical (HO•) and nonradical (1O2) oxidation mechanisms, thereby facilitating PAE catalytic degradation over SDB in real sediments, which clearly proved the efficacy of ferromanganese-bearing SDB and PC for the remediation of contaminated sediments. The cytotoxicity exhibited by human skin keratinocyte cells exposure to high SDB concentration (100–400 µg mL−1) for 24–48 h was low indicating insignificant cellular toxicity and oxidative damages. This study provides a new strategy for freshwater sludge treatment and reutilization, which enables a water-cycle-based circular economy and waste-to-resource recycling.

Fractionation of natural algal organic matter and its preservation on the surfaces of clay minerals

The sequestration of algal organic matter (AOM) in clays constitute important carbon sinks in lake sediments. The composition of AOM was proven recently to critically influence its preservation in sediments. Yet it remains unclear which AOM components and types of clay minerals contribute to AOM burial in lake sediments. Here we investigated the AOM fractionation in kaolinite and illite via their adsorption, to ascertain the distribution of AOM components on these clay surfaces. The results showed that the AOM adsorbed quantity was 2-fold higher for illite than kaolinite. The adsorption isotherm data of illite and kaolinite were well fitted by a Freundlich model. The three-dimensional excitation emission matrix fluorescence spectroscopy (3D EEM) with parallel factor analysis (PARAFAC) modeling identified the AOM component under fractionation. The AOM solution mainly consisted of humic acid-like, tyrosine-like, and tryptophan-like components. Notably, large amounts of the hydrophilic tyrosine-like components were adsorbed onto the surface of both kaolinite and illite, whereas the hydrophobic tryptophan-like components were seldom adsorbed onto neither of the clay materials, while humic acid-like components were only adsorbed onto illite. Therefore, illite is more suitable for the preservation of AOM. Both transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDS) and the X-ray photoelectron spectroscopy (XPS) analysis further confirmed the high adsorption of AOM on the surface of illite; i.e., the molar content of carbon in AOM adsorbed to illite was 22.04%, almost a double of that adsorbed to kaolinite (11.59%). Overall, our results demonstrate the selective preservation of AOM on clay surfaces and highlight the role of clay minerals as sequesters of organic matter in eutrophic lakes.

Characterization of Fluorescent Dissolved Organic Matter in an Affected Pollution Raw Water Source using an Excitation-Emission Matrix and PARAFAC

Cikapundung River is the main raw water source for 2-millions inhabitants of Bandung city but has been severely deteriorated due to organic pollution such as cattle manure, domestic, and agriculture wastes. Dissolved Organic Matter (DOM) in raw water can influence the process of water treatment. This study characterized and identified the origins of fluorescent DOM (FDOM) in Cikapundung River. Raw water samples were collected from intake outlets during dry and rainy seasons and analyzed using Fluorescence Excitation Emission Matrix spectroscopy combined with parallel factor (PARAFAC). FDOM origins were identified by Fluorescence-Index (FI) while autochthonous process contribution in water body was determined by Biological-Index (BIX). Chromophoric DOM as UV absorbance at 254 nm (A254) and Chemical Oxygen Demand (COD) were also measured. The FI were 1.82 (dry season) and 1.77 (rainy season), and the BIX were 0.92 (dry season) and 0.65 (rainy season). PARAFAC identified three compounds: water contaminant-like (C1), humic-like (C2) and tryptophan-like (C3) compounds. C2 was predominantly present in the rainy season with a C3/C2 ratio of 0.33. In the dry season, C3 increased substantially with a C3/C2 of 1.60. Strong correlation between C1 and C3 (R=0.86) was evidence that contaminant-like and tryptophan-like compounds were from the same anthropogenic sources. Strong correlation with A254 may indicate these identified compounds are aromatics.

High-precision and on-line measurement of dissolved organic matter in Electro-Fenton process based on dual wavelength analysis with combination of fluorescence emission and ultraviolet absorption spectroscopy

Electro-Fenton (EF) process is a significant water treatment method for the degradation of dissolved organic matter (DOM) in water and has been widely studied and applied in the past decade to degrade various dissolved organics. During water treatment, in order to monitor the degradation efficiency, it is in dire need to develop rapid and accurate methods that are favorable to assay on-line and on-site to provide feedback in a timely manner. UV–Visible absorption spectroscopy and Excitation-Emission Matrix (EEM) fluorescence spectroscopy techniques are most potential to realize on-line DOM measurement, but the measurement accuracy is unsatisfactory because of the obligatory involvement of iron-containing interferents. This study aims to simplify the measurement system complexity while overcoming the effect of iron-containing interferents during the measurement. An intrinsic relationship between the measured DOM concentration and the ultraviolet absorption at λ1 and the light intensities of the fluorescence emission at λ2 is derived theoretically and proved, based on which the influence of iron ions and their complexes on the spectrum can be eliminated, thus the content of DOM in the Electro-Fenton process is accurately determined. The proposed dual wavelength analysis with combination of fluorescence emission and ultraviolet absorption spectroscopy can achieve high precision (R2=0.9882,RMSE=0.0131mg/L). Furthermore, the on-line measurement design, called ultraviolet absorption-fluorescence emission dual wavelength analyzer, only includes one ultraviolet LED and two photodetectors. Its structure is simple and suitable for on-line monitoring DOM in EF process.

Effect of Mn2+ on the phosphorus removal and bioflocculation under anoxic condition

Manganese ion (Mn2+) generated from metallurgical, steel making and chemical industries enters sewage treatment plants and affects the sludge activity and flocculation. The effect of Mn2+ on the removal of chemical oxygen demand (COD) and total phosphorus (TP) and sludge activity were investigated in anoxic zone of an anaerobic/anoxic/oxic (A2O) process. The compositions and structures of extracellular polymeric substances (EPS) were characterized using three-dimensional excitation emission matrix fluorescence spectroscopy (3D-EEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) to reveal the relationship among Mn2+, EPS and sludge flocculation.The results showed that low concentration of Mn2+ (<5 mg/L) improved removal efficiencies of COD and TP and increased the activity of alkaline phosphatase, acid phosphatase and dehydrogenase. Meanwhile, the addition of Mn2+ increased total EPS, sludge contact angle, Zeta potential and sludge particle size, and thus enhanced sludge flocculation. However, high concentration of Mn2+ (>10 mg/L) hindered microbial flocculation and reduced removal efficiencies of the pollutants. When Mn2+was 5 mg/L, removal efficiencies of COD and TP reached 65% and 90%, respectively. Sludge flocculation was the best and SVI was 70.56 mL/g. The changes of Mn2+ concentration caused deviation of groups’ compositions in LB-EPS and TB-EPS, where the main components were always protein (PN) and polysaccharide (PS). The addition of Mn2+ resulted in the degradation of humic acids. However, it did not give rise to significant morphology changes of EPS.