Excitation-emission Matrix Spectra Research Articles

Bio-oxidation of Elemental Mercury into Mercury Sulfide and Humic Acid-Bound Mercury by Sulfate Reduction for Hg0 Removal in Flue Gas.

Bioconversion of elemental mercury (Hg0) into immobile, nontoxic, and less bioavailable species is of vital environmental significance. Here, we investigated bioconversion of Hg0 in a sulfate-reducing membrane biofilm reactor (MBfR). The MBfR achieved effective Hg0 removal by sulfate bioreduction. 16 S rDNA sequencing and metagenomic sequencing revealed that diverse groups of mercury-oxidizing/sulfate-reducing bacteria (Desulfobulbus, Desulfuromonas, Desulfomicrobium, etc.) utilized Hg0 as the initial electron donor and sulfate as the terminal electron acceptor to form the overall redox. These microorganisms coupled Hg0 bio-oxidation to sulfate bioreduction. Analysis on mercury speciation in biofilm by sequential extraction processes (SEPs) and inductively coupled mass spectrometry (ICP-MS) and by mercury temperature programmed desorption (Hg-TPD) showed that mercury sulfide (HgS) and humic acid-bound mercury (HA-Hg) were two major products of Hg0 bio-oxidation. With HgS and HA-Hg comprehensively characterized by X-ray diffraction (XRD), excitation-emission matrix spectra (EEM), scanning electron microscopy-energy disperse spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR), it was proposed that biologically oxidized mercury (Hg2+) further reacted with biogenic sulfides to form cubically crystallized metacinnabar (β-HgS) extracellular particles. Hg2+ was also complexed with functional groups -SH, -OH, -NH-, and -COO- in humic acids from extracellular polymeric substances (EPS) to form HA-Hg. HA-Hg may further react with biogenic sulfides to form HgS. Bioconversion of Hg0 into HgS was therefore achieved and can be a feasible biotechnique for flue gas demercuration.

Mg2+ distribution in activated sludge and its effects on the nitrifying activity and the characteristics of extracellular polymeric substances and sludge flocs

Abstract Divalent cations act as bridges among extracellular polymeric substances (EPS) and form cross-linkage for the self-immobilization of microbial biomass. However, their effects on the nitrification performance during the biological nitrogen removal are still unclear. In the present study, the effects of Mg2+ on the nitrifying activity, EPS and floc characteristics were investigated using a lab-scale sequencing batch reactor. The distribution of Mg2+ was quantified at different level of sludge floc. The results indicated that the nitrification activity was significantly improved when influent Mg2+ was below 1.1 mmol/L, but suppressed at 3 mmol/L. The overall performance characterized by COD, NH4+-N and TN, the particle size and sludge flocculation ability rapidly increased with the increase of Mg2+ concentration. Mg2+ was mainly distributed in the pellet and changed slightly in supernatant, LB-EPS and TB-EPS. The four fluorescence peaks detected by three-dimensional excitation-emission matrix spectra were attributed to PN-like substances and humic acid-like substances in the LB-EPS and TB-EPS. The results of XPS analysis demonstrated that LB-EPS and TB-EPS comprised similar elements. Therefore, the types of EPS functional groups was unchanged under varied Mg2+ concentrations, while their proportions changed and LB-EPS/EPS was key factor for the changes of bioflocculation.

Characterization of chromophoric dissolved organic matter in lakes across the Tibet-Qinghai Plateau using spectroscopic analysis

Fluorescent dissolved organic matter (FDOM) has a significant influence on global inland water carbon cycling and biogeochemical processes. The alpine lakes on Tibet-Qinghai Plateau (TQP) are exposed to high-intensity ultraviolet radiation, long retention time with less anthropogenic influences. Yet, limited studies were conducted on FDOM of lakes on the highest plateau in the world with unique aquatic environments. Spatiotemporal variations of FDOM components from 63 lakes (32 fresh lakes, N = 135; 31 brackish lakes, N = 109) were grouped according to salinity across the TQP collected during 2014–2017. FDOM were examined using excitation-emission matrix spectra (EEM) and fluorescence regional integration (FRI). CDOM absorption and FDOM fluorescence indices, average fluorescence intensities of the five fluorescent components (φi,i = I, II, III, IV, V) and total fluorescence intensities (φT) are significantly different between brackish and freshwater lakes (p < 0.05). High correlations (−0.51** < r < −0.86**, p < 0.01) were revealed between FDOM and dissolved organic carbon (DOC) concentrations with salinity > 10‰. A comparatively prolonged retention time and terrestrial allochthonous inputs caused higher DOC accumulation in brackish water. Strong UV radiation resulted in an important effect on CDOM photo-absorption characteristics, and that contributed to DOC variability and fate. Likewise, average CDOM spectroscopic indices in each basin with different land covers showed a moderate correlation between DOC and normalized humic-like φV for 20 basins (r = −0.46**, p < 0.01). The results suggest that studies on the highest alpine lakes across the TQP should focus on the impact of the evapo-concentration, ultraviolet irradiance and landscape features within different basins on FDOM characteristics. It demonstrated that the FDOM was dominated by the allochthonous sources in brackish lakes from the TQP and had a similarity to those observed in marine environments.

Environmentally friendly approach for advanced treatment of municipal secondary effluent by integration of micro-nano bubbles and photocatalysis

Abstract Numerous organic contaminants existing in the municipal secondary effluent (SE) have gained considerable attention because of their persistent nature and adverse environmental effects. In this study, micro-nano bubbles (MNB) and UV/Titanium dioxide (TiO2) system, both individual and in combination, were investigated for advanced treatment of the SE. The integrated MNB and photocatalysis system significantly improved the removal of chemical oxygen demand (COD) and persistent organic pollutants by 27.52 and 14.38%, respectively. The hybrid system efficiently decreased all five categories of organic contaminants according to excitation-emission matrix (EEM) spectrum, while the molecular weight (MW) fractions were decreased and the UV-absorbance at wavelength 254 nm (UV254) of MW (

Developing an Excitation-Emission Matrix Fluorescence Spectroscopy Method Coupled with Multi-way Classification Algorithms for the Identification of the Adulteration of Shanxi Aged Vinegars

In this paper, an excitation-emission matrix (EEM) fluorescence spectroscopy method coupled with two kinds of multi-way classification algorithms was developed for the identification of the adulteration of Shanxi aged vinegars. The first classification model was built from selective information provided by parallel factor analysis (PARAFAC) based on partial least squares-discriminant analysis (PLS-DA) algorithm and the other one was modeled based on strictly multi-way classification algorithm multi-way partial least squares-discriminant analysis (N-PLS-DA). Both classification models showed good clustering tendency for authentic and adulterated Shanxi aged vinegars. Compared with the PARAFAC-PLS-DA method, more accurate and reliable classification results were provided by the N-PLS-DA method because it is a strictly multi-way classification method and can make the utmost use of the EEM fluorescence information of the vinegar samples. The N-PLS-DA model constructed from the EEM spectra enabled the recognition of adulterated samples with accurate rate of 100% both in training and prediction sets and obtained maximum sensitivity and specificity. This study showed that EEM fluorescence spectroscopy combined with multi-way classification algorithm N-PLS-DA could be used as a good method for the identification of the adulteration of Shanxi aged vinegar samples.

Fenton cleaning strategy for ceramic membrane fouling in wastewater treatment

Membrane fouling is an obstacle impeding the wide applications of ceramic membranes and organics are responsible for most of the membrane fouling issues in wastewater treatment. In this study, Fenton cleaning strategy was firstly proposed to clean ceramic membrane fouling in wastewater treatment. Fe2+ efficiently catalyzed fouling cleaning with H2O2 (1.5%) to recover the filterability of ceramic membrane. The maximum ∆TMP recovery (over 99%) was achieved at an optimal Fe2+ dosage of 124 mg/L after 6 hr of immersion cleaning. The total residual membrane fouling resistance decreased gradually from this optimum value as the Fe2+ dosage increased above 124 mg/L. The residual hydraulically reversible fouling resistance accounted for most of the membrane fouling and was basically removed (≤3.0 × 109 m−1) when Fe2+ dosages higher than 124 mg/L were used. The foulants responsible for the formation of a residual hydraulically reversible fouling layer (DOC (dissolved organic carbon), proteins, polysaccharides, EEM (fluorescence excitation-emission matrix spectra), SS (suspended solids), and VSS (volatile suspended solids)) were gradually removed as the Fe2+ dosage increased. These residual organic foulants were degraded from biopolymers (10–200 kDa) to low molecular weight substances (0.1–1 kDa), and the particle size of these residual foulants decreased significantly as a result. The strong oxidation power of hydrogen peroxide/hydroxy radicals towards organic foulants was enhanced by Fe2+. Fe2+ played a significant role in the removal of hydraulically reversible fouling and irreversible fouling from the ceramic membrane. However, Fe2+ (≥124 mg/L) increased the likelihood of forming secondary iron-organics aggregates.

Influence of Ligneous Bulking Agents on the Complexation of Heavy Metals to Humic Substances Formed in Pig Manure Composting.

In order to investigate the influence of different lignin sources on humic substance formation during composting, this study selected two lignin sources, including wood sawdust and maize straw, to be co-composted with pig manure. Humic substances (HS) were characterized based on their fluorescence characteristics and complexing behaviors with heavy metals. The results showed that lignin sources, especially wood sawdust, were more conducive in promoting the formation of humic acids (HAs) than inorganic matter. The fluorescence excitation-emission matrix spectra also proved the positive effects of lignin on the formation of HAs during the humification process. The binding capacities of HAs isolated from mature composts for Cu and Cd followed the order of WS-90 > MS-90 > I-90, indicating that organic bulking agents are superior at increasing the complexing capacity of HAs. This finding suggests that the co-composting of pig manure with ligneous bulking agents is more advantageous at reducing the environmental risk of heavy metals.

Extracellular polymeric substances extraction and recovery from anammox granules: Evaluation of methods and protocol development

Selection of appropriate extraction methods of extracellular polymeric substances (EPSs) is crucial, affecting the yield, composition and the properties of EPSs. However, there is still a lack of standard methods for EPS extraction. In this study, seven methods were compared to extract EPS from anaerobic ammonium oxidation (anammox) granules, and the effectiveness and cell lysis of these methods were evaluated. The heating-Na2CO3 based method obtained a higher EPS yield with limited cell lysis. Proteins (PN) and polysaccharides (PS) were predominant in extractable EPSs. Particularly, PN-related substances were substantially enriched and high PN/PS ratios resulted in most methods. Different methods resulted in EPSs with a different size distribution. By analysis of Attenuated total reflectance-Fourier transform infrared spectra (ATR-FTIR), amide- and polysaccharide-associated bands were dominant. ATR-FTIR and fluorescence density of excitation-emission matrix spectra indicated EPS compositions and structures varied with the extraction methods. Moreover, the extraction/recovery protocol based on the heating-Na2CO3 method was remarkably improved, by varying heating time and using a centrifugal filter device with membrane (CFDM) to replace concentration and purification steps. Eventually, the thermal method with an extraction time of 45 mins was identified to be most effective. The application of CFDM was demonstrated as an alternative approach to concentrate and purify for EPS recovery. To our best knowledge, this is the first original study to systematically evaluate the different EPS extraction methods from anammox granules.

Pollutant Removal Performance and Membrane Fouling Characteristics in Marine Aquaculture Wastewater Treatment by a Microalgae Membrane Reactor

In order to treat mariculture wastewater, the pollutant removal performance and membrane fouling characteristics of a microalgae membrane reactor were investigated using Platymonas helgolandica tsingtaoensis. After 60 days of operation, the total nitrogen (TN) and total phosphorus (TP) removal efficiency of the reactor were 73.6% and 77.9%, respectively, and the removal rates of TN and TP reached 15 g·(m3·d)-1 and 2.8 g·(m3·d)-1. The microalgae in the reactor could be enriched rapidly, with a maximum growth rate of 53.3 mg·(L·d)-1 and a maximum biomass of 1.4 g·L-1. The microalgae in the reactor were harvested on day 18 and day 36; harvesting did not affect the nitrogen and phosphorus removal efficiency of the reactor. To some extent, the membrane fouling phenomenon was alleviated. The increase in the microalgae biomass would significantly increase the pollutant content of the membrane. The three-dimensional excitation-emission matrix (EEM) spectra results confirmed that tryptophan-like substances and aromatic proteins had a significant effect on membrane fouling.

Recognizing Dissolved Organic Matter with an Improved Fluorescence Regional Integral Method

The aim of this paper was to study transformations of Dissolved Organic Matter (DOM) in marl rock groundwater. To achieve this, we carried out a series of soil column experiments, using a DOM solution as the water sample and marl rock as the testing rock sample. Three-Dimensional Excitation-Emission Matrix Spectra (3DEEMS) were generated for DOM solutions and the Analytic Hierarchy Process (AHP) was introduced to improve the traditional method of fluorescence regional integral (TMFRI). We termed this approach the Improved Method of Fluorescence Regional Integral (IMFRI) and used it to identify the type of DOM in the marl rock. The result shows that DOM recognition using TMFRI is only 50% accurate and consequently transformations are hard to recognize. In contrast, our results show that use of IFRIM has a DOM type recognition accuracy of 83.33% and so this method can be used with confidence to describe transformation characteristics. And we find that in the marl rock, the leaching test showed a new fluorescence peak at 312 h and the humic acid was degraded into soluble microbial products by microorganisms.

Sources, Characteristics and Transformation Dynamics of Fluorescent Dissolved Organic Matter in the Silin Reservoir

The aim of this study was to examine the sources and characteristics of various fluorescent dissolved organic matter (FDOM) components as well as their transformation dynamics. FDOM was determined in the incoming, surface (0 m), deeper (20 m), and outflowing waters of the Silin Reservoir in winter (January), spring (April), summer (June), and autumn (October) using excitation-emission matrix (EEM) spectra coupled with parallel factor (PARAFAC), EEM-PARAFAC modelling. The EEM-PARAFAC modelling results demonstrated that dissolved organic matter (DOM) in the Silin Reservoir waters was composed of three fluorescent components. These included terrestrial humic-like substances (C type) of terrestrial origin (component 1), microbial humic-like substances (M type) of phytoplankton origin (component 2), and protein-like or tryptophan-like or tyrosine-like (component 3) of phytoplankton origin. In addition, the terrestrial humic-like substances (C type) was identified from two fluorescence peaks (peak C at Ex/Em=305-355/414-458 nm and peak A at Ex/Em 245-270/414-458 nm) while the microbial humic-like substances (M type) was identified from peaks that included peak M at Ex/Em 280-305/380-398 nm and peak A 230-235/380-417 nm. Similarly, protein-like or tryptophan-like or tyrosine-like components were also detected from two fluorescence peaks, including peak T 270-285/316-354 nm and peak Tuv 225-230/316-354 nm. The fluorescence intensity of terrestrial humic-like substances gradually decreased in incoming waters to surface (0 m), deeper (20 m), and subsequently, in outflowing waters. This indicates the gradual degradation of the humic-like substances and their recalcitrant nature during water transport during the incoming-surface-deeper-outflowing water cycle in both summer and winter seasons by numerous environmental factors. These included photochemical, microbial, and dam barrier-affected physical processes. Conversely, from the fluorescence intensity results of microbial humic-like substances (M type), production or partial (in some cases complete) degradation in surface-deeper-outflowing waters, fluctuated. This suggests that microbial humic-like substances are autochthonously produced from phytoplankton, but are highly labile in response to photochemical, microbial, and dam barrier-affected physical processes. From the fluorescence intensity results of protein-like or tryptophan-like or tyrosine-like substances, it demonstrated that they were newly produced in surface (0 m) waters in the summer season, but in the winter season they were significantly produced in both surface and deeper waters of the reservoir, and then decreased in the outflowing waters. This suggests that protein-like or tryptophan-like or tyrosine-like substances are autochthonously produced by phytoplankton that simultaneously reproduced and then were degraded in surface and deeper waters by photochemical, microbial, and dam barrier-affected physical processes. These results therefore imply that the FDOM components identified by EEM-PARAFAC modelling are crucial to better understand the source characteristics of bulk DOM, its transformation mechanisms, and its the dynamics in a reservoir water system.

Tripolyphosphate-assisted electro-Fenton process for coking wastewater treatment at neutral pH.

The first application of a novel electro-Fenton (EF) for coking wastewater (CW) treatment at the original pH (6.80) by using tripolyphosphate (TPP) ligand was proposed. Total organic carbon (TOC) decay of CW followed a pseudo-first kinetic rate constant with an apparent rate constant (kapp) of 1.07 × 10-2min-1 for the EF in the presence of TPP (EF/TPP), which was 2.10 times higher than that of conventional EF (kapp= 5.10 × 10-3min-1) working at pH3. The high efficiency of EF/TPP at neutral pH was mainly attributed to the newly formed Fe-O-P coordination in the iron-ligand compound (Fe2+-TPP) supported by UV-absorption spectra results, activating oxygen to produce •OH and hence enhancing the oxidation capacity. Key operating parameters of CW mineralization by EF/TPP including Fe2+ concentration and pH value were systematically investigated. Excitation-emission matrix (EEM) spectra technique was used to assess the variance of dissolved organic matters during the EF/TPP process. Results showed an 81% mineralization of CW after 3h electrolysis coupled with a low energy consumption (0.129kWhg-1 TOC) which were obtained by the EF/TPP process. Microtox toxicity demonstrated that TPP could reduce the toxicity of raw CW and importantly, it showed that EF/TPP was effective for detoxification. Mechanism study via simulated matrix with similar components as CW revealed that •OH produced both from Fenton and Fe2+-TPP activation together with the generated active chlorine was responsible for CW mineralization. In summary, the TPP-assisted EF process was presented as a promising technique for extending coking wastewater treatment at near-neutral pH with a high mineralization.

Bisphenol S Adsorption Behavior on Ferralsol and Biochar Modified Soil with Dissolved Organic Matter.

Bisphenol S (BPs) has been found in a variety of common consumer products surrounding human living, despite the fact that it could damage the human digestive system and genital system. In China, straw-returning to the field is a common soil improvement technology used to increase the concentration of dissolved organic matter (DOM), which plays an important role in the natural environment as a microreactor of contaminants. Additionally, the biochar obtained by the straw is an effective soil conditioner. DOM is a key influencing factor when biochar is employed as the conditioner of BPs contaminated soil. However, the BPs adsorption behavior on the Ferralsol affected by DOM and biochar is also unclear. Hence, DOM was prepared and the effect of DOM on the BPs adsorption behavior on soil and biochar modified soil was investigated. DOM was characterized by Elemental analysis, Fourier transforming infrared spectra (FT-IR), and three-dimensional excitation-emission matrix spectra (3D-EEM). The results of the adsorption experiments indicated that both biochar and DOM could improve the BPs adsorption capacity in Ferralsol, while DOM suppressed the BPs adsorption capacity of biochar modified soil, indicating that DOM and BPs could not be applied at the same time for BPs adsorption.

Cultivation of Chlorella vulgaris in sludge extracts: Nutrient removal and algal utilization

In order to utilize the excess sludge and reduce the cost of algal cultivation, Chlorella vulgaris was cultivated in increasing proportions of sludge extracts for simultaneous nutrients removal and algal utilization. Results showed that C. vulgaris cultivated in the 100% sludge extract gained the highest total biomass (33.98 ± 0.30 × 106 cells/mL) and showed good results in TOC (absolute value 175 mg/L) and nutrients (TN: 77.1%; TP: 95.0%) removals. According to the Excitation-emission matrix spectra (EEMs) analysis, the 8th day was suggested as the optimal time for biomass harvesting. Although the lipid contents showed a negative correlation with the proportion of sludge extract, the FAME analysis showed that the saturated fatty acids (SFA) contents decreased and the unsaturated fatty acids (UFA) content increased as the concentration of sludge extract increased. The 100% sludge extract could be a desirable alternative medium for the algae cultivation.

Characterizing the weathering induced degradation of Poly(ethylene-terephthalate) using PARAFAC modeling of fluorescence spectra

Poly(ethylene-terephthalate) (PET) film is widely used in photovoltaic module backsheets, for its dielectric breakdown strength, and in applications requiring high optical clarity. PET degrades under exposure to ultraviolet (UV) irradiance, heat, and moisture, which leads to loss of optical clarity and performance properties. To study the weathering driven degradation of PET films, three grades of PET, including unstabilized and stabilized grades, were exposed to three types of accelerated weathering exposure. Fluorescence excitation-emission matrix (EEM) spectra were collected after predetermined exposure intervals. Parallel factor analysis (PARAFAC) was applied to the resulting spectra to decompose the fluorescence data into individual fluorophore components and monitor their relative concentrations over time. EEM-PARAFAC was used to identify and distinguish between the formation of monohydroxy-terephthalate and dihydroxy-terephthalate units in PET over time under the UV-light bearing accelerated exposures. The relative concentrations of these fluorophores were found to increase, while the relative concentration of the PARAFAC component assigned to PET was found to generally decrease. ATR-FTIR was used to support findings from EEM-PARAFAC. Results were also used to assess the impact of additives (UV stabilizer and TiO2) on degradation.

Enhanced dark hydrogen fermentation of Enterobacter aerogenes/HoxEFUYH with carbon cloth

Long-range extracellular electron transfer through microbial nanowires is critical for efficient bacterial behaviors. The application of carbon cloth on the dark hydrogen fermentation using transgenic Enterobacter aerogenes (E. aerogenes/HoxEFUYH) was first proposed to enhance hydrogen production from glucose. Scanning electron microscopy images showed that the microbial nanowires between E. aerogenes/HoxEFUYH cells almost vanished due to the presence of carbon cloth. Approximately 59.1% of microorganisms concentrated in biofilms on the surface of carbon cloth, which probably promoted the intercellular electron transfer. The results from Fourier transform infrared spectra and Excitation Emission Matrix spectra indicated that carbon cloth biofilms primarily included polysaccharide and protein. Moreover, the fluorophore of biofilms (88.1%) was much higher than that of supernatant (11.9%). The analysis of soluble metabolic degradation byproducts revealed that carbon cloth selectively enhanced the acetate pathway (C6H12O6+2H2O→2CH3COOH+2CO2+4H2), but weakened the ethanol pathway (C6H12O6→2C2H5OH+2CO2). With 1.0 g/L carbon cloth, the hydrogen yield increased by 26.6% to 242 mL/g, and the corresponding peak hydrogen production rate increased by 60.3%.

Photodegradation response of humic acid using UV-Visible absorption and Excitation-Emission Matrix Spectra

湖泊生态系统作为自然界重要的碳库，光照强度的变化对于湖泊的碳循环过程可能产生重要的影响.以云南老君山高山湖泊天才湖周边土壤中的腐殖酸作为外源溶解性有机物（DOM）的代表物，通过腐殖酸模拟光降解实验，考察光照强度对外源DOM光降解过程的影响.研究结果表明：腐殖酸光吸收系数a₄₄₀、465 nm和665 nm波长处吸光度比值E₄/E₆的下降幅度均为：对照组 < 20 W光照组 < 40 W光照组，a₄₄₀、E₄/E₆和光谱斜率S_R显著相关，表明紫外辐射使得腐殖酸溶液浓度降低、相对分子量下降，且光照强度越强，腐殖酸的光降解程度越大.通过EEM-PARAFAC模型识别出光降解过程中腐殖酸溶液中含有5种荧光组分：UV类腐殖质（C1）、UVA类腐殖质（C2）、类色氨酸（C3）、UVC类腐殖质（C4）和类络氨酸（C5）.40 W光照组中4种荧光组分的降解程度与降解速率均大于20 W光照组，降解程度均为：C4 > C3 > C2 > C1，降解速率为C2 > C4 > C3 > C1，说明不同的荧光组分对光照强度的响应不同.该研究有助于阐明外源DOM的光降解途径与归趋.;UV irradiation intensity changes have great influence on carbon cycle in lake, which is one of the most important carbon pools in nature. To understand the effects of UV irradiation on allochthonous dissolved organic matter(DOM)in lakes, simulated photodegradation experiments were conducted. We extracted humic acid from soil surrounding an alpine Lake Tiancai as allochthonous DOM. During the photo-irradiation process, the order of decreasing level of a₄₄₀ and E₄/E₆ was 40 W group, followed by 20 W group and control group. Moreover, S_R, a₄₄₀ and E₄/E₆ were significantly correlated, suggesting that the concentration and relative molecular weight of humic acid decreased with increasing UV irradiation intensity. Five fluorescent components were identified through using EEM-PARAFAC models, included UV humic-like component (C1), UVA humic-like component (C2), tryptophan-like component (C3), UVC humic-like component (C4), tyrosine-like component (C5). The photodegradation rate and degree of four fluorescent components in 40 W group were greater than 20 W group, the order of photodegradation rate was C4 > C3 > C2 > C1 and the order of photodegradation degree was C2 > C4 > C3 > C1, indicating that fluorescent components response diversely to different UV irradiation intensities.

Influence of amoxicillin after pre-treatment on the extracellular polymeric substances and microbial community of anaerobic granular sludge

A combined process coupling a Fe3O4 nanoparticles (Fe3O4 NPs) heterogeneous Fenton-like reaction and an anaerobic biological technology was investigated in order to effectively treat amoxicillin-containing wastewater. With the increase in the pretreatment degree, the average COD removal rate correspondingly increased from 84.8% to 92.4% using the anaerobic biological treatment, and the biodegradability and COD removal efficiency was improved by the pretreatment processes. During the process of amoxicillin degradation, hydroxyl free radicals tended to attack the lactamide, amide and pentacyclic rings of amoxicillin. In the excitation-emission matrix (EEM) spectra of soluble microbial products (SMPs), the absorption peak of humic acid gradually decreased with application of the pretreatment. The pretreatment products were more beneficial to the characteristics of anaerobic granular sludge. For the microbial community structure, the proportion of Methanothrix and Clostridia increased with addition the heterogeneous Fenton-like pretreatment, which favored conversion of organic contaminants to volatile fatty acids and biogas.

Characterization of CDOM in saline and freshwater lakes across China using spectroscopic analysis

Colored dissolved organic matter (CDOM) is a major component of DOM in waters, and plays a vital role in carbon cycling in inland waters. In this study, the light absorption and three-dimensional excitation-emission matrix spectra (EEMs) of CDOM of 936 water samples collected in 2014–2017 from 234 lakes in five regions across China were examined to determine relationships between lake water sources (fresh versus saline) and their fluorescence/absorption characteristics. Results indicated significant differences regarding DOC concentration and aCDOM(254) between freshwater (6.68 mg C L−1, 19.55 m-1) and saline lakes (27.4 mg C L−1, 41.17 m-1). While humic-like (F5) and fulvic-like (F3) compounds contributed to CDOM fluorescence in all lake waters significantly, their contribution to total fluorescence intensity (FT) differed between saline and freshwater lakes. Significant negative relationships were also observed between lake altitude with either F5 (R2 = 0.63, N = 306) or FT (R2 = 0.64, N = 306), suggesting that the abundance of humic-like materials in CDOM tends to decrease with increased in lakes altitude. In high-altitude lakes, strong solar irradiance and UV exposure may have induced photo-oxidation reactions resulting in decreased abundance of humic-like substances and the formation of low molecular weight compounds. These findings have important implications regarding our understanding of C dynamics in lacustrine systems and the contribution of these ecosystems to the global C cycle.

Study on Different Fractions of Organic Molecules in the Baltic Sea Surface Microlayer by Spectrophoto- and Spectrofluorimetric Methods

The sea surface microlayer (SML), created by surface active organic molecules (called: surfactants), is a highly active interface between the sea and the atmosphere. In this study we used the dissolved organic matter absorption and fluorescence properties for description of changes in molecular size and weight distribution of organic molecules as well as in their composition in the SML compared to subsurface water layer (SS), of 1 m depth. Data were collected during three research cruises in the Baltic Sea. Spectral values of the CDOM absorption coefficient were higher in the SML about 29 % (in the UV light) to 17 % (in a blue spectral range), while spectral slope coefficients at different spectral ranges, S_Δλ, were lower in SML by 2.3 and 10.5% compared to SS in 275-295 nm and 350-400 nm, respectively. The fluorescence intensities of main Excitation Emission Matrix spectra peaks belonging to the main fluorescing components of marine organic matter, called: A, C, M, T, were higher in SML by 41, 43, 41 and 14% compared to SS. The ratio of fluorescence intensities, ((M+T))⁄((A+C) ) and humification index, HIX, values in SML were, respectively higher by 17.9% and lower by 10.7 % compared to SS. These two parameters where coupled with inverse non-linear relationship. This relationship indicated faster removal of humic components of high MW in the SML compared to SS. We have observed decreasing trend of spectral slope ratio, S_R, with increasing salinity. The S_R decreased 33.5 and 23.6 % in the SML and SS, respectively in the salinity gradient from 4.5 to 7.94 (of practical salinity ). The fluorescence intensity of all FDOM peaks decreased by in the same salinity gradient. The decrease rate was higher in SML for all fluorescing peaks by 34, 36 and 26 % for A, C and M, respectively than in the SS. Decrease rate indicated the susceptibility to photochemical degradation of respective peaks. This effect was strongest for C while T peak was almost unbleached. The fluorescence intensity decrease rate was smaller in SS what indicated shielding effect of the SML.