Aquatic Fulvic Acid Research Articles

Towards enhanced treatment of piggery biogas slurry in tidal flow constructed wetlands by regulation of hydraulic retention time

Livestock farming wastewater is complex in composition, containing a large number of pathogenic microorganisms and ammonia nitrogen (NH4+-N) with high concentration, which makes biological treatment difficult. In this study, tidal flow constructed wetlands were applied to treat piggery biogas slurry. Compared with a continuous flow constructed wetland, two tidal influent modes (hydraulic retention time: idling time for 12 h:12 h and 20 h:4 h, namely TFCW1 and TFCW2) were set up to explore treatment performances on chromaticity, turbidity, chemical oxygen demand (COD), total nitrogen (TN), NH4+-N and total phosphorus (TP), and determine the relationship between nitrogen transfer and dissolved oxygen (DO) contents. The fluorescence spectra of dissolved organic matter (DOM) in constructed wetlands were analyzed by excitation-emission matrix spectroscopy-parallel factor analysis to reveal its composition and content of humus. The results showed that tidal flow constructed wetlands obviously improved the removal of chromaticity and turbidity by 44.6% and 10.1%, in comparison to continuous flow constructed wetland. TFCW2 had enhanced reduction on pollutants, with removal efficiencies of COD, NH4+-N and TP at 78.6%, 82.1% and 84.0%, respectively. Furthermore, three fluorescent components were detected in TFCW2, and the value of Fmax was increased in the effluent, among which the Fmax of C3 (Humic-like substances) increased obviously from 0.320 to 9.39. The ratio of C2 (Aquatic fulvic acids) to C3 showed a slow increasing trend in the daily outflow of TFCW2, while C1 (dark-incubation substances) remained relatively constant. Fluorescence index (FI), humification index (HIX) and biological index (BIX) increased from 1.35 to 2.09, 0.210–1.51, and 0.240–1.05, respectively, showing that the effluent from the tidal flow constructed wetland had a high microbial activity. This study provided a new insight for the advanced treatment of livestock biogas slurry with a high NH4+-N content.

Carbon-based nanomaterials mediated adsorption and photodegradation of typical organic contaminants in aqueous fulvic acid solution.

In this work, the formation of carbon-based nanomaterials-fulvic acid (CNMs-FA) composites and their capacities for the adsorption and photodegradation of typical organic contaminants in aqueous solutions were investigated. The results suggested that the formation of CNMs-FA composites was dominated by adsorbing FA on CNMs via the physisorption process, which fit the pseudo-first-order kinetic model and the Langmuir isotherm model. The formed CNMs-FA composites were characterized by using the Brunauer-Emmett-Teller, scanning electron microscopy, and infrared spectroscopy techniques and further applied for examining their effects on the adsorption and photodegradation of selected organic contaminants in aqueous solutions. The adsorption of organic contaminants on CNMs-FA composites is mainly involved in hydrogen bonding and electrostatic interactions between organic contaminants and FA species adhering to CNMs. In addition, the CNMs-FA composites are able to promote the photosensitive degradation of organic contaminants due to the photogenerated reactive species including ROS and CNMs-3FA* under sunlight irradiation. This study provided a deeper and more comprehensive understanding of the environmental behavior of CNMs in real natural surface water and clarified the underlying mechanisms.

Fulvic acid isolation and characterisation from water of a Ramsar Lake Mansar, J&K, India

The present study was undertaken with the aim to understand the chemical properties of aquatic fulvic acid in a clear water Lake Mansar. Along with that, the physical and chemical environment of the lake was also analysed. Fulvic acid was isolated from the water of Lake Mansar following IHSS recommended methodology and was subjected to characterisation, viz. elemental analysis, H-NMR and FTIR spectroscopy. The yield of fulvic acid from water of Lake Mansar was 0.22 mg/L that was far less than coloured aquatic systems. Elemental analysis revealed per cent carbon, hydrogen, nitrogen and oxygen content to be 53.6%, 5.04%, 6.3% and 35.06%, respectively. H-NMR and FTIR spectra revealed the presence of various functional groups like aliphatic, hydroxyl, amide, quinones, ketones, carbonyl, cellulose, etc. Based on the present studies, it was concluded that the origin of humic material in Lake Mansar is mostly from algae and non-vascular plants that have undergone less degree of humification.

A predictive thermodynamic framework of cloud droplet activation for chemically unresolved aerosol mixtures, including surface tension, non-ideality, and bulk–surface partitioning

Abstract. This work presents a thermodynamically consistent framework that enables self-contained, predictive Köhler calculations of droplet growth and activation with considerations of surface adsorption, surface tension reduction, and non-ideal water activity for chemically complex and unresolved surface-active aerosol mixtures. The common presence of surface-active species in atmospheric aerosols is now well-established. However, the impacts of different effects driven by surface activity, in particular bulk–surface partitioning and resulting bulk depletion and/or surface tension reduction, on aerosol hygroscopic growth and cloud droplet activation remain to be generally established. Because specific characterization of key properties, including water activity and surface tension, remains exceedingly challenging for finite-sized activating droplets, a self-contained and thermodynamically consistent model framework is needed to resolve the individual effects of surface activity during droplet growth and activation. Previous frameworks have achieved this for simple aerosol mixtures, comprising at most a few well-defined chemical species. However, atmospheric aerosol mixtures and more realistic laboratory systems are typically chemically more complex and not well-defined (unresolved). Therefore, frameworks which require specific knowledge of the concentrations of all chemical species in the mixture and their composition-dependent interactions cannot be applied. For mixtures which are unresolved or where specific interactions between components are unknown, analytical models based on retrofitting can be applied, or the mixture can be represented by a proxy compound or mixture with well-known properties. However, the surface activity effects evaluated by such models cannot be independently verified. The presented model couples Köhler theory with the Gibbs adsorption and Szyszkowski-type surface tension equations. Contrary to previous thermodynamic frameworks, it is formulated on a mass basis to obtain a quantitative description of composition-dependent properties for chemically unresolved mixtures. Application of the model is illustrated by calculating cloud condensation nuclei (CCN) activity of aerosol particles comprising Nordic aquatic fulvic acid (NAFA), a chemically unresolved and strongly surface-active model atmospheric humic-like substance (HULIS), and NaCl, with dry diameters of 30–230 nm and compositions spanning the full range of relative NAFA and NaCl mixing ratios. For comparison with the model presented, several other predictive Köhler frameworks, with simplified treatments of surface-active NAFA, are also applied. Effects of NAFA surface activity are gauged via a suite of properties evaluated for growing and activating droplets. The presented framework predicts a similar influence of surface activity of the chemically complex NAFA on CCN activation as was previously shown for single, strong surfactants. Comparison to experimental CCN data shows that NAFA bulk–surface partitioning is well-represented by Gibbs adsorption thermodynamics. Contrary to several recent studies, no evidence of significantly reduced droplet surface tension at the point of activation was found. Calculations with the presented thermodynamic model show that throughout droplet growth and activation, the finite amounts of NAFA in microscopic and submicron droplets are strongly depleted from the bulk, due to bulk–surface partitioning, because surface areas for a given bulk volume are very large. As a result, both the effective hygroscopicity and ability of NAFA to reduce droplet surface tension are significantly lower in finite-sized activating droplets than in macroscopic aqueous solutions of the same overall composition. The presented framework enables the influence of surface activity on CCN activation for other chemically complex and unresolved aerosol mixtures, including actual atmospheric samples, to be systematically explored. Thermodynamic input parameters can be independently constrained from measurements, instead of being either approximated by a proxy or determined by retrofitting, potentially confounding several mechanisms influenced by surface activity.

Differences in quinone redox system of humic substances between endemic and disease-free areas in Kashin-Beck disease-affected Changdu Region, Tibet, China.

Kashin-Beck disease (KBD) is an endemic disease in China with the highest incidence rate in Tibet region. Promoted generation of oxygen free radicals by semiquinone structure of humic substance (HS) in drinking water was considered to be one of its pathogeneses. Therefore, detailed analysis of HS was performed in water and sediment samples collected from three endemic and three disease-free areas in Changdu Region, Tibet, China. After purification of the HS in the samples, the fractions of HS were characterized using electron paramagnetic resonance, 13C nuclear magnetic resonance, fluorescence spectroscopy with parallel factor analysis and Fourier transform infrared spectroscopy (FTIR). The organic carbon content of HS did not show a significant difference between endemic and disease-free areas or correlation with KBD-associated morbidity. Except FTIR, all techniques succeeded in characterization of the quinone redox system, indicating their validity and consistency. The quinone redox system in aquatic HS exhibited significantly higher level of the following indexes in endemic areas than disease-free areas: semiquinone radical content of fulvic acid (FA) (p < 0.05), aromaticity of FA (p < 0.05), fluorescence intensity (per gram carbon) of reduced quinone-like component of FA (p < 0.05) and humic acid (HA) (p < 0.1). Semiquinone radical content (r = 0.781, p < 0.1), aromaticity of FA (r = 0.891, p < 0.05), intensity of oxidized quinone-like component (r = 0.875, p < 0.05) and reduced quinone-like component of FA (r = 0.793 p < 0.1) showed medium to strong correlation with KBD-associated morbidity. Generally, the content of reduced quinone and aquatic FA showed stronger differences between endemic and disease-free areas than oxidized quinone and aquatic HA, respectively. The quinone redox system in sediment HS did not show any significant relationship with KBD. The present study is a successful attempt to combine the three indexes, semiquinone radical content, aromaticity and fluorescence intensity, in characterizing quinone redox system in HS, facilitating more comprehensive understanding of the characteristics of HS in KBD-affected regions.

Comparison of the properties of standard soil and aquatic fulvic and humic acids based on the data of differential absorbance and fluorescence spectroscopy

This study compared effects of pH, ionic strength and complexation with Mg2+ on the chromophores and fluorophores of aquatic and terrestrial NOM exemplified by the standard isolates Suwannee River fulvic and humic acid (SRFA and SRHA) and Pahokee Peat fulvic and humic acids (PPFA and PPHA) provided by the International Humic Substance Society (IHSS). The intensity of the differential spectra of the NOM isolates increased monotonically with pH. These spectra comprised contributions of similar chromophore systems associated with the carboxylic and phenolic moieties. The intensity of SRFA and PPFA fluorescence changed non-monotonically vs. pH indicating that the deprotonation of the phenolic fluorophores decreased their emission yields. Examination of the effects of pH on the slopes of the log-transformed absorbance of NOM showed that the influence of deprotonation on the conformations of PPFA and PPHA molecules was less prominent than those for SRFA but not dissimilar to those of SRHA. Changes of the differential spectra and spectral slopes showed that Mg2+/PPFA and Mg2+/PPHA complexation was more effected by electrostatic interactions while the involvement of phenolic groups was notable for SRFA. The observed trends highlight similarities and differences in the properties of the chromophores and fluorophores in the standard isolates of soil and aquatic NOM. These results necessitate further systematic comparison of the properties of NOM isolates and those of unaltered NOM.

Effects of surface tension time-evolution for CCN activation of a complex organic surfactant.

The physical processes and time scales underlying the evolution of surface tension in atmospheric solution droplets are largely unaccounted for in present models describing cloud droplet formation. Adsorption of surface-active molecules at the surface of a solution droplet depresses the droplet surface tension but also depletes solute from the droplet bulk, which have opposing and sometimes canceling effects in cloud droplet formation. In this work, we study the effect of time-evolving surface tension for cloud droplet activation of particles composed of Nordic Aquatic Fulvic Acid (NAFA) mixed with sodium chloride (NaCl). We model the formation of cloud droplets using Köhler theory with surface tension depression and bulk/surface partitioning evaluated from two different thermodynamic surface models. Continuous ternary parameterizations were constructed from surface tension measurements of macroscopic droplets at different time steps after the formation of a droplet surface. The predicted results are compared to previous measurements of mixed NAFA-NaCl cloud condensation nuclei (CCN) activity and a bulk solution model that does not take the NAFA bulk/surface partitioning equilibrium into account. Whereas the bulk model shows a trend in cloud droplet formation following that of macroscopic surface tension depression with time, the variation with time essentially disappears when bulk/surface partitioning is taken explicitly into account during droplet activation. For all equilibrium time steps considered, the effect of surface tension depression in the NAFA-NaCl system is counteracted by the depletion of solute from the finite-sized droplet bulk phase. Our study highlights that a comprehensive data set is necessary to obtain continuous parameterizations of surface tension and other solution properties required to fully account for the bulk/surface partitioning in growing droplets. To our knowledge, no similar data set currently exists for other aqueous organic systems of atmospheric interest. Additional work is necessary to deconvolve the effects of bulk/surface partitioning in the context of time-evolution on cloud droplet activation and to determine whether the results presented here can be further generalized.

Photodegradation of metoprolol in the presence of aquatic fulvic acids. Kinetic studies, degradation pathways and role of singlet oxygen, OH radicals and fulvic acids triplet states

Metoprolol is a pharmaceutical used for the treatment of cardiovascular diseases and disorders, whose frequent detection in surface waters raises concern. Indirect photodegradation is an important degradation pathway in waters and dissolved organic matter has a major role as photosensitizer. In this study, metoprolol photodegradation, in the absence and in the presence of fulvic acids extracted from the Vouga River (Portugal) (VRFA), was assessed under simulated sunlight. While metoprolol direct photodegradation was deniable, indirect photolysis occurred under the presence of VRFA. It followed a pseudo-first order kinetics and after 72 h of irradiation there was a decrease of metoprolol concentration of ∼80 %. The OH radical (OH) was verified to be the main reactive species (RS) responsible for the photosensitized degradation of metoprolol, but other RS are also involved, probably triplet excited states of FA (3FA*) and singlet oxygen (1O2), as demonstrated by the higher inhibition of the photodegradation in presence of sodium azide than in presence of 2-propanol. Based on a previous identification of photoproducts, tentative degradation mechanisms were here proposed. Photoproducts analysis after 24 h irradiation in the absence and presence of scavengers, shown that different RS are involved in the formation of different products/intermediates.

Preparation of graphene by exfoliating graphite in aqueous fulvic acid solution and its application in corrosion protection of aluminum

Liquid phase exfoliation (LPE) method has great potential for the large-scale production of graphene due to its simplicity, scalability, and low cost. In this work, fulvic acid (FA) was chosen to assist the exfoliation of graphite into graphene for the first time via sonication in aqueous medium. The concentration of obtained graphene dispersion can reach 0.63 ± 0.04 mg mL−1. The graphene flakes mostly consisted of 1–5 layers with sizes range in submicron to micron and few defects in the basal-plane. The π–π interaction between graphene and FA, along with the electrostatic repulsion between negatively charged FA, played a major role in stabilization of the graphene dispersion. By adjusting the pH of graphene dispersion to 14, the nanosheets of graphene came to flocculation. The formed graphene slurry is favorable for storage and transportation due to the greatly decreased volume. The annealed coating of FA-graphene on aluminum sheets was used as corrosion inhibitor for aluminum in 0.5 M H2SO4 and 0.6 M NaCl solutions, with inhibition efficiencies of up to 85.5% and 99.4%, respectively. This shows that as-prepared graphene has great potential applications in the anti-corrosion of aluminum.

Impact of natural organic matter in water on in vitro bioactivity assays

Surface water can be contaminated with pollutants from multiple sources and contain a vast number of various chemicals. In vitro bioassays are valuable tools to assess the total bioactivity of micropollutants in water samples. Besides anthropogenic chemicals, natural organic matter (NOM) is ubiquitous in water, which also may have an impact on the bioactivity in water samples.In the present study we investigated concentration-dependent effects of Nordic Aquatic fulvic acid (NA-FA) and Nordic reservoir NOM (NR-NOM) on bioactivity measured by a panel of luciferase reporter gene assays. The assays included measurements of both induction of activities and inhibition of induced activation on aryl hydrocarbon receptor (AhR), androgen receptor (AR), estrogen receptor (ER), peroxisome proliferator-activated receptor alpha, and on the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) activity as a marker of oxidative stress.At non-cytotoxic concentrations both NA-FA and NR-NOM induced AhR activity, inhibited AR activity with and without the known inducer dihydrotestosterone, inhibited Nrf2 activity, and NR-NOM induced ER activity. The results indicate that the presence of NOM in water samples may lead to false positive results for AhR activity and false positive results for AR and Nrf2 activity, when assessing inhibition of induced bioactivities from anthropogenic substances. We have demonstrated that NA-FA and NR-NOM have an impact on in vitro bioactivities and conclude that the impact of NOM in water should be considered in the evaluation of results from bioactivity assays.

Fractionation of Dissolved Organic Matter by Co-Precipitation with Iron: Effects of Composition

Interactions between dissolved organic matter (DOM) and different physical-chemical forms of iron (Fe) represent important biogeochemical processes in the organic carbon cycle. Due to the effect of climate change and anthropogenic activities such as land-use change, the loading of terrestrial DOM into aquatic systems is increasing, and thus, enhancing the organic matter-based acidity in aquatic ecosystems. While complexation of Fe with DOM and the sorption of DOM on iron oxides and (oxy)hydroxides have been reported, less is known about how co-precipitation processes might affect by DOM composition. Here the co-precipitation of two DOM standards, namely the Suwannee River Standard Humic Acid Standard II (SRHA) and Nordic Aquatic Fulvic Acid Reference (NAFA), with Fe was investigated in a pH range of 4.0–8.0. The DOM remaining after co-precipitating with Fe was systematically characterized by various analytical methods to reveal the molecular fractionation of DOM. The co-precipitation of SRHA or NAFA with Fe was enhanced by decreasing the pH, where at pH 4.0, about 70~80% DOC of SRHA or NAFA was removed at Fe(III)/C ratios higher than 0.12. The decrease in SUVA254 and the humification index (HIX) during the co-precipitation process suggests that DOM with high aromatic character was preferentially co-precipitated with Fe. DOM molecular weight influenced the selectivity to co-precipitation, with high molecular weight (HMW) DOM showing a stronger affinity. DOM co-precipitation with Fe was clearly dependent on DOM composition, showing an affinity order of terrestrial humic-like> ubiquitous humic-like> microbial humic-like components. The difference in the reactivity and the relative abundances of excitation emission matrix fluorescence combined with parallel factor analysis (EEM-PARAFAC) components explained the difference in DOC removal efficiency between SRHA and NAFA. This study provides direct insights into the effects of DOM composition on its fractionation specifically through co-precipitation with Fe, and suggests that for aquatic systems rich in iron-based (oxy)hydroxides, and for environmental redox interfaces, co-precipitation of DOM with iron might affect optical properties of the aqueous phase, and represent an important sink for terrestrially-derived organic matter.

Surface adsorption of Nordic aquatic fulvic acid on amine-functionalized and non-functionalized mesoporous silica nanoparticles

Mesoporous silica nanoparticles (MSNs) have the potential to be released into the environment and to then adsorb natural organic matter.

Photosensitized Degradation of Amitriptyline and Its Active Metabolite Nortriptyline in Aqueous Fulvic Acid Solution.

Amitriptyline is a frequently prescribed tricyclic antidepressant. Although amitriptyline and its active metabolite, nortriptyline, have been widely detected in natural waters, their environmental fate due to photodegradation is poorly understood. Here we describe a study conducted to investigate the photodegradation of amitriptyline and its active metabolite under simulated sunlight. Neither amitriptyline nor nortriptyline underwent direct photodegradation, but rapid photosensitized degradation did occur in fulvic acid (FA) solutions. The photodegradation of amitriptyline and nortriptyline followed pseudo-first-order kinetics with rate constants 0.24 and 0.16 h, respectively, at pH 8.0 in air-saturated FA solutions. The photodegradation of the substrates increased markedly with pH. The deprotonation of amitriptyline and nortriptyline facilitated the availability of nonbonding electrons on nitrogen (N-electrons). The excited triplet state of FA (FA*) was verified as the main reactive species responsible for the photosensitized degradation. An electron transfer mechanism for the interaction between substrates and FA* was proposed on the basis of a series of quenching experiments, kinetic model and photoproducts determination. Demethylation at the α-carbon of amine and hydroxylation were two primary photochemical processes initiated by the electron transfer reaction in the air-saturated FA solution; these were followed by generation of demethyl amine and mono-hydroxylation isomers. Our results suggest that indirect photodegradation is an important elimination process for amitriptyline and its active metabolite in natural waters.

Composition and copper binding properties of aquatic fulvic acids in eutrophic Taihu Lake, China

Fulvic acid (FA) plays a significant role in biogenic-elemental cycling in aquatic ecosystems which is highly dependent on their organic composition. In this study, the aquatic FA contents and binding properties during bloom and non-bloom periods in Taihu Lake were investigated by two-dimensional correlation spectroscopy Fourier transform infrared spectroscopy (2D-COS-FTIR), nuclear magnetic resonance (NMR) and elemental analysis. Compared with non-bloom FA, bloom FA was of lower nitrogen content and higher C/N ratio. It contained more carboxylic and aliphatic groups while less amide groups. 2D-COS-FTIR spectra evidenced the carboxyl groups in bloom FA had the fastest response to Cu(II) binding. Also, polysaccharide in bloom FA was more susceptive to Cu(II) concentrations than that in non-bloom FA. While comparing with bloom FA, the N-rich organic compounds in non-bloom FA exhibited faster binding sequence with Cu(II). A comprehensive scheme about the interaction process of FA-Cu(II) showed that both nitrogenous and oxygenic groups in FAs were active in binding to Cu(II). The alteration in binding behaviors of organic groups in FAs to Cu(II) may have been driven by algal products and microbial community variety in Taihu Lake. Our results here have the potential to contribute significantly to future studies of dissolved organic matter dynamic biogeochemistry processes and trace metal cycling processes in eutrophic lakes.

Uptake of ammonium and soluble reactive phosphorus in forested streams: influence of dissolved organic matter composition

Many microbes responsible for inorganic nutrient uptake and transformation utilize dissolved organic matter (DOM) as a nutrient or energy source, but little is known about whether DOM composition is an important driver of nutrient uptake in streams. Our goal was to determine whether incorporating DOM composition metrics with other more commonly considered biological, physical, and chemical variables improved our ability to explain patterns of ammonium ( $${\text{NH}}_{4}^{ + }$$ –N) and soluble reactive phosphorus (SRP) uptake across 11 Lake Superior tributaries. Nutrient uptake velocities (Vf) ranged from undetectable to 14.6 mm min−1 for $${\text{NH}}_{4}^{ + }$$ –N and undetectable to 7.2 mm min−1 for SRP. Logistic regressions suggested that DOM composition was a useful predictor of where SRP uptake occurred (4/11 sites) and $${\text{NH}}_{4}^{ + }$$ –N concentration was a useful predictor of where $${\text{NH}}_{4}^{ + }$$ –N uptake occurred (9/11 sites). Multiple regression analysis revealed that the best models included temperature, specific discharge, and canopy cover, and DOM composition as significant predictors of $${\text{NH}}_{4}^{ + }$$ –N Vf. Partial least squares revealed fluorescence index (describing the source of aquatic fulvic acids), specific ultraviolet absorbance at 254 nm (an indicator of DOM aromaticity), temperature, and conductivity were highly influential predictors of $${\text{NH}}_{4}^{ + }$$ –N Vf. Therefore, streams with higher temperatures, lower solute concentrations, more terrestrial DOM signal and greater aromaticity had greater $${\text{NH}}_{4}^{ + }$$ –N Vf. Our results suggest that DOM composition may be an important, yet often overlooked, predictor of $${\text{NH}}_{4}^{ + }$$ –N and SRP uptake in deciduous forest streams that should be considered along with commonly measured predictors.

Experimental evidence of incomplete fluorescence quenching of pyrene bound to humic substances: implications for Koc measurements.

Fluorescence quenching (FQ) is extensively used for quantitative assessment of partition coefficients (KOC) of polycyclic aromatic hydrocarbons (PAHs) to natural organic materials - humic substances (HS). The presence of bound PAHs with incompletely quenched fluorescence would lead to underestimation of the KOC values measured by this technique. The goal of this work was to prove the validity of this assumption using an original experimental setup, which implied FQ measurements upon excitation into two distinct vibronically coupled electronic states. Pyrene was used as a fluorescent probe, and aquatic fulvic acid (SRFA) and leonardite humic acid (CHP) were used as the humic materials with low and high binding affinity for pyrene, respectively. Excitation of pyrene into the forbidden (S0-S1) and allowed (S0-S2) electronic states yielded two pairs of nonidentical FQ curves. This was indicative of incomplete quenching of the bound pyrene, and the divergence of the two FQ curves was much more pronounced for CHP as compared to SRFA. The two component model of fluorescence response formation was proposed to estimate the KOC values from the data obtained. The resulting pyrene KOC value for CHP (220 ± 20) g L(-1) was a factor 3 higher compared to the KOC value determined with the use of the Stern-Volmer formalism (68 ± 2) g L(-1). At the same time for aquatic FA the difference in FQ curves was almost negligible, which enables the use of the Stern-Volmer formalism for weakly interacting HS and PAHs.

Influence of operating parameters on performance of SO2 absorption in fulvic acid solution

A novel process of flue gas desulfurization by aqueous fulvic acid (FA) solution with acid-base buffering capacity was developed. Experiments were carried out to investigate the influence of operating parameters such as the FA concentration, pH, temperature, gas flow rate, fly ash, O2, SO2 inlet concentration, CO2 and NO2 on SO2 absorption efficiency and Duration Time of High Efficiency (DTHE, the time of the SO2 absorption efficiency above 95%) in a lab-scale bubbling reactor. The results show high FA concentration has more absorption capacity for SO2, and the optimum concentration of FA solution is 0.08gmL−1, at which point the absorption efficiency is above 98%. The inlet SO2 concentration has little influence on absorption efficiency, but DTHE reduces with increasing inlet SO2 concentration. O2 has a little effect on absorption efficiency. The SO2 absorption efficiency is not affected by pH change in the range from 5.5 to 3.3, and maintained above 97.4%. Fly ash can improve SO2 absorption efficiency and DTHE. NO2 can accelerate the oxidation of bisulfite to sulfate and promote SO2 absorption. CO2 hardly influences on SO2 absorption efficiency, but the SO2 absorption capacity decreases with the increasing of CO2 partial pressure. Furthermore, the thermal stability and regenerability of FA were also evaluated by TG-DTG and XRD, respectively. The results demonstrate that FA with stable performances is a promising regenerative absorbent for the removal of SO2.

Studies of interactions of aquatics disinfectants (chlorine dioxide and chlorine) with tropical aquatic fulvic acids monitored by differ-ential absorbance spectroscopy

Studies of interactions of aquatics disinfectants (chlorine dioxide and chlorine) with tropical aquatic fulvic acids monitored by differ-ential absorbance spectroscopy

Fulvic acid complexation of Eu(III) and Cm(III) at elevated temperatures studied by time-resolved laser fluorescence spectroscopy.

The interaction of Eu(III) and Cm(III) with three different aquatic fulvic acids (FA) was studied as a function of the temperature (T = 20-80 °C) in 0.1 M NaCl solution by time-resolved laser fluorescence spectroscopy. The speciation of both trivalent metal ions was determined by peak deconvolution of the recorded fluorescence spectra. For each studied metal ion-FA system only one complexed species is formed under the given experimental conditions. The stability constants at 20, 40, 60 and 80 °C (log β'(T)) were determined according to the charge neutralization model. The log β' (20 °C) for the different FAs show similar values (log β(20 °C) = 5.60-6.29). The stability constants increase continuously with increasing temperature by approximately 0.3-1.0 orders of magnitude. The reaction enthalpies and entropies are derived from the integrated Van't Hoff equation. The results show that all investigated complexation reactions are endothermic and entropy-driven.

Probing the pH Dependent Optical Properties of Aquatic, Terrestrial and Microbial Humic Substances by Sodium Borohydride Reduction

Chemically reducing humic (HA) and fulvic acids (FA) provides insight into spectroscopically identifiable structural moieties generating the optical properties of HA/FA from aquatic, microbial and terrestrial sources. Sodium borohydride reduction provides targeted reduction of carbonyl groups. The contrast between the pH induced optical changes of untreated, reduced and reoxidized HA/FA highlights differences in the quantity, and physicality of structural components generating optical properties associated with HA/FA. Because borohydride reactions alter pH, pH re-adjustment to the original pH is required. Careful titrations of selected HA/FA provided the mmole H+ g-1 HA/FA required to titrate reduced and reoxidized HA/FA from pH 2-11; and the pH dependent spectral slope (S) at low (pH 2-3), neutral (pH 7-7.5) and high (pH 11.0). Molar extinction coefficients (e) (Lmg-1cm-1) at pH 7.6 and 350 nm provide a point of consistency linking intrinsic pH dependent optical properties to the concentration of material used for titrations. Soil derived humic acids differ from aquatic humic acids in the heterogeneity of optically identifiable group as well as the overall concentration of those groups. The microbial source of FA has a limited concentration of homogeneous titratable groups when compared to aquatic FA generated terrestrially. Microbial FA exhibits pH linked optical recovery upon reoxidation when compared to aquatic FA which is consistent with the presence of quinones in microbial FA.