Effects of UV-visible irradiation on natural organic matter from the Amazon basin

Fate of Naturally Dissolved Organic Matter and Synthetic Organic Compounds Subjected to Drinking Water Treatment Using Membrane, Activated Carbon, and UV/H2O2 Technologies

Organic pollutants are toxic and are present in drinking water. The conventional processes of most water plants can basically meet the discharge standard. However, based on the improvement of the objective of organic pollutants control and the constant change of water characteristics, the results may not be ideal. This study evaluates the effectiveness of different treatments such as microfiltration, nanofiltration, reverse osmosis, activated carbon, and ultraviolet irradiation/H₂O₂ in terms of the removal of organic pollutants. Among the DOM results, nanofiltration, reverse osmosis, and activated carbon showed optimal performance due to the characteristics of processes and the compound properties. However, the risks of low-molecular-weight organic residue and byproduct formation are still present. Thirty-nine species of synthetic organic compounds (SOC) were qualitatively and semiquantitatively analyzed. Different technologies showed varying removal capabilities for SOC based on their properties and many substances coexisted leading to abnormal removal performances. These residual organics showed the characteristics of lower molecular weight, more hydrophilicity, further unknown impacts, and with risk of DBPs. Based on the above insights, possible methods can be rationally chosen for on-demand decontamination of organics in unconfined aquatic environment and long-time impact on water characteristics and human health also should be considered.

Review of Fluorescence Spectroscopy in Environmental Quality Applications

Fluorescence spectroscopy is an optical spectroscopic method that has been applied for the assessment of environmental quality extensively during the last 20 years. Most of the earlier works have used conventional light sources in spectrofluorometers to assess quality. Many recent works have used laser sources of light for the same purpose. The improvement of the energy sources and of the higher resolution spectrometers has led to a tremendous increase in applications. The motivation for the present review study is the increasing use of laser sources in environmental applications. The review is divided in two parts. The fundamental principles of fluorescence spectroscopy are described in the first part. The environmental applications are described in the second part.

A review on fluorescence spectroscopic analysis of water and wastewater

In recent years, the application of fluorescence spectroscopy has been widely recognized in water environment studies. The sensitiveness, simplicity, and efficiency of fluorescence spectroscopy are proved to be a promising tool for effective monitoring of water and wastewater. The fluorescence excitation-emission matrix (EEMs) and synchronous fluorescence spectra have been widely used analysis techniques of fluorescence measurement. The presence of organic matter in water and wastewater defines the degree and type of pollution in water. The application of fluorescence spectroscopy to characterize dissolved organic matter (DOM) has made the water quality assessment simple and easy. With the recent advances in this technology, components of DOM are identified by employing parallel factor analysis (PARAFAC), a mathematical trilinear data modeling with EEMs. The majority of wastewater studies indicated that the fluorescence peak of EX/EM at 275 nm/340 nm is referred to tryptophan region (Peak T1). However, some researchers identified another fluorescence peak in the region of EX/EM at 225-237 nm/340-381 nm, which described the tryptophan region and labeled it as Peak T2. Generally, peak T is a protein-like component in the water sample, where T1 and T2 signals were derived from the <0.20μm fraction of pollution. Therefore, a more advanced approach, such as an online fluorescence spectrofluorometer, can be used for the online monitoring of water. The results of various waters studied by fluorescence spectroscopy indicate that changes in peak T intensity could be used for real-time wastewater quality assessment and process control of wastewater treatment works. Finally, due to its effective use in water quality assessment, the fluorescence technique is proved to be a surrogate online monitoring tool and early warning equipment.

Relating natural organic matter conformation, metal complexation, and photophysics

We investigated the relationship between changes in fluorescence intensity and in fluorescence anisotropy for Suwannee River Natural Organic Matter (SRNOM) due to the formation of NOM-metal complexes with divalent and trivalent metals commonly present in both fresh water and sea water environments. We chose metal ions whose complexes give rise to both fluorescence quenching (Fe3+, Cu2+) and fluorescence enhancement (Al3+, Mg2+). Stern–Volmer type analyses quantified the changes in the SRNOM fluorescence as a function of metal concentration. All metals display strong complexation with SRNOM, associated with their effect on fluorescence. Experiments with Fe3+ further show strong effects due to NOM aggregation at all but the lowest metal concentrations studied here. There was little to no change in the conformation of SRNOM as inferred from fluorescence anisotropy caused by increasing metal concentration. These results suggest that there is no correlation between photophysical changes and conformational changes in NOM associated with complexation by the metal ions.

Effect of UVC pre-irradiation on the Suwannee river Natural Organic Matter (SRNOM) photooxidant properties

The present study aimed to investigate the changes in the chemical composition, and in the optical and photooxidant properties of Suwannee River Natural Organic Matter (SRNOM) induced by UVC (254 nm) treatment. The extent of the photodegradation was first assessed by UV-visible/fluorescence spectroscopies and organic carbon analysis. An in-depth investigation of the chemical changes was also conducted using liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry after derivatizations. A series of mono, di and tricarbonyls and mono and dicarboxylic acids in C₁C₆ were identified in samples irradiated from 1 to 4 h. After 3 h of irradiation, carbonyls accounted for 46% of the organic carbon remaining in solution whereas carboxylic acids represented about 2%. Then, we investigated the modifications of the photooxidant properties of SRNOM induced by these chemical changes. At 254 nm, UVC pre-irradiated SRNOM photodegraded glyphosate 29 times faster than original SRNOM and the reaction was fully inhibited by 2-propanol (5 × 10^-3 M). This enhanced photooxidant properties at 254 nm toward glyphosate was therefore reasonably due to •OH radicals formation, as confirmed by additional ESR measurements. A mechanism involving a chain reaction was proposed based on independent experiments conducted on carbonyl compounds, particularly pyruvic acid and acetone. The findings of this study show that UVC pre-treatment of NOM can enhance the removal of water pollutants and suggests a possible integration of a NOM pre-activation step in engineered water treatment sytems.

Interplay of oxygen and light in the photo-oxidation of dissolved organic carbon

Light energy and oxygen drive photo-oxidation of dissolved organic carbon (DOC). The longer the wavelength the greater its depth of penetration into water, changing the spectral environment with depth. We asked how oxygen concentration and light spectral composition might affect photo-oxidation processes in DOC. Outdoor experiments compared responses of fluorescence and absorbance indices to photo-oxidation of filtered (0.45 µm) Rio Negro water (Amazon Basin) under near-anoxia, normoxia and hyperoxia exposed to natural sunlight or reduced sunlight (≥340, reduced-UVR). Near-anoxia decreased all absorbance and fluorescence indices. Absorbance changed across the spectrum (≥250 nm) even under reduced-UVR provided that oxygen was present. This phenomenon maintains broader photo-oxidation and the release of CO₂ at depth. Slope_350-400 was responsive to changes in the irradiance field but not to oxygen concentration, while Slope_275-295 responded to both. Thus, larger molecules are broken down near the water's surface and medium to smaller molecules continue to be processed at depth. The production of fulvic acid-like fluorescence required both UVB and oxygen, restricting its production to surface waters. The relatively small increase in R_254/365 compared with the loss of SUVA₂₅₄ under near-anoxia indicated a slower breakdown of larger DOC molecules as oxygen becomes limiting. Breakdown of larger molecules which absorb in the 350-400 nm range, appears to involve two steps - one by radiant energy and another involving oxygen. The study results reflect the dynamic gradients in photo-oxidation with depth.

Photochemical Reactivity of Humic Substances in an Aquatic System Revealed by Excitation-Emission Matrix Fluorescence

The photochemical reactivity of humic substances plays a critical role in the global carbon cycle, and influences the toxicity, mobility, and bioavailability of contaminants by altering their molecular structure and the mineralization of organic carbon to CO₂. Here, we examined the simulated irradiation process of Chinese standard fulvic acid (FA) and humic acid (HA) by using excitation-emission matrix fluorescence combined with fluorescence regional integration (FRI), parallel factor (PARAFAC) analysis, and kinetic models. Humic-like and fulvic-like materials were the main materials (constituting more than 90%) of both FA and HA, according to the FRI analysis. Four components were identified by the PARAFAC analysis: fulvic-like components composed of both carboxylic-like and phenolic-like chromophores (C1), terrestrial humic-like components primarily composed of carboxylic-like chromophores (C2), microbial humic-like overwhelming composed of phenolic-like fluorophores (C3), and protein-like components (C4). After irradiation for 72 h, the maximum fluorescence intensity (F _max) of C1 and C2 of FA was reduced to 36.01-58.34%, while the F _max of C3 of both FA and HA also decreased to 0-9.63%. By contrast, for HA, the F _max of its C1 and C2 increased to 236.18-294.77% when irradiated for 72 h due to greater aromaticity and photorefractive tendencies. The first-order kinetic model (R ² = 0.908-0.990) fitted better than zero-order kinetic model (R ² = 0-0.754) for the C1, C2, and C3, of both FA and HA, during their photochemical reactivity. The photodegradation rate constant (k ₁) of C1 had values (0.105 for FA; 0.154 for HA) that surpassed those of C2 (0.059 for FA, 0.079 for HA) and C3 (0.079 for both FA and HA) based on the first-order kinetic model. The half-life times of C1, C2, and C3 ranged from 6.61-11.77 h to 4.50-8.81 h for FA and HA, respectively. Combining an excitation-emission matrix with FRI and PARAFAC analyses is a powerful approach for elucidating changes to humic substances during their irradiation, which is helpful for predicting the environmental toxicity of contaminants in natural ecosystems.

The physiology of fish in acidic waters rich in dissolved organic carbon, with specific reference to the Amazon basin: Ionoregulation, acid-base regulation, ammonia excretion, and metal toxicity

Although blackwaters, named for their rich content of dissolved organic carbon (DOC), are often very poor in ions and very acidic, they support great fish biodiversity. Indeed, about 8% of all freshwater fish species live in the blackwaters of the Rio Negro watershed in the Amazon basin. We review how native fish survive these harsh conditions that would kill most freshwater fish, with a particular focus on the role of DOC, a water quality parameter that has been relatively understudied. DOC, which is functionally defined by its ability to pass through a 0.45-µm filter, comprises a diverse range of compounds formed by the breakdown of organic matter and is quantified by its carbon component that is approximately 50% by mass. Adaptations of fish to acidic blackwaters include minimal acid-base disturbances associated with a unique, largely unknown, high-affinity Na⁺ uptake system that is resistant to inhibition by low pH in members of the Characiformes, and very tight regulation of Na⁺ efflux at low pH in the Cichliformes. Allochthonous (terrigenous) DOC, which predominates in blackwaters, consists of larger, more highly colored, reactive molecules than autochthonous DOC. The dissociation of protons from allochthonous components such as humic and fulvic acids is largely responsible for the acidity of these blackwaters, yet at the same time, these components may help protect organisms against the damaging effects of low water pH. DOC lowers the transepithelial potential (TEP), mitigates the inhibition of Na⁺ uptake and ammonia excretion, and protects against the elevation of diffusive Na⁺ loss in fish exposed to acidic waters. It also reduces the gill binding and toxicity of metals. At least in part, these actions reflect direct biological effects of DOC on the gills that are beneficial to ionoregulation. After chronic exposure to DOC, some of these protective effects persist even in the absence of DOC. Two characteristics of allochthonous DOC, the specific absorbance coefficient at 340 nm (determined optically) and the PBI (determined by titration), are indicative of both the biological effectiveness of DOC and the ability to protect against metal toxicity. Future research needs are highlighted, including a greater mechanistic understanding of the actions of DOCs on gill ionoregulatory function, morphology, TEP, and metal toxicity. These should be investigated in a wider range of native fish Orders that inhabit one of the world's greatest biodiversity hotspots for freshwater fishes.

Microfluidic approach for controlled ultraviolet treatment of colored and fluorescent dissolved organic matter

Using microfluidic systems to address the optical properties of Colored and Fluorescent Dissolved Organic Matter (CDOM/FDOM) offers new ways for researching its interactions with the environment, and its response to rapid, as well as extreme, changes of abiotic conditions. Here we present a microfluidic device with an Ultraviolet (UV) component. The manufactured microfluidic device consists of passing a dissolved organic matter sample through a microchannel applying a combination of treatments using different UV wavelengths and exposure times. Here we test the workability of the microdevice by analyzing the effect of UV light on CDOM and FDOM, using as irradiations UVA and UVB to incite photodegradation, over different times. We then compare the absorbance and fluorescence, measured from both treated and non-treated samples. The analysis of the measurements is done by the calculation of the slope ratio, as indicative of molecular weight and dissolved organic carbon, besides the fluorescence humification index (HIX) as an overview of the difference between treated and non-treated of the excitation-emission matrices (EEMs). Our results show the efficiency of the microdevice by demonstrating a direct relation of degradation degree with exposure time. FDOM exposure to UVB shows a possible relation to humic-like fluorophores intensity, shown in HIX and the overview difference. Furthermore, the changes showed in the slope ratio demonstrate photodegradation in all treatments, with UVB exhibiting an increased influence. The combination of microfluidic sample treatment within in situ applications of optical sensors will enhance our capacities in addressing biogeochemical processes in the marine environment, which were not accessible with conventional bulk methods.

Effects of natural light and depth on rates of photo-oxidation of dissolved organic carbon in a major black-water river, the Rio Negro, Brazil

Systems rich in terrigenous dissolved organic carbon (DOC), like the Rio Negro, can contribute significant amounts of carbon dioxide back to the atmosphere and support important microbial communities. We investigated photo-oxidation in the Rio Negro: (1) the depth to which light causes complete photo-oxidation to CO₂ and changes in DOC structure, (2) the daily rate of change of absorbance indices, (3) the relationship between sub-surface rates of photo-oxidation to CO₂ and light exposure, (4) the areal rates of photo-oxidation, and (5) the stability of fluorophore signals. Experiments were run in an outdoor pool of Rio Negro water, under natural sunlight during the dry seasons of 2015 and 2018. In 2018, rates of complete photo-oxidation and changes in absorbance indices decayed exponentially, approaching their asymptotes between 9 and 15 cm depth. In 2015, direct absorbance indices ceased changing at 14 cm depth. Fluorescence of humic acid-like moieties continued to decrease, sometimes to 35-43 cm depth. This indicates that partial photo-oxidation of DOC, and thus interaction with the microbial community, occurs to greater depths than previously expected. Areal rates of CO₂ production were 28.8 and 39.3 mg C m^-2 d^-1 (two experiments, October 2018). Sub-surface (1.1 cm) rates were strongly related to light levels, reaching a maximum of 0.68 mg C l^-1 d^-1 in September. Complete photo-oxidation ceased below 29.6 mW cm^-2 d^-1 UV radiation, providing a daily baseline for observable production of CO₂. Absorbance indices changed by 9 to 14% d^-1 at high light levels, except for R_254/365 (4.4% d^-1). Fluorophore emission ranges were stable between 2014 and 2018, indicating that emissions can be compared across time and space. This study contributes to better estimates and understanding of photo-oxidation in tropical, black-water rivers, which will be useful for carbon modelling.

Photocatalytic degradation of DOM in urban stormwater runoff with TiO2 nanoparticles under UV light irradiation: EEM-PARAFAC analysis and influence of co-existing inorganic ions

In situ photocatalytic degradation of dissolved organic matter (DOM) of stormwater runoff can efficiently improve the aquatic environment quality and relieve the wastewater treatment pressure. In this work, photocatalytic degradation of DOM in TiO₂ (AEROXIDE^® P-25) photocatalyst under illumination of ultraviolet (UV) light was carried out, considering the influence of various factors like TiO₂ dosage, solution pH along with the existence of co-existing ions (Cu²⁺ and H₂PO₄^-). Generally, the variations of dissolved organic carbon (DOC), UV-based parameters and peak intensities of fluorescent constituents with UV exposure time fitted perfectly with the pseudo-first-order kinetics model. The total DOM removal efficiency was affected by diversiform factors like adsorption capacity of TiO₂, UV light utilization efficiency, reactive free radicals produced and the influence of co-existing ions. The results of fluorescence excitation-emission matrix (EEM) coupled with parallel factor analysis (PARAFAC) modeling demonstrated that all the photodegradation rates for three identified fluorescent constituents (protein-like constituent 1 and 3, humic-like constituent 2) were faster than UV-absorbing chromophores, suggesting the DOM molecules in urban stormwater runoff contained much more π*-π transition structures. In addition, H₂PO₄^- ions affected the photodegradation of DOM by capturing positive holes (h⁺) and hydroxyl radical (·OH), whereas Cu²⁺ ions were inclined to generate Cu-protein complexes that were more difficult to degrade than the other Cu-DOM complexes. This study supplied novel insights into the photocatalytic degradation mechanism of individual organic constituent in urban stormwater runoff and explored the influences of co-existing contaminants on their adsorption-photocatalysis processes.

Cation-induced coagulation of aquatic plant-derived dissolved organic matter: Investigation by EEM-PARAFAC and FT-IR spectroscopy

Complexation and coagulation of plant-derived dissolved organic matter (DOM) by metal cations are important biogeochemical processes of organic matter in aquatic systems. Thus, coagulation and fractionation of DOM derived from aquatic plants by Ca(II), Al(III), and Fe(III) ions were investigated. Metal ion-induced removal of DOM was determined by analyzing dissolved organic carbon in supernatants after addition of these metal cations individually. After additions of metal ions, both dissolved and coagulated organic fractions were characterized by use of fluorescence excitation emission matrix-parallel factor (EEM-PARAFAC) analysis and Fourier transform infrared (FT-IR) spectroscopy. Addition of Ca(II), Fe(III) or Al(III) resulted in net removal of aquatic plant-derived DOM. Efficiencies of removal of DOM by Fe(III) or Al(III) were greater than that by Ca(II). However, capacities to remove plant-derived DOM by the three metals were less than which had been previously reported for humic materials. Molecular and structural features of plant-derived DOM fractions in associations with metal cations were characterized by changes in fluorescent components and infrared absorption peaks. Both aromatic and carboxylic-like organic matters could be removed by Ca(II), Al(III) or Fe(III) ions. Whereas organic matters containing amides were preferentially removed by Ca(II), and phenolic materials were selectively removed by Fe(III) or Al(III). These observations indicated that plant-derived DOM might have a long-lasting effect on water quality and organisms due to its poor coagulation with metal cations in aquatic ecosystems. Plant-derived DOM is of different character than natural organic matter and it is not advisable to attempt removal through addition of metal salts during treatment of sewage.

Characterization of dissolved organic matter in an urbanized estuary located in Northeastern Brazil

The Sal River estuary, which is located in the state of Sergipe, Northeastern Brazil, stands out as an urban estuary, anthropogenically impacted by untreated and treated wastewater discharge. Synchronous fluorescence spectroscopy and measurement of dissolved organic carbon (DOC) were used for characterization of dissolved organic matter (DOM) in the estuarine water. Dissolved organic carbon concentrations ranged from 7.5 to 19.0 mg L^-1 and, in general, the highest values were recorded during dry season. For both seasons (dry and rainy), DOC presented an inverse linear relationship with salinity, which indicates a conservative dilution of organic matter coming into the estuary. During rainy season, anthropogenic organic constituents and humic substances from land-based sources predominated in DOM composition, carried by river flow. Whereas during the dry season, it has been observed a significant increase of products generated by microbial degradation of anthropogenic organic matter. The relationships between fluorescence intensity and salinity suggest a conservative behavior during rainy season and a non-conservative behavior during dry season, with addition of fluorescent organic matter into the intermediate zone of the estuary. Photodegradation by action of sunlight caused a decrease in fluorescence intensity of humic and tryptophan-like constituents and the release of photoproducts, resulting in an increase in fluorescence intensity of protein-like constituents.

Preferential sorption of some natural organic matter fractions to titanium dioxide nanoparticles: influence of pH and ionic strength

Natural organic matter (NOM) sorption to nanoparticles (NPs) can influence their transport and bioavailability in the aquatic environment. The sorption affinity of NOM to surfaces including NPs is size dependent, and depending on environmental conditions, NOM may enhance or mitigate NPs toxicity. The aim of this study was to investigate the preferential sorption of different-sized fractions of NOM to titanium dioxide (TiO2) NPs. We specifically investigated the influence of pH, ionic strength, and NOM concentration on the extent of this preferential sorption using a constant sorbent concentration (400 mg/L TiO2 NPs). Additionally, sorption of NOM to TiO2 NPs at varying pH was investigated. The nonsorbed NOM was separated from the sorbed, by 50 nm polycarbonate membrane filters and ultracentrifugation. High-performance size exclusion chromatography (HPSEC) was used to determine the average molecular weights of NOM (MWw). Corroborative evidence of preferential sorption of different-sized molecular weight fractions of NOM was obtained from optical techniques such as absorbance and fluorescence spectrophotometry. The total organic carbon was measured by the Total Organic Carbon Analyzer-Shimadzu (TOC-VCPH). The results indicated that there is preferential sorption of larger sized fractions of NOM to TiO2 NPs irrespective of NOM concentration. It was observed that the sorption of larger sized fractions of NOM was much enhanced at lower pH and at higher ionic strength. Both absorbance and fluorescence spectrophotometric techniques gave credible corroborative evidence on the extent of preferential sorption of lager sized fractions of NOM with respect to pH and ionic strength. The sorption results demonstrated higher sorption at lower pH than at higher pH. Overall, the results of this study suggest that the environmental conditions are key factors that can contribute to NOM's fractional preferential sorption to NPs in the aquatic environment.

Effects of charging on the chromophores of dissolved organic matter from the Rio Negro basin

This study demonstrates that the deprotonation of dissolved organic matter (DOM) originating from a small creek characteristic for DOM-rich waters located in the Rio Negro basin can be quantified based on measurements of pH effects on its absorbance spectra. The method was ascertained by the data of Near-Edge X-Ray Absorbance Spectroscopy (NEXAFS), potentiometric titration to quantify the structural and compositional differences between the colloidal and hydrophobic fractions that contribute 91% of black-water creek DOM. Changes in the absorbance spectra of the DOM fractions caused by deprotonation quantified via numeric deconvolution which indicated the presence of six well-resolved Gaussian bands in the differential spectra. The emergence of these bands was determined to be associated with the engagement of carboxylic and phenolic functionalities and changes of inter-chromophore interactions in DOM molecules. Interpretation of the data based on the NICA-Donnan approach showed that behavior of DOM chromophores was consistent with results of potentiometric titrations. Similar trends were observed for changes of the spectral slope of the DOM absorbance spectra in the range of wavelengths 325-375 nm (DSlope325-375). The behavior of DSlope325-375 values was modeled based on the NICA-Donnan approach and correlated with potentiometrically-estimated charges attributed to the carboxylic and phenolic groups. The correlations between DSlope325-375 and charges of low- and high-affinity protonation-active groups in DOM were monotonic but not linear and had important differences between the colloidal and hydrophobic fractions.

Photobleaching of lignin derived compounds from pulp mill effluents upon irradiation: the key role of receiving waters

Lignin derived macromolecular compounds are the main constituents responsible for the hazardous effects of discharged effluents from the pulp and paper industry in receiving waters. It was shown by ultraviolet-visible (UV-vis) and fluorescence spectroscopies that a selective photodegradation of these structures occurred upon irradiation of fulvic acids (FA) from a kraft pulp mill effluent. Though photodegradation was not remarkably affected by the presence of the natural photosensitizer nitrate, it was inhibited under the presence of chloride. These results indicate that the fate of macromolecular organic matter from kraft pulp mill effluents may be different depending on the type of receiving waters, having a higher persistence when effluents are discharged in estuarine or marine waters than when they are discharged in fresh water.

Fibre optic sensors for selected wastewater characteristics

Demand for online and real-time measurements techniques to meet environmental regulation and treatment compliance are increasing. However the conventional techniques, which involve scheduled sampling and chemical analysis can be expensive and time consuming. Therefore cheaper and faster alternatives to monitor wastewater characteristics are required as alternatives to conventional methods. This paper reviews existing conventional techniques and optical and fibre optic sensors to determine selected wastewater characteristics which are colour, Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD). The review confirms that with appropriate configuration, calibration and fibre features the parameters can be determined with accuracy comparable to conventional method. With more research in this area, the potential for using FOS for online and real-time measurement of more wastewater parameters for various types of industrial effluent are promising.

Altering the characteristics of a leaf litter-derived humic substance by adsorptive fractionation versus simulated solar irradiation

Changes in the characteristics of a leaf litter-derived humic substance (LLHS) that resulted from its adsorption onto kaolinite or exposure to simulated solar irradiation were tracked using selected spectroscopic descriptors, apparent weight-average molecular weight (MW(w)) and pyrene binding. Heterogeneity within the original bulk LLHS was confirmed by a range of different characteristics obtained from ultrafiltration-based size fractions. In general, trends of some changing LLHS characteristics were similar for the adsorption and irradiation processes when tracked against percent carbon removal. For example, the overall values of specific ultraviolet absorbance (SUVA), MW(w), and humification index (HIX) all decreased with increasing irradiation time and with increasing concentration of mineral adsorbent in the respective experiments, indicating that both processes resulted in less aromatic and smaller-sized LLHS components remaining in solution. In addition, both the adsorption and irradiation experiments resulted in enrichment of the relative distribution of protein-like fluorescence (PLF), implying the PLF-related components had low affinities for phototransformation and mineral surface adsorption. Despite these apparently similar overall trends in LLHS characteristics caused by the adsorption and irradiation processes, closer examination revealed considerable differences in how the two processes altered the original material. Net production of intermediate-sized constituents was observed only with the irradiation experiments. In addition, residual LLHS resulting from the adsorptive fractionation experiments exhibited consistently higher pyrene binding versus the irradiated LLHS despite having comparable MW(w) values. Changes in LLHS characteristics due to adsorption by kaolinite were likely caused by physical mechanisms (primarily hydrophobic interactions between LLHS components and the kaolinite surface) whereas the irradiation-induced changes appear to have been governed by the combined effects of several alteration mechanisms, including the transformation of more condensed aromatic structures to less aromatic constituents, conformational changes resulting from selective photooxidation, and the photochemical disruption of intramolecular charge-transfer interactions.

Bacterioplankton features and its relations with doc characteristics and other limnological variables in Paraná river floodplain environments (PR/MS-Brazil)

Since the introduction of the Microbial Loop concept, many studies aimed to explain the role of bacterioplankton and dissolved organic carbon (DOC) in aquatic ecosystems. Paraná River floodplain system is a very complex environment where these subjects were little explored. The aim of this work was to characterize bacterial community in terms of density, biomass and biovolume in some water bodies of this floodplain and to verify its temporal variation and its relation with some limnological variables, including some indicators of DOC quality, obtained through Ultraviolet-visible (UV-VIS) and fluorescence spectroscopic analysis. Bacterial density, biomass and biovolume are similar to those from other freshwater environments and both density and biomass were higher in the period with less rain. The limnological and spectroscopic features that showed any relation with bacterioplankton were the concentrations of N-NH₄ and P-PO₄, water transparency, and some indicators of DOC quality and origin. The analysis of these relations showed a possible competition between bacterioplankton and phytoplankton for inorganic nutrients and that the DOC used by bacterioplankton is labile and probably from aquatic macrophytes.

A model approach to assess the long-term trends of indirect photochemistry in lake water. The case of Lake Maggiore (NW Italy)

A model-based approach is here developed and applied to predict the long-term trends of indirect photochemical processes in the surface layer (5m water depth) of Lake Maggiore, NW Italy. For this lake, time series of the main parameters of photochemical importance that cover almost two decades are available. As a way to assess the relevant photochemical reactions, the modelled steady-state concentrations of important photogenerated transients ((•)OH, ³CDOM* and CO₃(-•)) were taken into account. A multivariate analysis approach was adopted to have an overview of the system, to emphasise relationships among chemical, photochemical and seasonal variables, and to highlight annual and long-term trends. Over the considered time period, because of the decrease of the dissolved organic carbon (DOC) content of water and of the increase of alkalinity, a significant increase is predicted for the steady-state concentrations of the radicals (•)OH and CO₃(-•). Therefore, the photochemical degradation processes that involve the two radical species would be enhanced. Another issue of potential photochemical importance is related to the winter maxima of nitrate (a photochemical (•)OH source) and the summer maxima of DOC ((•)OH sink and ³CDOM* source) in the lake water under consideration. From the combination of sunlight irradiance and chemical composition data, one predicts that the processes involving (•)OH and CO₃(-•) would be most important in spring, while the reactions involving ³CDOM* would be most important in summer.

Spectroscopic changes on fulvic acids from a kraft pulp mill effluent caused by sun irradiation

Large volumes of wastewater with a high organic load are generated by the pulp and paper industry that negatively affect the quality of receiving waters. The main waste products in the pulp mill effluents are lignin derived macromolecular compounds, which are similar to natural humic substances and very resistant to wastewater treatments. Fulvic acids (FA) represent the higher percentage of these humic substances and it was observed that solar irradiation modify their properties. Several analytic tools, namely, UV-Visible, molecular fluorescence and FTIR spectroscopies, were used to assess the effect of solar exposition on fulvic acids from a kraft pulp mill effluent. It may be concluded that sun irradiation may alter to a high extent the physicochemical properties of macromolecular organic matter, namely fulvic acids, released by kraft pulp mill effluents. After solar exposition, the aromaticity decreases, the aliphatic structures become more oxygenated, and the fulvic acids from the pulp mill effluent remaining in solution are more similar to aquatic fulvic acids from non polluted sites.

Effects of solar radiation on the fluorescence properties and molecular weight of fulvic acids from pulp mill effluents

The pulp and paper industry generates large volume of wastewater that adversely affects water resources. Lignin derived macromolecular compounds, similar to natural humic substances, are the main waste products in the pulp mill effluents. The UV-Vis and fluorescence spectroscopies were used to assess the effect of solar exposition on fulvic acids from a kraft pulp mill effluent. Solar irradiation of the solutions of these fulvic acids caused solution acidification and decay both in the UV-Vis absorbance and in the fluorescence. This decay was not the same for the whole spectra but pointed to the selective photodegradation of lignin typical structures. Furthermore, by sequential ultrafiltration it was found that during irradiation, the high-molecular weight fractions were destroyed and low-molecular-weight constituents, potentially more able to penetrate the cell membranes of living organisms were formed. Photodegradation of macromolecular organic matter from a kraft pulp mill effluent may be a key process occurring in natural waters that modifies the physicochemical properties of such effluents.

Changes in optical properties caused by UV-irradiation of aquatic humic substances from the amazon river basin: seasonal variability evaluation

Aquatic humic substances (AHS) isolated from two characteristic seasons of the Negro river, winter and summer corresponding to floody and dry periods, were structurally characterized by 13C nuclear magnetic ressonance. Subsequently, AHS aqueous solutions were irradiated with a polychromatic lamp (290-475 nm) and monitored by its total organic carbon (TOC) content, ultraviolet-visible (UV-vis) absorbance, fluorescence, and Fourier transformed infrared spectroscopy (FTIR). As a result, a photobleaching up to 80% after irradiation of 48 h was observed. Conformational rearrangements and formation of low molecular complexity structures were formed during the irradiation, as deduced from the pH decrement and the fluorescence shifting to lower wavelengths. Additionally a significant mineralization with the formation of CO2, CO, and inorganic carbon compounds was registered, as assumed by TOC losses of up to 70%. The differences in photodegradation between samples expressed by photobleaching efficiency were enhanced in the summer sample and related to its elevated aromatic content. Aromatic structures are assumed to have high autosensitization capacity effects mediated by the free radical generation from quinone and phenolic moieties.

An investigation into reservoir NOM reduction by UV photolysis and advanced oxidation processes

A comparison of four treatment technologies for reduction of natural organic matter (NOM) in a reservoir water was made. The work presented here is a laboratory based evaluation of NOM treatment by UV-C photolysis, UV/H(2)O(2), Fenton's reagent (FR) and photo-Fenton's reagent (PFR). The work investigated ways of reducing the organic load on water treatment works (WTWs) with a view to treating 'in-reservoir' or 'in-pipe' before the water reaches the WTW. The efficiency of each process in terms of NOM removal was determined by measuring UV absorbance at 254 nm (UV(254)) and dissolved organic carbon (DOC). In terms of DOC reduction PFR was the most effective (88% removal after 1 min) however there were interferences when measuring UV(254) which was reduced to a lesser extent (31% after 1 min). In the literature, pH 3 is reported to be the optimal pH for oxidation with FR but here the reduction of UV(254) and DOC was found to be insensitive to pH in the range 3-7. The treatment that was identified as the most effective in terms of NOM reduction and cost effectiveness was PFR.