Thermal fluorescence quenching properties of dissolved organic matter

The fluorescence excitation-emission matrices of dissolved organic matter (DOM) are investigated between 10 and 45 degrees C for river and waste waters and organic matter standards. With increased temperature, fluorescence intensity is quenched. It is demonstrated that for a range of river and wastewater samples, that tryptophan-like fluorescence exhibits a greater range of quenching (between 20+/-4% and 35+/-5%) than fulvic-like fluorescence (19+/-4 to 26+/-3%) over this temperature range. Humic substance standards exhibit similar fulvic-like (23+/-4%) fluorescence thermal quenching properties to river water samples (23+/-3%); however none of the samples exhibit quenching of tryptophan-like fluorescence to the same extent as the tryptophan standards (approximately 50%). Thermal fluorescence quenching is related to the exposure of the fluorophores to the heat source; our findings suggest that the tryptophan-like groups within DOM is more exposed in untreated wastewaters than in treated wastewaters riverine DOM. Thermal fluorescence properties have the potential to be used to source DOM, to provide additional chemical structural information, to temperature correct laser-induced remotely sensed DOM fluorescence, and to characterise DOM through the wastewater treatment process.     

Estimation of the hydrophobic fraction of dissolved organic matter in water samples using UV photometry

In this study, we tested a simple and rapid method for the estimation of carbon in the hydrophobic fraction of dissolved organic matter (DOM) of different origin (spruce, pine, and beech litter) in soil water. The method is based on the fact that the hydrophobic fraction of DOM contains almost entirely the aromatic moieties of DOM. Thus, it showed a clearly distinct light absorption at 260 nm compared to the hydrophilic fraction. This light absorption was directly proportional to the concentration of the hydrophobic fraction. Moreover, it was independent of the concentration of the hydrophilic fraction. We compared the concentrations of hydrophobic DOM estimated by the UV method with those of the conventional fractionation using chromatographic columns of XAD-8 macroporous resin and found an excellent agreement between the two methods for both solutions from laboratory sorption experiments and field samples of forest floor leachates and subsoil porewaters. In addition, the absorption at 260 nm of hydrophobic DOM proved to be independent of pH values ranging from 2.0 to 6.5. Compared to the conventional chromatographic fractionation, the method using the UV absorption at 260 nm is less time consuming, needs a much smaller sample volume, and showed a better reproducibility. However, its use is restricted to water samples of low nitrate (<25 mg L⁻¹) and Fe (<5 mg L⁻¹) concentrations and, probably, with the hydrophobic fraction dominated by aromatic compounds deriving from degradation of lignin.     

Development and application of functional assays for freshwater dissolved organic matter

A series of 11 standardised, reproducible, assays have been developed of physico-chemical functions of dissolved organic matter (DOM) in freshwaters. The assays provide quantitative information on light absorption, fluorescence, photochemical fading, pH buffering, copper binding, benzo(a)pyrene binding, hydrophilicity and adsorption to alumina. To obtain DOM for the assays, a 45 L sample of filtered freshwater was rotary-evaporated to reduce the volume to ca. 500 cm3. The concentrate was then passed through a strong cation exchanger, in the Na+ form, to remove alkaline-earth cations, and then through 0.7 and 0.2 microm filters. Eight samples, two each from a lake and three streamwaters, were processed. The yields of dissolved organic carbon (DOC) ranged from 70% to 107% (average 91%). The samples of DOM, stored in the dark at 4 degrees C, retained their functional assay characteristics for up to 7 months. When assaying the concentrates, parallel assays were performed with Suwannee River fulvic acid (SRFA), as a quality control standard. For most of the assays, the results for eight freshwater DOM samples are similar to those obtained with SRFA, the chief exception being the greater hydrophilicity of the DOM samples. For eight of the assays, variability among the DOM samples is significantly (p < 0.01) greater than can be explained by analytical error, i.e. by comparison with results for the SRFA quality standard; the three exceptional assays are photochemical fading, copper binding and benzo(a)pyrene binding. The two lakewater samples studied gave the most extreme assay results, probably because of the influence of phytoplankton-derived DOM. Significant correlations of hydrophilicity and adsorption with optical absorbance may mean that some DOM functional properties can be predicted from comparatively simple measurements.     

Continuous fluorescence excitation-emission matrix monitoring of river organic matter

Real-time fluorescence monitoring has been mostly performed in marine systems, with little progress being made in the application of fluorescence excitation-emission matrix (EEM) spectroscopy, especially for freshwater monitoring. This paper presents a two weeks experiment where real-time fluorescence EEM data have been obtained for Bourn Brook, Birmingham, UK, using an in-situ fibre-optic probe. Fluorescence EEMs were measured every 3 min for two weeks, with control ‘grab’ samples every hour analyzed for fluorescence EEMs as well as pH, conductivity and dissolved organic carbon. Comparison of real-time and control samples showed an excellent agreement, with no evidence of fibre-optic probe fouling. EEMs of different character were identified using self-organizing maps, which demonstrated seven clusters of fluorescence EEMs which related to the intensity of fluorescence and relative intensities of peak T₁ and T₂ vs. peak C and peak A fluorescence. Fluorescence intensity of peaks A and C were observed to increase with rainfall, and a diesel pollution event was detected through an increase in T₂ fluorescence.     

Relating freshwater organic matter fluorescence to organic carbon removal efficiency in drinking water treatment

Monthly raw and clarified water samples were obtained for 16 UK surface water treatment works. The fluorescence excitation-emission matrix (EEM) technique was used for the assessment of total organic carbon (TOC) removal and organic matter (OM) characterisation. The impact of algae presence in water on TOC removal, and its relationship with fluorescence, was analysed. Fluorescence peak C intensity was found to be a sensitive and reliable measure of OM content. Fluorescence peak C emission wavelength and peak T intensity (reflecting the degree of hydrophobicity and the microbial fraction, respectively) were found to characterize the OM; the impact of both on TOC removal efficiency was apparent. OM fluorescence properties were shown to predict TOC removal, and identify spatial and temporal variations. Previous work indicates that the trihalomethane (THM) concentration of treated water can be predicted from the raw water TOC concentration. The simplicity, sensitivity, speed of analysis and low cost, combined with potential for incorporation into on-line monitoring systems, mean that fluorescence spectroscopy offers a robust analytical technique to be used in conjunction with, or in place of, other approaches to OM characterisation and THM formation prediction.     

An overall isotherm for activated carbon adsorption of dissolved natural organic matter in water

Design and analysis of activated carbon processes in water treatment often requires the adsorption isotherm for dissolved natural organic matter (NOM). Of the isotherm models available, the Summers and Roberts (SR) equation, capable of describing the adsorbent dose effect with the fewest parameters, has been successfully used to normalize NOM isotherm data. In this study, we show that the adsorbent dose in the SR equation can be eliminated as an intermediate variable and the initial concentration effect on NOM adsorption is then described explicitly. Comparing with the original SR equation, the derived isotherm equation is in a form more amenable to analysis. To ensure that the prediction is physically attainable, we introduced the limiting adsorption capacity by taking the adsorbent pore volume and size exclusion into consideration. Subsequently, we develop a simple relationship that can be used to determine the minimum adsorbent usage required for any desirable level of treatment. By comparing with extensive isotherm data previously published by Li et al. [2003a. Polydisperse adsorbability composition of several natural and synthetic organic matrices. J. Colloid Interface Sci. 265(2), 265-275], we demonstrated that the isotherm equation derived herein yields predictions that agree with the much more complicated fictive component-ideal adsorbed solution theory (IAST)-based model for NOM from different sources and over a range of initial concentrations.     

Nutrient and dissolved organic carbon removal from water using mining and metallurgical by-products

Excess nutrient input to water bodies frequently results in algal blooms and development of oxygen deficient conditions. Mining or metallurgical by-products can potentially be utilised as filtration media within water treatment systems such as constructed wetlands, permeable reactive barriers, or drain liners. These materials may offer a cost-effective solution for the removal of nutrients and dissolved organic carbon (DOC) from natural waters. This study investigated steel-making, alumina refining (red mud and red sand) and heavy mineral processing by-products, as well as the low-cost mineral-based material calcined magnesia, in laboratory column trials. Influent water and column effluents were analysed for pH and flow rate, alkalinity, nutrient species and DOC, and a range of major cations and anions. In general, by-products with high Ca or Mg, and to a lesser extent those with high Fe content, were well-suited to nutrient and DOC removal from water. Of the individual materials examined, the heavy mineral processing residue neutralised used acid (NUA) exhibited the highest sorption capacity for P, and removed the greatest proportions of all N species and DOC from influent water. In general, NUA and mixtures containing NUA, particularly those with calcined magnesia or red mud/red sand were the most effective in removing nutrients and DOC from influent water. Post-treatment effluents from columns containing NUA and NUA/steel-making by-product, NUA/red sand and NUA/calcined magnesia mixtures exhibited large reductions in DOC, P and N concentrations and exhibited a shift in nutrient ratios away from potential N- and Si-limitation and towards potential P-limitation. If employed as part of a large-scale water treatment scheme, use of these mining and metallurgical by-products for nutrient removal could result in reduced algal biomass and improved water quality. Identification and effective implementation of mining by-products or blends thereof in constructed wetlands or other intervention structures to augment nutrient and DOC retention has considerable potential as an aquatic ecosystem management tool.     

Characterization of dissolved organic matter in a submerged membrane bioreactor by using three-dimensional excitation and emission matrix fluorescence spectroscopy

Three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy was employed to characterize dissolved organic matter (DOM) in a submerged membrane bioreactor (MBR). Three fluorescence peaks could be identified from the EEM fluorescence spectra of the DOM samples in the MBR. Two peaks were associated with the protein-like fluorophores, and the third was related to the visible humic acid-like fluorophores. Only two main peaks were observed in the EEM fluorescence spectra of the extracellular polymeric substance (EPS) samples, which were due to the fluorescence of protein-like and humic acid-like matters, respectively. However, the EEM fluorescence spectra of membrane foulants were observed to have three peaks. It was also found that the dominant fluorescence substances in membrane foulants were protein-like substances, which might be due to the retention of proteins in the DOM and/or EPS in the MBR by the fine pores of the membrane. Quantitative analysis of the fluorescence spectra including peak locations, fluorescence intensity, and different peak intensity ratios and the fluorescence regional integration (FRI) analysis were also carried out in order to better understand the similarities and differences among the EEM spectra of the DOM, EPS, and membrane foulant samples and to further provide an insight into membrane fouling caused by the fluorescence substances in the DOM in submerged MBRs.     

Freeze/thaw and pH effects on freshwater dissolved organic matter fluorescence and absorbance properties from a number of UK locations

The UV-visible and fluorescence excitation-emission matrix spectrophotometric properties of dissolved organic matter (DOM) were compared for the effects of both pH and freeze/thaw on a wide range of freshwater DOM samples from the United Kingdom. It was observed that the spectrophotometric properties of our freshwater samples were sensitive to pH and that the recorded change varies with fluorescence and absorbance intensity, DOC concentration and the wavelength observed. Large and variable responses to pH were particularly severe at extremes of pH, but within the natural levels typically observed in freshwaters the response to pH was limited. For the same sample set large and variable responses were observed when subjected to freeze/thaw. From our data, knowledge of the original properties cannot be used to determine the amount of change that will occur with freezing and subsequent thawing. It is therefore recommended that in future research, to maintain the natural signal of the DOM, analysis is conducted at natural pH and without freezing to facilitate ease of comparison between studies. Our results also have implications for studies that utilise spectrophotometric techniques to investigate long-term trends in dissolved organic carbon in rivers. Spectrophotometric parameters from upland derived samples show varied responses of samples to pH and there is clear potential to complicate trends in the interpretation of long-term water colour data if pH is changing over time in a system or if samples are treated with different storage protocols with respect to acidification and freezing.     

Characterisation of dissolved organic matter in karst spring waters using intrinsic fluorescence: relationship with infiltration processes

From analysis of spectrophotometric properties of dissolved organic matter (OM) and the hydrochemical responses of some karst springs under different hydrologic conditions, an assessment of the origin and transfer pathway of OM present in karst spring waters, from soil and epikarst toward the spring, has been conducted for three karst aquifers in southern Spain: Alta Cadena, Sierra de Enmedio and Los Tajos. Intrinsic fluorescence (excitation-emission matrices or EEMs), together with major water chemistry (electrical conductivity, temperature, alkalinity, Cl⁻, Mg^+ 2) and P_CO2 along with natural hydrochemical tracers (TOC and NO₃⁻), have been monitored in 19 springs which drain the three karst aquifers examined in this study. The spring water EEM spectra indicate that fulvic acid-like substances, produced in the soil as a consequence of the decomposition of OM, are the dominant fluorophores, although some of the OM appears to originate from in situ microbiological activity but could be indicative of contamination present in recharge waters from livestock. During each recharge event, TOC and NO₃⁻ concentrations increased and variations in fluorescence intensities of peaks attributed to fulvic acid-like compounds were observed. In areas with minimal soil development, spatial and temporal variations in the fluorescence intensity of fulvic acid-like substances and other fluorophores derived from microbiological activity, together with other hydrochemical parameters, provide insights into the hydrogeological functioning of karst aquifers and the infiltration velocity of water from soil and facilitate assessment of contamination vulnerability in these aquifers.     

Evaluation of the catalytic reduction of nitrate for the determination of dissolved organic nitrogen in natural waters

The catalytic reduction of nitrate ions into nitrogen gas was tested to partly remove dissolved inorganic nitrogen (DIN) before the determination of dissolved organic nitrogen (DON). Experiments were conducted on nitrate solutions enriched with natural organic matter (NOM) isolates previously extracted from surface waters. Three catalysts Pd-In/Al2O3, Pd-Sn/Al2O3 and Pd/SnO2 were tested. Their noble metal (palladium) and promoter metal (indium or tin) contents are 5 and 1.75 wt%, respectively. Preliminary experiments performed on a solution containing 17 amino acids showed that most compounds were removed by less than 15%, probably due to sorption onto the catalysts. Reduction of nitrate in absence of NOM was complete after 20 min of reaction time and the removal of DIN was about 80% (about 19% formation of ammonium). In the presence of NOM (DOC 20 mgC/L, DON 0.67 mg N/L), the kinetic of nitrate reduction was slower and the reduction in DIN content was limited to 15% i.e. selectivity toward ammonium reached 85%. Adsorption tests showed a similar removal of both DOC and DON of about 70% and 30% onto Pd-Sn/Al2O3 and Pd/SnO2 catalysts, respectively, which confirmed that NOM probably compete with nitrate for active catalytic sites. In conclusion, catalytic reduction of nitrate before DON determination cannot be used because of DON sorption and low DIN removal.     

Photo-dissolution of flocculent, detrital material in aquatic environments: contributions to the dissolved organic matter pool

This study shows that light exposure of flocculent material (floc) from the Florida Coastal Everglades (FCE) results in significant dissolved organic matter (DOM) generation through photo-dissolution processes. Floc was collected at two sites along the Shark River Slough (SRS) and irradiated with artificial sunlight. The DOM generated was characterized using elemental analysis and excitation emission matrix fluorescence coupled with parallel factor analysis. To investigate the seasonal variations of DOM photo-generation from floc, this experiment was performed in typical dry (April) and wet (October) seasons for the FCE. Our results show that the dissolved organic carbon (DOC) for samples incubated under dark conditions displayed a relatively small increase, suggesting that microbial processes and/or leaching might be minor processes in comparison to photo-dissolution for the generation of DOM from floc. On the other hand, DOC increased substantially (as much as 259 mgC gC⁻¹) for samples exposed to artificial sunlight, indicating the release of DOM through photo-induced alterations of floc. The fluorescence intensity of both humic-like and protein-like components also increased with light exposure. Terrestrial humic-like components were found to be the main contributors (up to 70%) to the chromophoric DOM (CDOM) pool, while protein-like components comprised a relatively small percentage (up to 16%) of the total CDOM. Simultaneously to the generation of DOC, both total dissolved nitrogen and soluble reactive phosphorus also increased substantially during the photo-incubation period. Thus, the photo-dissolution of floc can be an important source of DOM to the FCE environment, with the potential to influence nutrient dynamics in this system.     

Reconsidering the quantitative analysis of organic carbon concentrations in size exclusion chromatography

The evaluation of the molecular size distribution of natural organic matter (NOM) in aquatic environments via size exclusion chromatography (SEC) is important for the understanding of environmental processes such as nutrient cycling and pollutant transport as well as of technical water treatment processes. The use of organic carbon (OC) detectors has become popular in recent studies due to improved availability and quantification possibilities, which supposedly are superior to those of ultraviolet (UV) detectors. A set of 12 NOM samples was used to demonstrate the limitations of online OC detection (OCD) when analyzing complex aquatic organic matter. A novel evaluation approach for SEC data is introduced by combining the information from UV absorbance (UVA) and OCD chromatograms as well as offline total OC (t-OC) and dissolved OC-specific UVA (SUVA) measurements. It could be shown that about 70% of certain OC components were not detected with the OCD system used in this study. For the investigated samples, these types of carbon accounted for up to 72% of the t-OC, i.e. for such NOM samples quantification by OCD is not possible or at least highly questionable. The addition of an oxidant improved the overall oxidation efficiency only slightly. Most likely NOM that predominantly consists of polysaccharides and features a nominal molecular weight of 150 kg/mol or more was responsible for low OCD yields. For future applications, a further improvement of the OCD system would be worthwhile so that quantitative analytical data on the molecular size distribution of NOM and its structural characteristics such as the SUVA distribution can be obtained.     

Concentrations and fluxes of dissolved organic carbon in UK topsoils

Dissolved organic carbon (DOC) concentrations in soil water samples collected from depths of 5 to 20 cm at 10 moorland and 11 forest sites during the period 2000-2006 were obtained from new measurements and from the monitoring programmes of the UK Environmental Change Network and the International Cooperative Programme (ICP) on Forests. Data on soil properties and vegetation type were also assembled. Considering data from Prenart tension collectors, which were used at nearly all the sites, mean annual concentrations ranged from 1.3 to 97.5 g m(-3) with means of 19.5 (standard deviation 15.2) and 27.6 (SD 23.3) g m(-3) for moorland and forest sites respectively. Interannual mean DOC concentration at an individual site varied by only 1.5-fold, averaged over all sites with at least three years' data. Concentrations during summer months (April to September) were on average 17% greater than those in winter (October to March). If data from two sites (the single peatland and an unusual forest site) were ignored, DOC concentrations were strongly inversely related to water flux, estimated from rainfall and evaporation data. Fluxes of DOC, calculated by combining concentration with water flux, ranged from 2.2 to 71.9 gC m(-2) yr(-1) over all sites and years, with overall means of 19.2 (SD 13.6) and 12.2 (SD 13.9) gC m(-2) yr(-1) for the moorland and forest sites respectively. However, if the two exceptional sites were omitted, the overall mean was 9.1 gC m(-)(2) yr(-1) with a standard deviation of only 4.9 gC m(-2) yr(-1). Annual DOC flux was strongly dependent upon annual water flux, varying by 3.5-fold between years when averaged over all sites. On average, 75.5% of the DOC was exported during the winter period (October to March).     

Comparison of river and canal water dissolved organic matter fluorescence within an urbanised catchment

Recently, growing interest has been shown in the study of canal water quality, yet no research using continuous fluorescence monitoring to characterise dissolved organic matter (DOM) has been performed. This paper evaluated DOM characteristics at hourly resolution. A comparison was made between canal and nearby urban river fluorescence spectra, to emphasise the specific nature of canal water DOM. Results showed that canal water had a significant proportion of microbially derived DOM, while the urban river had a greater proportion of terrestrially derived fractions. The microbial character of canal water DOM originated from the low flow of water, the nutrients predominance and continuous DOM processing. Hence, DOM fluorescence is invariant over a timescale of days, and recreational navigation and precipitation events have no major influence on DOM characteristics. Our results are expected to be applicable to future research on highly regulated freshwater systems for DOM quantity estimation or for water quality models.     

Natural versus wastewater derived dissolved organic carbon: implications for the environmental fate of organic micropollutants

The interaction of organic micropollutants with dissolved organic carbon (DOC) can influence their transport, degradation and bioavailability. While this has been well established for natural organic carbon, very little is known regarding the influence of DOC on the fate of micropollutants during wastewater treatment and water recycling. Dissolved organic carbon-water partition coefficients (K_DOC) for wastewater derived and reference DOC were measured for a range of micropollutants using a depletion method with polydimethylsiloxane disks. For micropollutants with an octanol-water partition coefficient (log K_OW) greater than 4 there was a significant difference in K_DOC between reference and wastewater derived DOC, with partitioning to wastewater derived DOC over 1000 times lower for the most hydrophobic micropollutants. The interaction of nonylphenol with wastewater derived DOC from different stages of a wastewater and advanced water treatment train was studied, but little difference in K_DOC was observed. Organic carbon characterisation revealed that reference and wastewater derived DOC had very different properties due to their different origins. Consequently, the reduced sorption capacity of wastewater derived DOC may be related to their microbial origin which led to reduced aromaticity and lower molecular weight. This study suggests that for hydrophobic micropollutants (log K_OW > 4) a higher concentration of freely dissolved and thus bioavailable micropollutants is expected in the presence of wastewater derived DOC than predicted using K_DOC values quantified using reference DOC. The implication is that naturally derived DOC may not be an appropriate surrogate for wastewater derived DOC as a matrix for assessing the fate of micropollutants in engineered systems.     

Behavior and characteristics of dissolved organic matter during column studies of soil aquifer treatment

Soil column experiments were performed to investigate the behavior and characteristics of dissolved organic matter (DOM) during soil aquifer treatment (SAT), and to differentiate among the mechanisms responsible for the changes in the structural and functional properties of DOM during SAT. To determine the biological transformation of DOM, biodegradability tests using a biodegradation-column system were conducted. DOM was fractionated using XAD resins into 5 fractions: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N) and hydrophilic fraction (HPI). Dissolved organic carbon (DOC) was removed by 70% during SAT, and the sorption and anaerobic biodegradation in SAT led to a DOC reduction of 27.4%. The significant changes in fluorescence properties of DOM were observed during SAT. However, the sorption and anaerobic biodegradation in SAT seemed to have no significant effect on the chemical structure of fluorescing constituents in DOM. The DOM fractions exhibited different changes in Fourier-transform infrared (FT-IR) spectra characteristics during SAT. Biodegradation resulted in the enrichment of aromatic structures and the decreased content of the oxygen-containing functional groups, such as CO and C-O, in DOM. On the other hand, the production of C-O and amide-2 functional groups occurred as a result of the sorption combined with anaerobic biodegradation in SAT.     

Atrazine removal from water by polycation-clay composites: Effect of dissolved organic matter and comparison to activated carbon

Atrazine removal from water by two polycations pre-adsorbed on montmorillonite was studied. Batch experiments demonstrated that the most suitable composite poly (4-vinylpyridine-co-styrene)-montmorillonite (PVP-co-S90%-mont.) removed 90-99% of atrazine (0.5-28 ppm) within 20-40 min at 0.367% w/w. Calculations employing Langmuir's equation could simulate and predict the kinetics and final extents of atrazine adsorption. Column filter experiments (columns 20 × 1.6 cm) which included 2 g of the PVP-co-S90%-mont. composite mixed with excess sand removed 93-96% of atrazine (800 ppb) for the first 800 pore volumes, whereas the same amount of granular activated carbon (GAC) removed 83-75%. In the presence of dissolved organic matter (DOM; 3.7 ppm) the efficiency of the GAC filter to remove atrazine decreased significantly (68-52% removal), whereas the corresponding efficiency of the PVP-co-S90%-mont. filter was only slightly influenced by DOM. At lower atrazine concentration (7 ppb) the PVP-co-S90%-mont. filter reduced even after 3000 pore volumes the emerging atrazine concentration below 3 ppb (USEPA standard). In the case of the GAC filter the emerging atrazine concentration was between 2.4 and 5.3 μg/L even for the first 100 pore volumes. Thus, the PVP-co-S90%-mont. composite is a new efficient material for the removal of atrazine from water.     

The effects of dissolved natural organic matter on the adsorption of synthetic organic chemicals by activated carbons and carbon nanotubes

Understanding the influence of natural organic matter (NOM) on synthetic organic contaminant (SOC) adsorption by carbon nanotubes (CNTs) is important for assessing the environmental implications of accidental CNT release and spill to natural waters, and their potential use as adsorbents in engineered systems. In this study, adsorption of two SOCs by three single-walled carbon nanotubes (SWNTs), one multi-walled carbon nanotube (MWNT), a microporous activated carbon fiber (ACF) [i.e., ACF10] and a bimodal porous granular activated carbon (GAC) [i.e., HD4000] was compared in the presence and absence of NOM. The NOM effect was found to depend strongly on the pore size distribution of carbons. Minimal NOM effect occurred on the macroporous MWNT, whereas severe NOM effects were observed on the microporous HD4000 and ACF10. Although the single-solute adsorption capacities of the SWNTs were much lower than those of HD4000, in the presence of NOM the SWNTs exhibited adsorption capacities similar to those of HD4000. Therefore, if released into natural waters, SWNTs can behave like an activated carbon, and will be able to adsorb, carry, and transfer SOCs to other systems. However, from an engineering application perspective, CNTs did not exhibit a major advantage, in terms of adsorption capacities, over the GAC and ACF. The NOM effect was also found to depend on molecular properties of SOCs. NOM competition was more severe on the adsorption of 2-phenylphenol, a nonplanar and hydrophilic SOC, than phenanthrene, a planar and hydrophobic SOC, tested in this study. In terms of surface chemistry, both adsorption affinity to SOCs and NOM effect on SOC adsorption were enhanced with increasing hydrophobicity of the SWNTs.     

Coagulation of humic substances and dissolved organic matter with a ferric salt: an electron energy loss spectroscopy investigation

Transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDXS) was used to investigate the coagulation of natural organic matter with a ferric salt. Jar-test experiments were first conducted with a reconstituted water containing either synthetic or natural extracts of humic substances, and then with a raw water from Moselle River (France). The characterization of the freeze-dried coagulated sediment by EELS in the 250-450 eV range, showed that Fe-coagulant species predominantly associate with the carboxylic groups of organic matter, and that this interaction is accompanied by a release of previously complexed calcium ions. The variation of Fe/C elemental ratio with iron concentration provides insightful information into the coagulation mechanism of humic substances. At acid pH, Fe/C remains close to 3 over the whole range of iron concentrations investigated, while a much lower atomic ratio is expected from the value of optimal coagulant dosage. This suggests that a charge neutralization/complexation mechanism is responsible for the removal of humic colloids, the aggregates being formed with both iron-coagulated and proton-neutralized organic compounds. At pH 8, the decrease in Fe/C around optimal coagulant concentration is interpreted as a bridging of stretched humic macromolecules by Fe-hydrolyzed species. Aggregation would then result from a competition between reconformation of humic chains around coagulant species and collision of destabilized humic material. EELS also enabled a fingerpriting of natural organic substances contained in the iron-coagulated surface water, N/C elemental analyses revealing that humic colloids are removed prior to proteinic compounds.