Tracking natural organic matter (NOM) in a drinking water treatment plant using fluorescence excitation-emission matrices and PARAFAC

Natural organic matter (NOM) in water samples from a drinking water treatment train was characterized using fluorescence excitation emission matrices (F-EEMs) and parallel factor analysis (PARAFAC). A seven component PARAFAC model was developed and validated using 147 F-EEMs of water samples from two full-scale water treatment plants. It was found that the fluorescent components have spectral features similar to those previously extracted from F-EEMs of dissolved organic matter (DOM) from diverse aquatic environments. Five of these components are humic-like with a terrestrial, anthropogenic or marine origin, while two are protein-like with fluorescence spectra similar to those of tryptophan-like and tyrosine-like fluorophores. A correlation analysis was carried out for samples of one treatment plant between the maximum fluorescence intensities (F_max) of the seven PARAFAC components and NOM fractions (humics, building blocks, neutrals, biopolymers and low molecular weight acids) of the same sample obtained using liquid chromatography with organic carbon detection (LC-OCD). There were significant correlations (p < 0.01) between sample DOC concentration, UVA₂₅₄, and F_max for the seven PARAFAC components and DOC concentrations of the LC-OCD fractions. Three of the humic-like components showed slightly better predictions of DOC and humic fraction concentrations than UVA_254. Tryptophan-like and tyrosine-like components correlated positively with the biopolymer fraction. These results demonstrate that fluorescent components extracted from F-EEMs using PARAFAC could be related to previously defined NOM fractions and that they could provide an alternative tool for evaluating the removal of NOM fractions of interest during water treatment.     

三维荧光技术用于给水的水质测定

采用三维荧光分析技术分类研究了原水中可溶解性有机物在传统水处理工艺中的去除过程。结果表明,三维荧光分析方法能够将原水中有机物区分成不同类型的腐殖酸和蛋白质,并揭示其在传统水处理工艺中去除效率的变化,而且三维荧光数据与COD、DOC和UV254等水质指标存在着良好的相关性。     

Characterizing chromophoric dissolved organic matter in Lake Tianmuhu and its catchment basin using excitation-emission matrix fluorescence and parallel factor analysis

Chromophoric dissolved organic matter (CDOM) is an important optically active substance that transports nutrients, heavy metals, and other pollutants from terrestrial to aquatic systems and is used as a measure of water quality. To investigate how the source and composition of CDOM changes in both space and time, we used chemical, spectroscopic, and fluorescence analyses to characterize CDOM in Lake Tianmuhu (a drinking water source) and its catchment in China. Parallel factor analysis (PARAFAC) identified three individual fluorophore moieties that were attributed to humic-like and protein-like materials in 224 water samples collected between December 2008 and September 2009. The upstream rivers contained significantly higher concentrations of CDOM than did the lake water (a(350) of 4.27 ± 2.51 and 2.32 ± 0.59 m⁻¹, respectively), indicating that the rivers carried a substantial load of organic matter to the lake. Of the three main rivers that flow into Lake Tianmuhu, the Pingqiao River brought in the most CDOM from the catchment to the lake. CDOM absorption and the microbial and terrestrial humic-like components, but not the protein-like component, were significantly higher in the wet season than in other seasons, indicating that the frequency of rainfall and runoff could significantly impact the quantity and quality of CDOM collected from the catchment. The different relationships between the maximum fluorescence intensities of the three PARAFAC components, CDOM absorption, and chemical oxygen demand (COD) concentration in riverine and lake water indicated the difference in the composition of CDOM between Lake Tianmuhu and the rivers that feed it. This study demonstrates the utility of combining excitation-emission matrix fluorescence and PARAFAC to study CDOM dynamics in inland waters.     

Dissolved organic matter in leachate from different treatment processes

The main objectives of this study were to investigate the characteristics of dissolved organic matter (DOM) extracted from the leachate of different treatment process using the chemical and spectroscopic analysing methods. The humic acid (HA), fulvic acid (FA) and hydrophilic (HyI) were isolated and purified by the XAD-8 resin combined with the cation exchange resin method. The analytical results of fluorescence excitation-emission matrix spectroscopy (EEMs) revealed that the fluorescence peaks were protein-like fluorescence for equalization basin and discharge of reverse osmosis (RO), while the fluorescence peaks for second sedimentation tank were humic-like and fulvic-like fluorescence. Moreover, the results also showed that protein-like organic matter are readily removed by biological process and HA and FA can be removed by RO process. Elemental analysis indicated that the nitrogen content in these isolated fractions followed: HA>HyI>FA. The information on the characteristics of DOM indicated important role in optimization of leachate treatment processes.     

Characterization of DOM as a function of MW by fluorescence EEM and HPLC-SEC using UVA,DOC, and fluorescence detection

To investigate the composition of dissolved organic matter (DOM) as a function of apparent molecular weight (MW) by rapid analytical methods, high performance liquid chromatography (HPLC)-size exclusion chromatography (SEC) was conducted with sequential on-line detectors consisting of UV, fluorescence, and quantitative DOC measurement. Fluorescence excitation-emission matrix (EEM) spectrophotometry was used to select wavelengths for the HPSEC on-line fluorescence system. The chosen peak maxima locations of excitation-emission wavelengths were 278-353 nm for protein-like substances and 337-423 nm for fulvic-like substances based on an analysis of EEM spectra for various samples and reference materials. This system provides quantitative and qualitative information on the specific MW components of DOM, including proportion of DOC (by DOC measurement), aromaticity (by comparison of UV and DOC measurements), and chemical properties (by fluorescence measurement). It further allows determination of organic matter characteristics (e.g., fulvic-like, protein-like, and polysaccharide-like substances) as a function of MW. Three types of samples (Irvine Ranch ground water (IRWD-GW), Barr Lake surface water (BL-SW), and Hawaii wastewater secondary effluent) were analyzed by the HPSEC-UVA-fluorescence-DOC system. These results were compared with fluorescence EEM for samples fractionated by HPLC-SEC. The DOM fraction in the high apparent MW range (over 10,000g/mol) consisted of polysaccharide-like substances for IRWD-GW and a mixture of polysaccharide-like/protein-like substances for BL-SW and wastewater secondary effluent. Minimal amounts of fulvic-like substances were found in the wastewater secondary effluent sample. The DOM fractions in a medium apparent MW range (5000-1000 g/M) showed higher aromaticity (fulvic in character) than any other fractions for all samples. For the DOM fraction in the low apparent MW range (below 680 g/M), additional aliphatic organic matter was found in IRWD-GW, while BL-SW contained protein-like processes. DOM plays an important role in drinking water and wastewater treatment processes. An enhanced HPSEC technique with multiple on-line detectors enables a better understanding of quantitative and qualitative DOM properties and can help to design and optimize water/wastewater treatment facilities.     

Insight into the heavy metal binding potential of dissolved organic matter in MSW leachate using EEM quenching combined with PARAFAC analysis

Dissolved organic matter (DOM) plays an important role in heavy metal migration from municipal solid waste (MSW) to aquatic environments via the leachate pathway. In this study, fluorescence excitation-emission matrix (EEM) quenching combined with parallel factor (PARAFAC) analysis was adopted to characterize the binding properties of four heavy metals (Cu, Pb, Zn and Cd) and DOM in MSW leachate. Nine leachate samples were collected from various stages of MSW management, including collection, transportation, incineration, landfill and subsequent leachate treatment. Three humic-like components and one protein-like component were identified in the MSW-derived DOM by PARAFAC. Significant differences in quenching effects were observed between components and metal ions, and a relatively consistent trend in metal quenching curves was observed among various leachate samples. Among the four heavy metals, Cu(II) titration led to fluorescence quenching of all four PARAFAC-derived components. Additionally, strong quenching effects were only observed in protein-like and fulvic acid (FA)-like components with the addition of Pb(II), which suggested that these fractions are mainly responsible for Pb(II) binding in MSW-derived DOM. Moreover, the significant quenching effects of the FA-like component by the four heavy metals revealed that the FA-like fraction in MSW-derived DOM plays an important role in heavy metal speciation; therefore, it may be useful as an indicator to assess the potential ability of heavy metal binding and migration.     

Characterization of organic membrane foulants in a submerged membrane bioreactor with pre-ozonation using three-dimensional excitation-emission matrix fluorescence spectroscopy

This study focuses on organic membrane foulants in a submerged membrane bioreactor (MBR) process with pre-ozonation compared to an individual MBR using three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy. While the influent was continuously ozonated at a normal dosage, preferable organic matter removal was achieved in subsequent MBR, and trans-membrane pressure increased at a much lower rate than that of the individual MBR. EEM fluorescence spectroscopy was employed to characterize the dissolved organic matter (DOM) samples, extracellular polymeric substance (EPS) samples and membrane foulants. Four main peaks could be identified from the EEM fluorescence spectra of the DOM samples in both MBRs. Two peaks were associated with the protein-like fluorophores, and the other ones were related to the humic-like fluorophores. The results indicated that pre-ozonation decreased fluorescence intensities of all peaks in the EEM spectra of influent DOM especially for protein-like substances and caused red shifts of all fluorescence peaks to different extents. The peak intensities of the protein-like substances represented by Peak T₁ and T₂ in EPS spectra were obviously decreased as a result of pre-ozonation. Both external and internal fouling could be effectively mitigated by the pre-ozonation. The most primary component of external foulants was humic acid-like substance (Peak C) in the MBR with pre-ozonation and protein-like substance (Peak T₁) in the individual MBR, respectively. The content decrease of protein-like substances and structural change of humic-like substances were observed in external foulants from EEM fluorescence spectra due to pre-ozonation. However, it could be seen that ozonation resulted in significant reduction of intensities but little location shift of all peaks in EEM fluorescence spectra of internal foulants.     

农家乐污水中溶解性有机质的三维荧光特性研究

采用三维荧光光谱(3DEEM)技术考察了农家乐污水中溶解性有机质的三维荧光特性.结果表明,农家乐污水中的有机污染物荧光峰以类蛋白质荧光峰为主,其中高激发波长类色氨酸荧光峰Peak T最强,其次是低激发波长类色氨酸荧光峰Peak S和低激发波长类酪氨酸荧光峰Peak D;综合性农家乐污水的Peak S和Peak D荧光强度比以餐饮为主的农家乐污水的要强.农家乐污水经受纳水体稀释和净化后,类蛋白质荧光强度仍远高于地表水的.其对受纳水体的污染不容忽视.     

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.     

Improving on SUVA 254 using fluorescence-PARAFAC analysis and asymmetric flow-field flow fractionation for assessing disinfection byproduct formation and control

Several challenges with disinfection byproduct (DBP) control stem from the complexity and diversity of dissolved organic matter (DOM), which is ubiquitous in natural waters and reacts with disinfectants to form DBPs. Fluorescence parallel factor (PARAFAC) analysis and asymmetric flow-field flow fractionation (AF4) were used in combination with free chlorine DBP formation potential (DBPFP) tests to study the physicochemical DOM properties and DBP formation in raw- and alum-coagulated waters. Enhanced coagulation with alum became more effective at removing DBP-precursors as the pH decreased from 8 to 6. AF4-UV₂₅₄ fractograms indicated enhanced coagulation at pH 6 preferentially removed larger DOM, whereas no preferential size removal occurred at pH 8. Fluorescence-PARAFAC analysis revealed the presence of one protein-like and three humic-like fluorophore groups; stronger linear correlations were found between chloroform and the maximum intensity (F_MAX) of a humic-like fluorophore (r² = 0.84) than with SUVA₂₅₄ (r² = 0.51). This result indicated that the fluorescence-PARAFAC approach used here was an improvement on SUVA₂₅₄, i.e., fluorescence-based measurements were stronger predictors of chloroform formation.     

Ozonation effect on natural organic matter adsorption and biodegradation - Application to a membrane bioreactor containing activated carbon for drinking water production

More stringent legislation on dissolved organic matter (DOM) urges the drinking water industry to improve in DOM removal, especially when applied to water with high dissolved organic carbon (DOC) contents and low turbidity. To improve conventional processes currently used in drinking water treatment plants (DWTPs), the performances of a hybrid membrane bioreactor containing fluidised activated carbon were investigated at the DWTP of Rennes. Preliminary results showed that the residual DOC was the major part of the non-biodegradable fraction. In order to increase the global efficiency, an upstream oxidation step was added to the process. Ozone was chosen to break large molecules and increase their biodegradability. The first step consisted of carrying out lab-scale experiments in order to optimise the necessary ozone dose by measuring the process yield, in terms of biodegradable dissolved organic carbon (BDOC). Secondly, activated carbon adsorption of the DOC present in ozonated water was quantified. The whole process was tested in a pilot unit under field conditions at the DWTP of Rennes (France). Lab-scale experiments confirmed that ozonation increases the BDOC fraction, reduces the aromaticity of the DOC and produces small size organic compounds. Adsorption tests led to the conclusion that activated carbon unexpectedly removes BDOC first. Finally, the pilot unit results revealed an additional BDOC removal (from 0.10 to 0.15 mg L⁻¹) of dissolved organic carbon from the raw water considered.     

Identifying the sources and fate of anthropogenically impacted dissolved organic matter (DOM) in urbanized rivers

Anthropogenic activities have dramatically changed the loads and compositions of dissolved organic matter (DOM) in urbanized streams. In this study, the spatial and temporal variations of DOM in the anthropogenically impacted Zhujiang River were investigated by analyzing the water samples in an upstream, urbanized area and downstream of the rivers on different days of one year. The results indicated that the levels of dissolved organic carbon (DOC) and total phosphorus (TP) were unaffected by seasonal changes, but the specific UV₂₅₄ absorbance (SUVA) values and the total nitrogen (TN) content were greater in the winter than those in the summer. Parallel factor (PARAFAC) analysis of the excitation emission matrices (EEM) revealed the presence of three anthropogenically derived components [tryptophan-like (C1) and tyrosine-like proteins (C3) and anthropogenic humic substances (C5)] in the urbanized rivers, and they had greater seasonal and spatial variability than the terrestrial and microbial humic substances (C2 and C4). Cluster analysis revealed that treated wastewater was an important source of DOM in the urbanized streams. Photodegradation experiments indicated that the DOM in the populous area of the rivers had greater photodegradation potentials than that in the downstream region or in the natural waters. Interestingly, that the anthropogenic humic substances (C5) were considerably more photoreactive than the other four PARAFAC components, which exhibited a decrease of 80% after exposure to sunlight for 0.5 d. This study suggests that the treated wastewater could be an important input to the DOM in the urbanized rivers and the naturally occurring photodegradation could help in eliminating the anthropogenic DOM during their transport.     

Freshwater DOM quantity and quality from a two-component model of UV absorbance

We present a model that considers UV-absorbing dissolved organic matter (DOM) to consist of two components (A and B), each with a distinct and constant spectrum. Component A absorbs UV light strongly, and is therefore presumed to possess aromatic chromophores and hydrophobic character, whereas B absorbs weakly and can be assumed hydrophilic. We parameterised the model with dissolved organic carbon concentrations [DOC] and corresponding UV spectra for c. 1700 filtered surface water samples from North America and the United Kingdom, by optimising extinction coefficients for A and B, together with a small constant concentration of non-absorbing DOM (0.80 mg DOC L⁻¹). Good unbiased predictions of [DOC] from absorbance data at 270 and 350 nm were obtained (r² = 0.98), the sum of squared residuals in [DOC] being reduced by 66% compared to a regression model fitted to absorbance at 270 nm alone. The parameterised model can use measured optical absorbance values at any pair of suitable wavelengths to calculate both [DOC] and the relative amounts of A and B in a water sample, i.e. measures of quantity and quality. Blind prediction of [DOC] was satisfactory for 9 of 11 independent data sets (181 of 213 individual samples).     

城市污水生化处理后水中溶解性有机物的特性研究

采用XAD树脂分离技术和超滤膜法对青岛市某城市污水处理厂生物化学处理后出水中溶解性有机物（DOM）进行了分类分离,研究了出水中DOM的亲疏水特性及分子量分布规律,探讨了各类DOM组分与芳香度之间的关系.研究结果表明,在DOM中,酸性物质（包括过渡亲水酸性物质和疏水酸性物质）所占比例最高,占总溶解性有机碳（DOC）的79.8%,疏水非酸性物质的芳香度最高,并依疏水酸性物质、过渡亲水酸性物质、亲水性物质的顺序递减,且羰基、羧基、羟基、脂类对芳环的取代程度表现为亲水性物质〈过渡亲水酸性物质〈疏水非酸性物质〈疏水酸性物质;该污水处理厂二级出水中的DOM以小分子量有机物（相对分子质量小于1kDa）为主,其占总DOC的59.13%,表明水中腐殖酸类等难降解有机物质含量较高,增加了消毒副产物的生成势.因此,若该种水体需要深度处理时,应重点考虑提高对腐殖酸类等难降解有机物质的处理程度,确保回用水水质的安全性.     

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.     

Characteristics of dissolved organic matter following 20 years of peatland restoration

The changes in the amounts and composition of dissolved organic matter (DOM) following long-term peat restoration are unknown, although this fraction of soil organic matter affects many processes in such ecosystems. We addressed this lack of knowledge by investigating a peatland in south-west Germany that was partly rewetted 20 years ago. A successfully restored site and a moderately drained site were compared, where the mean groundwater levels were close to the soil surface and around 30 cm below surface, respectively. The concentrations of dissolved organic carbon (DOC) at 4 depths were measured over one year. The specific absorbance was measured at 280 nm and the fluorescence spectra were used to describe the aromaticity and complexity of DOM.The investigations showed that 20 years of peatland restoration was able to create typical peatland conditions. The rewetted site had significantly lower DOC concentrations at different depths compared to the drained site. The specific UV absorbance showed that the rewetted site had a lower level of aromatic DOM structures. The decreasing specific UV absorbance might indicate an increasing contribution of small organic molecules to DOM. It was hypothesized that the decreasing DOC concentrations and the relative enrichment of small, readily degradable organic molecules, reflect the slower decomposition of organic matter after the re-establishment of the water table. Seasonal trends provided substantial evidence for our hypothesis that reduced DOC concentrations were caused by reduced peat decomposition. During summer, the elevated DOC values were accompanied by an increase in DOM aromaticity and complexity. Our results demonstrated a close link between C mineralization and DOC production. We concluded that long-term peatland restoration in the form of the successful re-establishment of the water table might result in reduced peat decomposition and lower DOC concentrations. The restoration of peatlands seems to have a positive impact on C sequestration.     

Sorption of phenols onto sandy aquifer material: the effect of dissolved organic matter (DOM)

The influence of dissolved organic matter (DOM) on the sorption of four phenols, 2,4,6-trichlorophenol (2,4,6-TCP), pentachlorophenol (PCP), 2,4-dinitrophenol (2,4-DNP) and 2-methyl-4,6-dinitrophenol (2-M-4,6-DNP), onto sandy aquifer material at different pH values was investigated using flow through column experiments. The pH-dependent sorption of the chlorinated phenols 2,4,6-TCP and PCP was not significantly affected by DOM (measured as dissolved organic carbon, DOC), whereas in the case of nitrophenols a significant lower retardation was found, depending on the DOC concentration and pH value of the aqueous solution. Sorption decreases with increasing DOC concentration, which indicates a binding of these compounds by DOM. The degree of sorption reduction depends on the pH value and increases with increasing fraction of neutral species. The different behaviour of nitrophenols in comparison to the chlorophenols is assumed to be a result of specific charge-transfer interactions. A combined sorption and complex formation model was used to describe the effect of pH and DOC concentration on the sorption of nitrophenols onto aquifer material and to estimate binding coefficients of neutral nitrophenols on DOM.     

The contribution of phytoplankton degradation to chromophoric dissolved organic matter (CDOM) in eutrophic shallow lakes: Field and experimental evidence

Eight field campaigns in the eutrophic, shallow, Lake Taihu in the summers from 2005 to 2007, and a phytoplankton degradation experiment of 33 days, were carried out to determine the contribution of phytoplankton degradation to CDOM. Significant and positive correlations were found between the CDOM absorption coefficient at 355 nm [a_CDOM(355)], normalized fluorescence emission (QSU) at 450 nm from excitation at 355 nm [F_n(355)], and the chlorophyll a (Chla) concentration for all eight field campaigns, which indicates that the decomposition and degradation of phytoplankton is an important source of CDOM. In the degradation experiment, the CDOM absorption coefficient increased as phytoplankton broke down during the first 12 days, showing the production of CDOM from phytoplankton. After 12 days, a_CDOM(355) had increased from the initial value 0.41 ± 0.03 m⁻¹ to 1.37 ± 0.03 m⁻¹ (a 234% increase), and the Chla concentration decreased from the initial value of 349.1 ± 11.2 μg/L to 30.4 ± 13.2 μg/L (a 91.3% decrease). The mean daily production rate of CDOM from phytoplankton was 0.08 m⁻¹ for a_CDOM(355). Parallel Factor Analysis (PARAFAC) was used to assess CDOM composition from EEM spectra, and four components were identified: a terrestrial-like humic component, two marine-like humic components, and a protein-like component. The rapid increase in marine-like humic fluorophores (C3 and C4) during the degradation experiment suggests that in situ production of CDOM plays an important role in the dynamics of CDOM. The field campaigns and experimental data in the present study show that phytoplankton can be one of the important CDOM producers in eutrophic shallow lakes.     

Characterization of dissolved organic matter in effluents from wastewater treatment plants

Dissolved organic matter (DOM) in effluents from sewage and human-wastes treatment plants (STPEs and HWTPEs) was fractionated using resin adsorbents into six classes: aquatic humic substances (AHS), hydrophobic bases (HoB), hydrophobic neutrals (HoN), hydrophilic acids (HiA), hydrophilic bases (HiB), and hydrophilic neutrals (HiN). DOM-fraction distribution varied substantially depending on the kind of wastewater and the type of treatment process. AHS and HiA dominated in all effluents, collectively accounting for more than 55% of the DOM measured as dissolved organic carbon (DOC). In particular, HiA were the most abundant fraction in the effluents, constituting 32-74% of the DOM. AHS appeared to be the second most dominant fraction and varied considerably, accounting for 3-28% of the DOM. The HoN fraction also varied from 0-21%. AHS, HoN, and HiA were the fractions that changed substantially and differed characteristically among the samples studied. The ratios of ultraviolet absorbance to DOC (UV: DOC ratio) in all effluents exhibited a common relationship: AHS> total DOM > HiA. Nevertheless, the ratios were substantially different between STPEs and HWTPEs and among HWTPEs. For HWTPEs, the effluent from the chemical coagulation process had the highest UV: DOC ratios. On the other hand, the effluent from the ultrafiltration and activated carbon adsorption processes had the lowest ratios. Molecular size distribution of the effluents was determined by size exclusion chromatography and found to exhibit a relatively narrow size range and low weight-averaged molecular weights ranging from 380 to 830 g mol(-1). The weight-averaged molecular weight of DOM increased as the UV: DOC ratio of total DOM increased.     

The influence of forestry activity on the structure of dissolved organic matter in lakes: implications for mercury photoreactions

It is well known that dissolved organic matter (DOM) increases in lakes associated with forestry activity but characterization of the DOM structure is incomplete. Twenty-three lakes with a wide range of forestry activities located in central Quebec, Canada were sampled and analyzed for dissolved organic carbon (DOC) concentration, DOC fluorescence, and ultra violet-visible (UV-VIS) absorption spectra. The results show that DOC increases (as does the associated DOC fluorescence) with increased logging (slope=0.122, r2=0.581, p<0.001; and slope=0.283, r2=0.308, p<0.01, respectively) in the 23 lakes sampled however, the aromaticity of the DOM does not change with changes in logging (as found by UV-VIS ratios, absorbance slope in the UV region, and DOC normalized fluorescence (slope=1.42x10(-2), r2=0.331, p<0.01). The DOM from four of these lakes was concentrated using reverse osmosis (RO) followed by freeze-drying. The structures of the concentrated dissolved organic matter (DOM) samples were analyzed using X-ray analysis of near edge structures (XANES), X-ray diffraction (XRD), and 13C solid-state nuclear magnetic resonance (13C NMR) analysis. XANES analysis of functional groups in the four concentrated samples shows that there are significant differences in reduced sulphur between the samples, however there was no clear relationship with forestry activity in the associated catchment. XRD data showed the presence of amorphous sulphide minerals associated with the DOM concentrate that may be important sites for mercury binding. The 13C NMR spectra of these samples show that the percentage of carbon present in carboxylic functional groups increases with increasing logging. Such structures are important for binding photo-reducible mercury and their presence may limit mercury photo-reduction and volatilization. We propose a mechanism by which increased logging leads to increased carboxylic groups in DOM and thereby increased weak binding of photo-reducible mercury. These results, in part, explain the decrease in dissolved gaseous mercury (DGM) production rates with increased logging found in our previous work.