Characterization of aquatic humic substances to DBPs formation in advanced treatment processes for conventionally treated water

Application of Alkaline Deep Eutectic Solvents as a Green Alternative to the Traditional Extractants for the Isolation of Humic Substances

The presented study focused on the possibility of using alkaline deep eutectic solvents (ADESs) as green extractants for the isolation of humic substances (HSs) from peat and lignite in a process intensified by ultrasound. For this purpose, the extraction procedure was statistically described on the basis of the Box-Behnken design, and the carboxyl group content in the obtained products was optimized due to the ADES composition, ultrasound intensity, and extraction time. For optimal extraction conditions, the experimental carboxyl content in the isolated products was equal to 3.71 and 2.96 mmol g-1 for the HSs extracted from peat and lignite, respectively. These values were similar to the results for the reference samples, which were HSs extracted using 0.1 M NaOH, as well as humic acids and sodium humates purchased from Sigma-Aldrich. The qualitative assessment of the products obtained was based on spectroscopic methods, including FTIR, 1H NMR, and UV-vis. The analyses carried out for the isolated samples revealed the characteristic structures of HSs, including components of aliphatic chains and aromatic core as well as carboxyl, ester, and amino groups. Simultaneously, the results of the spectral ratio of E 280/E 472 showed the significant differences between the relative amount of lignin for the samples tested.

Quartz Crystal Microbalance as a Holistic Detector for Quantifying Complex Organic Matrices during Liquid Chromatography: 1. Coupling, Characterization, and Validation

A matrix in highly complex samples can cause adverse effects on the trace analysis of targeted organic compounds. A suitable separation of the target analyte(s) and matrix before the instrumental analysis is often a vital step for which chromatographic cleanup methods remain one of the most frequently used strategies, particularly high-performance liquid chromatography (HPLC). The lack of a simple real-time detection technique that can quantify the entirety of the matrix during this step, especially with gradient solvents, renders optimization of the cleanup challenging. This paper, along with a companion one, explores the possibilities and limitations of quartz crystal microbalance (QCM) dry-mass sensing for quantifying complex organic matrices during gradient HPLC. To this end, this work coupled a QCM and a microfluidic spray dryer with a commercial HPLC system using a flow splitter and developed a calibration and data processing strategy. The system was characterized in terms of detection and quantification limits, with LOD = 4.3-15 mg/L and LOQ = 16-52 mg/L, respectively, for different eluent compositions. Validation of natural organic matter in an environmental sample against offline total organic carbon analysis confirmed the approach's feasibility, with an absolute recovery of 103 ± 10%. Our findings suggest that QCM dry-mass sensing could serve as a valuable tool for analysts routinely employing HPLC cleanup methods, offering potential benefits across various analytical fields.

Response mechanism of soil leachate and disinfection by-product formation to extreme precipitation events under continuous drought scenario

In this study, a rainfall simulation device was employed to investigate the response mechanism of soil leachate and disinfection by-products formation potential (DBPsFP) to extreme precipitation events. The results revealed that the aromaticity of dissolved organic matter (DOM) and the concentration of hydrophobic DOM containing aromatic carbon groups in leachate decreased with rising temperature. The humification degree of DOM decreased at 25 °C (99 mm/h), while the humification degree and protein-like level of DOM increased under high temperatures droughts (45 °C and 65 °C). Higher temperatures resulted in the leach of more microbial-derived humus and low molecular phenolic compounds from soil and broadened the range of molecular weight distribution. Increasing temperature increased DBPsFP and DBPs species and caused the precursors of haloacetic acids (HAAs) in leachate to become more hydrophobic, while the precursors of trihalomethanes (THMs) became more hydrophilic. Most importantly, the increased temperature attenuated the rainfall-mediated dilution of organic pollutant concentration, and temperature has a more significant effect than extreme rainfall in DOM abundance and the formation potential (or species) of DBPs. The results help to better understand the impact of climate change on the physicochemical processes of water quality.

Perspectives and understanding on the occurrence, toxicity and abatement technologies of disinfection by-products in drinking water

Disinfection by-products (DBPs) are one of the significant emerging contaminants that have caught the attention of researchers worldwide due to their pervasiveness. Their presence in drinking water, even in shallow concentrations (in levels of parts per billion), poses considerable health risks. Therefore, it is crucial to understand their kinetics to understand better their formation and persistence in the water supply systems. This manuscript demonstrates different aspects of research carried out on DBPs in the past. A systematic approach was adopted for the bibliographical research that started with choosing appropriate keywords and identifying the most relevant manuscripts through the screening process. This follows a quantitative assessment of the extracted literature sample, which included the most productive and influential journal sources, the most widely used keywords, the most influential authors active in the research domain, the most cited articles, and the countries most actively engaged in the research field. Critical observations on the literature sample led to the qualitative assessment, wherein the past and current research trends were observed and reported. Finally, we identified the essential gaps in the available literature, which further led to recommending the course ahead in the research domain. This study will prove fruitful for young and established researchers who are or wish to work in this emerging field of research.

High formation of trichloroacetic acid from high molecular weight and ultra-hydrophilic components in freshwater raphidophytes upon chlorination

Raphidophytes are flagellate unicellular algae that causes algal blooms in drinking water sources. In Japan, it was recently reported that the concentration of trichloroacetic acid (TCAA), a major chlorinated disinfection byproduct (DBP), increased dramatically in drinking water when the source water contained raphidophytes. Additionally, raphidophytes produced haloacetic acid (HAA) precursors, especially TCAA precursors, in high concentrations. However, their properties are still unknown, and thus, well-designed countermeasures against DBP formation have not yet been established. Therefore, in this study, the HAA precursors originated from raphidophytes in natural water collected from the algal blooms in Muro Dam (Nara Prefecture, Japan) and Gonyostomum semen (G. semen), a raphidophyte species, cultivated in the laboratory, were characterized to provide the information for establishing suitable treatment strategies. Using several high-performance liquid chromatography columns, solid-phase extraction cartridges, and ultrafiltration devices, and the spectral profiles, we discovered that the HAA precursors are highly hydrophilic and high-molecular-weight compounds with acidic and phenolic functional groups. Further characterization of the high-molecular-weight fraction (> 3 kDa) from the G. semen culture showed that the HAA precursors had a molecular weight of ~10-60 kDa, and that they were not protein molecules despite containing a large amount of nitrogen atoms. Furthermore, the TCAAFP of the fraction (310 ± 25 μg/mg C) were as high as phenol, known as a reactive TCAA model precursor. The presence of unique and unreported DBP precursors was confirmed.

A new process to further remove dissolved organic matter and disinfection by-product formation potential during drinking water treatment

Biological activated carbon (BAC) will produce soluble microbial products (SMPs), which affect effluent quality. To clarify the mechanism by which BAC affects effluent water quality, the processes of a drinking water plant in Jiangsu Province were investigated. It was found that during the O₃-BAC process, although ozonation could remove dissolved organic matter (DOC) to a certain extent, the DOC increased from 4.44 to 4.47 mg/L after BAC. Dissolved organic matter (DOM) in effluent from different processes was divided into five fractions based on hydrophilicity and hydrophobicity by resin fractionation. Through fluorescence excitation-emission matrix (EEM) spectroscopy combined with DOC analysis, it was found that SMPs are mainly included in transitional hydrophilic neutral (TPIN) fraction, which was the main cause of the DOC increase. Therefore, a new combined process was designed to remove TPIN effectively by coagulation after biological treatment, and found that coagulation had a good removal rate (13.2%) on TPIN. The trihalomethane formation potential (THMFP) of TPIN could be reduced effectively by 44.9% after coagulation. Compared with the old process, the new combined process had a higher removal rate (14.2-30.0%) of DOC, as well as a greater reduction of THMFP (29.0-78.6%) and haloacetic acid formation potential (HAAFP) (46.4-75.3%). This study aims to reveal the mechanism by which SMPs affect effluent water quality and exacerbate health risks, and to propose a solution to provide theoretical support for the design and optimization of drinking water treatment processes.

Pollutant-removal and DOM characteristics in an urban stormwater wetland

Stormwater wetlands play a crucial role in the urban environment, providing many ecosystem services. In this work, a stormwater wetland was developed to study the effects on the removal of pollutants and the characteristics of dissolved organic matter (DOM) under different operating conditions, such as hydraulic retention time (HRT) and water depth. The results showed that the stormwater wetland exhibited excellent pollutant-removal performance, such as NH₄^+_N, TN, TP, COD, and suspended solids (SS). The removal rates for these substances reached 79.1%, 73.2%, 89.0%, 84.3%, 80.4%, and 73.77, respectively, with 24 h of HRT and 15 cm of water depth. An increase in HRT can improve the removal rates of TN, TP, COD, and TOC. The removal rates for these parameters decreased with increasing water depth, though, except for TP; the UV-VIS spectral parameters indicated that an obvious decrease occurred in the degrees of humification and aromaticity of DOM with increasing HRT and water depth after the stormwater wetland treatment. Parallel factor (PARAFAC) analysis identified six fluorescent components (one combination of freshly produced biologically labile matter and a tryptophan-like component, one fulvic-like, one humic-like, and three tryptophan-like), whose fluorescence intensity was weakened after the stormwater wetland treatment. The lowest intensity appeared with 24 h of HRT and 15 cm of water depth. This study could be beneficial for understanding and managing stormwater wetlands, thus alleviating the impacts of pollutants on urban environments.

Understanding the Effect of pH on the Solubility and Aggregation Extent of Humic Acid in Solution by Combining Simulation and the Experiment

Molecular dynamics (MD) simulations were performed to investigate the dynamics of humic acid (HA) in an aqueous solution and the influence of pH, temperature, and HA concentration. The HA model employed in MD simulations was chosen and validated using experimental chemical composition data and Fourier transform infrared (FTIR) spectra. The simulations showed that the HA molecule has a strong propensity to adopt a compact conformation in water independent of pH, while the aggregation of HA was found to be pH-dependent. At high pH, the ionized HAs assembled into a thread-like structure, maximizing contact with water. At low pH, the neutral HAs formed a droplet-like aggregate, minimizing contact with the solvent. The simulation results are consistent with experimental data from dynamic light scattering (DLS) measurements and transmission electron microscopy (TEM) imaging. This work provides new insight into the folding and aggregation of HA as a function of pH and a molecular-level understanding of the relationship between the acidity and the structure, solubility, and aggregation of HA, with direct implications for HA-based remediation strategies of contaminated sites.

Solution-state NMR evaluation of molecular interaction between monoaromatic carboxylic acids and dissolved humic acid

Understanding the nature of interactions between the aromatic organic pollutants with dissolved humic acid (HA) is fundamental for the prediction of their environmental fate and subsequent development of efficient remediation methods. The present study employs solution-state ¹H/¹⁹F NMR methods to investigate the non-covalent interaction between aqueous peat humic acid (Aldrich HA) and monoaromatic carboxylic acids (CA), viz., 2, 6 diflourobenzoic acid (DFBA) and its non-fluorinated analog, benzoic acid (BA). NMR self-diffusion measurement of HA protons confirmed micellar nature indicating possibility of encapsulation of small molecules through host-guest interaction. ¹⁹F-¹H and ¹H-¹H saturation transfer difference (STD) experiments reveal the mode of insertion of CA into HA superstructure. The strength of interaction has been evaluated by analyzing T₁/T₂ relaxation times and self-diffusion coefficients of CA as a function of HA concentration. Association constants extracted for CA-HA complexes from NMR diffusion experiments reflected that the association between DFBA-HA (2.34 mM^-1) is significantly higher than that of BA-HA (0.97 mM^-1). The experimental outcome reiterated that substitution of -H with halogen atoms (-F in specific) to aromatic ring plays a dominant role in modulating the strength of association and mode of insertion of organic pollutants into HA superstructure. The present study emphasizes that AHA can be a potential remediating agent for organic contaminants due to its superior binding affinity compared to less humified extracted HA (EHA) from Karwar, Rajasthan, India.

Analysis of ultrasonic pre-treatment for the ozonation of humic acids

This paper presents an intensification study of an ozonation process through an ultrasonic pre-treatment for the elimination of humic substances in water and thus, improve the quality of water treatment systems for human consumption. Humic acids were used as representative of natural organic matter in real waters which present low biodegradability and a high potential for trihalomethane formation. Ultrasonic frequency (98 kHz, 300 kHz and 1 MHz), power (10-40 W) and sonicated volume (150-400 mL) was varied to assess the efficiency of the ultrasonic pre-treatment in the subsequent ozonation process. A direct link between hydroxyl radical (HO) formation and fluorescence reduction was observed during sonication pre-treatment, peaking at 300 kHz and maximum power density. Ultrasound, however, did not reduce total organic carbon (TOC). Injected ozone (O₃) dose and reaction time were also evaluated during the ozonation treatment. With 300 kHz and 40 W ultrasonic pre-treatment and the subsequent ozonation step (7.4 mg O₃/L_gas), TOC was reduced from 21 mg/L to 13.5 mg/L (36% reduction). HO attack seems to be the main degradation mechanism during ozonation. A strong reduction in colour (85%) and SUVA₂₅₄ (70%) was also measured. Moreover, changes in the chemical structure of the macromolecule were observed that led to the formation of oxidation by-products of lower molecular weight.

Advances in the characterization and monitoring of natural organic matter using spectroscopic approaches

Natural organic matter (NOM) is ubiquitous in environment and plays a fundamental role in the geochemical cycling of elements. It is involved in a wide range of environmental processes and can significantly affect the environmental fates of exogenous contaminants. Understanding the properties and environmental behaviors of NOM is critical to advance water treatment technologies and environmental remediation strategies. NOM is composed of characteristic light-absorbing/emitting functional groups, which are the "identification card" of NOM and susceptive to ambient physiochemical changes. These groups and their variations can be captured through optical sensing. Therefore, spectroscopic techniques are elegant tools to track the sources, features, and environmental behaviors of NOM. In this work, the most recent advances in molecular spectroscopic techniques, including UV-Vis, fluorescence, infrared, and Raman spectroscopy, for the characterization, measurement, and monitoring of NOM are reviewed, and the state-of-the-art innovations are highlighted. Furthermore, the limitations of current spectroscopic approaches for the exploration of NOM-related environmental processesand how these weaknesses/drawbacks can be addressed are explored. Finally, suggestions and directions are proposed to advance the development of spectroscopic methods in analyzing and elucidating the properties and behaviors of NOM in natural and engineered environments.

Current trends and advances in analytical techniques for the characterization and quantification of biologically recalcitrant organic species in sludge and wastewater: A review

The study of organic matter in wastewater is a major regulatory and environmental issue and requires new developments to identify non-biodegradable refractory compounds, produced mainly by thermal treatments. Recent advances linking physicochemical properties to spectroscopic analyzes (UV, Fluorescence, IR) have shown that the refractory property is favored by several physicochemical parameters: weight, hydrophobicity, aromaticity and chemical functions. Currently, the most effective developments for the quantification of refractory compounds are obtained with hyphenated methods, based on steric separation of the macromolecular species by steric exclusion chromatography (SEC)/PDA/Fluorescence systems. Hyphenated techniques using High Resolution Mass Spectrometry (HRMS), ultra-high-resolution mass spectrometry with Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and NMR have been developed to analyze macromolecules in wastewater with minor sample preparation procedures. A particular class has been identified, the melanoidins, generated by Maillard reactions between sugars, amino acids, peptides and proteins present in wastewater and sludge, but low molecular weight compounds formed as intermediates, such as ketones, aldehydes, pyrazines, pyridines or furans, are also recalcitrant and are complex to identify in the complex matrices. The lack of available standards for the study of these compounds requires the use of specific techniques and data processing. Advances in chemometrics are obtained in the development of molecular or physicochemical indices resulting from the data generated by the analytical detectors, such as aromaticity calculated by SUVA₂₅₄ and determined by UV, fluorescence, molar mass, H/C ratio or structural studies (measuring the amount of unsaturated carbon) given by hyphenated techniques with SEC. It is clear that nitrogen compounds are widely involved in refractoriness. New trends in nitrogen containing compounds characterization follow two axes: through SEC/PDA/Fluorescence and HRMS/NMR techniques with or without separation. Other techniques widely used in food or marine science are also being imported to this study, as it can be seen in the use of "omics" methods, high-performance thin layer chromatography (HPTLC) and chromatography at the critical condition, rounding out the important developments around SEC. While improving the performance of stationary phases is one of the challenges, it results in a fundamental understanding of the retention mechanisms that today provide us with more information on the structures identified. The main objective of this review is to present the spectroscopic and physicochemical techniques used to qualify and characterize refractoriness with a specific focus on chemometric approaches.

Algal softening followed by ozonation: The fate of persistent micropollutants and natural organic matter in groundwater

A proof-of-concept study evaluates the performance of a novel strategy using photosynthetic microorganisms to soften groundwater instead of using caustic chemicals. The microalga Scenedesmus quadricauda was used to increase the pH of the groundwater via natural photosynthesis. This work applied softening as a pretreatment to ozonation of hard groundwater and mainly focused on investigating the multiple effects of algal softening on the degradation of persistent micropollutants upon subsequent ozonation. The algae-induced alkaline conditions (pH > 10) were favorable to catalyze the formation of OH radicals directly from O₃ molecules. Moreover, algal softening removed the strong radical-scavenging carbonate species (HCO₃^- and CO₃^2-) to a much greater extent than that achieved by chemical softening, which was attributed to the combination of mineral carbonation and metabolic CO₂ reduction. The fate of the natural organic matter (NOM) was characterized with spectroscopy, chromatography, and bioassay, which indicates that algal treatment decomposed the NOM to be less susceptible to attack by OH radicals. Consequently, the ozonation of alkaline groundwater achieved a better removal of the micropollutant residues in groundwater. Carbamazepine and diclofenac were used as model chemicals of persistent groundwater contaminants and were almost completely removed with an addition of 1.25 mg O₃ L^-1 (0.63 mg-O₃ mg-C^-1).

Assessing the chemical compositions and disinfection byproduct formation of biofilms: Application of fluorescence excitation-emission spectroscopy coupled with parallel factor analysis

There are increased concerns over the contributions of biofilms to disinfection byproduct (DBP) formation in engineered water systems (EWS). However, monitoring the biomolecular characteristics of biofilms to understand their impacts on DBP formation has been a great challenge as it requires complex analytical techniques. This study aimed to examine the applicability of fluorescence excitation-emission matrices (EEMs) coupled with parallel factor analysis (PARAFAC) to assess the chemical compositions and DBP formation of biofilms. Biofilms were collected from reactors grown on R2A media, as well as two drinking water-related organic substrates such as humic substances and algal organic matter. The chemical composition and formation of carbonaceous and nitrogenous DBPs of biofilms were continuously monitored every 21 days for 168 days and correlated with the derived EEM-PARAFAC components. Results indicated that all biofilm samples comprised mostly of protein-like components (∼90%), and to a lesser extent, humic-like components (∼10%). Strong correlations were generally found between tryptophan-like substances and the studied DBP formation (R2min ≥ 0.76, P < 0.05), indicating that they play a major role in producing biofilm-derived DBPs upon chlorination. Moreover, significant discrepancies between the chemical compositions and DBP formation of biofilms and their corresponding feed solutions were observed, likely due to biotransformation and biosorption processes. Overall, this work highlights that EEM-PARAFAC analysis is a promising tool to monitor the biomolecular characteristics of biofilm components and to predict the subsequent DBP formation in optimizing disinfection protocols for EWS.

Probing size characteristics of disinfection by-products precursors during the bioavailability study of soluble microbial products using ultrafiltration fractionation

Soluble microbial products (SMPs) discharged into surface water may increase the formation of disinfection by-products (DBPs) in downstream drinking water treatment plants. In this study, ultrafiltration (UF) fractionation was used to separate SMPs into homogenous components. An aerobic microbial experiment was conducted to evaluate the bioavailability of individual molecular weight (MW) fractions of SMPs in surface water and the impact on their DBP formation, facilitating the interpretation of SMPs characterization and DBPs reactivity. For SMPs, organics with MW < 1 kDa were the primary fraction, containing the most abundant humic substances. The 30 kDa < MW < 100 kDa fraction was the lowest in SMPs but had the highest SUVA values. After biodegradation, the bioavailability of physical fractions increased with the increasing MW size. However, the SUVA value, except for MW < 1 kDa, increased in individual fraction after biodegradation. Low molecular weight SMPs fractions (MW<10 kDa) were major precursors for DBP in which trichloromethane (TCM) was the most abundant. The 10 kDa <MW < 100 kDa fractions were found to be more active in formation of chloral hydrate (CH), and MW> 100KDa had relative abundant dichloroacetonitrile (DCAN) formation. After biodegradation, TCM precursors with MW < 1 kDa were removed by approximately 20%, whereas the increase of TCM formation was observed in 1 kDa < MW < 100 kDa fraction. CH formation from 1 kDa < MW < 10 kDa increased considerably, but those from 10 kDa < MW < 30 kDa decreased after biodegradation, as a result of the biotransformation of large organic acids to small organic acids. In terms of DBP reactivity, the TCM yield for the MW < 1 kDa fraction had no significant change while the 30 kDa < MW < 100 kDa fraction exhibited the greatest increase (approximately 8 times) in TCM yield.

Using fluorescence surrogates to track algogenic dissolved organic matter (AOM) during growth and coagulation/flocculation processes of green algae

Tracking the variation of the algogenic organic matter (AOM) released during the proliferation of green algae and subsequent treatment processes is crucial for constructing and optimizing control strategies. In this study, the potential of the spectroscopic tool was fully explored as a surrogate of AOM upon the cultivation of green algae and subsequent coagulation/flocculation (C/F) treatment processes using ZrCl₄ and Al₂(SO₄)₃. Fluorescence excitation emission matrix coupled with parallel factor analysis (EEM-PARAFAC) identified the presence of three independent fluorescent components in AOM, including protein-like (C1), fulvic-like (C2) and humic-like components (C3). Size exclusion chromatography (SEC) revealed that C1 in AOM was composed of large-sized proteins and aromatic amino acids. The individual components exhibited their unique characteristics with respect to the dynamic changes. C1 showed the highest correlation with AOM concentrations (R² = 0.843) upon the C/F processes. C1 could also be suggested as an optical predictor for the formation of trihalomethanes upon the C/F processes. This study sheds a light for the potential application of the protein-like component (C1) as a practical surrogate to track the evolution of AOM in water treatment or wastewater reclamation systems involving Chlorella vulgaris green algae.

Removal of disinfection byproduct precursors and reduction in additive toxicity of chlorinated and chloraminated waters by ozonation and up-flow biological activated carbon process

The variations of disinfection byproduct (DBP) precursors and DBPs-associated toxic potencies were evaluated by ozonation, followed by a up-flow biological activated carbon (O₃/UBAC) filter treating two reconstituted water samples, featuring either high bromide (105.3 μg/L) or dissolved organic nitrogen (0.73 mg N/L) concentration, respectively. Ozonation contributed to ∼20% decrease in dissolved organic carbon (DOC) concentration at a dosage of 0.7 mg of O₃/mg of DOC, but no further reduction in DOC level was observed with an increased dose of 1.0 mg of O₃/mg of DOC. When chlorine or preformed monochloramine was used as a disinfectant, UBAC process led to ∼40% reduction in the sum of detected DBP formation potential (FP) due to the removal of precursors at a feasible empty bed contact time of 15 min. The integrated effect of ozonation and UBAC biofiltration decreased the sum of DBP FP by ∼50% including halonitromethanes (THNMs), N-nitrosamines (NAs), and bromate, which increased in the effluent of ozonation. Chloramination produced less DBPs by weight as well as DBPs-associated additive toxic potencies than chlorination. The reduction in additive toxic potencies was generally lower than the removal efficiency of DBP FP after chlor(am)ination of treated waters by O₃/UBAC, indicating that the removal of DBPs-associated additive toxic potencies should be focused to better understand on the residual risk to public health in controlling DBP precursors.

An overview of the uses of high performance size exclusion chromatography (HPSEC) in the characterization of natural organic matter (NOM) in potable water, and ion-exchange applications

Natural organic matter (NOM) constitutes the terrestrial and aquatic sources of organic plant like material found in water bodies. As of recently, an ever-increasing amount of effort is being put towards developing better ways of unraveling the heterogeneous nature of NOM. This is important as NOM is responsible for a wide variety of both direct and indirect effects: ranging from aesthetic concerns related to taste and odor, to issues related to disinfection by-product formation and metal mobility. A better understanding of NOM can also provide a better appreciation for treatment design; lending a further understanding of potable water treatment impacts on specific fractions and constituents of NOM. The use of high performance size-exclusion chromatography has shown a growing promise in its various applications for NOM characterization, through the ability to partition ultraviolet absorbing moieties into ill-defined groups of humic acids, hydrolysates of humics, and low molecular weight acids. HPSEC also has the ability of simultaneously measuring absorbance in the UV-visible range (200-350 nm); further providing a spectroscopic fingerprint that is simply unavailable using surrogate measurements of NOM, such as total organic carbon (TOC), ultraviolet absorbance at 254 nm (UV₂₅₄), excitation-emission matrices (EEM), and specific ultraviolet absorbance at 254 nm (SUVA₂₅₄). This review mainly focuses on the use of HPSEC in the characterization of NOM in a potable water setting, with an additional focus on strong-base ion-exchangers specifically targeted for NOM constituents.

Removal of organics by combined process of coagulation-chlorination-ultrafiltration: optimization of overall operation parameters

To gain the run parameters of the combined process of coagulation/in situ chlorination/ultrafiltration (UF) so that the system can remove as much organic contaminants as possible without serious membrane fouling, the impacts of operation conditions in coagulation and pre-chlorination unit were investigated in a pilot-scale test. The characteristics of organics in UF influent were examined by excitation emission matrix spectroscopy to find out fouling behavior of different natural organic matter compositions to UF membrane. Thereafter, the operation parameters of different processing units of the hybrid device were optimized by response surface methodology (RSM). The results showed that the tests with the agitation speed of 40 r min^-1 had the lowest membrane fouling rate and the highest COD_Mn removal, in addition, inappropriate dosage of sodium hypochlorite in membrane influent might exert negative impacts on membrane by lowering UV₂₅₄ rejection, especially during the high algae laden period. The predominant factors of membrane fouling were the existence of tryptophan protein-like substances and the soluble microbial products. Optimum values of the mechanical rotation speed in coagulation unit, chemical dosage in pre-chlorination unit, and membrane flux in UF unit of the integrative process were 41.79 r min^-1, 1.40 mg L^-1, and 82.26 LMH, respectively.

Effect of climate change on humic substances and associated impacts on the quality of surface water and groundwater: A review

Humic substances (HS), a highly transformed part of non-living natural organic matter (NOM), comprise up to 70% of the soil organic matter (SOM), 50-80% of dissolved organic matter (DOM) in surface water, and 25% of DOM in groundwater. They considerably contribute to climate change (CC) by generating greenhouse gases (GHG). On the other hand, CC affects HS, their structure and reactivity. HS important role in global warming has been recognized and extensively studied. However, much less attention has been paid so far to effects on the freshwater quality, which may result from the climate induced impact on HS, and HS interactions with contaminants in soil, surface water and groundwater. It is expected that an increased temperature and enhanced biodegradation of SOM will lead to an increase in the production of DOM, while the flooding and runoff will export it from soil to rivers, lakes, and groundwater. Microbial growth will be stimulated and biodegradation of pollutants in water can be enhanced. However, there may be also negative effects, including an inhibition of solar disinfection in brown lakes. The CC induced desorption from soil and sediments, as well as re-mobilization of metals and organic pollutants are anticipated. In-situ treatment of surface water and groundwater may be affected. Quality of the source freshwater is expected to deteriorate and drinking water production may become more expensive. Many of the possible effects of CC described in this article have yet to be explored and understood. Enormous potential for interesting, multidisciplinary studies in the important research areas has been presented.

Humic substances, their microbial interactions and effects on biological transformations of organic pollutants in water and soil: A review

Depicted as large polymers by the traditional model, humic substances (HS) tend to be considered resistant to biodegradation. However, HS should be regarded as supramolecular associations of rather small molecules. There is evidence that they can be degraded not only by aerobic but also by anaerobic bacteria. HS presence alters biological transformations of organic pollutants in water and soil. HS, including humin, have a great potential for an application in aerobic and anaerobic wastewater treatment as well as in bioremediation. Black carbon materials, including char (biochar) and activated carbon (AC), long recognized effective sorbents, have been recently discovered to act as effective redox mediators (RM), which may significantly accelerate degradation of organic pollutants in a way similar to HS. Humic-like coating on the biochar surface has been identified. Explanation of mechanisms and possibility of applications of black carbon materials have only started to be explored. Results of many original and review papers, presented and discussed in this article, show an enormous potential for an interesting, multidisciplinary research as well as for a development of new, green technologies for biological wastewater treatment and bioremediation. Future research areas have been suggested.

Structural Memory Effect of Mg-Al and Zn-Al layered Double Hydroxides in the Presence of Different Natural Humic Acids: Process and Mechanism

The structural memory effect of layered double hydroxides (LDHs) is one of the important reasons for their extensive use in environmental remediation. In this study, humic acid (HA) was extracted from black soil and sediments and characterized to determine their structures. The regeneration mechanisms of calcinated LDHs (CLDHs) including different divalent metals (Mg-CLDH and Zn-CLDH) in deionized water and different HA solutions were carefully elucidated, and the reasons for the behavior differences in the two materials were explained. The presence of the HAs significantly increased the dissolution rate of Mg²⁺ ions from Mg-CLDHs and subsequent regeneration of Mg-LDH. Because of the diverse functional groups in the HAs, these groups were complexed with metallic ions such as Mg²⁺ on the surface of Mg-CLDH in the beginning. During the process, the HAs adsorbed the regenerated LDHs on the surfaces. Therefore, the crystallinity, morphology, and specific surface area of the regenerated Mg-LDH significantly changed, especially in the presence of high concentrations of HA. In the case of Zn-CLDH, the regeneration rate of the LDH increased in the presence of HA, but the surface of Zn-CLDH was covered with regenerated Zn-LDH and HA. Then, the inside of the particles could not transform to LDH, leading to poor crystallinity and a significant increase in the ZnO content of the HA system.

Formation of known and unknown disinfection by-products from natural organic matter fractions during chlorination, chloramination, and ozonation

Natural organic matter (NOM) is the main precursor of disinfection by-products (DBPs) formed during drinking water treatment processes. Previous studies of the relationships between DBP formation and NOM fractionation have mainly been focused on currently regulated DBPs and a few certain emerging DBPs. In this work, the Suwannee River NOM solution was fractionated into groups with different hydrophobicities using DAX-8 resins, and volatile and semi-volatile DBPs formed during the chlorination, chloramination and ozonation of the NOM fractions were examined by a nontargeted screening of comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry procedure. The results showed that a total of 302 DBPs representing nine chemical classes were detected, of which 266 were possibly newly detected, based on library searching with NIST 08 library (using similarity and reverse values of at least 600 and 700, respectively) and linear retention indices. The characterization of DBP precursors suggests that hydrophobic (HPO) NOM contains the major fraction of precursor for the formation of nitrogenous DBPs (contributing about 60% of the total nitrogenous DBPs) during all three disinfection processes. Much larger amounts of heterocyclic DBPs were formed from the HPO fraction than from the hydrophilic fraction during chlorination. During chloramination and ozonation, 5-15 times more ketones were formed from the hydrophilic fraction than from the HPO fraction. During ozonation, more than twice the amounts of esters and alcohols were formed from the hydrophilic fraction than from the HPO fraction. Three-dimensional excitation-emission matrix spectra suggest that similar to the formation of regulated DBPs, humic acid-like substances are probably the precursors of halogen-containing DBPs. Relatively higher nitrogenous DBPs formation from the HPO fraction might be because of the existence of protein-like materials.

Integration of coagulation and adsorption for removal of N-nitrosodimethylamine (NDMA) precursors from biologically treated municipal wastewater

This study investigated the N-nitrosodimethylamine (NDMA) formation potential of various dissolved organic matter (DOM) fractions in biologically treated municipal wastewater by UF fractionation, XAD-8 resin adsorption isolation, and excitation and emission matrix (EEM) fluorescence spectroscopy. Removal of various NDMA precursor fractions was also analyzed to evaluate the efficiency of traditional water treatment processes (coagulation, adsorption, and coagulation-adsorption). Results showed that NDMA were mainly formed by low molecular weight (MW) fractions (<30 kDa) and hydrophilic fractions (HiS) in biologically treated municipal wastewater. Integrated coagulation-adsorption treatments showed the highest reduction capacity for NDMA formation potential (57%), followed by isolated adsorption treatment (50%) and isolated coagulation treatment (28%). The powdered activated carbon (PAC) adsorption process could reduce the high MW precursors (>30 kDa) by 48%, which was higher than other treatments. In contrast, the highest uptake (66%) of low MW precursors (<30 kDa) was achieved by the coagulation-adsorption process. All treatments preferentially removed the hydrophobic acids (HoA) fraction compared to other fractions. Coagulation could remove more fulvic acid-like substances and adsorption could remove more microbial by-products and aromatic proteins.

Transformation of humic acid and halogenated byproduct formation in UV-chlorine processes

The synergistic effect of ultraviolet light (UV) and chlorine on the structural transformation of Humic Acid (HA) and formation of chloro-disinfection byproducts (DBPs) in water were investigated, with chlorination as a reference. The transformation and mineralization of HA were enhanced upon co-exposure to UV and chlorine. Electron spin resonance (ESR) studies revealed that hydroxyl radical (OH) and chlorine radical (Cl) were predominant active species in a pH range from 4 to 7, while Cl dominated at pH 2 and pH higher than 7. The impact of different radicals on the transformation of HA was investigated by UV254, fluorescence and TOC measurements. OH were found to be responsible for the removal of chromophoric groups and mineralization of HA, while Cl mainly reacted with HA and intermediates from HA degradation. Due to the competitive and synergistic reaction of OH and Cl with HA, higher removal of HA and lower formation of chloro-DBPs appeared in UV-chlorine than chlorination, thus the combined UV-chlorine processes should be a promising method for water purification.

Evaluating integrated strategies for robust treatment of high saline piggery wastewater

In this study, we integrated physicochemical and biological strategies for the robust treatment of piggery effluent in which high levels of organic constituents, inorganic nutrients, color, and salts remained. Piggery effluent that was stabilized in an anaerobic digester was sequentially coagulated, micro-filtered, and air-stripped prior to biological treatment with mixotrophic algal species that showed tolerance to high salinity (up to 4.8% as Cl(-)). The algae treatment was conducted with continuous O2 supplementation instead of using the combination of high lighting and CO2 injection. The microalga Scenedesmus quadricauda employed as a bio-agent was capable of assimilating both nitrogen (222 mg N g cell(-1) d(-1)) and phosphorus (9.3 mg P g cell(-1) d(-1)) and utilizing dissolved organics (2053 mg COD g cell(-1) d(-1)) as a carbon source in a single treatment process under the heterotrophic growth conditions. The heterotrophic growth of S. quadricauda proceeded rapidly by directly incorporating organic substrate in the oxidative assimilation process, which coincided with the high productivity of algal biomass, accounting for 2.4 g cell L(-1) d(-1). The algae-treated wastewater was subsequently ozonated to comply with discharge permits that limit color in the effluent, which also resulted in improved biodegradability of residual organics. The integrated treatment scheme proposed in this study also achieved 89% removal of COD, 88% removal of TN, and 60% removal of TP. The advantage of using the hybrid configuration suggests that this would be a promising strategy in full-scale treatment facilities for piggery effluent.

Probing Coagulation Behavior of Individual Aluminum Species for Removing Corresponding Disinfection Byproduct Precursors: The Role of Specific Ultraviolet Absorbance

Coagulation behavior of aluminum chloride and polyaluminum chloride (PACl) for removing corresponding disinfection byproduct (DBP) precursors was discussed in this paper. CHCl3, bromine trihalomethanes (THM-Br), dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) formation potential yields were correlated with specific ultraviolet absorbance (SUVA) values in different molecular weight (MW) fractions of humic substances (HS), respectively. Correlation analyses and principal component analysis were performed to examine the relationships between SUVA and different DBP precursors. To acquire more structural characters of DBP precursors and aluminum speciation, freeze-dried precipitates were analyzed by fourier transform infrared (FTIR) and C 1s, Al 2p X-ray photoelectron spectroscopy (XPS). The results indicated that TCAA precursors (no MW limits), DCAA and CHCl3 precursors in low MW fractions (MW<30 kDa) had a relatively good relations with SUVA values. These DBP precursors were coagulated more easily by in situ Al13 of AlCl3 at pH 5.0. Due to relatively low aromatic content and more aliphatic structures, THM-Br precursors (no MW limits) and CHCl3 precursors in high MW fractions (MW>30 kDa) were preferentially removed by PACl coagulation with preformed Al13 species at pH 5.0. Additionally, for DCAA precursors in high MW fractions (MW>30 kDa) with relatively low aromatic content and more carboxylic structures, the greatest removal occurred at pH 6.0 through PACl coagulation with aggregated Al13 species.

Monitoring changes in the structure and properties of humic substances following ozonation using UV-Vis, FTIR and (1)H NMR techniques

The main objective of this work is to conduct a comprehensive structural characterization of humic substances using the following experimental techniques: FTIR, 1H NMR and several UV–Vis parameters (Specific UV Absorbance at 254 nm or SUVA254, SUVA280, A400, the absorbance ratios A210/254, A250/365, A254/203, A254/436, A265/465, A270/400, A280/350, A465/665, the Absorbance Slope Index (ASI), the spectral slopes S275–295, S350–400 and the slope ratio SR). These UV–Vis parameters have also been correlated with key properties of humic substances such as aromaticity, molecular weight (MW) and trihalomethane formation potential (THMFP). An additional objective of this work is also to evaluate the usefulness of these techniques to monitor structural changes in humic substances produced by the ozonation treatment. Four humic substances were studied in this work: three of them were provided by the International Humic Substances Society (Suwannee River Fulvic Acid Standard: SRFA, Suwannee River Humic Acid Standard: SRHA and Nordic Reservoir Fulvic Acid Reference: NLFA) and the other one was a terrestrial humic acid widely used as a surrogate for aquatic humic substances in various studies (Aldrich Humic Acid: AHA). The UV–Vis parameters showing the best correlations with aromaticity in this study were SUVA254, SUVA280, A280/A350 ratio and A250/A364 ratio. The best correlations with molecular weight were for SUVA254, SUVA280 and A280/A350 ratio. Finally, in the case of the THMFP it was STHMFP-per mol HS the parameter showing good correlations with most of the UV–Vis parameters studied (especially with A280/A350 ratio, A265/A465 ratio and A270/A400 ratio) whereas STHMFP-per mg C showed poor correlations in most cases. On the whole, the UV–Vis parameter showing the best results was A280/A350 ratio as it showed excellent correlations for the three properties studied (aromaticity, MW and THMFP). A decrease in aromaticity following ozonation of humic substances can be readily monitored by 1H NMR and FTIR; the latter technique also allows to monitor an increase in carboxylic acidity with ozone dosage. This organic matter originated following ozonation (more aliphatic in character and more polar) is expected to be recalcitrant to further oxidation. The terrestrial humic acid (AHA) showed some structural differences with the aquatic humic substances and its behavior upon ozonation also differed in some extent from that shown by them.

Fate of natural organic matter at a full-scale Drinking Water Treatment Plant in Greece

The aim of this study was to investigate the fate of natural organic matter (NOM) and subsequent changes during the various treatment processes at a full-scale Drinking Water Treatment Plant (DWTP). Monthly sampling campaigns were conducted for 1 year at six sites along DWTP of Thessaloniki, Northern Greece including raw water from the Aliakmonas River that supplies DWTP and samples from various treatment processes (pre-ozonation, coagulation, sand filtration, ozonation, and granular activated carbon (GAC) filtration). The concentration of NOM and its characteristics as well as the removal efficiency of various treatment processes on the basis of dissolved organic carbon, UV absorbance, specific ultra-violet absorbance, fluorescence intensity, hydrophobicity, biodegradable dissolved organic carbon, and formation potential of chlorination by-products trihalomethanes (THMs) and haloacetic acids (HAAs) were studied. The concentration of dissolved organic carbon (DOC) in reservoir of the Aliakmonas River ranged from 1.46 to 1.84 mg/L, exhibiting variations regarding UV, fluorescence, and hydrophobic character through the year. Along DWTP, a significant reduction of aromatic, fluorophoric, and hydrophobic character of NOM was observed resulting in significant elimination of THM (63%) and HAAs (75%) precursors.

Trihalomethanes (THMs) precursor fractions removal by coagulation and adsorption for bio-treated municipal wastewater: Molecular weight, hydrophobicity/hydrophily and fluorescence

Due to concerns over health risk of disinfection byproducts (DBPs), removal of trihalomethanes (THMs) precursor from bio-treated wastewater by coagulation and adsorption was investigated in this study. Ultrafiltration (UF) membranes and nonionic resins were applied to fractionate THMs precursor into various molecular weight (MW) fractions and hydrophobic/hydrophilic fractions. Characteristics of coagulated water and adsorbed water were evaluated by the three-dimensional excitation and emission matrix (3DEEM) fluorescence spectroscopy. Results showed that coagulation and adsorption were suitable for removing different hydrophobic/hydrophilic and fluorescent fractions. Coagulation decreased THMs concentration in hydrophobic acids (HoA) fraction from 59 μg/L to 39 μg/L, while the lowest THMs concentration (9 μg/L) in hydrophilic substances (HiS) fraction was obtained in adsorbed water. However, both coagulation and adsorption were ineffective for removing fractions with MW<5 kDa. Although coagulation and adsorption processes could reduce THMs formation, some specific THMs formation potential (STHMFP) in residual dissolved organic matter (DOM) fractions increased in this study. Hydrophobic acid and hydrophilic fractions increased after coagulation treatment, and low MW and hydrophobic fractions increased after adsorption treatment. In addition, active carbon adsorbed more organic matter than coagulant, but brominated disinfection byproducts (Br-DBPs) in adsorbed water turned to the major THMs species after chlorination.

A multi-parametric approach assessing microbial viability and organic matter characteristics during managed aquifer recharge

Soil column (SC) experiments were conducted to investigate the feasibility of using silver nanoparticles (AgNPs) as microbial inhibitors; the microbial viability affecting the degradation of pharmaceutically active compounds (PhACs) and the characteristics of organic matter during managed aquifer recharge were specifically evaluated. Natural surface water samples treated with AgNPs (0, 2.5, 5, and 10 mg L(-1)) were continually fed into the soil columns for 2 years. The adverse impact of AgNPs on the cell membrane integrity and microbial enzymatic activity was quantitatively determined using flow cytometry and adenosine triphosphate analysis. The increase in AgNP concentration in the feed water (up to 10 mg L(-1)) resulted in a corresponding deterioration in the performance of the managed aquifer recharge (MAR), with respect to the removal of organic carbon, oxidation of nitrogenous compounds, and PhAC attenuation. The fluorescence excitation-emission matrices of feed water and treated water showed the favorable removal of protein-like substances compared to humic-like substances regardless of the AgNP concentrations; however, the extent of removed fractions decreased noticeably when the microbial viability was lowered via AgNP treatment. The biological oxidation of organic nitrogen was almost completely inhibited when 10 mg L(-1) AgNP was added during soil passage. The attenuation of bezafibrate, ketoprofen, diclofenac, clofibric acid, and gemfibrozil was strongly associated with the significant deterioration in biodegradation as a result of AgNP activity.

Removal of soluble microbial products as the precursors of disinfection by-products in drinking water supplies

Water pollution worsens the problem of disinfection by-products (DBPs) in drinking water supply. Biodegradation of wastewater organics produces soluble microbial products (SMPs), which can be important DBP precursors. In this laboratory study, a number of enhanced water treatment methods for DBP control, including enhanced coagulation, ozonation, and activated carbon adsorption, were evaluated for their effectiveness in treating SMP-containing water for the DBP reduction purpose. The results show that enhanced coagulation with alum could remove SMPs only marginally and decrease the DBP formation potential (DBPFP) of the water by less than 20%. Although ozone could cause destruction of SMPs in water, the overall DBPFP of the water did not decrease but increased after ozonation. In contrast, adsorption by granular activated carbon could remove the SMP organics from water by more than 60% and reduce the DBPFP by more than 70%. It is apparent that enhanced coagulation and ozonation are not suitable for the removal of SMPs as DBP precursors from polluted water, although enhanced coagulation has been commonly used to reduce the DBP formation caused by natural organic matter. In comparison, activated carbon adsorption is shown as a more effective means to remove the SMP content from water and hence to control the wastewater-derived DBP problem in water supply.

Characterization of soluble microbial products as precursors of disinfection byproducts in drinking water supply

Water pollution by wastewater discharge can cause the problem of disinfection byproducts (DBPs) in drinking water supply. In this study, DBP formation characteristics of soluble microbial products (SMPs) as the main products of wastewater organic biodegradation were investigated. The results show that SMPs can act as DBP precursors in simulated wastewater biodegradation process. Under the experimental conditions, stabilized SMPs had DBPFP (DBP formation potential) yield of around 5.6 μmol mmol(-1)-DOC (dissolved organic carbon) and DBP speciation profile different from that of the conventional precursor, natural organic matter (NOM). SMPs contained polysaccharides, proteins, and humic-like substances, and the latter two groups can act as reactive DBP precursors. SMP fraction with molecular weight of <1 kDa accounted for 85% of the organic carbon and 65% of the DBP formation. As small SMP molecules are more difficult to remove by conventional water treatment processes, more efforts are needed to control wastewater-derived DBP problem in water resource management.

Dissolved organic carbon and trihalomethane precursor removal at a UK upland water treatment works

The removal of dissolved organic carbon (DOC) during potable water treatment is important for maintaining aesthetic water quality standards, minimising concentrations of micro-pollutants, controlling bacterial regrowth within distribution systems and, crucially, because it contains a sub-component that can act as trihalomethane (THM) precursors. In this study, the concentration and characteristics of raw water DOC and THM formation potential (THMFP) entering an upland potable water treatment works were analysed over twelve months. Correlations between raw water DOC characteristics, standardised THMFP (STHMFP) and % DOC removal were also investigated. DOC and THM precursor removal during a series of treatment stages was examined over this period, as well as potential selectivity in the removal of DOC fractions, to assess the importance of different treatment stages for DOC removal and THM amelioration. Though THMFP removal remained high and fairly stable throughout the study period (83-89%), the data suggest that this was mostly the result of high DOC removal rates rather than the selective removal of THM precursors. Whilst this chemical agnosticism makes DOC removal more robust, it may make the overall process more vulnerable to exceeding permissible THM concentrations under changing climatic conditions. The kinetics of the reaction between DOC and chlorine appeared to vary seasonally, indicating temporal changes in the proportions of fast- and slow-reacting precursors with implications for THM concentrations at the point of delivery to the consumer. The initial treatment stages, comprising coagulation-flocculation and dissolved air floatation (DAF) were by far the most important in terms of bulk DOC removal and the preferential removal of THM precursors, though, surprisingly, DOC quality was also modified following chlorination and secondary rapid gravity filtration (RGF). Though net THM concentration decreased following initial treatment stages, a doubling in the proportion of brominated THMs (BrTHMs), which are reported to be more carcinogenic, was also observed.

Characterization and treatment of organic constituents in landfill leachates that influence the UV disinfection in the publicly owned treatment works (POTWs)

Landfill leachates strongly quench UV light. When discharged to POTWs, leachates can interfere with UV disinfection. To investigate the UV quenching problem of landfill leachates, a variety of landfill leachates with a range of conditions were collected and characterized. The UV blocking component was found to be resistant to biological degradation so they pass through wastewater treatment plants and impact the subsequent UV disinfection system. Leachate samples were fractionated into humic acids (HAs), fulvic Acids (FAs) and hydrophilic (Hpi) fractions to investigate the source of UV absorbing materials. Results show that for all leachates examined, the specific UV254 absorbance (SUVA254) of the three fractions follows: HA>FA>Hpi. However, the overall UV254 absorbance of the Hpi fraction was important because there was more hydrophilic organic matter than humic or fulvic acids. The size distribution was also investigated to provide information about the potential for membrane treatment. It was found that the size distribution of the three fractions follows: HA>FA>Hpi. This indicates that membrane separation following biological treatment is a promising technology for removal of humic substances from landfill leachates. Leachate samples treated in this manner could meet the UV transmittance requirement of the POTWs.

Spectroscopic techniques for quantitative characterization of Cu (II) and Hg (II) complexation by dissolved organic matter from lake sediment in arid and semi-arid region

Dissolved organic matter (DOM) was extracted from six sediment samples in arid and semi-arid region, which was characterized by fluorescence excitation-emission matrices (EEMs). The results showed that four fluorescent peak, fulvic-like (peak A), humic-like (peak C) and two tryptophan-like (peaks B and D), were identified in lake sediment DOM. Fluorescence quenching titration showed that peaks B and D were quenched gradually by adding additional Cu (II) and Hg (II), whereas humic-like substances had no systematic trend of the change of fluorescence intensity. Increasing fluorescence intensity value of humic-like substances can also be found. The modified Stern-Volmer model was used to calculate conditional stability constants (logK) and the percent of fluorophores (f %) which participate in the complexation between DOM and Cu (II), and Hg (II). The results showed that DOM-Cu (II) and DOM-Hg (II) complexes had higher logK values of 4.21-5.23 and the logK values of DOM-Cu (II) are much larger than the corresponding values for Hg (II). Peak B showed relatively low logK and high f % values than those of peak D. Different pollution sources which are mainly obtained from the upstream industrial wastewater, domestic sewage and return water of farmland irrigation tend to affect the stability constants and complexing capacities of Cu (II) and Hg (II).

A comparative study of the effects of ozonation and TiO2-catalyzed ozonation on the selected chlorine disinfection by-product precursor content and structure

This study compares the effects of ozonation (0.4-3.0 mg O(3)/mg DOC) and TiO(2)-catalyzed ozonation - TiO(2)-O(3) (0.4-3.0 mgO(3)/mg DOC; 1.0 mgTiO(2)/L) at pH 6 on the content and structure of natural organic matter (NOM) and trihalometane (THM) and haloacetonitrile (HAN) precursors in groundwater. The investigated groundwater from Northern Serbia is rich in NOM (9.85 mg/L DOC) which is mostly of hydrophobic character (65% fulvic acid and 14% humic acid fraction). It was found that the TiO(2)-catalyzed process, by favoring the radical mechanism of NOM oxidation, resulted in a more effective reduction in the content of total NOM (up to 18% DOC) compared to ozonation alone (up to 6% DOC). The use of TiO(2) also resulted in an improvement of ozonation in terms of THM precursor content removal (up to 80%). On the other hand, the application of both oxidation treatments resulted in an increase in the HANFP compared to the raw water. NOM oxidation during ozonation and TiO(2)-O(3) caused changes in their structure in the direction of an increased proportion of the hydrophilic fraction (up to 70%), which has the most reactive THM and HAN precursors, as well as the fraction with the highest content of their brominated species.

Investigation of the degradation of cresols in the treatments with ozone

The reaction between ozone and the three cresol isomers was investigated in pure water. Cresols were selected as model substrates representing an important component of humic material. Cresols carry both a hydroxyl and a methyl group, each theoretically increasing the reactivity of ozone with the aromatic ring. Direct comparison of the aromatic ring and the methyl group reactivities was made possible by the analysis of reaction products. The substrate degradation kinetics was studied by preparing aqueous solutions of each cresol and treating them with ozone for increasing time periods. It had been hypothesized that hydroxybenzaldehydes and hydroxybenzoic acids could be possible degradation intermediates of cresols. To verify this hypothesis, the degradation kinetics of three hydroxybenzaldehydes and two hydroxybenzoic acids were also studied. The reaction products were studied using gas chromatography (GC)-electron capture negative ionization (ECNI)-mass spectrometry (MS) analysis after direct derivatization of the samples with 5-chloro-2,2,3,3,4,4,5,5-octafluoro-1-pentyl chloroformate (ClOFPCF). This new analytical approach enables the extraction and analysis of highly polar polycarboxylic and hydroxycarboxylic acids, as well as highly polar aldehydes and hydroxy aldehydes that are difficult to extract and measure using conventional methods. As such, this new approach offered insights into ozone reaction intermediates that had been previously hypothesized, but not confirmed. Several highly hydrophilic degradation intermediates were identified, including malic, citraconic, itaconic, malonic, methylmuconic, and tartronic acid, but no hydroxybenzaldehydes were observed. The results support a 3-stage mechanism previously hypothesized, which involves ring-opening of the phenolic group, followed by the generation of several intermediates of increasing oxidation state, finally leading to relatively stable products, such as malonic and oxalic acids. We demonstrated that oxidation of the methyl group does not occur during cresol degradation.

An overview of the methods used in the characterisation of natural organic matter (NOM) in relation to drinking water treatment

Natural organic matter (NOM) is found in all surface, ground and soil waters. During recent decades, reports worldwide show a continuing increase in the color and NOM of the surface water, which has an adverse affect on drinking water purification. For several practical and hygienic reasons, the presence of NOM is undesirable in drinking water. Various technologies have been proposed for NOM removal with varying degrees of success. The properties and amount of NOM, however, can significantly affect the process efficiency. In order to improve and optimise these processes, the characterisation and quantification of NOM at different purification and treatment processes stages is important. It is also important to be able to understand and predict the reactivity of NOM or its fractions in different steps of the treatment. Methods used in the characterisation of NOM include resin adsorption, size exclusion chromatography (SEC), nuclear magnetic resonance (NMR) spectroscopy, and fluorescence spectroscopy. The amount of NOM in water has been predicted with parameters including UV-Vis, total organic carbon (TOC), and specific UV-absorbance (SUVA). Recently, methods by which NOM structures can be more precisely determined have been developed; pyrolysis gas chromatography-mass spectrometry (Py-GC-MS), multidimensional NMR techniques, and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). The present review focuses on the methods used for characterisation and quantification of NOM in relation to drinking water treatment.

Multi-wavelength spectroscopic and chromatography study on the photocatalytic oxidation of natural organic matter

The effect of TiO2 photocatalytic oxidation on the natural organic matter (NOM) properties of two Australian surface waters were quantified using UV-vis spectroscopy, high performance size exclusion chromatography (HPSEC) with a multi-wavelength UV detector, liquid chromatography with organic carbon detector (LC-OCD), and trihalomethane formation potential (THMFP) analyses. Both the UV absorbance at wavelengths greater than 250 nm and dissolved organic carbon (DOC) content decreased significantly with treatment, although complete mineralization of NOM could not be achieved. Multi-wavelength UV detection of HPSEC analysis was shown to be useful to display further changes to NOM composition and molecular weight profiles because the organic molecules was transformed into compounds that absorb weakly at the typical detection wavelength of 250-260 nm. The multi-wavelength HPSEC results also revealed that photocatalytic oxidation yields by-products with a low aromaticity and low molecular weight. The LC-OCD chromatograms indicated that low molecular acids and neutral compounds remained after photocatalytic oxidation. Those groups of compounds did not seem to contribute significantly to the formation of trihalomethanes.

Disinfection characteristics of the dissolved organic fractions at several stages of a conventional drinking water treatment plant in Southern China

Dissolved organic matter (DOM) influences many aspects of drinking water treatment, including the formation of harmful disinfection by-products (DBPs) when disinfectants are applied. DOM was isolated and fractionated using membrane ultra-filtration (UF) and reverse osmosis (RO) to eight individual fractions based on molecular weight cut-offs from a conventional surface water treatment plant (WTP) in Guangzhou of PR China. Molecular weights of these eight fractions were further calibrated using high performance size exclusion chromatography (HPSEC) and they ranged from 0.36 to 182.6 kDa. Fractions with molecular weight <0.80 kDa obtained by YC-05 UF membrane and RO were the major ones in all four stages of the water treatment processes; both ZM-500 and YM-100 membranes showed the highest removal efficiency when coupling with conventional coagulation and sedimentation processes. The elemental analysis showed that YC-05 fraction had greater polarity and aromaticity than any of the others. Furthermore, disinfection characteristics and trihalomethane formation potential (THMFP) were determined for all DOM fractions obtained in this study. YC-05 fraction was the major precursor for trihalomethane (THMs) formation among the samples tested and could be removed effectively by particulate activated carbon (PAC) adsorption. RO fraction could not be removed by PAC adsorption and, as a result, consumed more chlorine in the disinfection process. The results suggested that advanced drinking water treatment should focus on the removal of low molecular weight DOM in the source water.

Reduction of trihalomethane precursors of dissolved organic matter in the secondary effluent by advanced treatment processes

Wastewater effluent collected from the Wenchang Wastewater Treatment Plant (Harbin, China) was used as source water for advanced treatment and reclamation. Since dissolved organic matter (DOM) in the secondary effluent contains a high concentration of trihalomethanes (THMs) precursors, several processes of advanced treatments including granular activated carbon (GAC) adsorption, sand column biodegradation, horizontal subsurface flow wetland (HSFW) treatment, laboratory-scale soil aquifer treatment (SAT) and GAC+SAT were used in this study to compare and differentiate the removal mechanisms of DOM. DOM in the secondary effluent and the treated effluents was fractionated into five classes using XAD resins: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N), and hydrophilic fraction (HPI). Results showed that HPO-A and HPI were two main fractions of the DOM in the secondary effluent, accounting for 30.0% and 45.5% of the bulk DOM, respectively. HPO-A exhibited higher trihalomethane formation potential (THMFP) and specific THMFP (STHMFP) than HPI during the chlorination process. The order of the dissolved organic carbon (DOC) removal with respect to different advanced treatments was observed to be GAC+SAT>SAT>GAC>sand column>HSFW. As for the DOM removal mechanisms, the advanced treatment processes of GAC adsorption, SAT and GAC+SAT tended to adsorb more HPO-A, HPO-N and TPI-A and could reduce the aromaticity of those DOM fractions efficiently. Correspondingly, the advanced treatment processes of sand column, SAT, HSFW and GAC+SAT removed more HPI and TPI-N through biodegradation and each of the DOM fractions had an increased aromaticity. The removal order of the THMs precursor by the advanced treatment processes was GAC+SAT>GAC>SAT>sand column>HSFW. The adsorption reduced the STHMFP of the DOM fractions effectively, whereas the biodegradation mechanism of the treatments (sand column, SAT, GAC+SAT and HSFW) showed a converse trend. Moreover, the THMFP and STHMFP of the DOM in the HSFW effluent were obviously affected by the DOM derived from the leaves and roots.