Natural Organic Matter Surrogates Research Articles

Elucidating the inhibitory effects of natural organic matter on the photodegradation of organic micropollutants: Atrazine as a probe compound

Natural organic matter (NOM) is a complex mixture of heterogeneous compounds with varying functional groups and molecular sizes. Understanding the impact of NOM on the generation of photochemically produced reactive intermediates (PPRIs) and their potential inhibitory effects on photolysis has remained challenging due to the variations in the reactivities and concentrations of these functional groups. To address this gap, tannic acid (TA), gallic acid (GA), catechin (CAT), and tryptophan (Trp), were chosen as potential substitutes for NOM. Their effects on the photochemical transformation process were evaluated and compared with the widely used Suwannee River NOM (SRNOM). Atrazine (ATZ) was selected as a probe organic micropollutant (OMP). In this investigation, a significantly higher concentration of HO• was observed compared to O21, and the triplet excited state ( NOM*3). The findings suggest that the substituted phenols, particularly those with carboxylate-substitutions, played a substantial role in HO• formation, while electron-rich moieties acted as antioxidants, consuming NOM*3. Hydroxyl, carboxylic, and amino acid were the active groups for O21 formation. However, the inhibitory effects induced by the NOM surrogates were significant and mainly attributed to the direct photolysis inhibition caused by the inner filter effect. The scope of this work was further extended to include SRNOM, where similar trends with less pronounced formation of PPRIs and inner filter effects were observed. Therefore, this study sheds some light on the role of the functional groups in NOM during photochemical transformations of OMPs, thereby deepening our understanding of their fate in aqueous systems.

Fate of sulfamerazine by synchronous adsorption and photocatalysis dependent on natural organic matter properties

ABSTRACT Natural organic matter (NOM) can impede the removal of organic micro-pollutants (OMPs) through several mechanisms, including inner filter effect, competition with the target OMP, and radical scavenging, during synchronous adsorption/photocatalysis of multi-functional composites. In this study, the fate and inhibitory mechanisms of sulfamerazine (SMZ, a model OMP) that occurred in presence of seven different NOM samples (i.e. three standard NOM surrogates, a river water sample, a carbon filter effluent and two different sand filter effluents) during the adsorption/photocatalysis by a composite of Bi2O3-TiO2 supported on powdered activated carbon (Bi2O3-TiO2/PAC, abbreviated as BTP) when exposed to visible light irradiation were revealed. The results indicated that adsorption played a greater attribution than photocatalysis on SMZ removal. The primary impediment to the adsorption and photocatalytic degradation of SMZ was attributed to the presence of terrestrial-derived, humic-like NOM fractions with high aromaticity. The adsorption efficacy of SMZ was weakened by the absorption of NOM and its degradation products onto the BTP surface. The inner filter effect, competition between NOM and SMZ, and radical scavenging were responsible for the reduced photocatalysis of SMZ. In the cases of real water matrices, the presence of inorganic anion and co-existed NOM reduced the removal of SMZ. In summary, the findings of this work offer a comprehensive comprehension of the impact of NOM fractions on photocatalysis, emphasizing the necessity to examine the interplay between NOM and background inorganic constituents in the degradation of OMP via adsorption/photocatalysis.

Electrospun Silica-Polyacrylonitrile Nanohybrids for Water Treatments.

In this work, the removal of NOM (natural organic matter) as represented by humic acid by means of electrospun nanofiber adsorptive membranes (ENAMs) is described. Polyacrylonitrile (PAN) was used for the preparation of ENAMs incorporating silica nanoparticles as adsorbents. The addition of silica to the polymer left visible changes on the structural morphology and fibers' properties of the membrane. The membrane samples were characterized by pure water permeability, contact angle measurement, SEM, XPS, and XRD. This study assesses the preliminary performance of PAN-Si membranes for the removal of natural organic matter (NOM). The membrane rejected the humic acid, a surrogate of NOM, from 69.57% to 87.5%.

The formation of furan-like disinfection byproducts from phenolic precursors

Eleven furan-like disinfection byproducts were reported for the first time as byproducts from the chlorination of phenolic natural organic matter surrogates.

Catalytic wet peroxide oxidation to remove natural organic matter from real surface waters at urban and rural drinking water treatment plants

Al/Fe-pillared-clay-activated catalytic wet peroxide oxidation (CWPO) of dissolved natural organic matter (NOM) in real surface water streams at both urban drinking water treatment plants (DWTPs) and rural plants (R) was investigated. The clay-catalyst prepared from technical-grade reagents exhibited textural properties quite comparable to those of the one obtained from analytical-grade, costly reagents. The mineralization of dissolved organic carbon (DOC) was improved to around 90 % under ambient conditions of temperature (10–19 °C) and pH (6.07–8.12), and not governed by adsorption of the complex on the catalyst’s surface. Optimal dose of hydrogen peroxide per unit mass of DOC and Fe in the solid was found to be 0.037 mg H2O2/mg C.mg Fe. The maximal efficiency of hydrogen peroxide consumption in the degradation of a synthetic surrogate of NOM (0.437 mg C/mg H2O2) was significantly enhanced in comparison with recent studies on phenol spiked solutions (≤0.124 mg C/mg H2O2), but also when real water samples were treated (0.176 mg C/mg H2O2), while the selectivity to DOC mineralization remained close to 90 %. Sulfates and chlorides in real surface waters showed the most detrimental effect on the DOC mineralization. The more cost-effective couplings of the Al/Fe-PILC-catalyzed CWPO treatment to improve urban drinking water treatment plants by promoting both DOC mineralization and improved H2O2 consumption as a function of the input SUVA254 were (raw water → CWPO → physicochemical treatment) for values < 2.0 dm3/mg DOC.m, and (raw water → physicochemical treatment → CWPO) for values > 2.0 dm3/mg DOC.m.

Optimized CWPO oxidation of natural organic matter in continuous fixed bed reactor catalyzed by an extruded Al/Fe-PILC clay catalyst

Catalytic wet peroxide oxidation of dissolved natural organic matter (NOM) has been optimized in a continuous-flow, fixed bed reactor by using an extruded Al/Fe-pillared clay catalyst using a Synthetic Surrogate of NOM (SS-NOM) resembling typical composition and molecular weight distributions in real surface waters. Proper humidity of the extrudate’s precursor mix was found to be 38 %. Mass fraction of catalyst (xc = 0.5), absolute humidity (H = 0.6), and a height/diameter ratio = 2.0 (particle ϕ ∼ 3.0 mm and height ∼ 6.0 mm) showed the best combined mechanical and textural properties (compression strength 121 N, tenacity 1.1325 mJ, attrition 1.45 (%), BET surface 76 m2/g, and microporous surface 52 m2/g) and catalytic performance. The main parameters governing the catalytic wet peroxide oxidation (height of the catalyst bed and the ratio (H2O2/SS-NOM) were optimized in terms of mineralization of the total organic carbon and H2O2 reaction efficiency, under constant and rather short 9.2 min of residence time. Inlet concentrations of the SS-NOM (TOC = 6.63–13.7 mg C/dm3), pH (5.9–7.8) and temperature (20.0 °C – 24.0 °C) were covariates within the typical ranges exhibited by surface waters. The optimal multi-response catalytic performance using desirability function (d = 0.73) displayed 24.3 % of TOC mineralization and 51.2 % of reacted H2O2 with a height of catalyst bed 22 cm and inlet ratio (H2O2/SS-NOM) = 5.9 (mg H2O2/mg TOC), room temperature (20.0 ± 1.0 °C), and circumneutral pH.

Characterisation and performance of three Kenaf coagulation products under different operating conditions

The Sustainable Development Goal (SDG) 6.1, established by the United Nations General Assembly in 2015, targets universal and equitable access to safe and affordable drinking water for all by 2030. An essential factor in achieving this goal is the harnessing of “green” coagulants – naturally occurring, environmentally friendly materials which are effective coagulants for use in water treatment, with good availability in developing countries, inherent renewable properties and ease of biodegradation. In order to gain from these benefits, it is essential to fully understand how such coagulants may best be utilised, particularly concerning their practical application in developing countries. In this study, three different plant-based coagulation products (PCPs), namely Hexane (HxKP), saline (StKP) and crude (CrKP) extracts of Kenaf plant seed (Hibiscus cannabinus, a species of the Hibiscus plant), were applied to high (HTW), medium (MTW) and low (LTW) turbidity water in order to determine their performance and coagulation ability. The ability of the three Kenaf coagulant products (KCPs) to remove hydrophobic fractions of natural organic matter (NOM) was measured. The impact of KCPs on the treated water organic matter content (a known disinfection by-product (DBP) precursor) was examined using known surrogates of natural organic matter (NOM) i.e. the dissolved organic carbon (DOC), ultraviolet absorbance at 254 (UV254) and specific ultraviolet absorbance (SUVA254). Results obtained quantify the implications of using these coagulants during the water disinfection process. A parametric study, measuring the effect of different operating parameters, such as untreated water turbidity, pH, dosages, retention time, and KCP storage time, was completed. Turbidity removal performance for HxKP and StKP was very good with > 90% removal recorded for HTW and MTW, respectively, at pH seven within 2 hours retention time. Images obtained from scanning electron microscopy (SEM) analysis revealed a high likelihood of the coagulation mechanism of KCPs to be adsorption-interparticle bridging brought about by their flake-like structures and surfaces charges. Varying pH had no measurable influence on the coagulation performance of the KCPs. Comparing their efficiency with MoringaOleifera (MO, a previously researched PCP) and alum showed that HxKP had a negligibly different particle removal as MO. StKP turbidity removal performance was below HxKP by 1% for HTW and LTW and 2% for MTW but performed higher than the CrKP by 5% and 7% in HTW and MTW, respectively. The optimum dosage of HxKP and StKP reduced DBP surrogate values, indicating that its precursor is also minimized, although a slight shift from this optimum dosage showed a significant rise in their concentration thus signifying a potential increase in DBPs during disinfection.

Photocatalytic performance of titanium dioxide and zinc oxide binary system on degradation of humic matter

Application of photocatalysis using TiO2 or ZnO for the removal of natural organic matter (NOM) dates back more than two decades. Aiming to overcome the drawbacks of sole photocatalysts, use of multiphasic systems has received recent interest. ZnO/TiO2 binary oxide specimens were synthesized by a simple solid state dispersion method in different weight ratios of 1:1; 1:3; and 3:1 (ZT11, ZT13 and ZT31 respectively) and characterized by XRD, SEM, XPS, Raman, UV-DRS, PL and BET techniques. As a surrogate of NOM, humic acid (HA) was subjected to solar photocatalysis and degradation was followed by UV–vis and fluorescence spectroscopic tools along with dissolved organic carbon (DOC) contents. Photocatalytic degradation of HA was approximated to first order kinetic model. Referring to UV–vis parameters, ZT11 binary oxide expressed slightly higher photocatalytic performance with regard to TiO2, ZnO, ZT13 and ZT31 contrary to the mineralization extents as TiO2>ZT13 > ZT31 > ZT11 > ZnO. Excitation-emission matrix fluorescence (EEM) contour plots of the organic matrix displayed almost complete removal of humic-like and fulvic-like fluorophores upon use of sole TiO2 and ZnO. Regional distribution of the fluorophores were still evident with emergence of the new fluorophoric regions upon use of binary oxides. ZnO/TiO2 could be considered as an efficient photocatalyst for the degradation of humic acids under solar irradiation.

Influence of pH on the Kinetics and Mechanism of Photoreductive Dissolution of Amorphous Iron Oxyhydroxide in the Presence of Natural Organic Matter: Implications to Iron Bioavailability in Surface Waters.

In this study, we investigate the influence of pH on the kinetics and mechanism of photoreductive dissolution of amorphous iron oxyhydroxide (AFO) in view of the recognition that the light-mediated dissolution of iron oxides controls Fe availability in many natural waters. Our results show that both ligand-to-metal charge transfer (LMCT) and photogenerated superoxide (O2•-) play an important role in AFO photoreductive dissolution in the presence of the chosen surrogate of natural organic matter, Suwannee river fulvic acid (SRFA). The pH dependence of LMCT-mediated AFO photoreductive dissolution is mainly controlled by the influence of pH on AFO solubility. A decrease in pH increases the concentration of the dissolved and more photolabile Fe(III)-SRFA complex present in equilibrium with AFO, a complex in which Fe(III) is readily reduced by LMCT. The pH dependence of superoxide-mediated Fe(III) reduction (SMIR) is also controlled by the influence of pH on AFO solubility with an increase in the dissolved inorganic Fe(III) concentration with the decrease in pH resulting in an increased rate of SMIR. No influence of pH was observed on the steady-state O2•- concentration generated on SRFA irradiation as well as the O2•- decay rate in the presence of SRFA, suggesting that the concentration and lifetime of O2•- are not important factors in controlling the pH dependence of O2•--mediated AFO dissolution. Overall, the results of this study show that the impact of acidification of natural waters on Fe availability will be much more pronounced when Fe is present as iron oxyhydroxide compared to that observed when organically bound Fe dominates with this effect because of the strong dependency of iron oxyhydroxide solubility on pH. The increased rate and extent of dissolution of iron oxyhydroxides on the acidification of natural waters will also have implications to the fate of other contaminants (such as heavy metals and organic compounds) that may be present on the iron oxyhydroxide surface.

Photocatalytic degradation of organic micropollutants: Inhibition mechanisms by different fractions of natural organic matter

Natural organic matter (NOM) can inhibit the photocatalytic degradation of organic micropollutants (OMPs) through inner filter effect, reactive oxygen species (ROS) scavenging, and competitive adsorption. However, previous studies have focused solely on the bulk properties of NOM and our understanding of the inhibition mechanism by NOM fractions during photocatalytic degradation of OMP is still fragmentary. In this study, five well-characterized different NOM samples (i.e., secondary treated wastewater, river water, and three standard NOM surrogates) were used to elucidate the inhibition mechanisms during photocatalytic degradation of carbamazepine (a model OMP) using TiO2 and its composites with carbon nanotubes (CNT-TiO2) under UVC and solar-light irradiation. The results indicated that terrestrially derived NOM with high aromaticity, a low oxygen/carbon atom ratio, and large molecular weight is the major fraction that participates in ROS scavenging, competitive adsorption, and inner filter effect. Furthermore, the modeling analysis suggested that inner filter effect due to NOM and ROS scavenging was the most influential inhibitory mechanism. In the case of secondary treated wastewater, the presence of high concentrations of inorganic species (e.g., PO43−, Cl−, and NO3−) together with NOM significantly reduced the photocatalytic degradation of carbamazepine. Overall, the methods and the results of this study provide a comprehensive understanding of the effects of NOM fractions on photocatalysis and highlight the need to further consider the interplay between NOM and background inorganic constituents in photocatalytic degradation of OMP.

Suspended state heteroaggregation kinetics of kaolinite and fullerene (nC60) in the presence of tannic acid: Effect of π-π interactions

The colloidal heteroassociation between natural mineral colloids and engineered nanoparticles (ENPs) can reduce the bioavailability and toxicity of the ENPs. However, the efficacy of this heteroassociation-based entrapment of ENPs depends on the intrinsic material properties of the particles and the physicochemical parameters of the aquatic environment. Natural organic matter (NOM)-induced surface modifications of clay colloids, functionalization of ENPs, and efficiency of counterions as effective coagulants profoundly affect the effectiveness of heteroaggregation-based attenuation of anthropogenic colloids. In this study, tannic acid (TA), a surrogate of NOM, prevented the edge-to-face self-association of sodium-saturated kaolinite (Na-kaolinite) at acidic pH, as evaluated from the transverse proton spin–spin relaxation data (T2). Likewise, fullerene water suspension (FWS) adhesion to Na-kaolinite prevented the self-association of Na-kaolinite and enhanced the colloidal stability. At pH 4 and diffusion-limited aggregation regime salt concentrations, the Na-kaolinite and FWS heteroaggregation rates were lower than the Na-kaolinite homoaggregation rates, and eventually reached a plateau. The higher colloidal stability of the Na-kaolinite and FWS binary mixture than that of Na-kaolinite, regardless of stronger charge screening by Ca2+, reflects steric stabilization. However, at pH 7, the increased electrostatic barrier reduces the feasibility of colloidal heteroassociation between Na-kaolinite and FWS; thus, higher salt concentrations are required to initiate aggregation. Weak adsorption of TA on Na-kaolinite at pH 7 facilitated stronger π-π interactions with FWS. All suspensions exhibited faster aggregate growth at pH 7 than pH 4, possibly due to the stronger cation response at pH 7. In situ atomic force microscopy imaging and line profile plots of Na-kaolinite, TA, and FWS mixture in CaCl2 further corroborated the difference in the heteroaggregation rates observed at the two different pH values. Thus, TA-induced surface functionalization of FWS and the consequent increased electrostatic barrier to heteroassociation with Na-kaolinite may facilitate the environmental mobility of FWS in aquatic media.

MS2 coliphage inactivation by Al/Fe PILC-activated Catalytic Wet Peroxide Oxidation: multiresponse statistical optimization

The optimization of the Catalytic Wet Peroxide Oxidation (CWPO) assisted by an Al/Fe-pillared clay (Al/Fe-PILC) was assessed in the inactivation of the MS2 coliphage in the presence of a synthetic surrogate of natural organic matter (NOM). The simultaneous effect of two experimental factors (i) H2O2 dose - (H2O2)d (3.00–25.50 % of the H2O2 theoretically required for full mineralization) and (ii) catalyst concentration (0.33–2.60 g/L), and four non-controllable variables (covariates) (a) circumneutral pH (6.00–9.00), (b) temperature (5.00–25.0 °C), (c) synthetic NOM concentration (2.0–20.0 mg C/L) and (d) MS2 titer (104, 105 and 106 PFU/mL) was investigated by Response Surface Methodology (RSM). Every response was modeled and maximized: (1) MS2 inactivation, (2) fraction of reacted H2O2, (3) decolourization and (4) NOM mineralization. Multi-response optimization via desirability function based on responses (1) to (3) achieved excellent fitting (0.94 out of 1.0) and following set of optimal experimental conditions: 0.33 g Al/Fe-PILC/L, 3.36 % (H2O2)d ​(Feactive/H2O2) = 0.46, giving rise to 92.9 % of MS2 inactivation and 100 % of reacted H2O2 at pH 7.07, 25.0 +/- 0.1 °C, 16.06 mg C/L as starting NOM concentration, and MS2 titer of 106 PFU/mL after just 70 min ​of reaction.

Effect of copper corrosion products on the formation and speciation of haloacetamides and haloacetonitriles during chlorination

The catalytic effect of copper corrosion products, including copper ions, cupric oxide, and cuprous oxide, on the formation of haloacetamides and haloacetonitriles during chlorination of natural organic matter (NOM), model nitrogenous precursors, and real water samples was investigated. During chlorination of NOM, the presence of these copper corrosion products facilitated chlorine decay, and enhanced the formation of dichloroacetonitrile (DCAN) and dichloroacetamide (DCAcAm) with enhancement ratios of 45–59% and 64–137% after 10 h contact time, respectively. Six amino acids were selected as nitrogenous NOM surrogates for chlorination, and the results show that the enhancement of DCAN and DCAcAm formation by copper corrosion products was only observed for slow reacting amino acids, including glutamine, glutamic acid, and phenylamine, suggesting that copper corrosion products may enhance DCAN and DCAcAm formation by catalyzing NOM portions that are relatively inefficient precursors. When bromide and copper corrosion products were present, the formation of dihaloacetonitriles (DHANs) and dihaloacetamides (DHAcAms) could be enhanced during chlorination of NOM, but the degrees of bromine substitution for DHANs and DHAcAms decreased. Although copper corrosion products facilitated DHAN and DHAcAm hydrolysis with the facilitation increasing as the halogens shifted from chlorine to bromine, increased DHAN and DHAcAm concentrations was observed during chlorination of real water samples in the presence of copper corrosion products, confirming that the copper corrosion products had a catalytic effect on DHAN and DHAcAm formation that exceeded their catalytic effect on DHAN and DHAcAm hydrolysis. This study provides basic knowledge of disinfectant residuals and the fate of haloacetonitriles and haloacetamides in drinking water distribution systems where copper is used, which will be helpful for the management of safe water distribution.

Characterization of Natural Organic Matter by FeCl3 Coagulation

Natural organic matter (NOM) is heterogenous mixture of organic compounds that enter the water from various decomposition and metabolic reactions, including animal, plant, domestic and industrial wastes. NOM refers to group of carbon-based compounds that are found in surface water and ground water. The aim of the study is to assess organic matter characteristics in Jagir River as drinking water source and to characterize the organic components that could be removed during coagulation. Coagulation is the common water treatment process can be used to remove NOM with FeCl3 coagulant in various dosage. NOM surrogates, including total organic carbon (TOC), ultraviolet absorbance at 254 nm (UV254) and specific UV absorbance (SUVA) were chosen to assess the organic removal. Results of jar test experiments showed that NOM can be removed about 40% of NOM surrogates with 200 mg/L FeCl3. About 60% removal of total organic fraction, which is mainly humic substances, as detected by size exclusion chromatography (SEC).

Effect of phosphate buffer on aggregation kinetics of citrate-coated silver nanoparticles induced by monovalent and divalent electrolytes.

The attachment efficiency (α) is an important parameter that can be used to characterize nanoparticle (NPs) aggregation behavior and has been a topic of discussion of several papers in the past few years. The importance of α is because it is one of the key parameters that can be used to model NP environmental fate and behavior. This study uses UV-vis and laser Doppler electrophoresis to monitor the aggregation behavior of citrate-coated silver nanoparticles (cit-AgNPs) induced by Na+ and Ca2+ as counter ions in the presence and absence of Suwannee River fulvic acid (SRFA) as a surrogate of natural organic matter and different concentrations of phosphate buffer (0-1mM). Results demonstrate that phosphate buffer, which serves to maintain pH nearly constant over the course of a reaction, is an important determinant of NP aggregation behavior. Increasing phosphate buffer concentration results in a decrease in the critical coagulation concentrations (CCC) of cit-AgNPs to lower counter ion concentration and an increase of α at the same counter ion concentration, both in the absence and presence of SRFA. SRFA stabilizes AgNPs and increases the CCC to higher counter ion concentrations. The outcome of this study can be used to rationalize the variation in α and CCC values reported in the literature for NPs with similar physicochemical properties, where different α and CCC values are reported when different types of buffers and buffer concentrations are used in different studies.

Effects of metal ions on disinfection byproduct formation during chlorination of natural organic matter and surrogates.

The effects of calcium, cupric, ferrous and ferric ions on the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) were investigated using natural organic matter (NOM), small molecular weight NOM surrogates and natural water samples. The results showed that the effects were greatly dependent on the disinfection byproduct (DBP) precursor structure and molecular weight, and metal ions species. While using NOM as precursors, addition of 4.00 mM calcium ions increased the formation of THMs, dihaloacetic acids (DHAAs) and trihaloacetic acids (THAAs) by 24-47%, 51-61% and 15-25%, respectively. Addition of cupric ions at 0.02 mM increased the formation of THMs and DHAAs by 74-83% and 90-100%, respectively, but decreased the formation of THAAs by 26-27%. Similar effect was not observed when 0.04 mM ferrous or ferric ions were added. The effects of calcium and cupric ions on DBP formation were generally more evident for the NOM surrogates than that for NOM. The primary catalytic effect of calcium ions was due to complexation and less sensitive to molecular structure or weight, while that of cupric ions was attributed to redox reactions and greatly dependent on molecular structure. Both ferric and ferrous iron had substantial effects on the DBP formation of surrogates (citric acid and catechol in particular), which implied that the catalytic effects of ferric and ferrous iron mainly depended on molecular weight. The catalytic effect of cupric ions was also observed on natural water samples, while the effects of calcium, ferrous and ferric ions on natural water samples were not evident.

Comparison of three-dimensional fluorescence analysis methods for predicting formation of trihalomethanes and haloacetic acids

This work investigated the application of several fluorescence excitation–emission matrix analysis methods as natural organic matter (NOM) indicators for use in predicting the formation of trihalomethanes (THMs) and haloacetic acids (HAAs). Waters from four different sources (two rivers and two lakes) were subjected to jar testing followed by 24hr disinfection by-product formation tests using chlorine. NOM was quantified using three common measures: dissolved organic carbon, ultraviolet absorbance at 254nm, and specific ultraviolet absorbance as well as by principal component analysis, peak picking, and parallel factor analysis of fluorescence spectra. Based on multi-linear modeling of THMs and HAAs, principle component (PC) scores resulted in the lowest mean squared prediction error of cross-folded test sets (THMs: 43.7 (μg/L)2, HAAs: 233.3 (μg/L)2). Inclusion of principle components representative of protein-like material significantly decreased prediction error for both THMs and HAAs. Parallel factor analysis did not identify a protein-like component and resulted in prediction errors similar to traditional NOM surrogates as well as fluorescence peak picking. These results support the value of fluorescence excitation–emission matrix–principal component analysis as a suitable NOM indicator in predicting the formation of THMs and HAAs for the water sources studied.

Chlorinated and nitrogenous disinfection by-product formation from ozonation and post-chlorination of natural organic matter surrogates

Ozonation before chlorination is associated with enhanced formation of chloropicrin, a halonitromethane disinfection by-product (DBP), during drinking water treatment. In order to elucidate reasons for this, five natural organic matter (NOM) surrogates were treated using both chlorination and ozonation–chlorination under controlled laboratory conditions. Selected surrogates comprised two phenolic compounds, two free amino acids and one dipeptide; these were resorcinol, 3-aminophenol, L-aspartic acid, β-alanine and ala-ala, respectively. Quantified DBPs included chloropicrin, chloroform, dichloroacetonitrile and trichloroacetonitrile. Relative to chlorination alone, increases in the formation of chloropicrin from ozonation–chlorination varied from 138% for 3-aminophenol to 3740% for ala-ala for the four amine surrogates. This indicates that ozone is more effective than chlorine in mediating a rate-limiting oxidation step in chloropicrin formation, most plausibly involving conversion of an amine group to a nitro group. While both hydrophilic and hydrophobic surrogates acted as chloropicrin precursors, ala-ala was the most reactive precursor following ozonation–chlorination. Since peptides are far commoner in drinking water sources than free amino acids, further research into chemical oxidation of these species by ozone and chlorine is recommended. In contrast, oxidation with ozone prior to chlorination reduced chloroform formation moderately for the two phenolic compounds.

The kinetic and thermodynamic sorption and stabilization of multiwalled carbon nanotubes in natural organic matter surrogate solutions: The effect of surrogate molecular weight

Styrene sulfonate (SS) and polystyrene sulfonates (PSSs) were used as surrogates of natural organic matter to study the effect of molecular weight (from 206.2 to 70,000 Da) on their sorption by a multiwalled carbon nanotube (MWCNT) and an activated carbon (AC) and on their stabilization of MWCNT suspension. Results indicate that surface-diffusion through the liquid-sorbent boundary was the rate-controlling step of the kinetic sorption of both MWCNTs and AC, and surface-occupying and pore-filling mechanisms respectively dominated the thermodynamic sorption of MWCNTs and AC. Sorption rates and capacities of MWCNTs and AC in molecular concentration of SS and PSS decreased with increasing molecular weight. The PSSs but not SS facilitated the stabilization of MWCNT suspension because of the increased electrosteric repulsion. The PSSs with more monomers had greater capabilities to stabilize the MWCNT suspension, but the capabilities were comparable after being normalized by the total monomer number.

Reduction of disinfection byproduct formation by an oxidative coupling reaction with birnessite

This study investigates the reduction of Disinfection Byproduct (DBP) formation from Natural Organic Matter (NOM) surrogates, resorcinol and phloroglucinol by oxidative coupling reaction induced by birnessite. Birnessite was introduced into an aqueous solution of resorcinol or phloroglucinol under various birnessite dose, pH, and ionic strength. After reaction, a part of the dissolved fraction was characterized by UV/Vis spectroscopy, fluorescence spectroscopy, size exclusion chromatography. Another part was reacted with sodium hypochlorite to investigate the DBP formation and chlorine consumption. Polymerization of resorcinol and phloroglucinol by an oxidative coupling reaction was verified by spectroscopic analysis and molecular weight distribution analysis. Total DBP and chloroform formation from the NOM surrogates greatly decreased after reaction with birnessite. Chloroform formation further decreased when pH and ionic strength remained low during oxidative coupling. Meanwhile, the fraction of chloroacetic acids of total DBPs increased after the coupling of phenolic compounds due to increases in intermediates containing a carbonyl group. This study would contribute to establish a new and efficient alternative for DBPs formation control.