Hydrophobic Natural Organic Matter Fractions Research Articles

The occurrence of natural organic matter in South African water treatment plants

Water supplied to customers must be safe and fit for purpose. It is thus important that the water from water treatment plants (WTPs) meets World Health Organization standards or local standards such as the South African National Standard, before distribution. This study focuses on the treatment of natural organic matter (NOM) in South African WTPs. The problems associated with NOM include: (1) it affects the organoleptic properties of water; (2) increases coagulant demand; (3) reacts with chlorine to form disinfection by-products and (4) causes membrane fouling. The aim of the study was to characterise the NOM composition of various water sources. Specifically, the objectives were: (1) to assess the character of NOM in selected regions of South Africa; and (2) to evaluate the NOM removal efficiencies of the selected WTPs. To achieve these, various characterisation techniques were used to determine parameters such as dissolved organic carbon, ultraviolet absorbance, specific ultraviolet absorbance, and dissolved organic matter, using fluorescence excitation-emission matrix spectroscopy. The character of NOM evolved throughout the treatment process as a result of coagulation, sedimentation and filtration processes. As indicated by SUVA, a decrease in the hydrophobic fraction of NOM from raw to final water was observed, except for plant C2 in Region C where a drastic increase in SUVA from 1.26–31.95 L/mg.m was observed, indicating an increase in the hydrophobic compounds in water. All WTPs were shown to have different removal efficiencies because of the character of NOM in the raw water and the coagulation conditions used.

Ferrate(VI) decomposition in water in the absence and presence of natural organic matter (NOM)

The kinetics of ferrate(VI) decomposition in natural water were assessed in the absence and presence of natural organic matter (NOM) (pH = 7.50, [Fe(VI)] = 54 µM, DOC = 0.00–10.00 and 1.00–8.57 mg/L for a simulated natural water and six real natural waters, respectively). Without NOM, Fe(VI) decomposition in simulated natural water exhibited a biphasic kinetics pattern, i.e. a 2nd-order reaction with respect to Fe(VI) concentration followed by a 1st-order reaction. However, an additional instant Fe(VI) loss was observed at the onset in the presence of NOM for both simulated and real natural waters, thereby rendering Fe(VI) decay with NOM a unique three-stage kinetics pattern. The initial instant Fe(VI) loss was caused due to the homogenous Fe(VI) self-decay and the rapid reactions between Fe(VI) and NOM. The latter accounted for a major fraction of the initial Fe(VI) loss and was in direct proportion with the initial DOC (DOC0) (Δ[Fe(VI)]0DOC = αNOM DOC0; αNOM = 1.45 µM Fe(VI)·L/mg DOC for the simulated natural water, and 0.66–1.35 µM Fe(VI)·L/mg DOC for the six natural waters). Fe(VI) decomposition experiments with different Suwannee River NOM isolates revealed that hydrophobic NOM fractions (i.e. fulvic acid (FA) and humic acid (HA)) caused a more significant initial Fe(VI) loss than the hydrophilic group (HPI), suggesting that Fe(VI) preferentially reacted with hydrophobic NOM molecules rather than hydrophilic compounds. Furthermore, an approach developed for the estimation of αNOM revealed a linear correlation between αNOM and specific UV absorbance (SUVA) (αNOM = 0.27SUVA + 0.18, R2 = 0.71). This study provides essential information regarding Fe(VI) decomposition for the determination of Fe(VI) dose and exposure for effective water treatment.

Effect of bioflocculants on the coagulation activity of alum for removal of trihalomethane precursors from low turbid water

Reactivity of chlorine towards hydrophobic groups present in natural organic matter (NOM) provokes the formation of carcinogenic disinfection byproducts such as trihalomethanes in chlorinated water. The present study aimed to investigate the variations in coagulant activity of alum using two different bioflocculants (coagulant aid) namely, Moringa oleifera and Cyamopsistetragonoloba for the removal of hydrophobic fractions of NOM and subsequent chlorine consumption by treated water. Effect of dual coagulants on trihalomethane surrogate parameters such as total organic carbon, dissolved organic carbon, UV absorbing materials and prominent hydrophobic species such as phenolic groups along with aromatic chromophores, polyhydroxy aromatic moiety have also been studied. The concept of differential spectroscopy and absorbance slope index has been employed to understand the combined effects of alum-bioflocculants on the reactivity of NOM with chlorine. Our result shows that the combination of alum and C. tetragonoloba is more efficient for reducing trihalomethane surrogates from chlorinated water as compared to M. oleifera. C. tetragonoloba elicited synchronized effects of sweep coagulation and particle bridging-adsorption which eventually facilitated efficient removal of hydrophobic fractions of NOM. The variation in the mechanistic approach of bioflocculants was due to the presence of cationic charge on M. oleifera and adhesive property of C. tetragonoloba.

Electrocoagulation process considerations during advanced pretreatment for brackish inland surface water desalination: Nanofilter fouling control and permeate water quality

Pretreatment with coupled aluminum electrocoagulation (EC) – microfiltration (MF) successfully mitigated colloidal and organic fouling during nanofiltration (NF) of an inland natural brackish surface water. Natural organic matter (NOM) removal by EC was enhanced due to (i) greater degree of NOM protonation by maintaining a slightly acidic pH during electrolysis, compared with that of minimum aluminum solubility (pH of 5.5 compared to 6.2), (ii) providing sufficient contact time during electrolysis and flocculation by utilizing intermediate current density (10mA/cm2), and (iii) combination of charge neutralization and sweep coagulation by increasing aluminum dosage. Direct evidence for removal of the hydrophobic fraction of NOM along with a portion of the hydrophilic moieties by EC-MF compared to MF-only was provided by attenuated total reflectance-Fourier transform infrared spectroscopy. NF flux profiles with EC-MF pretreatment of natural saline water were nearly identical to that of a model solution with similar ionic composition with no added NOM suggesting insignificant role of organic fouling. X-ray photoelectron spectroscopy showed trace amounts of CaCO3 precipitates after EC-MF pretreatment, confirmed by electron microscopy, that caused only minor flux decline. Finally, NF achieves excellent strontium removal as well as other divalent ions and NOM.

Modeling and characterization of natural organic matter and its relationship with the THMs formation

<p>Natural organic matter (NOM) has been identified as the prominent precursor for disinfection by-products (DBPs) formation during chlorination. Various studies have shown that the characteristics of NOM influence the Trihalomethanes (THMs) formation mechanism. The present study represents NOM categorization in terms of total organic carbon (TOC), dissolved organic carbon (DOC), UV absorbance at 254 nm wavelengths (UV<sub>254</sub>) and specific ultraviolet absorbance (SUVA) to investigate the effects of NOM on THMs formation mechanism. The high rate of dependency was found for each representative of NOM with respect to water quality characteristics and operational condition of disinfection process. Values of SUVA and UV<sub>254</sub> is drastically reduced with respect from higher to a moderate chlorine dose which represent the chlorine contact is more predominant with hydrophobic fractions of NOM. The value of SUVA is decreasing with respect to temperature and reaction time, which reveled higher rate of utilization for hydrophobic fractions of NOM. Predictive modeling approach was carried out using multiple regression analysis with the combination of two surrogates at each stage of modeling with help of operational condition of disinfection process and water quality characteristics. The R<sup>2</sup> value of the model was found in the range of 0.927 to 0.937 from the developed model and a model could be recommended for prediction of THMs in drinking water.</p>

Hollow fiber ultrafiltration of Ottawa River water: Floatation versus sedimentation pre-treatment

Coagulation/flocculation/sedimentation is a common form of pre-treatment for UF (ultrafiltration) within water treatment plants, but little research has been conducted on floatation as a part of the pre-treatment. The objective of this study is to compare floatation with sedimentation in the pre-treatment of a water with a high hydrophobic NOM (natural organic matter) content. Fouling tests consisted of multiple filtration/backwashing cycles performed by an automated bench-scale UF hollow fiber membrane system. Alum coagulation coupled with floatation produced the least severe hydraulically irreversible fouling and also produced the highest quality permeate based on TOC (total organic carbon) concentrations. The hydrophobic fraction of NOM was found to affect hydraulically irreversible fouling in the earlier part of the runs while transphilic NOM and particulate organic carbon affected hydraulically reversible fouling.

The fate of natural organic matter during UV/H2O2 advanced oxidation of drinking water

At conditions within the range of those typically applied for commercial drinking water applications, the impact of ultraviolet and hydrogen peroxide (UV/H2O2) advanced oxidation (AO) on the concentration, spectral characteristics, hydrophobicity, and biodegradability of natural organic matter (NOM) in a raw surface water and ultrafiltered surface water was studied. At an initial H2O2 dose of 20 mg L−1, UV/H2O2 mineralized less than 15% of the NOM in raw surface water at a fluence of 1500 mJ cm−2. Natural organic matter in ultrafiltered surface water was mineralized by at least 27% after about 1500 mJ cm−2. Partial oxidation of NOM led to ring opening of aromatic structures, cleavage of conjugated double bonded carbon structures, and reduction in the degree of aromatic substitution. The UV/H2O2 AO preferentially reacted with hydrophobic fractions of NOM leading to the formation of hydrophilic products. The treatment oxidized recalcitrant NOM into more readily biodegradable compounds with significant increases in formaldehyde and acetaldehyde concentrations. Depending on NOM properties for a given water, UV/H2O2 AO may cause partial oxidation of NOM leading to the formation of biodegradable compounds. The presence of these species may need to be addressed with a downstream process capable of improving biological stability.

산화철 나노입자 부착 반응성 세라믹 멤브레인의 막 오염 제어

Hybrid ceramic membrane (HCM) processes that combined ozonation with a ceramic membrane (CM) or a reactive ceramic membrane (RM), an iron oxide nanoparticles (IONs) incorporated-CM were investigated for membrane fouling control. Alumina disc type microfiltration and ultrafiltration membranes doped with IONs by sintering method were tested under varying mass fraction of IONs. Scanning electron microscope (SEM) images showed that IONs were well-doped on the CM surface and doped IONs were approximately 50 nm in size. Change in the pure water permeability of RM was negligible compared to that of CM. These results indicate that IONs incorporation onto CM had little effect on CM performance in terms of the flux. Natural organic matter (NOM) fouling and fouling recovery patterns during HCM processes confirmed that the RM-ozonation process enhanced the destruction of NOM and reduced the extent of fouling more than the CM-ozonation process by hydroxyl radical formation in the presence of IONs on RM. In addition, analyses of NOM in the feed water and the permeate showed that the efficiency of membrane fouling control results from the NOM degradation during HCM processes; leading to removal and transformation of relatively high contents of aromatic, high molecular weight and hydrophobic NOM fractions.

MIEX® and PAC for removal of hydrophilic DBP precursors

The objective of this research was to investigate promising materials for potential reduction of disinfection by‐product (DBP) formation resulting from reactions with hydrophilic natural organic matter (NOM), a source of precursors that is difficult to remove with conventional drinking water treatment process units. DBP reduction in other reported research was attributable to greater removal of hydrophobic fractions of NOM. Two nonionic resins were used to fractionate NOM before and after treatment with magnetic ion exchange (MIEX®) and a powdered activated carbon. At the chosen doses of treatment materials, bulk NOM removal remained the same (< 10% difference in dissolved organic carbon after treatment with activated carbon versus MIEX); compared with the powdered activated carbon, however, MIEX provided greater reduction of trihalomethane and haloacetic acid formation potential resulting from reactions with hydrophilic NOM. Therefore, MIEX preferentially removed hydrophilic DBP precursors. Similar results were observed for the transphilic fraction, whereas differences in the hydrophobic fraction were minimal. This research has implications for treatment facilities with elevated levels of highly reactive hydrophilic NOM in their influents and highlights the importance of source water chemistry in the selection of DBP mitigation strategies.

Characterization of natural organic matter treated by iron oxide nanoparticle incorporated ceramic membrane-ozonation process

In this study, changes in the physical and structural properties of natural organic matter (NOM) were observed during hybrid ceramic membrane processes that combined ozonation with ultrafiltration ceramic membrane (CM) or with a reactive ceramic membrane (RM), namely, an iron oxide nanoparticles (IONs) incorporated-CM. NOM from feed water and NOM from permeate treated with hybrid ceramic membrane processes were analyzed by employing several NOM characterization techniques. Specific ultraviolet absorbance (SUVA), high-performance size exclusion chromatography (HPSEC) and fractionation analyses showed that the hybrid ceramic membrane process effectively removed and transformed relatively high contents of aromatic, high molecular weight and hydrophobic NOM fractions. Fourier transform infrared spectroscopy (FTIR) and 3-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy revealed that this process caused a significant decrease of the aromaticity of humic-like structures and an increase in electron withdrawing groups. The highest removal efficiency (46%) of hydroxyl radical probe compound (i.e., para-Chlorobenzoic acid (pCBA)) in RM-ozonation process compared with that in CM without ozonation process (8%) revealed the hydroxyl radical formation by the surface-catalyzed reaction between ozone and IONs on the surface of RM. In addition, experimental results on flux decline showed that fouling of RM-ozonation process (15%) was reduced compared with that of CM without ozonation process (30%). These results indicated that the RM-ozonation process enhanced the destruction of NOM and reduced the fouling by generating hydroxyl radicals from the catalytic ozonation in the RM-ozonation process.

Effects of UV/H 2O 2 on NOM fractionation and corresponding DBPs formation

In this study, UV/H 2O 2 treatment was used to evaluate its efficacy for control of natural organic matter (NOM) in different water sources in Taiwan and the results were compared with the conventional water treatment process. The NOM fractions analysis showed that compositions of NOM could be very different between the various water sources, and the raw water quality in Kin-Men (an off shore island of Taiwan) was characteristic when compared to other water sources. Raw water taken from Kin-Men generally had high dissolved organic carbon (DOC) concentrations and ~ 50% of the NOM in the raw water was hydrophilic. After UV/H 2O 2 treatment, a portion of the hydrophobic fractions of NOM in raw waters were transformed into hydrophilic ones. In conventional water treatment process, coagulation and slow filtration treatments have better efficiency to reduce the NOM in water especially for the hydrophobic portion. However, the pre-chlorination treatment for raw water increased the DOC concentration due to the lysis of algae cells. This study concluded that hydrophobic acids portion is the most sensitive portion of NOM to UV/H 2O 2 and conventional treatment processes. Trihalomethanes formation potential (THMFP) tests showed that hydrophobic acids portion is also the main contributor to THMs formation after chlorination process.

The fate of natural organic matter during UV/H2O2 advanced oxidation of drinking waterA paper submitted to the Journal of Environmental Engineering and Science.

At conditions within the range of those typically applied for commercial drinking water applications, the impact of ultraviolet and hydrogen peroxide (UV/H2O2) advanced oxidation (AO) on the concentration, spectral characteristics, hydrophobicity, and biodegradability of natural organic matter (NOM) in a raw surface water and ultrafiltered surface water was studied. At an initial H2O2 dose of 20 mg L–1, UV/H2O2 mineralized less than 15% of the NOM in raw surface water at a fluence of 1500 mJ cm–2. Natural organic matter in ultrafiltered surface water was mineralized by at least 27% after about 1500 mJ cm–2. Partial oxidation of NOM led to ring opening of aromatic structures, cleavage of conjugated double bonded carbon structures, and reduction in the degree of aromatic substitution. The UV/H2O2 AO preferentially reacted with hydrophobic fractions of NOM leading to the formation of hydrophilic products. The treatment oxidized recalcitrant NOM into more readily biodegradable compounds with significant increases in formaldehyde and acetaldehyde concentrations. Depending on NOM properties for a given water, UV/H2O2 AO may cause partial oxidation of NOM leading to the formation of biodegradable compounds. The presence of these species may need to be addressed with a downstream process capable of improving biological stability.

Characterizing dissolved organic matter and evaluating associated nanofiltration membrane fouling

Natural organic matter (NOM) characteristics were determined for three ground waters exhibiting different water quality conditions. The water quality of the three feed waters collected at various water table depths was characterized by XAD-8/-4 resin adsorption, high performance size exclusion chromatography with ultraviolet and dissolved organic carbon (DOC) detections, and Fourier transform infrared spectroscopy (FTIR) to determine NOM fractionation, molecular weight, and NOM functional groups, respectively. Systematic studies were conducted to identify potential NOM foulants in ground water for nanofiltration (NF) membrane fouling. The results show that the hydrophobic fraction of NOM in all of the samples was significantly high (71–93%) compared to the hydrophilic (1.7–22.6%) and transphilic (5.3–6.6%) fractions. However, insignificant flux-decline (less than 5%) was observed for the highest DOC (36.9 mg l −1) and hydrophobic NOM (93%) containing groundwater compared to the other lesser DOC and hydrophobic NOM containing ground waters. This is presumably due to either higher fractions of hydrophilic and transphilic NOM or inorganic interactions that may be major foulants. Based on FTIR, aromatic foulants were observed at 1662 cm −1 (CO-NH2 or CO conjugated with aromatic rings) for the fouled NF membrane with the relatively low DOC source waters. The contact angle of the clean membrane (52 °) decreased with fouling up to 42–47 ° for fouled membranes with the various samples.

Seasonal variations in natural organic matter and its impact on coagulation in water treatment

In the past decade, a number of UK and US water utilities have been experiencing operational difficulties connected with the increased dissolved organic carbon (DOC) levels during the autumn and winter periods. This has been observed as an increase in the production of disinfection-by-products (DBP), and a greater coagulant demand. Resin adsorption techniques were used to fractionate raw water and investigate the variation in surface charge and coagulant–humic interactions over a 36-month period. A change in the natural organic matter (NOM) composition throughout the year was observed, with the fulvic acid fraction (FAF) increasing from 36% in September to 61% in November. However, a reduction in treatment performance is not simply due to an increase in DOC concentrations (from 4.3 to 14.5 mg L − 1 ), but also a change in the charge density of the NOM. It was found that hydrophilic NOM fractions possess negligible charge density (< 0.06 meq g − 1 DOC), and it is the hydrophobic NOM fractions, FAF in particular, that exert the greater dominance on coagulation control. The hydrophilic NOM fractions are less amenable to removal through conventional coagulation with metal salts, and are therefore likely to indicate the DOC residual remaining after treatment. Understanding the seasonal changes in NOM composition and character and their reactivity with coagulants should lead to a better optimisation of the coagulation process and a more consistent water quality.

Experimental Evaluation of Cationic Polyelectrolytes for Removing Natural Organic Matter from Water

The effectiveness of water treatment processes in removing natural organic matter varies with the nature of the natural organic matter (NOM), its molecular size, polarity and charge density, and with properties of the raw water such as turbidity and hardness. In some cases conventional alum treatment is inefficient. We have compared NOM removals achieved by conventional and polymer-based processes in bench-scale treatment of reconstituted ground and surface waters of varying colour, made from NOM isolated from the same waters. NOM isolates were fractionated by adsorption on non-functionalised resins and an anion exchanger, and characterised by size exclusion chromatography. Jar tests with the isolated NOM compared coagulation with polyelectrolytes, alum, clays and metal oxides, with each of the inorganics being in conjunction with a polyelectrolyte. Jar tests on reconstituted waters with alum and/or cationic polyelectrolyte show synergistic benefits from combinations of the two. The more hydrophobic NOM fractions were the most easily removed by polymer. The performance of cationic polymers improved significantly with increasing charge density and molecular weight. An alum/polymer combination is the most attractive treatment option.

Experimental evaluation of cationic polyelectrolytes for removing natural organic matter from water

Abstract The effectiveness of water treatment processes in removing natural organic matter varies with the nature of the natural organic matter (NOM), its molecular size, polarity and charge density, and with properties of the raw water such as turbidity and hardness. In some cases conventional alum treatment is inefficient. We have compared NOM removals achieved by conventional and polymer-based processes in bench-scale treatment of reconstituted ground and surface waters of varying colour, made from NOM isolated from the same waters. NOM isolates were fractionated by adsorption on non-functionalised resins and an anion exchanger, and characterised by size exclusion chromatography. Jar tests with the isolated NOM compared coagulation with polyelectrolytes, alum, clays and metal oxides, with each of the inorganics being in conjunction with a polyelectrolyte. Jar tests on reconstituted waters with alum and/or canonic polyelectrolyte show synergistic benefits from combinations of the two. The more hydrophobic NOM fractions were the most easily removed by polymer. The performance of cationic polymers improved significantly with increasing charge density and molecular weight. An alum/polymer combination is the most attractive treatment option.