Hydrophobic Natural Organic Matter Research Articles

Characterization of natural organic matter in conventional water treatment processes for selection of treatment processes focused on DBPs control

Natural organic matter (NOM) from raw and process waters at a conventional water treatment plant was isolated into hydrophobic and hydrophilic fractions by physicochemical fractionation methods to investigate its characteristics. Formation potential of trihalomethanes (THMs) was highly influenced by the hydrophobic fraction, whereas haloacetic acids formation potential (HAAFP) depended more on the hydrophilic fraction. However the hydrophobic fraction was removed more than the hydrophilic fraction through conventional water treatment. Therefore residual hydrophilic NOM after conventional treatment needs to be removed to reduce HAAFP. Feasible additional processes are required to be evaluated by comparing preferential removal efficiency of hydrophilic NOM through pilot tests. The structural and chemical characteristics of hydrophobic NOM (i.e., humic substances (HS)) were further investigated to know how they are influenced by conventional treatment. The phenolic fraction in the hydrophobic NOM was mainly removed compared to the carboxylic fraction through water treatment, and a higher formation potential of THMs resulted from NOM with a higher phenolic content. The Fourier-transform infrared (FT-IR) and proton nuclear magnetic resonance ( 1H-NMR) employed for characterization of NOM through water treatment were insightful revealing that their results were quite close to each other. Decreases of ratio of UV absorbance at 253 and 203 nm, respectively ( A 253 / A 203 ratio) and trihalomethane formation potential/dissolved organic carbon (THMFP/DOC) showed consistent trends; therefore, the A 253 / A 203 ratio may be a good indicator of tendency for the formation potential of disinfection by-products (DBPs).

Adsorption of 3H-Labeled 17-β Estradiol on Powdered Activated Carbon

Three source waters, two model waters (Ultrapure (natural organic matter (NOM)-free)) water and Suwannee River NOM isolate by reverse osmosis (SR-NOM)) and a natural water (Colorado River water (CRW)), were tested. Those waters were selected to represent a relatively hydrophobic NOM (SR-NOM) and a relatively hydrophilic NOM (CRW) based on their specific ultraviolet absorbance (SUVA = UVA254/DOC) values. The adsorption of an estrogenic compound, 17β-estradiol (E2), on powdered activated carbons (PACs) was investigated. Kinetic and PAC dose-response experiments were performed with PACs at an initial concentration of 0.1 nM (27 ng L−1). Additional experiments were also performed at various initial concentrations ranging from 0.025 nM (6.8 ng L−1) to 5.0 nM (1360 ng L−1) to determine the effects of initial concentration on E2 adsorption. In separate experiments, 17β-estradiol was introduced to PAC as a pure component, in binary mixtures with other salts (NaCl, Na2SO4, and CaCl2), and under varying pH conditions (4.0, 7.5, and 11.0) to determine the effects of pH and background ions on E2 adsorption. Samples were measured by liquid scintillation counting using 3H radio-labeled E2. Without preconcentration, a method detection limit using the liquid scintillation counter was 0.005 nM (1.36 ng L−1), respectively. Increasing contact time and PAC dose improved compound removal. Activated carbon is a viable technology for water treatment plants.

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.

The fouling characterization and control in the high concentration PAC membrane bioreactor HCPAC-MBR

This study focuses on the experimental investigation to identify the effect of PAC at high concentrations on the fouling of membranes. A pilot-scale experimental apparatus was installed at a water treatment plant located downstream of Nakdong river basin, Korea. Effluent of rapid sand filter was used as influent of the system, which consists of PAC bio-reactor, submerged membrane module (hollow fiber with pore size 0.1 m) and air supply facility. PAC was dosed at 40 g/L initially and it was not replaced during the operation period. Suction type filtration was carried out at intervals of 12 min. suction and 3 min. idling. At the initial flux 0.36 m/d, the system could be operated stably for around 90 days at target trans-membrane pressure (TMP) of 40 kPa. Among total resistance of membrane filtration, cake and gel layer resistance, Rc+Rg, was the dominant fraction (more than 90% of the total) to increase the filtration pressure, which means that the filtration resistance could be controlled by the PAC cake layer and then irreversible membrane fouling could be prevented. Three minutes air backwashing every 3 days could extend the operation period to 127 days. Organics were analyzed in terms of molecular weight structure. The influent of the system consists of 15.0% and 74.4% of hydrophobic and hydrophilic natural organic matter (NOM), respectively. Hydrophobic and hydrophilic (electrostatic) interaction was the main factor on fouling of the membrane in the reactor. Hydrophobic fraction decreased slightly in the effluent, which means hydrophobic NOM removal in the reactor by adsorption. Organics accumulated in the membrane were extracted for analysis after a certain period of operation. The fraction of hydrophobic and hydrophilic organics was 41.4% and 38.9%, respectively. On the basis of the experimental results, the hydrophobic organics were the major materials causing the fouling of the membrane, which should be changed to other types of material.

Characterization of NOM in the Han River and evaluation of treatability using UF–NF membrane

Chlorine reacts with the natural organic matter (NOM) that remains in waters and forms halogenated by-products. Some of these products such as trihalomethanes (THMs) and haloacetic acids (HAAs) have been known to cause cancer and other toxic effects to human beings. Disinfection is a process for the inactivation of pathogenic microorganisms and prevention of waterborne diseases. Despite these advantages, disinfection needs to be evaluated and is of concern because of the serious risks to human health. Therefore, this study characterized NOM, which is a disinfection by-product (DBP) precursor, in the water treatment processes from the Han River and evaluated the removal efficiencies of NOM fractions by conventional and advanced processes. The raw water from the Han River contained higher hydrophilic fraction than the hydrophobic fraction. The hydrophilic NOM constituted still 55–70% of NOM in waters after each process. Since the hydrophilic NOM exhibited higher HAAFP than hydrophobic NOM, chlorination of the Han River water produced higher haloacetic acid formation potential (HAAFP) than trihalomethane formation potential (THMFP). When the fractions of DBPFP are expressed as percentage of total organic halide formation potential (TOXFP), THMFP, HAAFP, and others are 26%, 43%, and 31% of the TOXFP, respectively. UF membrane could replace conventional processes showing a little higher removal efficiency of NOM and DBPFP, but advanced processes will be required to meet future requirements. The ultrafiltration (UF)–nanofiltration (NF) combined membrane process had better removal efficiency of NOM compared to other processes. Therefore, the results of this study suggest that the UF–NF membrane process is one of the best available ways for removing NOM.

Removal Mechanism of Natural Organic Matter and Organic Acid by Ozone in the Presence of Goethite

ABSTRACT The oxidations of natural organic matter (NOM) and a model compound (p-chlorobenzoic acid) were characterized using ozonation and catalytic ozonation processes. In general, the catalytic ozonation showed better performance in the removal of organics tested in the study. The hydrophobic, transphilic, and hydrophilic NOM fractions were isolated using XAD-8 and -4 resins to evaluate the reaction characteristics. The catalytic ozonation in the presence of goethite accomplished the higher removal of NOM with simultaneous reduction of the three fractions than the ozonation which removed the hydrophobic portion only. The analysis of discrete size distributions of NOM revealed that ozonation yielded a removal of >1,000MW and an increase of <1,000MW, whereas all molecular weight fractions reduced after catalytic ozonation. The concentrations of model compound and aqueous and gaseous ozone were monitored during the oxidations, and efficiencies were compared for cases in the absence and presence of iron oxide (FeOOH).

Isolation of humic and non-humic NOM fractions: structural characterization.

The combination of RO concentration and XAD-8/XAD-4 resin adsorption techniques was used to isolate the different constituents of the Natural Organic Matter (NOM) from inorganic salts. NOM fractions i.e. colloids, hydrophobic NOM (HPO humic substances), transphilic NOM (TPI) and hydrophilic NOM (HPI) fractions isolated from different surface waters were characterized using 13C NMR and FT-IR spectroscopy and HPLC/Size Exclusion Chromatography coupled with UV and DOC detection. Results showed that the isolation procedure was suitable to quantitatively isolate the different fractions of NOM.

Characterization of anion exchange membranes with natural organic matter (NOM) during electrodialysis

Natural organic matter (NOM) is thought to be a major source of fouling during membrane filtration of natural waters. The organic matter present in surface waters was characterized in terms of its molecular weight distribution, acidity and electrokinetic properties. The fouling potentials of anion exchange membranes were predicted by the characterization. Changes in the physicochemical properties of anion exchange membranes were also examined during electrodialysis (ED) process of solutions containing NOM. The ED performances were evaluated for the three anion exchange membranes (AMX, AM-1 and ACM) in the presence of NOM. Fouling phenomena in terms of current efficiency and NaCl flux were in good agreement with the fouling potentials predicted by the characterization results. Observations of the molecular weight distribution and the constituents of NOM revealed that the hydrophobic NOM fraction with high molecular weights deposited mainly on the membrane surface, providing fouling effects on the anion exchange membrane.

Evaluation of drinking water treatment processes focusing on natural organic matter removal and on disinfection by-product formation

The aim of this study was to characterize and compare natural organic matter (NOM) removal and disinfection by-product (DBP) formation in the drinking water treatment train that can give valuable information, while optimizing the treatment process. In this study, the determination of the hydrophobic (HPO), transphilic (THP) and hydrophilic (HPI) NOM distribution was used in parallel with more related drinking water parameters to compare the selected waters. High-performance size-exclusion chromatography (HPSEC) was applied to evaluate the relative changes of molecular size distribution of NOM in different treatment steps and source waters. This showed that the quantity, speciation and activated carbon adsorption of DBPs could vary not only by water quality, but also by the distribution and properties of the organic molecules that comprise NOM.

Transport characterizations of natural organic matter in ion-exchange membrane for water treatment

A series of adsorption experiments were performed to investigate the factors affecting the transport of natural organic matter (NOM) in an ion-exchange (IX) membrane. In this study, the structure of the NOM was hypothesized to be an important factor in terms of the organic fouling of IX membrane. It was found that the adsorbed mass of hydrophobic NOM constituent on the membrane surface was higher than that of either the hydrophilic or transphilic NOM constituent. NOM adsorption was seriously affected by the apparent charge of the NOM. As the apparent charge increased, NOM adsorption also significantly increased. Moreover, the molecular mass of the hydrophobic NOM acids was too high to enable them to pass through the IX membrane, and this caused an accumulated adsorption of solutes on the membrane surface, i.e. NOM fouling. In addition, both pH and ionic strength affected NOM adsorption on the surface of the IX membrane. Lower NOM adsorption resulted from a lower pH and a higher ionic strength.

Cleaning strategies for flux recovery of an ultrafiltration membrane fouled by natural organic matter

One of the most common problems encountered in water treatment applications of membranes is fouling. Natural organic matter (NOM) represents a particularly problematic foulant. Membranes may be fouled by relatively hydrophilic and/or hydrophobic NOM components, depending on NOM characteristics, membrane properties, and operating conditions. To maximize flux recovery for an NOM-fouled ultrafiltration membrane (NTR 7410), chemical cleaning and hydraulic rinsing with a relatively high cross-flow velocity were investigated as cleaning strategies. The modification of the membrane surface with either an anionic or a cationic surfactant was also evaluated to minimize membrane fouling and to enhance NOM rejection. Foulants from a hydrophobic NOM source (Orange County ground water (OC-GW)) were cleaned more effectively in terms of permeate flux by acid and caustic cleanings than foulants from a relatively hydrophilic NOM source (Horsetooth surface water (HT-SW)). An anionic surfactant (sodium dodecyl sulfate (SDS)) was not effective as a cleaning agent for foulants from either hydrophobic or hydrophilic NOM sources. High ionic strength cleaning with 0.1 M NaCl was comparatively effective in providing flux recovery for NOM-fouled membranes compared to other chemical cleaning agents. Increased cross-flow velocity and longer cleaning time influenced the efficiency of caustic cleaning, but not high ionic strength cleaning. The membrane was successfully modified only with the cationic surfactant; however, enhanced NOM rejection was accompanied by a significant flux reduction.

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.

NOM Accumulation at NF Membrane Surface: Impact of Chemistry and Shear

The effects of solution chemistry, surface shear, and composition of natural organic matter (NOM) were investigated for their impact on accumulation of foulant material at the surface of charged polymeric nanofiltration membranes. The source of NOM was the Suwannee River. A bench-scale, batch recycle system was used with 20 hollow fiber, nanofiltration membranes. Membrane flux decline and foulant accumulation increased at low pH and high ionic strength as a result of neutralization of charge, electric double layer compression, and the apparent shift in conformation of charged NOM macromolecules. The rate of NOM accumulation decreased with operating time, suggestive of an eventual steady state between adsorption and desorption. The effect of NOM composition on membrane fouling could not be discerned by a standard technique to isolate hydrophobic and hydrophilic NOM fractions, quite possibly because of the fractionation methodology's failure to recover a small but important fouling fraction or because of NO...

Characterization of clean and natural organic matter (NOM) fouled NF and UF membranes, and foulants characterization

Contact angles, zeta potentials, and IR spectra of clean and NOM-fouled membranes were compared to demonstrate differences in hydrophobicity, surface charge, and functional groups, respectively. Contact angle increased and decreased for membranes fouled with hydrophobic and hydrophilic NOM, respectively. Zeta potential decreased negatively (less negative) for membranes fouled with both hydrophobic and hydrophilic NOM, suggesting that ionizable functional groups were coated with non-ionizable NOM components (possibly neutrals). The IR spectra reduced in absorbance intensity for NOM-fouled membranes, suggesting that aromatic groups were coated with non-aromatic or less aromatic NOM components. The results of XAD- 8 4 fractionations of foulants (desorbed NOM with NaOH) showed that hydrophilic and hydrophobic NOM components were the major foulants for membranes fouled with hydrophilic and hydrophobic NOM-source waters, respectively.

Influence of NOM composition on nanofiltration

Hydrophilic NOM caused little permeate flux decline and was poorly rejected compared with hydrophobic NOM.The influence of natural organic matter (NOM) composition on the rejection of total organic carbon (TOC), permeate water flux, and the strength and amount of NOM association with the membrane was examined in bench‐scale nanofiltration studies. NOM composition was manipulated by fractionation into hydrophilic and hydrophobic components and by powdered activated carbon (PAC) pretreatment with subsequent dilution to control for TOC concentration. Hollow‐fiber nanofilters made of negatively charged polysulfone were used in a batch recycle system. Hydrophobic NOM was shown to be responsible for nearly all permeate flux decline and was more highly rejected by the membrane than hydrophilic NOM. Using membrane‐feed solutions with the same TOC concentration, the authors found that the NOM remaining in solution after PAC pretreatment caused greater permeate flux decline and was more poorly rejected than the original mixture of NOM. NOM recovered from the membrane after nanofiltration was predominantly high‐molecular‐weight material (i.e., &gt; 30,000 daltons).

Mobility of natural organic matter in a study aquifer

Field-scale transport of natural organic matter (NOM) was studied in a two-well tracer test by injecting 80,000 L of [open quotes]brown water[close quotes] (66 mg of C L[sup [minus]1]) from a wetlands pond into a shallow, sandy, coastal plain aquifer. The basic features of NOM breakthrough observed in laboratory column studies (extending tailing and rapid decline in concentrations when NOM inputs are terminated) were observed in the field. Retardation of NOM in the field agreed with predictions from laboratory studies. In spite of natural heterogeneities, fractionation of NOM subcomponents occurred in transport. Smaller (< 3,000 MW) and more hydrophilic (by XAD-8 chromatography) components of NOM were more mobile than were larger (3--100K MW), more hydrophobic components. However, over the 2-week injection, the solid and solution phase reached an apparent steady state with respect to NOM adsorption, resulting in the unretarded transport of even the hydrophobic and macromolecular NOM. The results indicate that NOM can exhibit considerable mobility in an aquifer and suggest that NOM could alter the transport of contaminants in groundwater. 43 refs., 9 figs., 5 tabs.