Molecular Weight Natural Organic Matter Research Articles

Kinetics of natural organic matter (NOM) removal during drinking water biofiltration using different NOM characterization approaches

To better understand biofiltration, concentration profiles of various natural organic matter (NOM) components throughout a pilot-scale drinking water biofilter were investigated using liquid chromatography – organic carbon detection (LC-OCD) and fluorescence excitation and emission matrices (FEEM). Over a 2 month period, water samples were collected from six ports at different biofilter media depths. Results showed substantial removal of biopolymers (i.e. high molecular weight (MW) NOM components as characterized by LC-OCD) and FEEM protein-like materials, but low removal of humic substances, building blocks and low MW neutrals and low MW acids. For the first time, relative biodegradability of different NOM components characterized by LC-OCD and FEEM approaches were investigated across the entire MW range and for different fluorophore compositions, in addition to establishing the biodegradation kinetics. The removal kinetics for FEEM protein-like materials were different than for the LC-OCD-based biopolymers, illustrating the complementary nature of the LC-OCD and FEEM approaches. LC-OCD biopolymers (both organic carbon and organic nitrogen) and FEEM protein-like materials were shown to follow either first or second order biodegradation kinetics. Due to the low percent removal and small number of data points, the performance of three kinetic models was not distinguishable for humic substances. Pre-filtration of samples for FEEM analyses affected the removal behaviours and/or kinetics especially of protein-like materials which was attributed to the removal of the colloidal/particulate materials.

The effect of natural organic matter polarity and molecular weight on NDMA formation from two antibiotics containing dimethylamine functional groups

N-nitrosodimethylamine (NDMA) is a disinfection byproduct preferentially formed in chloraminated water. NDMA may be formed from certain chemicals containing dimethylamine (DMA) functional groups. This reaction may be slowed by the presence of natural organic matter (NOM). In this study, NOM fractionated by size or polarity was tested for its ability to slow or impede the formation of NDMA from two DMA-containing precursors, the antibiotics tetracycline and spiramycin. The high molecular weight NOM fractions (>10KDa) were shown to be the most effective in reducing the amount of NDMA formed from the precursor chemicals. The filtrate of a C-18 non-polar cartridge was also effective at reducing NDMA formation from tetracycline (spyramycin not tested). Therefore, polar and charged NOM components may be responsible for the reduction in NDMA formation. A possible mechanism for the reduction of NDMA formation from tetracycline is complexation due to the hydrogen bonding of the DMA functional group on tetracycline to polar phenolic functional groups in the NOM.

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.

Factors influencing natural organic matter sorption onto commercial graphene oxides

Nanosized graphene materials are being considered as a class of new, high surface area sorbents suitable for water treatment applications. This study explored commercially available graphene powders of differing sizes, surface areas, and surface compositions for their ability to sorb dissolved natural organic matter (NOM) from water under varying solution conditions within batch reactors. The sorption kinetics of NOM on graphene powders were rapid and reached equilibrium within hours. Sorption isotherms for all graphenes and all NOM types were all best described with the Freundlich model. Sorption affinity improved with increasing graphene specific surface area, more graphene carbon content, greater NOM aromatic content, and lower solution pH. Graphene sorption behavior is compared to carbon nanotubes and granular activated carbon, and high surface area graphene may possess superior sorption rates and capacities, whereas low surface area graphene may be entirely ineffective. The high surface area graphene examined here also showed selectivity for the aromatic and high molecular weight NOM fractions within measurements of specific UV absorbance and size exclusion chromatography. The results suggest that aromatic interactions significantly participate in NOM binding, but that electrostatic interactions may also influence sorption capacity depending on solution pH and graphene surface charge.

Effects of molecular weight-dependent physicochemical heterogeneity of natural organic matter on the aggregation of fullerene nanoparticles in mono- and di-valent electrolyte solutions

Given the wide presence of heterogeneous natural organic matter (NOM) and metal ions (Na+/Ca2+/Mg2+), as well as their significant role in governing nanoparticle stability in aqueous environments, it is of great importance to understand how the molecular weight (MW)-dependent physicochemical properties of NOM impact fundamental transportation processes like the aggregation of engineered nanoparticles (ENPs) in the presence of Na+/Ca2+/Mg2+. Here, we report on the aggregation behavior of a model ENP, fullerene nanoparticles (nC60) in the presence of five MW fractions of Suwannee River NOM (Mf-SRNOMs, separated by ultrafiltration techniques) and three electrolytes (NaCl, CaCl2 and MgCl2). We found that in all NaCl treatments and low concentration CaCl2/MgCl2 treatments, the enhancement of nC60 stability positively correlated with the MW of Mf-SRNOMs. Whereas, the stability efficiency of identical Mf-SRNOM in different electrolytes followed an order of NaCl > MgCl2 > CaCl2, and the enhanced attachment of nC60-SRNOM associations was observed in high MW Mf-SRNOM (SRNOM>100 kD and SRNOM 30–100 kD) at high concentration CaCl2/MgCl2. Our results indicate that although the high MW NOM with large humic-like material is the key component for stabilizing nC60 in monovalent electrolyte, it could play a reversed role in promoting the attachment of nC60, especially in long term aggregations and at high concentrations of divalent cations. Therefore, a detailed understanding of the effects of heterogeneous NOM on the aggregation of ENPs should be highly valued, and properly assessed against different cation species and concentrations.

Natural Organic Matter Transport Modeling with a Continuous Time Random Walk Approach

In transport experiments through columns packed with naturally Fe/Al oxide-coated quartz sand, breakthrough curves (BTCs) of natural organic matter (NOM) displayed strong and persistent power law tailing that could not be described by the classical advection-dispersion equation. Tailing was not observed in BTCs for a nonreactive tracer (sulforhodamine B); therefore, the anomalous transport is attributed to diverse adsorptive behavior of the polydisperse NOM sample rather than to physical heterogeneity of the porous medium. NOM BTC tailing became more pronounced with decreases in pH and increases in ionic strength, conditions previously shown to be associated with enhanced preferential adsorption of intermediate to high molecular weight NOM components. Drawing from previous work on anomalous solute transport, we develop an approach to model NOM transport within the framework of a continuous time random walk (CTRW) and show that under all conditions examined, the CTRW model is able to capture tailing of NOM BTCs by accounting for differences in transport rates of NOM fractions through a distribution of effective retardation factors. These results demonstrate the importance of considering effects of adsorptive fractionation on NOM mobility, and illustrate the ability of the CTRW model to describe transport of a multicomponent solute.

Trihalomethanes in drinking water: Effect of natural organic matter distribution

Effects of distribution of natural organic matter (NOM) on formation and distribution of trihalomethanes (THMs) in municipal water were investigated. Water samples were fractionated using serial ultrafiltration with membranes of molecularweight cut-off (MWCO) values of 500, 1 000 and 3 000 Da. The resulting 4 fractions of water with NOM of (i) < 500 Da; (ii) 500 Da – 1 kDa; (iii) 1 kDa – 3 kDa; and (iv) > 3 kDa were separated. Variable amounts of bromide ion (0, 40, 80, 120 and 200 μg/ℓ were added to these samples. The samples were chlorinated at pH of 6 and 8.5 and held at 20°C for various reaction periods (3, 8, 28, 48 and 96 h). The results demonstrate that the higher molecular weight NOM is strongly correlatedwith UV254 and specific ultraviolet absorbance (SUVA), while the lower molecular weight NOM is weakly correlated with UV254 and SUVA. Increase in bromide ion concentration increases total THM formation. Fractions of brominated THMs decrease with increasing NOM molecular size. Lower molecular weight NOM forms more brominated THMs than the corresponding higher molecular weight NOM. Increase of bromide to chlorine ratio decreases chloroform and increases brominated THMs. Increase in pH increases chloroform and decreases brominated THMs. This study demonstrates that the distribution of NOM and bromide ion can have important role on the distribution of THMs in drinking water.Keywords: bromide ion, molecular weight distribution, natural organic matter, trihalomethane distribution

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.

Effect of polydispersity on natural organic matter transport

The mobility of humic-substance dominated natural organic matter (NOM) concentrated from a freshwater wetland by reverse osmosis was examined in sand columns at pH 5–8, in 0.001 M and 0.01 M NaClO4. Greater mobility was observed at higher pH and lower ionic strength, although breakthrough curves (BTCs) for bulk NOM exhibited extensive tailing under all conditions examined. Based on observations from previous batch experiments indicating preferential adsorption of intermediate to high molecular weight (MW) NOM, we postulate that ‘adsorptive fractionation’ of the NOM pool leads to the observed tailing behavior, and develop a novel approach to assess the effects of polydispersity on transport of NOM and associated contaminants. BTCs for different NOM fractions were constructed by separating column effluent MW distributions determined by high-pressure size exclusion chromatography into five discrete intervals or ‘bins’ and calculating the mass of NOM within each bin at four sampling times. Observed retardation factors (Ro), reflecting median arrival time relative to that of a nonreactive tracer, ranged from 1.4 to 7.9 for the various bins and generally increased with MW. NOM retarded transport of the contaminant metal Cd (2.5 ppm, in 0.01 M NaClO4) slightly at pH 5 and more substantially at pH 8. Although Cd had little or no effect on bulk NOM transport, retention of the more aromatic, IMW-HMW NOM appeared to be slightly enhanced by Cd. Study results demonstrate that heterogeneity in retardation as a function of MW is likely a major factor contributing to bulk NOM BTC tailing and may have important implications for contaminant transport.

Effects of natural organic matters molecular weight distribution on the immersed ultrafiltration membrane fouling of different materials

Effects of natural organic matter molecular weight (MW) distribution in source water on the reversible and irreversible fouling of immersed ultrafiltration membranes of three different materials were systematically investigated using representative sources of natural waters. It was found from the bench-scale tests that the organic matters of the MW lower than 1 K and higher than 30 KDa were the main substances that induced reversible fouling regardless of the materials, and that of MW between 1 K and 5 KDa could cause reversible fouling for polyvinylidene fluoride (PVDF) and polysulfone (PS) membrane. As for the irreversible fouling, small organic molecules of the MW lower than 1 KDa were the main part due to the hydrogen bonds. In addition, the organic matters of MW between 1 K and 3 KDa can induce irreversible fouling for polyvinyl chloride and PVDF membrane. Results of long-term filtration tests showed that PVDF membrane was more vulnerable to small organic molecules due to its high electronegativity substances, and PS membrane had better resistance to organic fouling.

Formation of N-nitrosamines from chlorination and chloramination of molecular weight fractions of natural organic matter

N-Nitrosamines are a class of disinfection by-products (DBPs) that have been reported to be more toxic than the most commonly detected and regulated DBPs. Only a few studies investigating the formation of N-nitrosamines from disinfection of natural waters have been reported, and little is known about the role of natural organic matter (NOM) and the effects of its nature and reactivity on the formation of N-nitrosamines. This study investigated the influence of the molecular weight (MW) characteristics of NOM on the formation of eight species of N-nitrosamines from chlorination and chloramination, and is the first to report on the formation of eight N-nitrosamines from chlorination and chloramination of MW fractions of NOM. Isolated NOM from three different source waters in Western Australia was fractionated into several apparent MW (AMW) fractions using preparative-scale high performance size exclusion chromatography. These AMW fractions of NOM were then treated with chlorine or chloramine, and analysed for eight species of N-nitrosamines. Among these N-nitrosamines, N-nitrosodimethylamine (NDMA) was the most frequently detected. All AMW fractions of NOM produced N-nitrosamines upon chlorination and chloramination. Regardless of AMW characteristics, chloramination demonstrated a higher potential to form N-nitrosamines than chlorination, and a higher frequency of detection of the N-nitrosamines species was also observed in chloramination. The results showed that inorganic nitrogen may play an important role in the formation of N-nitrosamines, while organic nitrogen is not necessarily a good indicator for their formation. Since chlorination has less potential to form N-nitrosamines, chloramination in pre-chlorination mode was recommended to minimise the formation of N-nitrosamines. There was no clear trend in the formation of N-nitrosamines from chlorination of AMW fractions of NOM. However, during chloramination, NOM fractions with AMW <2.5 kDa were found to produce higher concentrations of NDMA and total N-nitrosamines. The precursor materials of N-nitrosamines appeared to be more abundant in the low to medium MW fractions of NOM, which correspond to the fractions that are most difficult to remove using conventional drinking water treatment processes. Alternative or advanced treatment processes that target the removal of low to medium MW NOM including activated carbon adsorption, biofiltration, reverse osmosis, and nanofiltration, can be employed to minimise the formation of N-nitrosamines.

Adsorption of methyl parathion on PAC from natural waters: the effect of NOM on adsorption capacity and kinetics

Source water pollution by agricultural chemicals poses great threat to drinking water safety and the removal of such contaminants is a challenge to the water treatment industry. In this work, the adsorption behaviors of methyl parathion (MP) from different natural waters onto different kinds of powdered activated carbons (PAC) were investigated systematically. On the basis of the characterization of the PACs and natural organic matter (NOM), the suitability of PAC with NOM for effective removal of MP was proposed, and the effect of competitive adsorption on MP removal under two PAC dosing patterns was evaluated. The results indicated that NOM adsorption was dependent on the molecular weight (MW) distribution of organic compounds and the pore size distribution of PAC. The mesopore surface area with pore size > 3 nm was dominant for the adsorption of the NOM fraction in the range of 500 Da < MW < 3000 Da. Competition for adsorption sites by smaller MW NOM had significant effect on the adsorption of target organic compound in the simultaneous adsorption pattern. Whereas in the NOM-preloaded adsorption pattern, pore blockage by relatively larger MW NOM resulted in markedly reduction in both adsorption capacity and adsorption kinetics, the diffusion rate of MP on PAC could be affected by the PAC dosage, pore size distribution and the MW distribution of NOM.

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.

Fouling of nanofiltration membrane: Effects of NOM molecular weight and microcystins

Toxic cyanotoxins such as microcystins represent a human health risk in water bodies. Nanofiltration is an effective technology to remove these micro-contaminants from drinking water. However, long-term operational sustainability is necessary because of decreases in membrane fluxes over time and increasing operation costs. The rejection of natural organic matter (NOM) is a key issue regarding membrane fouling and flux decline, and is also of great importance in the water industry due to its relationship with public health. Therefore, this study aimed to analyse the effect of microcystins and NOM properties on membrane fouling and to understand the fouling mechanisms, using a series of experiments with different water types. Results showed that nanofiltration was capable of reducing low molecular weight NOM fractions from water and that these fractions were responsible for flux decline and membrane fouling. The adsorption of NOM onto the membrane surface was reduced in the presence of microcystins due to the hydrophobic character of microcystins, which are the first to be adsorbed on the membrane surface. Microcystins contributed to the rejection of smaller natural organic fractions by blocking the membrane pores and reducing NOM adsorption onto the membrane pores.

Granular activated carbon (GAC) adsorption of two algal odorants, dimethyl trisulfide and β-cyclocitral

This study was to investigate granular activated carbon (GAC) adsorption of two algal odorants in water, dimethyl trisulfide and β-cyclocitral. Among the four isotherm models (Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich), Freundlich isotherm showed the best fitting with the equilibrium data in terms of the coefficient of determination (R 2) and Chi-square ( χ 2). Based on the parameters determined in the Freundlich isotherm equations for GAC adsorption of a single odorant, we successfully predicted the GAC adsorption behavior in a bisolute solution using the Ideal Solution Adsorption (IAS) model. In the kinetics study of the two odorants adsorption by GAC, pseudo first-order and pseudo second-order kinetic models both well fit the experimental data. The calculated Gibbs free-energy changes for GAC adsorption of dimethyl trisulfide and β-cyclocitral were − 3.61 and − 4.24 kJ/mol at 298 K, respectively. The pH effects on GAC adsorption of dimethyl trisulfide and β-cyclocitral were different. Alkaline condition (pH > 10) favored GAC adsorption of dimethyl trisulfide, however, adsorption of the β-cyclocitral was not significantly influenced by pH (2–13). The presence of natural organic matter (NOM) hindered adsorption of dimethyl trisulfide and β-cyclocitral to different degrees. Low molecular weight NOM fractions (particularly < 1000) showed the significant inhibiting effect in the GAC adsorption.

Reduction of natural organic matter by nanofiltration process

The objectives of this investigation were to characterize natural organic matter (NOM) in Kin-men raw water, to evaluate the performance of the nanofiltration (NF) membrane process for NOM removal, and to determine the good engineering practice (GEP) of the NF 270 membrane filtration performance. Three different samples: (1) raw water collected from the Tai Lake in Kin-men, Taiwan; (2) ultrafiltration (UF) pre-treated water; and (3) sand filtration (SF) treated water after the coagulation and sedimentation processes were employed in this study. The hydrophobic component (58%) was the predominant NOM fraction, and the NOM molecular weight was distributed broadly, i.e., lower than 1 kDa (30%), 1–5 kDa (32%) and larger than 5 kDa (38%). Hydrophobic NOM easily accumulated on the NF membrane surface and resulted in flux decline. The SF–NF was the proposed treatment process because it can reduce the NOMs effectively with lower energy consumption than UF–NF. It was noted that the dissolved organic carbon (DOC) rejection ratio was not affected by changing cross-flow velocity. However, at lower cross-flow velocity (0.15 m s −1), the reduction of organic matter in water sample was higher than that at higher cross-flow velocity (0.30 m s −1). By integrating the experimental results, it was concluded that a transmembrane pressure of 690 kPa and a cross-flow velocity of 0.30 m s −1 exhibited the GEP, yielding about 94% of both DOC and UV 254 reduction.

Change of Molecular Weight of Organic Matters through Unit Water Treatment Process and Associated Chlorination Byproducts Formation

The objectives of this study were to evaluate the change of molecular weight (MW) profiles in natural organic matter (NOM) through various treatment processes (coagulation, granular activated carbon (GAC), and ozonation) using high performance size exclusion chromatography based on ultraviolet absorbance and dissolved organic detection (HPSEC-UVA-DOC). In addition, relationships between MW profiles and disinfection by-production (DBP) formation were evaluated. Each treatment process results in significant different effects on NOM profiles. Coagulation is effective to remove high molecular weight NOM, while GAC is effective to remove low molecular weight NOM. Ozonation removes only a small portion of NOM, while it induces a significant reduction of UV absorbance due to breakdown of the aromatic groups. All treated waters are chlorinated, and chlorination DBPs such as trihalomethanes (THMs) and haloacetic acids (HAAs) are measured under formation potential conditions. Both THM and HAA formation potentials were significantly reduced through the coagulation process. GAC was more effective to reduce THM formation compared to HAA formation reduction, while ozonation showed significant HAA reduction compared to THM reduction.

Natural organic matter (NOM) and pesticides removal using a combination of ion exchange resin and powdered activated carbon (PAC)

The combination of anion exchange resins (AERs) and powdered activated carbon (PAC) was studied to remove both natural organic matter (NOM) and pesticides. Experiments were conducted with high dissolved organic carbon (DOC) surface water (about 6.0 mg DOC/L) spiked with both atrazine and isoproturon. AERs, like MIEX ® and IRA938 ®, showed up to 75% removal of DOC after 30 min contact time. The addition of PAC after treatment with these AERs only slightly decreased the residual DOC from 1.4 to 1.2 mg/L. Experiments conducted with high (200 μg/L) and low (1 μg/L) initial pesticide concentrations showed that simultaneous and successive combinations of AER and PAC significantly improve the removal of both pesticides compared with PAC treatment on raw water. The improvement of short-term adsorption kinetics was explained by the adsorption of pesticides on AERs (about 5%) and the removal of high molecular weight (MW) NOM structures by AERs that reduce pore blockage phenomena. For 24 h contact time with PAC (adsorption isotherms), the benefit of AER treatment was lower, which indicates that the refractory DOC to AER treatment still competes through direct site competition mechanism. MIEX ® resin had a distinct behavior since the simultaneous treatment with PAC showed no benefit on pesticide adsorption. The presence of fine residues of MIEX ® was shown to interfere with PAC adsorption.

Effects of Iron on the Molecular Weight Distribution, Light Absorption, and Fluorescence Properties of Natural Organic Matter

This study investigated the effects of iron on natural organic matter (NOM) absorbance, fluorescence, and molecular weight. Addition of iron(III) to 5 and 10 mg C/L XAD-8 isolated NOM samples at pH 5.5 caused absorbance of visible light to increase, fluorescence intensity of peaks at excitation/emission wavelengths 230/435 nm and 320/450 nm to decrease, and a small shift from intermediate to higher molecular weight components. Iron(II) had little or no effect on XAD-8 isolate properties. Addition of iron(III) to XAD-4 isolated NOM solutions also caused absorbance of visible light to increase. Iron(III) addition to XAD-4 isolate solutions caused a greater decrease in fluorescence intensity than was observed for the XAD-8 isolate, but little or no change in the molecular weight distribution. Overall, our results suggest that the effects of iron on NOM molecular weight, absorbance, and fluorescence properties depend upon the redox state of iron and the composition of the NOM. These results also suggest that the potential effects of iron should be considered when using fluorescence to infer NOM provenance or structure.

Disinfection by-products precursors removal by enhanced coagulation and PAC adsorption

Because of concerns over the health effects of disinfection by-products (DBPs), the removal of DBPs precursors from the Terkos Lake water (TLW) of the Istanbul City by enhanced coagulation and powdered activated carbon (PAC) adsorption was investigated. The results of this study clearly indicated that the effects of coagulation and PAC adsorption on the removal of dissolved organic carbon (DOC) and DBPs precursors from TLW were complementary. Maximum DOC removal efficiency of enhanced coagulation by ferric chloride was 45%, and this type of natural organic matter (NOM) is preferentially large organic molecules with negatively charged functional groups. However, supplementing enhanced coagulation with PAC adsorption increased the removal of DOC to 76%, and PAC adsorption removed mostly low molecular weight and uncharged NOM substances. This study shows that the combination of enhanced coagulation and PAC adsorption can be more effective than enhanced coagulation alone for meeting the Turkish trihalomethanes (THM) limit of 150 μg/L.