Natural Organic Matter Compounds Research Articles

Abatement of humic acid from aqueous solution using a carbonaceous conjugated microporous polymer derived from waste polystyrene.

Humic acid (HA) is a major constituent of natural organic matter (NOM) found in water systems. Although NOM generally does not have any known harmful effects to humans, it imparts repulsive organoleptic properties to water, reacts with disinfectants to produce toxic products, and interferes with the efficiency of water treatment processes. The removal of NOM and related compounds from water is therefore important to render water potable and suitable for other applications. In this work, a hitherto unreported carbonaceous conjugated microporous polymer (CCMP) prepared through the organic-polymeric-precursor-controlled carbonization of hypercrosslinked post-consumer waste polystyrene (WPS) was evaluated for its capacity to remove HA from synthetic wastewater. This advanced material retained the morphology of the precursor material, while its porosity and chemical integrity were significantly improved. The approach is an environmentally friendly way of handling WPS while at the same time remediating NOM-contaminated water. Overall, with a maximum adsorption capacity of 340mg/g in batch experiments, and a maximum initial removal rate of 95.7% in column experiments, the results showed that CCMP can be used for the remediation of HA-contaminated water at high pH.

Effect of NOM and Lime Softening on Geosmin Removal by PAC

Geosmin is a commonly occurring taste and odor compound that imparts an earthy/musty odor to drinking water even at very low concentrations (odor threshold concentration, 4–20 ng/L). In this research, jar tests were performed to determine the effect of natural organic matter (NOM) and lime softening on geosmin removal via powdered activated carbon (PAC). NOM significantly inhibited geosmin sorption to PAC. For Suwannee River NOM, geosmin removal efficiency decreased by 2.7% for every 1 mg/L increase in dissolved organic carbon concentration at a PAC dose of 7.5 mg/L. Comparing three Suwannee River organic matter types, the extent of inhibition increased as average molecular weight decreased, suggesting that smaller NOM compounds are primarily responsible for inhibiting geosmin sorption to PAC. Surprisingly, lime softening did not affect geosmin removal by PAC; thus, maximizing PAC contact time, regardless of when the lime or coagulants are added, should provide the greatest geosmin removal.

The efficiency of macroporous polystyrene ion-exchange resins in natural organic matter removal from surface water

Natural water sources used for water treatment contains various organic and inorganic compounds. Surface waters are commonly contaminated with natural organic matter (NOM). NOM removal from water is important e.g. due to lowering the risk of disinfection by-product formation during chlorination. Ion exchange with the use of synthetic ion-exchange resins is an alternative process to typical NOM removal approach (e.g. coagulation, adsorption or oxidation) as most NOM compounds have anionic character. Moreover, neutral fraction could be removed from water due to its adsorption on resin surface. In this study, applicability of two macroporous, polystyrene ion exchange resins (BD400FD and A100) in NOM removal from water was assessed including comparison of treatment efficiency in various process set-ups and conditions. Moreover, resin regeneration effectivity was determined. Obtained results shown that examined resins could be applied in NOM removal and it should be noticed that column set-up yielded better results (contrary to batch set-up). Among the examined resins A100 one possessed better properties. It was determined that increase of solution pH resulted in a slight decrease in treatment efficiency while higher temperature improved it. It was also observed that regeneration efficiency was comparable in both tested methods but batch set-up required less reagents.

Impact of natural organic matter on arsenic removal by modified granular natural siderite: Evidence of ternary complex formation by HPSEC-UV-ICP-MS

High arsenic (As) groundwater usually has high concentrations of natural organic matter (NOM). Effects of NOM on arsenic adsorption were investigated to evaluate the efficiency of modified granular natural siderite (MGNS) as an adsorbent for groundwater arsenic remediation. Humic and fulvic acids (HA/FA) were selected as model NOM compounds. In batch tests, HA or FA was either first adsorbed onto the MGNS, or applied together with dissolved arsenic to investigate effects of both adsorbed and dissolved NOM on arsenic removal. The kinetic data showed no significant effects of both adsorbed and dissolved HA/FA on As(III) adsorption. However, As(V) removal was inhibited, whereby the adsorbed NOM compounds had greater inhibitory effect. The inhibitory effect on As(V) removal increased with increasing NOM concentrations. FA exhibited higher inhibitory effect than HA at the same concentration. Steric Exclusion Chromatography-HPLC (SEC-HPLC), and High-Performance Size Exclusion Chromatography-UV-Inductively Coupled Plasma Mass Spectrometry (HPSEC-UV-ICP-MS) revealed that As(V) removal was mostly achieved by the oxyanion adsorption and adversely affected by dissolved FA via competitive adsorption for surface sites. In addition to oxyanion adsorption, removal of As(V) was related to scavenging of ternary HA-As-Fe complexes, which led to the less inhibitory effect of dissolved HA on As(V) removal than dissolved FA via competitive adsorption.

Combined use of resin fractionation and high performance size exclusion chromatography for characterization of natural organic matter

The number and complexity of natural organic matter (NOM) species limits identification of individual NOM compounds. The objective of this study was to employ several characterization techniques (resin fractionation, high performance size exclusion chromatography (HPSEC), and strategic UV254 absorbance) to samples from seven surface water sites in North America, and overcome the shortfalls of each tool. Resin fractionation indicated the samples were all high in hydrophobic acids (HOA), hydrophilic neutrals (HIN) and hydrophilic acids (HIA). Site B was the only site where HIAs were the highest NOM contributors. In the HPSEC analysis, each fraction exhibited a particular molecular weight (MW) range: 100–300 Da (HIN), 1-2 kDa (HOA), and the HIA fractions exhibited MWs between these two ranges. Strategic UV254 measurements were taken at two sites to supplement the HPSEC results, and determine the difference in UV absorbance per unit dissolved organic carbon (SUVA value). Most fractions showed SUVA values of approximately 5 L/mg-m; however, the hydrophilic bases and hydrophobic neutral fractions could not be accurately evaluated due to the very low DOC concentrations for these two fractions (< 0.2 mg/L). These methods are complimentary NOM characterization techniques, and the combined methodology addresses the analytical limits of each tool.

Influence of operating conditions on performance of ceramic membrane used for water treatment

AbstractThe removal of natural organic matter (NOM) is a critical aspect of potable water treatment because NOM compounds are precursors of harmful disinfection by-products, hence should be removed from water intended for human consumption. Ultrafiltration using ceramic membranes can be a suitable process for removal of natural substances. Previously reported experiments were dedicated to evaluating the suitability of ultrafiltration through ceramic membrane for water treatment with a focus on the separation of natural organic matter. The effects of the membrane operating time and linear flow velocity on transport and separation properties were also examined. The experiments, using a 7-channel 300 kDa MWCO ceramic membrane, were carried out with model solutions and surface water at trans-membrane pressure of 0.2–0.5 MPa. The results revealed that a loose UF ceramic membrane can successfully eliminate natural organic matter from water. The permeability of the membrane was strongly affected by the composition of the feed stream, i.e. the permeate flux decreased with an increase in the NOM concentration. The permeate flux also decreased over the period of the operation, while this parameter did not influence the effectiveness of separation, i.e. the removal of NOM. It was observed that the increased cross-flow velocity resulted in the decrease in the membrane-fouling intensity and slightly improved the retention of contaminants.

The Influence of the Removal of Specific NOM Compounds by Anion Exchange on Ozone Demand, Disinfection Capacity, and Bromate Formation

This research on a pilot scale focuses on the reaction of ozone with natural organic matter (NOM) for three water qualities with different dissolved organic carbon (DOC) concentrations and NOM compositions, obtained after several stages of an anion exchange process. It was shown that for the same ozone dosage per DOC, the ozone demand was higher, less bromate was formed and a lower disinfection capacity was reached for water containing mainly humic substances, than for water where the humic substances were partly removed. It can be concluded that NOM composition, specifically the humic substances, influences the ozone demand, disinfection capacity and bromate formation.

Role of natural organic matter (NOM), colloidal particles, and solution chemistry on ultrafiltration performance

Mechanistic studies on a charged ultrafiltration (UF) membrane fouled with natural organic matter (NOM) and colloidal particles are systematically investigated to understand the relative role of each NOM fraction and the presence of colloidal particulate to membrane fouling. Humic acid (HA), dextran, and kaolin were employed as surrogate model foulants representing the organic hydrophobic acid NOM, hydrophilic neutral NOM, and inorganic colloidal materials, respectively. The results obtained showed that the organic NOM of hydrophilic surrogate (dextran) plays a primary role in promoting membrane fouling, followed by hydrophobic acids and inorganic kaolin, but to a lesser extent than organic NOM compounds. Significant differences in the extent of fouling between dextran and HA have been observed despite filtering with identical membrane. Greater membrane fluxes and better DOC rejection shown by HA could be seen as evidence demonstrating the electrostatic interactions between HA and the negatively charged membrane surface, in addition to the steric hindrance mechanism, despite possessing relatively greater adsorptive interactions with the hydrophobic PSF membrane. These results suggest that NOM structural variations (aromatic versus aliphatic molecular structure), distribution (apparent molecular weight and size), and charge density are essential factors that determine the fouling potential of each NOM fraction. Feed solution containing all the NOM fractions (HA, dextran, and kaolin) fouled the membrane more readily than the individual organic and colloidal foulants, suggesting that an association of the latter two entities is responsible for the greater extent of membrane fouling. Furthermore, the electrokinetic effects of solution chemistry (ionic strength and Ca 2+) was employed to quantify the role of electrostatic interactions in providing principal effect that promotes better permeate flux and NOM rejection, particularly with the charged component such as HA. Moreover, observation of this study is beneficial in elucidating a clearer understanding on the influential factors and responsible mechanisms of UF fouling owing to single NOM solute and multiple NOM solute systems, with respect to membrane filterability and rejection efficiency.

Effects of coagulation on submerged ultrafiltration membrane fouling caused by particles and natural organic matter (NOM)

Natural organic matter (NOM) and particles in source water are responsible for the majority of ultrafiltration (UF) membrane fouling that occurs during drinking water treatment. This study was conducted to (1) understand the UF membrane fouling phenomena caused by NOM and turbidity-causing particles and (2) investigate the effect of coagulation pretreatment on the alleviation of membrane fouling. In this study, kaolinite and humic acid (HA) were used to simulate the particles and NOM present in source water. The results revealed that the particles contributed to reversible fouling due to cake layer formation on the membrane surface, but that could be effectively reduced by increasing the frequency of physical backwashing. The results of the molecular weight (MW) distribution measurements, resin fractionation, SEM and FTIR analyses showed that HA primarily contributed to irreversible fouling. Taken together, the results of this study imply that the particles and NOM compounds present in source water may have different fouling behavior, and that particles may mitigate the irreversible fouling caused by HA. The addition of coagulant can lead to a higher rate of removal of large-sized hydrophobic compounds. Coagulation pretreatment can improve membrane performance and postpone membrane fouling development effectively, as well as retard the implementation of membrane chemical cleaning.

Impact of backwash water composition on ultrafiltration fouling control

This paper investigates the impacts of different components in backwash water on ultrafiltration (UF) fouling control. Natural surface water was used as feed water, different backwash waters with different Ca 2+ and Na + concentrations were prepared by dosing CaCl 2 and NaCl into demineralized water. Furthermore, UF permeate containing mainly natural organic matter (NOM) with minimal cations (Ca 2+ and Na +) was produced by dialysis and used for backwashing as well. Thus, the efficiency of different backwash waters on UF fouling control was evaluated. Results show that the presence of both divalent (Ca 2+) and monovalent cations (Na +) in backwash water reduces the fouling control efficiency. Since the negative charges of UF membranes and NOM compounds are screened by the cations during filtration, NOM can easily deposit on the surface of the UF membrane, causing fouling. When the mono- and divalent cations are absent in the backwash water, the charge-screening effect around the negatively charged UF membrane and NOM is reduced, increasing the repulsion force between them. In addition to the charge-screening effect, the absence of calcium in backwash water can also reduce the calcium-bridging effect between the membrane and NOM, increasing the fouling control efficiency of the backwash. Measurements of the streaming potential indicate that backwashing with demineralized water can maintain the negative charge of the membrane. Organic compounds in the backwash water do not influence the fouling control efficiency of the backwash.

Degradation of natural organic matter by TiO 2 photocatalytic oxidation and its effect on fouling of low-pressure membranes

Natural organic matter (NOM) fouling continues to be the major barrier to efficient application of microfiltration (MF) and ultrafiltration (UF) in drinking water treatment. In this study, the potential of TiO 2/UV photocatalytic oxidation to control fouling of membranes by NOM was evaluated. Decomposition kinetics of NOM was investigated using a commercial TiO 2 catalyst, and the effect of various experimental parameters including TiO 2 dosage and initial total organic carbon (TOC) concentration were also determined. The reaction kinetics was found to increase with increasing TiO 2 dosage, but decrease with increasing initial TOC concentration. Even though the rate of TOC removal was relatively low, the TiO 2/UV process was very effective in controlling membrane fouling by NOM. At a TiO 2 concentration of 0.5 g/L, fouling of both an MF and a UF membrane was completely eliminated after 20 min of treatment. Careful analyses of specific UV absorbance (SUVA) and molecular weight (MW) distribution of NOM revealed that the effectiveness in membrane fouling control is the result of the changes in NOM molecular characteristics, namely MW and SUVA due to the preferential removal and transformation of large, hydrophobic NOM compounds. Results from this study show that TiO 2/UV photocatalytic oxidation is a promising pretreatment method for MF and UF systems.

NOM and MIB, who wins in the competition for activated carbon adsorption sites?

The adsorption of an odour compound common in drinking water, 2-methylisoborneol (MIB), was studied on two activated carbons in the presence of 13 well-characterised natural organic matter (NOM) solutions. It was found that, although the carbons and the NOM solutions had a wide range of characteristics, the major competitive mechanism was the same in all cases. The low molecular weight NOM compounds were the most competitive, participating in a direct competition with the MIB molecule for adsorption sites. Equivalent background concentration (EBC) calculations indicated a relatively low concentration of directly competing compounds in the NOM. Some evidence of pore restriction was also seen, with microporous carbons most affected by low molecular weight NOM, and mesoporous carbons impacted by the higher molecular weight compounds.

Fluorescence spectroscopic studies of natural organic matter fractions.

Because of the well-known molecular complexity and heterogeneity of natural organic matter (NOM), an aquatic bulk NOM was fractionated into well-defined polyphenolic-rich and carbohydrate-rich subfractions. These fractions were systematically characterized by fluorescence emission, three dimensional excitation-emission matrices, and synchronous-scan excitation spectroscopy in comparison with those of the reference International Humic Substances Society soil humic acid and Suwannee River fulvic acid. Results indicate that fluorescence spectroscopy can be useful to qualitatively differentiate not only NOM compounds from varying origins but also NOM subcomponents with varying compositions and functional properties. The polyphenolic-rich NOM-PP fraction exhibited a much more intense fluorescence and a red shift of peak position in comparison with the carbohydrate-rich NOM-CH fraction. Results also indicate that synchronous excitation spectra were able to provide improved peak resolution and structural signatures such as peak positioning, shift, and intensity among various NOM components as compared with those of the emission and excitation spectra. In particular, the synchronous spectral peak intensity and its red shift in the region of about 450-480 nm may be used to indicate the presence or absence of high molecular weight and polycondensed humic organic components, or the multicomponent nature of NOM or NOM subcomponents.

Relationship between strength of organic sorbate interactions in NOM and hydration effect on sorption.

According to a recent conceptual model for hydration-assisted sorption of organic compounds in natural organic matter (NOM), certain polar moieties of dry NOM are unavailable for compound sorption due to strong intra- and intermolecular NOM interactions. Water molecules solvate these moieties creating new sorption sites at solvated contacts. It is expected that the greater a compound's ability to undergo specific interactions with NOM, the greater will be the hydration-assisted sorption effect, because penetration of compounds into solvated contacts must involve competition with water at the solvated contact. To test this model, we compare the hydration effect on sorption kinetics and equilibrium for 4 compounds with differing abilities to undergo specific interactions with NOM. Sorption measured on Pahokee peat in aqueous systems was fast compared with n-hexadecane (dry) systems. No concentration effect on attainment of sorption equilibrium was observed. m-Nitrophenol exhibited the greatest hydration-assisted sorption effect, benzyl alcohol showed an intermediate effect and acetophenone and nitrobenzene showed no hydration-assisted sorption, on an activity scale. The extent of hydration-assisted sorption effect correlates with compound ability to undergo specific interactions. These results support the conceptual model and demonstrate the importance of polar NOM noncovalent links in organizing the NOM phase and in controlling the hydration effect on sorption of organic compounds.

In the (adsorption) competition between NOM and MIB, who is the winner, and why?

The adsorption of an odour compound common in drinking water, 2-methylisoborneol (MIB), was studied on four activated carbons in the presence of six well characterised natural organic matter (NOM) solutions. It was found that, although the carbons and the NOM solutions had a wide range of characteristics, the major competitive mechanism was the same in all cases. The low molecular weight NOM compounds were the most competitive, participating in a direct competition with the MIB molecule for adsorption sites. Equivalent background concentration (EBC) calculations indicated a relatively low concentration of directly competing compounds in the NOM. Some evidence of pore blockage, and or restriction was also seen, with microporous carbons most affected by low molecular weight NOM, and mesoporous carbons impacted by the higher molecular weight compounds.

Simultaneous adsorption of MIB and NOM onto activated carbon: II. Competitive effects

The adsorption of an odour compound common in drinking water, 2-methylisoborneol (MIB), was studied on six activated carbons in the presence of six well-characterised natural organic matter (NOM) solutions. It was found that, although the carbons and the NOM solutions had a wide range of characteristics, the major competitive mechanism was the same in all cases. The low-molecular-weight NOM compounds were the most competitive, participating in direct competition with MIB for adsorption sites. Equivalent background compound calculations indicated a relatively low concentration of directly competing compounds in the NOM. Some evidence of pore blockage and/or restriction was also seen, with microporous carbons being the most affected by low-molecular-weight NOM and mesoporous carbons impacted by the higher-molecular-weight compounds.

Release of Natural Organic Matter Sorbed to Oxides and a Subsoil

Sorption to mineral surfaces is an important process controlling the mobility and stability of natural organic matter (NOM) in soil, yet only knowledge of the reversibility of this process enables the prediction of element cycling and NOM‐induced transport in soils. We have elucidated the desorption of mineral‐bound NOM in batch experiments with amorphous Al(OH)3, goethite, and a subsoil low in organic C. These sorbents were equilibrated with increasing amounts of water‐extractable NOM from the Oa horizon of a mor forest‐floor layer and then extracted with solutions of different ionic strengths, pH, and concentrations of inorganic anions (Cl−, SO2−4, H2PO−4). Sorbed NOM was extracted after 24, 48, 72, and 120 h. We investigated structural and functional characteristics of the desorbed NOM by XAD‐8 (macroporous resin) fractionation and by 13C‐NMR spectroscopy. Desorption of NOM from minerals and soils was negligible (&lt;3%) under solution conditions similar to those during the sorption (hysteresis). It was not influenced by increasing concentrations of noncompeting inorganic anions such as Cl− Increased concentrations (≤0.1 M) of competing anions like SO2−4 or H2PO−4 increased the NOM desorption. Though H2PO−4 was most efficient in desorbing NOM, the extractability was only ≤60% at the highest H2PO−4 concentration. The most significant desorption occurred when solution pH was raised. For goethite, NOM desorption reached a maximum at a pH above the point of zero charge (PZC) of the mineral. With increasing surface coverage of the sorbent by NOM, the proportion of desorbable NOM decreased for all extractants. Increased sorption hysteresis was also observed with an increasing time period between sorption and desorption. The desorption was more pronounced for NOM compounds that exhibit hydrophilic properties and have low contents of aromatic structures and carboxyl groups. The irreversible binding of NOM, especially of the lignin‐derived portion, to soil minerals seems to result from its polyelectrolytic nature. This may favor the formation of multi‐site coordinative bonds and effective shielding of the binding ligands by other parts of the sorbed molecule.

Membrane filtration of natural organic matter: initial comparison of rejection and flux decline characteristics with ultrafiltration and nanofiltration membranes

Two source waters containing natural organic matter (NOM) with different physical and chemical characteristics were crossflow-filtered using four types of membranes having different material and geometric properties. Transport measurements of NOM rejection and flux decline were made. A resistances-in-series model was used to represent and quantitatively compare membrane flux decline and recovery. As anticipated, the resistance due to specific adsorption depended on the concentration at the membrane interface. For the two membranes showing evidence of NOM adsorption, reducing the initial flux (which we infer to also reduce the interfacial NOM concentration) also lowered the measured resistance assigned to adsorption in our protocol. Relative molecular mass (RMM) distribution measurements (by size exclusion chromatography) were used to calculate the average RMM of the NOM and persuasively illustrated that the nominal relative molecular mass cut-off (MWCO) of a membrane is not the unique predictor of rejection characteristics for NOM compounds. Size exclusion, electrostatic repulsion, and NOM aromaticity all influenced the NOM rejection. For a given water composition (including pH and ionic strength), membrane characteristics (such as the surface charge, hydrophobicity and nominal MWCO) can be combined with the NOM properties (such as total dissolved organic carbon, specific UV absorbance at 254nm and humic content) to provide a consistent qualitative rationale for the transport results.

Effect of ozonation on sorption of natural organic matter by biofilm

Experiments were conducted to determine the effects of ozonation on sorption of aquatic natural organic matter (NOM) onto biofilm using bench-scale packed-bed reactors. It was found that 18–22% of NOM measured as dissolved organic carbon (DOC), and 28–30% measured as chloroform formation potential, was removed from the water without biodegradation. The bulk of the NOM removal was attributed to biosorption of low-molecular-weight compounds—less than 3000 Da. At a dose of 1 g-O 3 g-DOC , ozonation was not found to have a significant effect on biosorption of NOM. Ozonation simultaneously decreased the molecular size and increased the acidity of NOM compounds, and it was concluded that the effects counterbalanced each other at an ozone dose of 1:1, resulting in no significant change in NOM sorption.