Separation Of Natural Organic Matter Research Articles

PH-regulated interfacially polymerized nanofiltration membranes to achieve high separation of NOM and moderate desalination for purifying ground water

Highly permeable nanofiltration (NF) membranes with efficient natural organic matter (NOM) removal yet preserving essential minerals are of great significance for purifying ground water. In this work, a novel pH-regulated interfacial polymerization (PRIP) strategy was proposed to fabricate ultra-low pressure NF membranes. This strategy was achieved by changing the aqueous solution pH (5, 7, 9, and 11) during IP process. The effects of pH-regulated processes on the structure, chargeability, and physicochemical properties of NF membranes were systematically investigated. Tailored NF membranes under acidic conditions (TFC-pH 5) achieved the ultrahigh permeability of 42.9 L m−2 h−1 bar−1 and 83.3 % moderate rejection of Na2SO4. For the NF membranes prepared under alkaline conditions (TFC-pH 11), the sieving capacity was obviously improved with fewer defects, and 99.4 % rejection of Na2SO4 was observed. In addition, the purification performance of NF membranes in ground water treatment was further studied. Modified NF membranes showed significant removal of NOM and retain moderate amounts of mineral salts. Finally, the mechanism of the pH-regulated influence on the polyamide active layer formation process was proposed. This study provides a feasible and facile design idea for ultralow-pressure NF membranes in purifying ground water.

Organic matter removal and antifouling performance of sulfonated polyaniline nanofiltration (S-PANI NF) membranes

Natural organic matter (NOM) removal from water prior to other treatment processes can improve treatment efficiency and final water quality. Here, NOM removal across five size fractions by newly developed sulfonated polyaniline nanofiltration (S-PANI NF) membranes was compared with a commercial membrane and conventional adsorption-coagulation-flocculation, optimized for NOM removal. Artificially prepared surface water and seawater containing 10 – 100 mg C L−1 NOM extract and a stabilized landfill leachate served as test solutions. S-PANI NF membranes showed best NOM separation performance for both surface and seawater followed by the commercial membrane and conventional treatment. For landfill leachate conventional treatment had the best performance followed by S-PANI NF membranes. S-PANI performed slightly better in removal of chemical oxygen demand (COD) (74%) compared to the commercial membrane (70%) and conventional treatment (70%). Both membranes performed consistent with increasing salinity and NOM concentration, while experiencing a modest carryover at higher salinity. During long-term fouling S-PANI exhibited slower growth in transmembrane pressure (TMP), less affinity towards organic matter and higher flux recovery compared to the commercial membrane, particularly at high NOM concentration. This is the first study to investigate S-PANI membranes for water treatment applications and under high-fouling conditions. Results indicate S-PANI NF membranes are promising for such applications. In addition, this study also provides an inter-process comparison for NOM removal over an extreme range of water matrix conditions.

The role of medium molecular weight organics on reducing disinfection by-products and fouling prevention in nanofiltration

Nanofiltration (NF) is utilized in water treatment for controlling disinfection by-products formation potential (DBPFP) and disinfection by-products (DBPs). Attention regarding NF-based technology has been paid on membrane fouling of NF and the rejection efficiency of contaminants by NF membranes. Natural organic matter (NOM) presenting in surface waters is one main removal target in drinking water treatment by NF-based technology, and is thereby a contributor to the membrane fouling of NF. In application, pretreatments of other membrane filtration (e.g., microfiltration (MF) and ultrafiltration (UF)) has been taken prior to NF, resulting in the separation of NOM of specific molecular weight. Meanwhile, it is well known that NOM is composed of organic compounds of different molecular weights. However, the effect of NOM of specific molecular weight has been seldom investigated from the aspects of membrane fouling and the resulting DBPFP after membrane filtration. By using combinations of MF and UF (molecular weight cut-off of 100K or 20K) as pretreatment prior to NF, the NOM of various molecular weight on DBPFP and DBPs in the NF-treated water were investigated. The experiments were conducted with two real-world surface water samples and one tap water sample. It was found that medium molecular weight NOM, defined as NOM that passed UF100K but did not pass UF20K in this study, reduced fouling of the NF membrane. This is supported by the excitation and emission matrix (EEM) fluorescence spectra, size exclusion chromatography (SEC) and flux analysis. In addition, the medium molecular weight NOM also reduced the DBPFP in the NF treated water and eventually the DBPs by participating in forming a protective layer on the NF surface, blocking the transfer of small molecular weight NOM into the NF filtrate, thereby reducing the DBPFP of the NF filtrate since small molecular weight NOM was the major contributor to DBPFP in this study.

Comprehensive Analysis of Spinel-Type Mixed Metal Oxide-Functionalized Polysulfone Membranes toward Fouling Resistance and Dye and Natural Organic Matter Removal.

Nanostructured polymeric membranes are of great importance in enhancing the antifouling properties during water filtration. Nanomaterials with tunable size, morphology and composition, surface modification, and increased functionality provide considerable opportunities for effective wastewater treatment. Thus, in this work, an attempt has been made to use spinel-structured MnCo2O4 as a nanofiller in the fabrication of nanostructured polysulfone (PSF) mixed matrix membranes and is investigated in terms of morphology, hydrophilicity, permeability, protein and natural organic matter separation, dye removal, and, finally, antifouling properties. The MnCo2O4 nanomaterials are synthesized and characterized via X-ray diffraction and field emission scanning electron microscopy and are loaded into a membrane matrix with varied concentrations (0 to 1.5 wt %). PSF nanocomposite membranes are prepared via a nonsolvent-induced phase-separation process. The results show an enhancement in hydrophilicity, porosity, and permeability with respect to the modified nanocomposite membranes because of oxygen-rich species in the membrane matrix, which increases affinity toward water. It was also found that the modified membranes display remarkably greater pure water flux (PWF) (220 L/m2 h), higher Congo red rejection coefficient (99.86%), higher humic acid removal (99.81%), higher fouling resistance, and a significant flux recovery ratio (FRR) (88%) when tested with bovine serum albumin protein when compared to a bare PSF membrane (30 L/m2 h PWF and 35% FRR). This is because the addition of MnCo2O4 nanoparticles into the polymeric casting solution yielded tighter PSF membranes with a denser skin layer and greater selectivity. Thus, the enhanced permeability, greater rejection coefficient, and antifouling properties show the promising potential of the fabricated PSF-spinel nanostructured membrane to be utilized in membrane technology for wastewater treatment.

Natural organic matter separation by forward osmosis: Performance and mechanisms

The purification performance of a forward osmosis (FO) membrane on natural organic matter (NOM) contained in real surface water by was investigated systematically. FO could reject the natural dissolved organic matter (DOM) effectively with removal efficiencies of approximately 99.0%. When the natural water samples (e.g., raw surface water) had lower fouling tendencies, the active layer facing the draw solution (AL-facing-DS mode) provided a higher water flux than that in the alternative membrane orientation because the isoflux point occurred later in the process. It was found that the concentration of calcium ions had a more severe effect on decreasing the fouling flux of the FO membrane than that of the organic foulant. Furthermore, the concentrated feed solution had a more significant effect on the fouling flux decline of the natural DOM containing more small molecules than natural DOM containing more macromolecules. Additionally, the fouling that occurred in the AL-facing-DS orientation was compensated by the reduced internal concentration polarization (ICP) level based on the occurrence of the critical compensation point. It was also revealed that the permeation drag caused by the water flux and the chemical interactions induced by the feed solution pH and the calcium ion concentration played a significant role in the adsorption of small natural DOM molecules in the porous structure of the FO membrane. Based on the analysis of the interfacial free energies, the interactions between the natural DOM and the surface of the support layer dominated the initial fouling of the FO membrane, while subsequent fouling was controlled by the interaction between the approaching DOM molecules and the already adsorbed DOM.

Separation characteristics of cations and natural organic matter in electrodialysis

Natural organic matter (NOM) in water can cause the formation of disinfection byproducts (DBPs) when NOM reacts with a disinfectant such as chlorine. Nanofiltration (NF) and reverse osmosis (RO) are effective treatment methods to remove NOM. However, the simultaneous presence of both NOM and divalent cations such as Ca2+ can enhance fouling in NF and RO. Therefore, an appropriate pretreatment to remove such cations before NF or RO would delay fouling and perhaps improve water recovery and NOM removal efficiency. Electrodialysis (ED) is potentially an excellent pretreatment method because it separates inorganic ions well using ion exchange membranes (IEMs) but does not separate NOM well because of its size and consequent low diffusivity. This research focused on ion and NOM separation with ED using three different types of commercially available IEM pairs, two different commercially available NOM sources, and six different influents at 500 mg/L total dissolved solids in the presence or absence of both hardness (Ca2+ and Mg2+) and NOM. The target waters of interest in this research were drinking water supplies that require little or no desalination but substantial removal of NOM; after NOM separation in NF or RO, some or all of the ED concentrate can be added to the NF/RO permeate to create the finished water prior to disinfection. The results indicate that ED can effectively separate alkaline earth metal ions without separation of NOM. Cation exchange membranes with high exchange capacity, high selectivity for divalent cations are desirable, and both anion and cation exchange membranes should have low affinity for organic adsorption. The process would work particularly well for NOM with relatively low hydrophobicity, since NOM adsorption to most surfaces increases with hydrophobicity.

Separation of natural organic matter and sodium chloride for salt recovery purposes in zero liquid discharge

The application of zero liquid discharge (ZLD) results in the generation of solid residual streams, which are often not fit for reuse. In this study, we assessed the separation of natural organic matter (NOM) and sodium chloride (NaCl) by nanofiltration (NF), electrodialysis (ED) and ion exchange (IEX) in reverse osmosis brine (RO-brine) and by the extraction of impurities from salt (SALEX) in the generated mixed solids of a full-scale ZLD water treatment plant.The NaCl recovery by NF, ED and IEX ranged 69-99% and the rejection of NOM ranged 18–19%, 43–65% and 53–76%, respectively. The recovery of NaCl by SALEX ranged 52–99%, while the rejection of NOM ranged 59–92%. The results show that NOM and NaCl can be separated both in RO-brine and mixed solids, opening opportunities for recovery of reusable salt from brines in ZLD.

Novel thin film nanocomposite membranes decorated with few-layered boron nitride nanosheets for simultaneously enhanced water flux and organic fouling resistance

Abstract Operational longevity of conventional thin film composite (TFC) nanofiltration (NF) membranes is significantly challenged by natural organic matter (NOM) fouling. Besides, surface modification of TFC membranes with nanomaterials results in their partial to complete confinement within the thin film, hampering the exploitation of nanomaterials full potential in improving NF performance. Incompatibility of nanomaterials with the polymeric matrix, and the resultant defect formation in the thin film can also lead to detachment of nanomaterial from the membrane surface. Herein, a modified interfacial polymerization (IP) reaction is developed to fabricate fouling-resistant thin film nanocomposite (TFN) NF membranes decorated with few-layered amine functionalized-boron nitride BN(NH2) nanosheets. The reactive edges of nanosheets are the geneses of fantastic properties; amine functionalities and electron deficient B atoms available at the edge regions render the nanosheets highly hydrophilic and negatively charged, respectively, favouring fouling mitigation. Compared with control counterparts, membranes decorated with BN(NH2) nanosheets revealed 59% enhancement in flux and 50% improvement in total fouling resistance, while maintaining NOM separation above 92%. BN(NH2)-decorated membranes showed long-term operational stability and enhanced recoverability, and nanosheet detachment tests eliminated the possibility of BN(NH2) leaching out during filtration.

Mitigation of NOM fouling of ultrafiltration membranes by pre-deposited heated aluminum oxide particles with different crystallinity

A major cause of ultrafiltration (UF) membrane fouling in surface water treatment is natural organic matter (NOM). Some studies have reported that heated aluminum oxide particles (HAOPs), prepared by boiling a suspension containing precipitates of the common coagulant alum, can remove substantial amounts of NOM and reduce fouling when they were pre-deposited on UF membranes. However, the influence of the size and structure of the HAOPs in mitigating NOM membrane fouling has not been fully explored so far. This work has investigated the change in microstructure of the HAOPs during the heating process and the subsequent effect on the performance of the membrane process, and especially on the mitigation of fouling. As the heating time increased, the structure of the HAOPs transformed gradually from an amorphous nature to a semi-crystal, and then to a microcrystalline phase. It was found that this micro-crystallization process played a key role in affecting the structural properties of the nano-scale particles and the membrane filtration performance. During the crystalline transition, a change of particle size distribution occurred and the average particle size was found to decrease gradually owing to a dehydration reaction. The smaller particle size of the HAOPs provides a denser pre-filtration layer for NOM separation, and their more rigid structure reduces layer compression and hydraulic resistance during operation. Optimization of the pre-heating condition and surface loading can effectively enhance the performance of the HAOPs layer in reducing NOM fouling in the UF membrane system.

Ion molecule reaction H/D exchange as a probe for isomeric fractionation in chromatographically separated natural organic matter

Mass spectrometry (MS) is a powerful tool for analyzing complex mixtures such as natural organic matter (NOM), humic substances (HS), and petroleum. MS disperses and resolves analyte ions with far greater peak capacity than any chromatographic technique. Unfortunately, even the highest-resolution MS cannot separate isomers. Therefore, tandem chromatography and MS techniques must be developed that combine isomeric separation with detailed compositional characterization. To develop such techniques, a means of identifying isomeric separation is requisite. Hydrogen/deuterium exchange (HDX) is an attractive means to distinguish isomers because the ability to exchange hydrogen(s) depends critically on structure. Here, both solution H/D exchange and ion-molecule reaction (IMR) H/D exchange were investigated. We present the first IMR results for fully resolved NOM isobars and the first direct evidence of isomeric separation of NOM through reversed-phase chromatography.

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.

An enhanced capillary electrophoresis method for characterizing natural organic matter

Natural organic matter (NOM) is ubiquitous and is one of the most complex naturally occurring mixtures. NOM plays an essential role in the global carbon cycle; atmospheric and natural water photochemistry; and the long-range transport of trace compounds and contaminants. There is a dearth of separation techniques capable of resolving this highly complex mixture. To our knowledge, this is the first reported use of ultrahigh resolution counterbalance capillary electrophoresis to resolve natural organic matter. The new separation strategy uses a low pH, high concentration phosphate buffer to reduce the capillary electroosmotic flow (EOF). Changing the polarity of the electrodes reverses the EOF to counterbalance the electrophoretic mobility. Sample stacking further improves the counterbalance separation. The combination of these conditions results in an electropherogram comprised up to three hundred peaks superimposed on the characteristic "humic hump" of NOM. Fraction collection, followed by three-dimensional emission excitation spectroscopy (EEMs) and UV spectroscopy generated a distinct profile of fluorescent and UV absorbing components. This enhanced counterbalance capillary electrophoresis method is a potentially powerful technique for the characterization and separation of NOM and complex environmental mixtures in general.

Resolving the chemical heterogeneity of natural organic matter: New insights from comprehensive two-dimensional liquid chromatography

For the purpose of resolving the chemical heterogeneity of natural organic matter (NOM), comprehensive two-dimensional liquid chromatography (LC×LC) was employed for the first time to map the hydrophobicity versus molecular weight (MW) distribution of two well-known complex organic mixtures: Suwannee River Fulvic Acids (SR-FA) and Pony Lake Fulvic Acids (PL-FA). Two methods have been developed using either a conventional reversed-phase (RP) silica column or a mixed-mode hydrophilic interaction column operating under aqueous RP mode in the first dimension, and a size-exclusion column in the second dimension. The LC×LC fractions were screened on-line by UV at 254nm, molecular fluorescence at excitation/emission wavelengths (λExc/λEm) of 240/450nm, and by evaporative light scattering. The MW distributions of these two NOM samples were further characterized by number (Mn) and weight (Mw) average MW, and by polydispersity (Mw/Mn). Findings suggest that the combination of two independent separation mechanisms is promising in extend the range of NOM separation. For the cases where NOM separation was accomplished, smaller Mw group fractions seem to be related to a more hydrophobic nature. Regardless of the detection method, the complete range of MW distribution provided by both comprehensive LC×LC methods was found to be lower than those reported in the literature.

Inorganics in Organics: Quantification of Organic Phosphorus and Sulfur and Trace Element Speciation in Natural Organic Matter Using HPLC-ICPMS

A method is presented for the chemical characterization of natural organic matter (NOM). We combined reversed-phase chromatographic separation of NOM with high resolution inductively coupled plasma mass spectrometry. A desolvation technique was used to remove organic solvent derived from the preceding chromatographic separation. We applied our method to solid-phase extracted marine dissolved organic matter samples from South Atlantic and Antarctic surface waters. The method provided a direct and quantitative determination of dissolved organic phosphorus and sulfur in fractions of differing polarity and also allowed simultaneous speciation studies of trace elements. Dissolved organic carbon/phosphorus and carbon/sulfur ratios for the different chromatographic fractions of our two samples ranged between 341-3025 for C/P and 11-1225 for C/S. Differences in elemental distribution between the fractions were attributed to different biochemical environments of the samples. Sulfur was exclusively found in one hydrophilic fraction, while uranium showed a strong affinity to the hydrophobic fractions. Our method was designed to be easily adapted to other separation techniques. The elemental information will deliver valuable information for ultrahigh resolution molecular analyses.

Organic nitrogen distribution in NOM size classes

In Norwegian lakes, organic nitrogen typically constitutes about 60% of the total dissolved pool of nitrogen. However, evaluation of its effect on aquatic ecosystems and its role as promoter of heterotrophic growth in water distribution systems is difficult because of restricted knowledge about the various forms of organically-bound nitrogen in water. On line standard wet chemical analysis of total nitrogen was combined with high-performance size exclusion chromatographic (HPSEC) separation of natural organic matter (NOM) for investigation of the distribution of nitrogen between size classes of NOM. It was found that the high molecular weight (HMW) size fractions (humic acids) are enriched in nitrogen relative to the low molecular weight (LMW) size fractions (fulvic acids, nominal molecular weights of about 1000 Daltons) by a factor of up to 10. The low molecular weight size fractions (a few hundred Daltons) are interpreted to be of autocthonous origin based on their low C/N ratios, and correlation with the eutrophic status of the source waters. It was observed that NOM from water sources surrounded by large catchments contains relatively more nitrogen in HMW size fractions than NOM from small catchments, except that bog-derived NOM is particularly enriched in HMW nitrogen.