Liquid Chromatography-organic Carbon Detection Research Articles

Composition of Stream Dissolved Organic Matter Across Canadian Forested Ecozones Varies in Three Dimensions Linked to Landscape and Climate

AbstractDissolved organic matter (DOM) is a key variable influencing aquatic ecosystem processes. The concentration and composition of DOM in streams depend on both the delivery of DOM from terrestrial sources and on aquatic DOM production and degradation. However, there is limited understanding of the variability of stream DOM composition at continental scales and the influence of landscape characteristics and disturbances on DOM across different regions. We assessed DOM composition in 52 streams at seven research sites across six forested ecozones in Canada in 2019–2022 using 26 indices derived from five analytical approaches: absorbance and fluorescence spectroscopy, liquid chromatography—organic carbon detection, Fourier‐transform ion cyclotron resonance mass spectrometry, and asymmetric flow field‐flow fractionation. Combined analyses showed clear clustering and redundancy across analytical techniques, and indicated that compositional variations were primarily related to three axes of DOM composition: (a) aromaticity, which was greater in low‐relief, wetland‐dominated catchments, (b) oxygenation, which was greater in colder and drier ecozones, and (c) biopolymer content, which was greater in lake‐influenced catchments. Variability in DOM composition among research sites was greater than variability of streams within a site and variability over time within a stream. Forest harvesting and wildfire disturbances had no common influence on DOM composition across research sites, emphasizing the need for regional studies. Our study provides a broad understanding of the variability of stream DOM composition and its associations with landscape and catchment characteristics at a subcontinental scale, and provides key insights for the choice and interpretation of DOM indices from various analytical approaches.

Membrane distillation of wastewater: comparison of model and real organics.

Fouling behaviour in membrane distillation (MD) processes plays a crucial role in determining their widespread acceptability. Most studies have primarily focused on model organic foulants, such as humic acid (HA) and sodium alginate (SA). This study investigates the fouling of a polytetrafluoroethylene membrane in a direct contact MD (DCMD) using model organics (i.e., HA and SA) and real wastewater. The results indicated that the flux decline (5-60%) was only observed during the initial phase of the operation with model organic foulants. In contrast, real wastewater caused a gradual decline in flux throughout the experiment in both the concentrate (40%) and continuous (90%) modes. The study also found significant differences in the fouling layer morphology, composition, and hydrophobicity between the model organic foulants and real wastewater. Fourier transform infrared spectroscopy findings demonstrated that the fouling layer formed by real wastewater varied significantly from model organics, which primarily comprised of protein-like and polysaccharide-like functional groups. Finally, liquid chromatography-organic carbon detection revealed that the fouling layer of the MD membrane with real wastewater was composed of 40.7% hydrophobic and 59.3% hydrophilic organics. This study suggests that model organics may not accurately reflect real wastewater fouling.

Evaluation of Organic Matter Contribution Using Absorbance and Chromatographic Parameters in Lake Paldang, Republic of Korea

Organic matter in lakes is categorized into allochthonous organic matter, such as leaves and sewage effluent, and autochthonous organic matter, generated by microorganisms within the water system. In this study, organic matter composition was analyzed using UV-vis spectroscopy and liquid chromatography-organic carbon detection (LC-OCD). Several allochthonous natural organic matter substances were collected including leaves, green leaves, forest soils, and paddy soils. The organic matter composition analysis in our study sites revealed that humic substances comprised the highest proportion (36.5–42.3%). Also, individual samples at each site exhibited distinct characteristics. This study used a humic substance-diagram (HS-diagram) and principal component analysis (PCA) to trace the sources affecting the river water quality and identify their origins. The humic substances of soil origin predominantly influenced the water quality, with the impact of organic matter significantly pronounced during the July rainfall period. Compared with the PCA results, the contribution of the humic substance (HS, 48.9%) and building block (BB, 42.0%) indices appeared higher between June and July in summer, likely due to non-degradable substances released by heavy rain. In fall, the contribution of low molecular weight neutrals increased from 71.2% to 85.2%, owing to a humic substance influx and decomposition. This study demonstrated the application of estimating the relative contributions of source materials in lakes utilized for drinking and agricultural water to identify sources, aiding in the development of efficient watershed management plans.

The influence of micro-flocculation on membrane fouling during ultrafiltration of dissolved organic matter

This study investigated the mitigating effect of micro-flocculation as an ultrafiltration (UF) membrane pretreatment process on membrane fouling caused by organic matter in urban micro-polluted river water. The removal characteristics of organic matter by micro-flocculation were analyzed using three-dimensional fluorescence excitation emission matrix (3D-FEEM) and liquid chromatography organic carbon detector (LC-OCD). Furthermore, the variation of floc properties such as flocculation index and fractal dimension of micro-flocs formed under different flocculant dosages and their effects on UF membrane flux were investigated. The experimental results show that micro-flocculation using ferric chloride (FeCl3) can effectively remove large molecular weight organics. The features of flocs, which are influenced by the amount of FeCl3, affect the formation of the cake layer. Micro-flocculation can control the formation of a floc cake layer with a larger size and lower fractal dimension. It is helpful to effectively delay the attenuation rate of membrane flux by reducing membrane pore blockage and forming a filter cake layer with high porosity, which is of great significance for improving membrane technology. After the FeCl3 micro-flocculation treatment, the final specific flux of the membrane increased by 57.0 %. The combination of FeCl3 micro-flocculation and UF is a superior technical and economical treatment scheme for micro-polluted river water.

Composition of planktonic foraminifera test-bound organic material and implications for carbon cycle reconstructions

IntroductionForaminiferal shells are extensively used to reconstruct the marine environment in the geological past. The foraminifera test-bound organic material (FBOM), sheltered by the test from potential diagenetic alteration and contamination, has great feasibility to improve our understanding of carbon and nitrogen cycling. The FBOM δ13C has been proposed as a proxy for reconstructing past environmental conditions. However, to fully exploit the proxy potential of FBOM, its molecular composition and the influence of the latter on the FBOM δ13C need to be assessed.MethodHere we use a novel combination of gas chromatography-mass spectrometry, flame ionization detection (GC-MS/FID) and liquid chromatography organic carbon and nitrogen detection (LC-OCD/ OND) analyses to study the FBOM chemical composition.ResultsOur results indicate that polysaccharides and proteins dominate FBOM, as proposed by earlier studies, with no evidence of detectable lipids (alkyl lipids, trimethylsilyl ethers of fatty alcohols, trimethylsilyl esters of fatty acids and steranes derivatives were targeted).DiscussionPrevious studies suggested that FBOM δ13C may be used to reconstruct past atmospheric CO2 concentrations. However, our results indicate that the use of FBOM δ13C to reconstruct CO2 carries an approximate uncertainty of ±21 ppm for past atmospheric CO2 abundance. We suggest that FBOM δ13C can be used as a novel proxy to reconstruct particulate organic material (POM) δ13C. This is also supported by the recently confirmed minor fractionation between POM and FBOM δ13C.

Organic Compounds Responsible for the Fouling of Ultrafiltration Membrane Treating Algae-Laden Water.

Fouling comparisons of the organic fractions in surface and algae-laden waters make it possible to determine the main compounds responsible for the fouling of ultrafiltration (UF) membranes. This study examined the fouling of UF membranes and its relationship to the characteristics of the organic fractions found in drinking-water supply. Four types of water were prepared by combining natural organic matter (NOM) from lake water with algal organic matter (AOM) from four algae species commonly found in freshwater. Liquid chromatography-organic carbon detection (LC-OCD) and a fluorescence excitation-emission matrix (FEEM) were used to analyze the feed water and permeate to assess the interactions between and fouling behavior of the organic fractions. The results showed that the interaction of large-molecular-weight AOMs on the membrane surfaces and their transport through the membrane pores were the main fouling mechanisms. Polysaccharides followed by protein-like substances were the organic compounds responsible for the fouling of the UF membranes. The fouling affinity of these substances was attributed to two processes, the adsorption of their carboxyl, hydroxyl and cationic groups on the membrane surfaces, and the molecular complexation of their organic groups. The humic substances' retention was marginal and attributed to the synergetic effects of the polysaccharides and proteins.

Integrating biological ion exchange with biological activated carbon treatment for drinking water: A novel approach for NOM removal, trihalomethane formation potential, and biological stability

Ion exchange resins (IEX) are used in drinking water utilities to remove natural organic matter (NOM) from surface water; however, the disposal of used brine can be a major drawback. Recently, biological ion exchange (BIEX) has been proposed as an alternative to biological activated carbon (BAC) for removing natural organic matter (NOM). The present study is, to the best of our knowledge, the first attempt to use a hybrid BIEX and BAC (BIEX+BAC) system for drinking water treatment. The removal of NOM, assimilable organic carbon, and trihalomethane formation potential was investigated by operating four columns comprising IEX, BIEX, BAC, and BIEX+BAC with 18,000 bed volumes. The BIEX+BAC system was the most effective at removing dissolved organic carbon (59.9%). Based on fluorescence excitation-emission matrix spectroscopy, the BIEX+BAC column showed the maximum removal rates in all peak regions of T1, T2, and A. Using liquid chromatography-organic carbon detection, resin-containing columns were found to effectively remove humic substances, which are the principal precursors of trihalomethanes. The lowest potential for trihalomethane formation was observed in BIEX+BAC. BIEX+BAC also had the highest assimilable organic carbon removal efficiency (61.2%) followed by BIEX (52.3%), BAC (49.5%), and IEX (47.1%). The BIEX+BAC hybrid was found to be the most effective method for removing NOM fractions and reducing the formation of disinfection byproducts.

Water quality characteristics and reuse potential using adsorption as a post-treatment option for a full-scale hydrocyclone, coagulation, flocculation, and dissolved air flotation system.

This study established a full-scale hybrid water treatment system combining a hydrocyclone, coagulation, flocculation, and dissolved air flotation unit (HCFD) and evaluated its performance in treating anthropogenically impacted lake water. The HCFD system offered the stable and efficient treatment of fluctuating influent loadings, meeting most of the highest water reclamation quality criteria except for that of organic matter. Adsorption was subsequently examined as a post-treatment process for the HCFD effluent, which has not been examined in many previous studies. As the adsorbent for the post-treatment, pine bark, a locally available agricultural waste feedstock, was modified using H2O2 to maximize its adsorption capacity. The surface modification increased its adsorption capacity for organic matter by 53-112%. The HCFD system in conjunction with the synthesized adsorbent thus demonstrated the ability to meet the highest standards for all water quality parameters, highlighting their synergistic potential for enhancement of water treatment. Liquid chromatography-organic carbon detection and Fourier transform infrared analysis were then employed to determine the mechanisms involved in the removal of specific contaminants using the HCFD system and post-adsorption unit. While the HCFD system successfully eliminated particulate and colloidal matter (e.g., phosphorous and biopolymers with a high molecular weight) using centrifugal and floating separation with the aid of two complementary polymers, the post-adsorption unit effectively adsorbed small-sized dissolved substances (e.g., low molecular weight acids and building blocks) via surface functional groups (-CH, -OH, -CH2, C=O, C=C, and C=O) using van der Waals forces, hydrogen bonding, and π-π or n-π interactions.

Short term fouling tests on homogeneous and heterogeneous anion-exchange membranes from food and bio-based industrial streams: Foulant identification and characterization

Electrodialysis is used in food and bio-based industries for selective separation and recovery of target ions and neutral molecules. Anion exchange membranes (AEM) are prone to fouling due to their complex interactions with organics. Currently, research has focussed mainly on fouling tests using model organic foulants. In this study, three different complex industrial feed streams: corn steep liquor (CSL), citric acid by-product (CA), and cheese whey (CW), were used to foul two commercial AEM types: Fujifilm type-10 (homogeneous) and RALEX (heterogeneous). A 1.5 – 2.3 fold higher membrane resistance after fouling was a result of a difference in membrane structure, ion exchange capacity, water uptake, and thickness (depending on the feed used). Liquid Chromatography – Organic Carbon Detection (LC-OCD) analysis of feed revealed highly hydrophilic (CDOC) fractions in CSL (85%), CA (87%), and CW (100%). This analysis was extended to foulant desorption solutions (NaCl (35 g/L) and EtOH-water-H2SO4 mixtures), which revealed that > 90 % of humic substances (HS) and building blocks (BB) desorbed when using NaCl (35 g/L), following a (concentration wise) desorption order: HS > BB > LMWN > BP > LMWA. For the EtOH-water-H2SO4 solution, low molecular weight neutrals and acids (LMW(A + N)) were desorbed majorly (>60%) and followed a desorption order: LMWN > LMWA > BB > BP > HS. Desorption due to the ion-exchange mechanism was dominant for NaCl (35 g/L) solution, while foulant-desorbant polar interactions were prevalent for the EtOH-water-H2SO4 solution. Upon foulant desorption using NaCl (35 g/L) solution, RALEX AEM owing to the presence of nanovoids in them, showed a 1.5 – 4 fold higher concentration difference vs. FF10 AEM, while this difference was not dominantly observed when EtOH-water-H2SO4 mixture was used. This study revealed that LMW fractions could possibly enter into the membrane matrix whereas HS and BB fractions owing to their high molecular weight, majorly adsorbed on surfaces.

Removal of Organics with Ion-Exchange Resins (IEX) from Reverse Osmosis Concentrate.

Reverse osmosis concentrate (ROC) produced as the by-product of the reverse osmosis process consists of a high load of organics (macro and micro) that potentially cause eco-toxicological effects in the environment. Previous studies focused on the removal of such compounds using oxidation, adsorption, and membrane-based treatments. However, these methods were not always efficient and formed toxic by-products. The impact of ion-exchange resin (IEX) (Purolite®A502PS) was studied in a micro-filtration-IEX hybrid system to remove organics from ROC for varying doses of Purolite® A502PS (5-20 g/L) at a flux of 36 L/m2h. The purolite particles in the membrane reactor reduced membrane fouling, evidenced by the reduction of transmembrane pressure (TMP), by pre-adsorbing the organics, and by mechanically scouring the membrane. The dissolved organic carbon was reduced by 45-60%, out of which 48-81% of the hydrophilics were removed followed by the hydrophobics and low molecular weight compounds (LMWs). This was based on fluorescence excitation-emission matrix and liquid chromatography-organic carbon detection. Negatively charged and hydrophobic organic compounds were preferentially removed by resin. Long-term experiments with different daily replacements of resin are suggested to minimize the resin requirements and energy consumption.

Quantitative and qualitative variations of biopolymers in a pilot-scale membrane bioreactor treating municipal wastewater throughout 3 years of operation

In this study, the fouling potential of mixed liquor suspension samples collected from a pilot-scale membrane bioreactor (MBR) that treated municipal wastewater was monitored for more than 3 years. The fouling potential was assessed by batch filtration experiments using the same type of membrane as equipped in the MBR. The fouling potential increased when the temperature of the mixed liquor suspension in the MBR decreased. However, the polysaccharide and protein concentrations in the mixed liquor suspension, which have been focused on many previous studies, did not correlate with the fouling potential (R2 = 0.15 and 0.39, respectively). In contrast, the concentration of biopolymers, quantified by liquid chromatography–organic carbon detection (LC-OCD), exhibited a marked correlation with the fouling potential (R2 = 0.89). A high concentration of biopolymers with large molecular weight (>1 million Da) was likely responsible for the high fouling potential. Fourier transform infrared (FTIR) analysis of the dissolved organic matter in the mixed liquor suspension indicated that the chemical properties of the biopolymers considerably varied with the seasonal temperature variation, which has rarely been reported and gives insights into fouling in MBRs. The effect of temperature on the biopolymer concentration and molecular weight of biopolymers was also investigated in a separate bench-scale experiment in which temperature was controlled. It was clearly shown that a low temperature induced an increase in the biopolymer concentration and an associated increase in the fouling potential of the mixed liquor suspension.

Effects of rhamnolipid pretreatment on DOM dissolution characteristics and anaerobic fermentation acid production of waste activated sludge

ABSTRACT In this paper, the change characteristics of DOM (dissolved organic matter) and acid production characteristics of anaerobic fermentation in waste activated sludge(WAS) pretreated with rhamnolipid (RL) were studied. The results showed that RL at the dose of 80 mg/gTS could significantly promote the disintegrating of EPS (extracellular polymers) and cell wall in WAS, and a large number of proteins and carbohydrates were dissolved. Three dimensional fluorescence parallel factor analysis showed that the addition of RL enhanced the dissolution and biodegradability of humus-like substances. LC-OCD (Liquid chromatography – organic carbon detection) analysis showed that RL promotes the dissolution of biodegradable components such as Biopolymer, Building Blocks and LMW Neutrals, and ensures the increase of VFA (volatile fatty acids) production in the process of anaerobic fermentation. Under the RL dose of 80 mg/gTS, the maximum VFA production of WAS was obtained at 108 h of anaerobic fermentation, which was 2699.39 mg/L. Acetic acid and propionic acid were the main components in the WAS fermentation broth pretreated by RL. The concentration of butyric acid increased with the increase of RL dose. The RL dose can significantly affect the composition of VFA in WAS fermentation broth.

Seasonal variations of natural organic matter (NOM) in surface water supplied to two coal-fired power stations.

Global issues such as pollution and global warming have resulted in changes in water characteristics over the past 20years. Natural organic matter (NOM) which is a major component in water systems has shown an increase globally. This increase in NOM concentration has negatively affected both water treatment processes and drinking water quality. It is subsequently critical to understand the seasonal variations and composition of NOM to be able to address issues related to NOM. In this study, techniques such as ultraviolet-visible spectroscopy, total organic carbon and liquid chromatography-organic carbon detection (LC-OCD) were used for characterisation and quantification of NOM. Two coal-fired power stations were selected for this study with each power station receiving water from a different source, i.e. power station A receives water from the Vaal River and power station B from the Nkomati River. Results from this study demonstrated that composition and concentration of NOM from these two water sources varied seasonally. Characterisation of NOM using the LC-OCD indicated that the different fractions of NOM, i.e. low molecular weight neutrals, low molecular weight acids, building blocks, humic substances and biopolymers, varied seasonally. The dissolved organic carbon concentration and specific ultraviolet absorbance values of the raw water at both power stations showed an increment amid the wet seasons and a decrease amid the dry seasons.

Low-temperature degradation of humic acid via titanium zirconium oxide@copper single-atom activating oxygen: Mechanism and pathways

Humic acid (HA), a refractory organic pollutant, has always been a key obstackle in wastewater treatment (such as biochemical landfill leachate). And catalytic air oxidation is one of the most promising methods to degrade HA efficiently and economically. In this study, a novel high-loading Cu single-atom catalyst (TiZrO4@CuSA) was facilely synthesized using isovolume vacuum impregnation and co-calcination method, and then used to accelerate the oxidation of HA at low temperatures. The TiZrO4@5%CuSA catalytic system showed a superior performance, and 91 % of HA was degraded and 90 % of organic carbon was removed from HA solution within 10 min at 90 °C. Aberration-corrected electron microscopy, electron paramagnetic resonance spectroscopy, and density functional theory calculations were applied to reveal the catalytic mechanism of TiZrO 4@5%CuSA. The active center of Cu single-atom co-catalyst with Cu − O coordination sites can quickly transfer electrons to O2 in the water to form O2.−, exhibiting high activation efficiency. Gas chromatography (GC), liquid chromatograph-mass spectrometer (LC-MS), liquid chromatography-organic carbon detection (LC-OCD), and Fourier-transform infrared spectroscopy (FT-IR) spectroscopy provided the results of intermediate products, including 3-phenoxy-benzaldehy, phenylglyoxal, ethanol, acetic acid, butyric acid, and valeric acid, and thus a catalytic degradation pathway of HA was speculated. Based on the new catalyst, a new process can be conceived for efficient and economic removal of HA from HA-containing wastewater.

Dissolved organic matter derived from aquatic plants in constructed wetlands: Characteristics and disinfection byproducts formation

Constructed wetlands are used to improve water quality in the drinking water sources, but aquatic plants planted in constructed wetlands may be a source of disinfection by-product (DBP) precursors. This study explored the characteristics of aquatic plant-derived dissolved organic matter (DOM) and DBP formation in micro-polluted raw water treated by constructed wetlands. A simulated surface flow wetland (SSFW) planted with the typical aquatic plants Lythrum salicaria and Acorus calamus was studied. Raw water, control samples, effluent, and Suwannee River natural organic matter (SRNOM) were analyzed. via ultraviolet-visible (UV-Vis) spectroscopy, three-dimensional excitation emission matrix (3D-EEM) fluorescence combined with a parallel factor (PARAFAC) analysis, liquid chromatography-organic carbon detection (LC-OCD), principal component analysis (PCA), and other detection and analysis methods. A DBP formation potential (DBPFP) index was also constructed. Treatment by the SSFW increased the effluent dissolved organic carbon (DOC), UV254, trihalomethane formation potential (THMFP), haloacetic acid formation potential (HAAFP) by 72.2%, 171.4%, 83.7% and 88.6%, respectively. Planting aquatic plants in surface wetlands will negatively affect the water quality of micro-polluted raw water, with the plants being an important source of increased DBP precursors in wetland effluent. The effluent properties were similar to those of SRNOM, and had a higher degree of aromatization and larger molecular weight than raw water. The increased DBP precursors were mainly fulic acid and humus with higher aromatic and molecular weight, which derived from the growth and metabolism of aquatic plants. Humic substances (HS) accounted for the highest proportion of DOM in this study, with the average molecular weight of HS increasing from 648 to 698 g·mol−1 as the DOM content increased. Results from this study are particularly applicable to the establishment of constructed wetlands planted with aquatic plants in the drinking water sources, and the DOM derived from aquatic plants in constructed wetlands may be important precursors in the subsequent water disinfection process.

Transformation mechanism and fate of dissolved organic nitrogen (DON) in a full-scale drinking water treatment

Dissolved organic nitrogen (DON) has attracted much attention in drinking water treatment due to its potential to produce nitrogenous disinfection by-products (N-DBPs). This work was designed to explore the transformation and fate of DON and dissolved inorganic nitrogen (DIN) in drinking water treatment. The changes of DON and formation of N-DBPs were evaluated along the water treatment route (i.e., pre-ozonation and biological-contact oxidation, delivery pipes’ transportation, coagulation-sedimentation, sand filtration, post-ozonation, biological activated carbon, ultrafiltration and disinfection) of drinking water treatment plant (DWTP). The transformation mechanism of DON was comprehensively investigated by molecular weight fractionation, three-dimensional fluorescence, LC-OCD (Liquid Chromatography-Organic Carbon Detection), total free amino acids. A detailed comparison was made between concentrations and variations of DON and DIN affected by seasons in the drinking water treatment. Regardless of seasonal variation in raw water concentration, the DON removal trends between different treatment processes remain constant in the present study. Compared to other treatment processes, pre-ozonation and coagulation-sedimentation exhibited the dominant DON removal in different seasons, i.e., 11.13%-14.45% and 14.98%-22.49%, respectively. Contrary, biological-contact oxidation and biological activated carbon negatively impacted the DON removal, in which DON increased by 1.76%-6.49% in biological activated carbon. This may be due to the release of soluble microbial products (SMPs) from bacterial metabolism, which was further validated by the rise of biopolymers in LC-OCD.

Advanced oxidation processes for removal of organics from cooling tower blowdown: Efficiencies and evaluation of chlorinated species

One of the major challenges in reusing cooling tower blowdown water (CTBD) utilizing membrane processes is its remaining organic compounds, e.g., humic substances leading to biofouling. Besides, the possible abundance of chloride in CTBD imposes the concern of the formation of chlorinated by-products. To choose a pre-treatment process for the studied CTBD composition, various advanced oxidation processes (AOPs), including electrooxidation (EO), photocatalytic degradation (PCD), heat-activated persulfate oxidation (PS), UVC/vacuum UV (UVC/VUV), and UVC processes, were evaluated and compared based on two main targets: i) highest removal and mineralization of the organics, especially humic substances; and ii) lowest formation of chlorinated by-products including adsorbable organic halides and oxychlorides. All the processes were conducted in the natural condition of the real CTBD, while solution pH was monitored. Based on results of chemical oxygen demand, total organic carbon, dissolved organic carbon, UV254 absorbance, liquid-chromatography–organic carbon detection (LC-OCD), and fluorescence excitation-emission matrices (FEEM), it is concluded that PS leads to complete removal of organic compounds along with the lowest formation of low molecular weight organic acids and organic neutrals. FEEM and LC-OCD data also indicated that EO, PCD, and UVC/VUV processes brought about substantial removal of organic compounds and broke down the humic substances into low molecular weight building blocks and organics. Besides, EO exhibited the highest AOX and oxychlorides formation, while these were limited when using the other AOPs. Summarizing, PS, PCD, and UVC/VUV were efficient processes for the degradation and mineralization of organics without generating significant amounts of chlorinated by-products.

Silt density index as a fouling propensity parameter of various membrane materials using dissolved organic matter

Silt density index (SDI) is the most widely used parameter for predicting fouling potential that occurs during reverse osmosis (RO) processes to assess and reduce fouling; however, this index cannot accurately predict fouling, particularly, organic fouling. Therefore, this study analyzed the application of five different membranes (i.e., mixed cellulose nitrate and cellulose acetate (MCE), cellulose nitrate (CN), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polycarbonate (PC)) for measuring SDI and discerning the characteristics of organic foulants. The properties of the organic foulants on the membranes used to measure the SDI value were compared to those on the RO membrane. The quantitative fouling of the MCE, CN, PVDF, PC, and PTFE membranes in terms of the total organic carbon were 6.01 ± 0.03, 6.30 ± 0.14, 10.27 ± 0.10, 2.26 ± 0.12, and 3.08 ± 0.06 mg/L, respectively. In addition, liquid chromatography–organic carbon detection revealed that the MCE and CN were effective in predicting the fouling caused by building blocks and low-molecular-weight substances, respectively. The PVDF was effective in predicting fouling caused by biopolymers. The contaminants compositions on the PTFE and PC were similar; however, the PTFE was more effecting in detecting fouling caused by humic and low-molecular-weight substances. The composition of foulants on the PC was similar to that on the RO membrane, indicating that it can successfully predict the organic fouling of RO membrane. These results indicate that it is important to standardize the SDI value for PC membranes to make SDI a reliable index in the municipal wastewater reuse.

Organic matter removal with bicarbonate-form ion exchange: water quality, kinetics and mass transfer mechanisms

Ion Exchange (IEX) has been widely explored for the removal of organic matter. Chloride is traditionally used as counter-ion, but its release into water can increase the risk of corrosion. Research has shown that bicarbonate IEX can be an efficient alternative, and whilst some studies have compared its efficiency to chloride IEX, none have compared their performance in relation to the potential for disinfection by-product (DBPs) formation. The differences in organic matter removal between the two regenerants were assessed by looking at the molecular weight fractions derived from liquid chromatography organic carbon detection (LC-OCD) and dissolved organic carbon (DOC). Uptake kinetics, resin age and mass transfer diffusion were also investigated. DOC removal was similar for both chloride and bicarbonate resins, achieving ca 50% DOC removal. LC-OCD analysis revealed that organic matter between 0.35 and 1 kDa was the most efficiently removed, with slightly better uptake with bicarbonate IEX. However, these differences did not impact DBP formation potential. Trihalomethane (THM) and haloacetic acid (HAA) formation potentials followed the trends of DOC removal with up to 70% reduction after IEX treatment with both resin forms. However, the bromine substitution factor (BSF) increased with resin age -from 5 to 10% for THMs and from 4 to 7% for HAAs. Resin age resulted in up to 20% decrease in the organic matter uptake rates (from 0.19 to 0.15 min−1) and up to 34% decrease in pore diffusivities (from 9.4 × 10−12 to 7.1 × 10−12 m2/s for chloride IEX and from 1.0 × 10−11 to 6.6 × 10−11 m2/s).

Effect of Changes in Physical Properties of Granular Activated Carbon (GAC) on the Adsorption of Natural Organic Matter (NOM) with Increasing the Number of Thermal Regeneration: Pore Size and NOM Molecular Weight

Objectives : The purpose of this study was to evaluate the effect of increasing the number of regeneration of granular activated carbon (GAC) on the adsorption capacity of natural organic matter (NOM), and to suggest the technical process options associated the limit number of regeneration and the efficient use of regenerated GAC.Methods : The physicochemical properties of virgin and thermally regenerated GAC were analyzed. To evaluate the NOM adsorption capacity of virgin- and regenerated-GAC, five laboratory-scale columns packed with virgin- and regenerated-GAC were used for treating effluent from pilot-scale drinking water treatment facility. The NOM concentration in the influent and the effluent treated by each column was analyzed by LC-OCD (liquid chromatography-organic carbon detector) to evaluate the adsorption capacity of each NOM fractions (humic substances (HS), building blocks (BB), low molecular weight organics (LMWs)).Results and Discussion : Due to the change in the pore structure of GAC by thermal regeneration, the volume of micropores (< 2 nm) decreased, while the volume of mesopores (> 2 nm) increased. The volume ratio of micropore in virgin-GAC was about 60%, but it gradually decreased as the number of regenerations increased, resulting that the volume ratio of micropore in the 5th-regenerated (5th-Re) GAC decreased to 23%. On the other hand, the volume ratio of mesopore increased in proportion to the number of regenerations from 40% of the virgin GAC to 77% of the 5th-Re-GAC. The DOC adsorption capacities of the regenerated GACs were higher than that of virgin GAC, and the DOC adsorption capacity increased as the number of regenerations increased. As a result of comparing the adsorption capacity of virgin- and regenerated-GAC by NOM fractions, the adsorption capacity of high molecular weight NOM, such as HS, increased by 1.5 to 1.7 times as the number of regenerations increased. In contrast, the adsorption capacity of low molecular weight NOM, such as BB and LMWs, decreased by 78% and 48% as the number of regeneration increased. The limit number of regeneration was evaluated based on that the adsorption capacity (qe) of each NOM fractions keep over than 70% relative to its virgin GAC. As a result, the adsorption capacity for low molecular weight NOM was greatly reduced in GAC regenerated over than 3rd time, so that the 2nd-Re-GAC was valid to keep 70% removal of whole NOM fractions. Low adsorption of low molecular weight NOM (BB and LMWs) by 3rd-Re-GAC could be complemented by using together with virgin-GAC, and low adsorption of high molecular NOMs (HS) could be compensated as well.Conclusions : Due to the change in the pore structure of GAC by thermal regeneration, the DOC adsorption capacity was higher in regenerated GAC than its virgin-GAC, and the adsorption capacity of DOC and high molecular weight NOM (HS) was enhanced as the number of regenerations increased. On the other hand, the pore volume of micropore was reduced by regenerations, and in more than 3rd times regenerations, the adsorption capacity of low molecular weight NOMs (BB and LMWs) was reduced by less than 70% compared to its virgin GAC, so that 2nd-Re-GAC was suggested for suitable GAC. When using a mixture of virgin- and 3rd-Re-GAC, low adsorption of low molecular weight NOM (BB and LMWs) by 3rd-Re-GAC could be complemented by using together with virgin-GAC, and low adsorption of high molecular NOMs (HS) could be compensated as well.