Liquid Chromatography With Organic Carbon Detection Research Articles

Impact of anionic ion exchange resins on NOM fractions: Effect on N-DBPs and C-DBPs precursors

The formation potential of carbonaceous and nitrogenous disinfection by-products (C-DBPs, N-DBPs) after ion exchange treatment (IEX) of three different water types in multiple consecutive loading cycles was investigated. Liquid chromatography with organic carbon detector (LC-OCD) was employed to gauge the impact of IEX on different natural organic matter (NOM) fractions and data obtained were used to correlate these changes to DBPs Formation Potential (FP) under chlorination. Humic (-like) substances fractions of NOM were mainly targeted by ion exchange resins (40-67% removal), whereas hydrophilic, non-ionic fractions such as neutrals and building blocks were poorly removed during the treatment (12-33% removal). Application of ion exchange resins removed 13-20% of total carbonaceous DBPs FP and 3-50% of total nitrogenous DBPs FP. Effect of the inorganic nitrogen (i.e., Nitrate) presence on N-DBPs FP was insignificant while the presence of dissolved organic nitrogen (DON) was found to be a key parameter affecting the formation of N-DBPs. DON especially the portion affiliated with humic substances fraction, was reduced effectively (∼77%) as a result of IEX treatment.

Organic characterisation of cave drip water by LC-OCD and fluorescence analysis

Cathedral Cave, Wellington, Australia, is a natural laboratory for studying water movement and geochemical processes in the unsaturated zone by using artificial irrigation to activate drip sites within the cave. Water sampled from two drip sites activated by irrigations carried out in summer 2014 was analysed for dissolved inorganic ions and fluorescent organic matter. The analysis allowed the development of a conceptual flow path model for each drip site. DOM analysis was further complemented by liquid chromatography with organic carbon detection (LC-OCD), applied for the first time to karst drip waters, allowing the characterisation of six organic matter fractions. The differences in organic matter fractions at each drip site are interpreted as a signature of the proposed flow paths. LC-OCD was also compared with parallel factor analysis (PARAFAC) of the fluorescence and good correlations were observed for high molecular weight organic matter. Strong positive correlations were also observed for high molecular weight matter and Cu and Ni. This is suggestive of colloidal transport of Cu and Ni by organic matter with high molecular weight, while small molecular weight colloids were not efficient transporters. LC-OCD uniquely provides information on non-fluorescent organic matter and can be used to further quantify drip water organic matter composition.

Confirmation of the correlation between membrane fouling in microfiltration and biopolymer concentrations in various Japanese surface waters

A variety of surface waters used for drinking water sources were collected from different parts of Japan to investigate a correlation between the concentration of hydrophilic biopolymer (e.g. proteins and polysaccharides) in the feed water and membrane fouling in microfiltration. Hollow-fiber membranes made from polyvinylidene fluoride with a nominal pore size of 0.1 μm were used in the series of experiments involving the constant-flow mode of operation with automatic periodical backwashing. Easily available indexes of water quality, such as dissolved organic carbon, UV absorbance, Ca concentration and turbidity could not explain the degree of fouling encountered in the filtration tests. In contrast, a clear correlation between the concentrations of biopolymers determined by liquid chromatography with organic carbon detection (LC-OCD) and membrane fouling was confirmed in this study. The concentrations of humics exhibited a weak correlation. The impacts of seasonal variation of feed water and coagulant dosage on membrane fouling were also explained well by biopolymer concentrations. Concentrations of biopolymers can be a useful indicator of the fouling potential of feed water in microfiltration.

Microfiltration of different surface waters with/without coagulation: Clear correlations between membrane fouling and hydrophilic biopolymers

Although low-pressure membranes (microfiltration (MF) or ultrafiltration (UF)) have become viable options for drinking water treatment, problems caused by membrane fouling must still be addressed. The objective of this study was to compare five different surface waters and to identify a relevant index of water quality that can be used for prediction of the fouling potential of the water. Bench-scale filtration tests were carried out with commercially available hollow-fiber MF membranes. Fairly long-term (a few days) filtrations in the constant-flow mode were carried out with automatic backwash. Membrane fouling in this study was shown to be irreversible as a result of the periodic backwash carried out throughout of the operation. Easily accessible indexes of water quality including dissolved organic carbon (DOC), UV absorbance, Ca concentration and turbidity could not explain the degree of fouling encountered in the filtration tests. Fluorescence excitation-emission matrix (EEM) could provide information on the presence of protein-like substances in water, and peaks for protein showed some correlation with the membrane fouling. Biopolymer (characterized by high molecular weights and insensitivity to UV light absorption) concentrations in the five waters determined by liquid chromatography with organic carbon detection (LC-OCD) exhibited an excellent correlation with the fouling rates. Coagulation with polyaluminum chloride could mitigate membrane fouling in all cases. The extent of fouling seen with coagulated waters was also correlated with biopolymer concentrations. The relationship between biopolymer concentrations and the fouling rates established for the raw waters could also be applied to the coagulated waters. These results suggested that the contribution of biopolymers to membrane fouling in the present study was significant, an observation that was supported by the analysis of foulants extracted at the termination of each test. Biopolymer concentrations determined by LC-OCD might be used as a key indicator of fouling potential of water for low-pressure membranes.

Impact of effluent organic matter on low-pressure membrane fouling in tertiary treatment

This study aims at comparing low-pressure membrane fouling obtained with two different secondary effluents at bench and pilot-scale based on the determination of two fouling indices: the total fouling index (TFI) and the hydraulically irreversible fouling index (HIFI). The main objective was to investigate if simpler and less costly bench-scale experimentation can substitute for pilot-scale trials when assessing the fouling potential of secondary effluent in large scale membrane filtration plants producing recycled water. Absolute values for specific flux and total fouling index for the bench-scale system were higher than those determined from pilot-scale, nevertheless a statistically significant correlation (r2 = 0.63, α = 0.1) was obtained for the total fouling index at both scales. On the contrary no such correlation was found for the hydraulically irreversible fouling index. Advanced water characterization tools such as excitation–emission matrix fluorescence spectroscopy (EEM) and liquid chromatography with organic carbon detection (LC-OCD) were used for the characterization of foulants. On the basis of statistical analysis, biopolymers and humic substances were found to be the major contribution to total fouling (r2 = 0.95 and r2 = 0.88, respectively). Adsorption of the low molecular weight neutral compounds to the membrane was attributed to hydraulically irreversible fouling (r2 = 0.67).

Organic Fouling of Ultrafiltration Membrane: Detailed Characterization by Liquid Chromatography with Organic Carbon Detector (LC-OCD)

Efficient control of membrane fouling in low-pressure membrane filtration is still required; however, our current understanding of the fouling mechanism is insufficient, and little is known about the preferential deposition of foulants on membrane surface during filtration. In this study, the strength of attachment of different organics on polyvinylidene fluoride (PVDF) hollow fiber ultrafiltration (UF) membrane was investigated. Sodium alginate (SA), bovine serum albumin (BSA), and humic acid (HA) were examined as foulants representing polysaccharides, proteins, and humic substances, respectively, and their relative degree of fouling was monitored. An increasing amount of cleaning force was applied during a four-step rigorous cleaning protocol to extract foulants from the membrane surface. Liquid chromatography with organic carbon detector (LC-OCD) was applied to better characterize the nature of the extracted foulant layers; so to obtain a more advanced understanding of preferential deposition of fouling material on membrane surface. The results obtained in this study demonstrated that organics, mainly biopolymers and low molecular weight (LMW) neutrals, exhibited the highest affinities with the membrane, and consequently caused irreversible fouling. Furthermore, higher bulk organic concentrations in the feed may not be necessarily responsible for a greater extent of membrane fouling, due to possible foulant-foulant interactions, as demonstrated by this initial assessment through LC-OCD.

Removal of NOM-constituents as characterized by LC-OCD and F-EEM during drinking water treatment

Natural organic matter (NOM) is of concern in drinking water because it causes adverse aesthetic qualities such as taste, odour, and colour; impedes the performance of treatment processes; and decreases the effectiveness of oxidants and disinfectants while contributing to undesirable disinfection by-products. The effective removal of NOM during drinking water treatment requires a good understanding of its character. Because of its heterogeneity, NOM characterization necessitates the use of multiple analytical techniques. In this study, NOM in water samples from two drinking water treatment trains was characterized using liquid chromatography with organic carbon detection (LC-OCD), and fluorescence excitation-emission matrices (F-EEMs) with parallel factor analysis (PARAFAC). These characterization methods indicate that the raw and treated waters are dominated by humic substances. The results show that whereas the coagulation process for both plants may be optimized for the removal of bulk DOC, it is not likewise optimized for the removal of specific NOM fractions. A five component PARAFAC model was developed for the F-EEMs, three of which are humic-like, while two are protein-like. These PARAFAC components and the LC-OCD fractions represented effective tools for the performance evaluation of the two water treatment plants in terms of the removal of NOM fractions.

Influence of hydraulic retention time on the nature of foulant organics in a high rate membrane bioreactor

The influence of hydraulic retention time (HRT) in a submerged hollow fibre membrane bioreactor was studied by conducting experiments at four different HRTs (4, 2, 1.3 and 1h) at room temperature of 25°C. It was found that a shorter HRT led to a higher development of trans-membrane pressure. The highest sludge cake and pore-blocking resistances of 4.02×1011m−1 and 0.77×1011m−1 respectively were noted for the shortest HRT (of 1h) application. UV and fluorescence spectroscopy analyses showed that the nature of organics in the biomass and sludge cakes were different. The organic fraction analysis by liquid chromatography with organic carbon detector (LC-OCD) showed a significant amount of biopolymers and a lower amount of humics for longer HRT.

Tracking natural organic matter (NOM) in a drinking water treatment plant using fluorescence excitation–emission matrices and PARAFAC

Natural organic matter (NOM) in water samples from a drinking water treatment train was characterized using fluorescence excitation emission matrices (F-EEMs) and parallel factor analysis (PARAFAC). A seven component PARAFAC model was developed and validated using 147 F-EEMs of water samples from two full-scale water treatment plants. It was found that the fluorescent components have spectral features similar to those previously extracted from F-EEMs of dissolved organic matter (DOM) from diverse aquatic environments. Five of these components are humic-like with a terrestrial, anthropogenic or marine origin, while two are protein-like with fluorescence spectra similar to those of tryptophan-like and tyrosine-like fluorophores. A correlation analysis was carried out for samples of one treatment plant between the maximum fluorescence intensities (Fmax) of the seven PARAFAC components and NOM fractions (humics, building blocks, neutrals, biopolymers and low molecular weight acids) of the same sample obtained using liquid chromatography with organic carbon detection (LC-OCD). There were significant correlations (p < 0.01) between sample DOC concentration, UVA254, and Fmax for the seven PARAFAC components and DOC concentrations of the LC-OCD fractions. Three of the humic-like components showed slightly better predictions of DOC and humic fraction concentrations than UVA254. Tryptophan-like and tyrosine-like components correlated positively with the biopolymer fraction. These results demonstrate that fluorescent components extracted from F-EEMs using PARAFAC could be related to previously defined NOM fractions and that they could provide an alternative tool for evaluating the removal of NOM fractions of interest during water treatment.

Multi-wavelength spectroscopic and chromatography study on the photocatalytic oxidation of natural organic matter

The effect of TiO 2 photocatalytic oxidation on the natural organic matter (NOM) properties of two Australian surface waters were quantified using UV–vis spectroscopy, high performance size exclusion chromatography (HPSEC) with a multi-wavelength UV detector, liquid chromatography with organic carbon detector (LC-OCD), and trihalomethane formation potential (THMFP) analyses. Both the UV absorbance at wavelengths greater than 250 nm and dissolved organic carbon (DOC) content decreased significantly with treatment, although complete mineralization of NOM could not be achieved. Multi-wavelength UV detection of HPSEC analysis was shown to be useful to display further changes to NOM composition and molecular weight profiles because the organic molecules was transformed into compounds that absorb weakly at the typical detection wavelength of 250–260 nm. The multi-wavelength HPSEC results also revealed that photocatalytic oxidation yields by-products with a low aromaticity and low molecular weight. The LC-OCD chromatograms indicated that low molecular acids and neutral compounds remained after photocatalytic oxidation. Those groups of compounds did not seem to contribute significantly to the formation of trihalomethanes.

An urban water cycle perspective of natural organic matter (NOM): NOM in drinking water, wastewater effluent, storm water, and seawater

Natural organic matter (NOM) occurs throughout the hydrologic cycle, varying in both amount and character. In this paper, a description of NOM in surface and drinking water, in groundwater and in seawater is presented. Water samples representing these environments were collected and characterized using multiple NOM characterization techniques, including fluorescence excitation emission matrices (F-EEM) and size exclusion liquid chromatography with organic carbon detection (LC-OCD). The results show that the raw surface water as well as the treated water comprises mainly (&amp;gt;70%) of humic substances. The biopolymers, which are more readily biodegradable, contribute up to 2% of the NOM in the raw water but this is completely removed after treatment. For sea water samples, humic substances represent about 50% of the dissolved organic carbon concentration (DOC), while the fraction with size bigger than 20 kDa (biopolymers) represents about 7%. During soil passage, there was preferential removal of non-humic substances (i.e., biopolymers) from wastewater effluent-impacted surface water while the specific ultraviolet absorbance (SUVA), which reflects the aromatic characteristics of organics in a sample, showed an increasing trend along the depth of the soil column. This is a consequence of the removal of non-humic substances (biopolymers) which results in an increase in aromaticity.

Removal of bulk dissolved organic carbon (DOC) and trace organic compounds by bank filtration and artificial recharge

Bank filtration and artificial recharge provide an important drinking water source to the city of Berlin. Due to the practice of water recycling through a semi-closed urban water cycle, the introduction of effluent organic matter (EfOM) and persistent trace organic pollutants in the drinking water is of potential concern. In the work reported herein, the research objectives are to study the removal of bulk and trace organics at bank filtration and artificial recharge sites and to assess important factors of influence for the Berlin area. The monthly analytical program is comprised of dissolved organic carbon (DOC), UV absorbance (UVA 254), liquid chromatography with organic carbon detection (LC-OCD), differentiated adsorbable organic halogens (AOX) and single organic compound analysis of a few model compounds. More than 1 year of monitoring was conducted on observation wells located along the flowpaths of the infiltrating water at two field sites that have different characteristics regarding redox conditions, travel time, and travel distance. Two transects are highlighted: one associated with a bank filtration site dominated by anoxic/anaerobic conditions with a travel time of up to 4–5 months, and another with an artificial recharge site dominated by aerobic conditions with a travel time of up to 50 days. It was found that redox conditions and travel time significantly influence the DOC degradation kinetics and the efficiency of AOX and trace compound removal.