NOM Fractions Research Articles

Removal of hydrophobic and hydrophilic constituents by anion exchange resin

The objective of this work was to compare the affinity of well characterized NOM fractions isolated from two surface waters with strong (gel matrix and macroporous matrix) and weak anion exchange resins (AER) using batch experiment conditions. The structural characterization of the fraction of NOM has shown that the higher the hydrophilic character, the lower the C/O atomic ratio, the lower the SUVA, the lower the aromatic carbon content and the lower the molecular weight. In general (not always), strong AER was more efficient to remove DOC than weak AER. For the same water source (Suwannee River), the higher the molecular weight of the NOM fraction, the lower the affinity with AER. Increasing the ionic strength favored the removal of the hydrophobic NOM fraction (“salting out” effect) while increasing the pH apparently reduced the removal of the hydrophilic NOM fraction. Results were discussed in terms of size exclusion, adsorption, anion exchange and also hydrophobic/hydrophilic repulsion.

Potential interactions between sedimentary dissolved organic matter and mineral surfaces

Abstract The sorptive properties of pore water organic matter and organic matter easily extracted from marine sediments were examined in a series of batch adsorption and desorption experiments. Pore water natural organic matter ( p NOM) and easily extracted natural organic matter ( e NOM) were isolated from Sinclair Inlet, WA (USA) sediments. The NOM fractions were concentrated ∼9 times via rotoevaporation and then sorbed to, and desorbed from, organic-free sediment, sediment size fractions (63–250, 38–63 and μ m), montmorillonite and iron oxide. Sorption isotherms of p NOM varied little with changing sediment grain size or mineralogy, and Freundlich linearity coefficients ( n ) were all near 1 (range 0.65–1.15). e NOM was more heterogeneous in its sorption to the various surfaces, having a wider range of linearity coefficients (0.38–1.36) and a greater tendency to sorb to the montmorillonite. Average partition coefficients ( K d ) for the p NOM and e NOM were small (0.1±0.04 and 0.08±0.03 l g −1 ), illustrating only a low affinity for the surfaces. Hystereses observed in the desorption isotherms relative to the adsorption isotherms extrapolate back to the origin, suggesting that the sorption of NOM was reversible. A multiple-component model fit to the sorption and desorption data suggests that both the p NOM and e NOM fractions can be described as ∼1:2 mixtures of two components with average K d 's of 3.2 and 0.02 l g −1 , respectively. This result was confirmed in a cumulative adsorption experiment, where less than 40% of the p NOM was found to be surface-reactive. The overall similarity of the sorptive properties of p NOM and e NOM suggest that the two isolates are subgroups of a single sedimentary NOM pool. At natural sediment porosities between 0.5 and 0.95, p NOM is buffered by a surface-bound e NOM pool that is many times larger than the p NOM pool with which it is undergoing exchange.

98/01271 Production of active carbon from Agacli lignite: Aksu, F. et al. Chim. Acta Turc., 1997, 25, (2), 67–72. (in German)

This study investigated the effect of disinfection by-products (DBPs) formation in pre-oxidation with ferrate(VI) (FeVIO42−, Fe(VI)) and relationship between subsequent chlorination of Suwannee river natural organic matter (SRNOM) and eight model compounds containing moieties of alcohol, aldehyde, amines, amino acids, and phenol. The DBPs studied were trihalomethanes (THMs), chloral hydrate (CH), haloacetonitriles (HANs), and trichloronitromethane (TCNM). When the interaction of Fe(VI) and SRNOM was independently examined at pH 7.0, a decrease was seen in dissolved organic carbon and in the hydrophobic and hydrophilic fractions of NOM. With the model compounds, the results showed that Fe(VI) pre-oxidation and subsequent chlorination decreased the formation of THMs with most of the compounds except amines and glycine. The effect of Fe(VI) preoxidation on CH and HANs formation from model compounds varied and was dependent on ferrate doses. Fe(VI) pre-oxidation significantly enhanced TCNM formation, compared to without pre-oxidation, from subsequent chlorination of methylamine, dimethylamine and glycine and the formation increased with increasing doses of ferrate. Correlations of DBPs formation between SRNOM and model compounds were sought to identify the moieties involved in influencing the formation of DBPs. The generation of DBPs is described using the parent molecules and the kinetics and reaction products of Fe(VI)/chlorine oxidation.

Distribution et caractérisation de la matière organique dissoute d'eaux naturelles de surface

Cette étude porte sur la caractérisation de la matière organique dissoute de différentes eaux de retenue et de rivière. Outre les outils analytiques généralement utilisés dans ce type d'approche, carbone organique dissous, carbone organique dissous biodégradable, absorbance dans l'ultraviolet, ultrafiltration et potentiels de réactivité avec le chlore et l'ozone, ce travail de recherche s'appuie sur la mise en œuvre d'une méthode de fractionnement du COD sur résines XAD-8 et XAD-4 utilisées en série permettant de distinguer trois fractions, les substances hydrophobes (substances humiques), les acides hydrophiles et les substances hydrophiles non adsorbées. Les eaux de retenue collectées affichent des teneurs en COD et des absorbances UV à 254 nm, synonyme de la présence de structures aromatiques, plus importantes que celles des eaux de rivière. Globalement, la matière organique de ces eaux est constituée de deux fractions, une hydrophobe (matière organique adsorbée sur résine XAD-8 à pH acide) et une hydrophile (matière organique non retenue sur résine XAD-8 à pH acide) quantitativement équivalentes. La fraction hydrophobe englobe toutefois l'essentiel des structures aromatiques. Néanmoins, il est intéressant de noter que la matière organique hydrophobe est proportionnellement plus abondante dans les eaux de retenue (51 à 62% du COD) que dans les eaux de rivière (41 à 50% du COD). En contre partie, les composés hydrophiles non adsorbés sur résines XAD représentent une fraction significativement plus importante dans les eaux de rivière que dans les eaux de retenue. Pour l'eau de la Loire, cas particulier pour lequel la distribution hydrophobes/hydrophiles correspond à 41%/59% en COD, l'étude de la distribution des masses moléculaires apparentes déterminée par filtration sur membrane 1000 daltons, a permis de souligner la prédominance des composés de plus faibles masses moléculaires (< 1000 daltons) comparativement aux autres eaux étudiées. Cet ensemble de résultats pourrait être associéà la présence plus importante de sédiments en suspension dans les eaux de rivière, les sédiments favorisant l'adsorption et/ou la complexation, en présence d'espèces métalliques, des matières humiques définies comme hydrophobes. En ce qui concerne la réactivité des eaux naturelles avec les oxydants, les demandes en chlore et en ozone, les PFTHMt et les PFTOX, sont proportionnels à la teneur en COD et à l'absorbance UV à 254 nm des eaux étudiées. Les potentiels de réactivité relatifs (rapportés à l'unité de carbone) sont d'autant plus élevés que l'absorbance relative des eaux (Abs UV/mg COD) est grande. Les eaux de retenue présentent, dans ce sens, des réactivités vis-à-vis des oxydants plus fortes que les eaux de rivière. Enfin, la teneur en CODB des eaux naturelles comprise entre 8 et 22% est difficilement reliable aux autres données obtenues.