Christian H. Specht

Characterization of NOM adsorption to clay minerals by size exclusion chromatography.

Abstract Mineral-bound humic substances modify the surfaces of clay minerals, changing the nature and number of adsorption sites for contaminants. Due to their effect on the surface charge of colloidal particles they can also change the particles mobility and thus their transport behavior. In this paper the influence of natural organic matter on the zetapotential of kaolinite and montmorillonite is shown. Adsorption experiments with kaolinite and montmorillonite show that due to adsorption the humic substances are fractionated. The equilibrium pH value does not influence the fractionation due to adsorption. Large hydrophobic molecules showed the strongest affinity towards the clay surfaces. Substances with a small apparent molecular size and a high content of carboxylic functional groups made up the non-adsorbing fraction of the NOM. Ca2+ had no measurable effect on the adsorption. The low influence of the adsorbed NOM on the zetapotential of the clay minerals suggests physical adsorption as the predominant adsorption mechanism.

An in situ ATR-FTIR study on the adsorption of dicarboxylic acids onto kaolinite in aqueous suspensions

ATR-FTIR spectroscopy was used to investigate in situ the adsorption of simple compounds, such as dicarboxylic acids, hydroxybenzoic acids and resorcinol, onto the clay mineral kaolinite. Identification of the absorption bands was based on changes which occur in the spectra of the compounds on changing the pH value of the aqueous solution. The band shifts which occur in the spectra of the dicarboxylic acids as a result of the interaction with the kaolinite surface suggest inner-sphere complexes, where either one or both oxygen atoms of the carboxylic group are bound to the kaolinite surface. A comparison of the spectra of the dicarboxylic acids showed that small structural differences had a great influence on the kind of surface complex formed. In the case of the hydroxybenzoic acids and resorcinol, the band shifts were too small to make any statements regarding possible surface complexes.

Alkaline hydrolysis of humic substances: spectroscopic and chromatographic investigations

To find out more on the structure of humic substances (HS), isolated dissolved organic carbon (DOC) samples from a brown water lake and a wastewater effluent were fractionated and subjected to alkaline hydrolysis. UV/Vis and fluorescence spectroscopy, as well as size-exclusion chromatography with on-line detection of UV absorption, fluorescence and DOC concentration were used to investigate the structural changes caused by the hydrolysis reaction. Following hydrolysis, the fluorescence intensity increased considerably despite a decrease in the UV absorption. The UV absorption and the DOC data from the SEC experiments revealed a strong shift to smaller molecular sizes after hydrolysis. The spectra of the hydrolysed samples, as well as the size-exclusion chromatograms, were compared to spectra of hydroxybenzoic acids and hydroxycinnamic acids. From this comparison, it can be concluded that the hydrolysis products have a structure similar to these organic acids.

Influence of oxidation of dissolved organic matter (DOM) on subsequent water treatment processes

Abstract The influence of oxidation processes on dissolved organic matter (DOM) with respect to its flocculation properties and its biodegradability was investigated. In the experiments, DOM samples of a brown water lake and of commercially available lignin sulfonic acids were used. Ozonation treatment, hydrogen peroxide (H 2 O 2 ) in combination with UV irradiation, and UV irradiation only were applied in the oxidation of the DOM samples. The impact of the oxidation on the DOM was characterized by size exclusion chromatography, UV absorbance, and fluorescence spectroscopy. In order to investigate the flocculation properties of the DOM before and after oxidation, sedimentation field-flow fractionation experiments were performed. The biodegradability was probed in a biofilm reactor. Due to the oxidation, the biodegradability and flocculation was changed depending on the process applied and the degree of oxidation of the DOM.

Non-linear calibration functions in ion chromatography with suppressed conductivity detection using hydroxide eluents.

The linearity of calibration curves in ion chromatography with suppressed conductivity detection using hydroxide eluents was investigated. Theoretical calibration curves were derived for strong electrolytes and weak monobasic acids and the results compared with experimental data. At low concentrations up to 1 micromol l(-1) the autoprotolysis of water induces left-curved calibration functions even for strong electrolytes like nitrate. The experimental data are best described by a quadratic function, the differences between linear and quadratic regression being up to 10%. At higher concentrations the calibration curves for strong electrolytes are linear. Due to incomplete dissociation, the calibration curves for weak mono- and dibasic acids show a right curvature. Thus, depending on the analyte and the concentration range of interest, analysts should carefully choose between a linear and a quadratic regression function.

Removal of hydrophilic compounds from water with organic polymers: Part II: Adsorption behavior of industrial wastewater

The adsorption behavior of organic substances from different industrial wastewaters onto activated carbon (F 300) was compared with the adsorption onto an organic polymer resin (Lewatit EP 63). The adsorption capacity of Lewatit EP 63 was lower at low equilibrium concentrations and similar at high equilibrium concentrations compared with activated carbon. The adsorption behavior is represented in similar portions for high K values for both sorbents obtained with the adsorption analysis. Steady-state and time-resolved fluorescence measurements showed that the fluorescent components of the wastewaters were not adsorbed on Lewatit EP 63 which means that there was selective adsorption.