Adsorption of humic substances: the effects of heterogeneity and system characteristics

Abstract

The study from which this article derives focused on the identification and quantification of parameters that affect the adsorption of humic substances by activated carbon and on the application of these findings to water treatment practice. Results reported here demonstrate the dependence of adsorption on pH, initial concentration of humic material, carbon dosage and particle size, and levels of various inorganic ions in solution. Many of the observed effects are attributable to the fact that humic substances are mixtures of compounds and that their adsorption is therefore a multicomponent process. The distribution of adsorptivities within these mixtures appears to vary with the presence of certain ions, most notably Ca 2+ and Mg 2+ . These findings have been applied to bench-scale granular carbon columns and to powdered carbon slurry systems. The results are discussed from both theoretical and application points of view.The presence of color-imparting humic substances in public water supplies was considered primarily an aesthetic nuisance prior to 1974. The discovery that year of the reactivity of these compounds with chlorine to produce trihalomethanes 1,2 (THMs) and subsequent evidence of the pervasiveness and possible public health implications of the resultant halogenated hydrocarbons 3,4 have provided increased incentive to study control of humic materials in water supply practice. Beyond the role of such species as color bodies and THM precursors, other

Competitive Effects of Nondisplaceable Organic Compounds on Trichloroethylene Uptake by Activated Carbon. I. Thermodynamic Predictions and Model Sensitivity Analyses

“…, [4] where E n represents the net adsorption energy calculated using a Polanyi-type potential with solubility as a reference state (22), C s is the sorbate solubility, R is the universal gas constant, T is the absolute temperature, and the remaining terms are as previously defined.…”

“…NOM is a heterogeneous mixture of complex organic materials including humic substances, hydrophilic acids, proteins, lipids, carboxylic acids, amino acids, and hydrocarbons. Humic substances, including humic and fulvic acids ranging in molecular weight from about 1000 to 10,000 mg/L, are the predominant components and are thought to be responsible for much of the reactivity of NOM (1)(2)(3)(4). It is present in nearly all natural waters, at median concentrations of 3.4 mg/L and 0.8 mg/L in surface waters and groundwaters, respectively (5,6).…”

Adsorption of NOM onto Activated Carbon: Effect of Surface Charge, Ionic Strength, and Pore Volume Distribution

“…Most of the literature dealing with the adsorption of NOM onto activated carbon describes the adsorption enhanced regime, where increased ionic strength increases adsorption (25)(26)(27). Summers and Roberts (16) detected an adsorption reduced regime (although not describing it as such) when they studied the adsorption of fractionated humic acid onto a positively charged activated carbon.…”

Influence du dodécylsulfate de sodium sur l'adsorption des acides humiques sur charbon actif en poudre

“…Plusieurs auteurs (Me CREARY et SNOEYINK, 1980 ;LEE et al, 1981 ;RANDTKE et JEPSEN, 1982 ;WEBER et al, 1983) ont mis en évidence une relation linéaire entre les résultats obtenus à partir de ces méthodes de dosage des SH avant et après adsorption sur charbon actif. DE LAAT (1988) a constaté que le dosage du carbone organique dans tes solutions d'acides humiques peut être peu précis en raison de l'oxydation incomplète des acides humiques dans l'analyseur, ce que nous avons effectivement vérifié, les différences pouvant atteindre jusqu'à 70 %.…”