Adsorption natural organic matter

Keywords granular activated carbon adsorption natural organic matter micro-pollutants atrazine water treatment water temperature... 

Water and Waste Water Treatment. PAG products are used in water treatment for removal of suspended soHds (turbidity) and other contaminants such as natural organic matter from surface waters. Microorganisms and colloidal particles of silt and clay are stabilized by surface electrostatic charges preventing the particles from coalescing. Historically, alum (aluminum sulfate hydrate) was used to neutralize these charges by surface adsorption of Al cations formed upon hydrolysis of the alum. Since 1983 PAG has been sold as an alum replacement in the treatment of natural water for U.S. municipal and industrial use. 

We conclude this section by a few general remarks about extrathermodynamic approaches. These quantitative methods involve empirical approaches that cannot be derived strictly from thermodynamic theory. They are widely used to predict and/ or to evaluate partition constants and/or partition coefficients (see Box 3.2 for nomenclature) of organic compounds. There are many situations in which some of the data required to assess the partitioning behavior of a compound in the environment are not available, and, therefore, have to be estimated. For example, we may need to know the water solubility of a given compound, its partition coefficient between natural organic matter and water, or its adsorption constant from air to a natural surface. In all these, and in many more cases, we have to find means to predict these unknown entities from one or several known quantities. 

Let us evaluate some experimental data. To this end, we use a dual-mode model (Eq. 9-6). This model is a combination of a linear absorption (to represent the sorbate s mixing into natural organic matter) and a Freundlich equation (as seen for adsorption to hydrophobic surfaces or pores of solids like activated carbons) ... 

The value of the partition coefficient, Kip, is given by the product, focKioc, where/ic and Kjoc apply only to the natural organic matter into which the sorbate can penetrate. The value of Kif is less well understood, but recent observations suggest it should be related to the quantity of adsorbent present (e.g., the fraction of black carbon in a solid matrix, /bc) and the particular compound s black-carbon-normalized adsorption coefficient (e.g., Klhc). Typical values of the Freundlich exponent are near 0.7. Hence, in a first approximation the data should fit ... 

All water sources may contain natural organic matter, but concentrations (usually measured as dissolved organic carbon, DOC) differ from 0.2 to more than 10 mg L l. NOM is a direct quality problem due to its color and odor, but more important are indirect problems, such as the formation of organic disinfection by-products (DBPs, e. g. M -halomethanes (THMs) due to chlorination), support of bacterial regrowth in the distribution system, disturbances of treatment efficiency in particle separation, elevated requirements for coagulants and oxidants or reductions in the removal of trace organics during adsorption and oxidation, etc. 

Gu, B., Schmitt, J., Chen, Z., Liang, L., and McCarthy, F. (1994). Adsorption and desorption of natural organic matter on iron oxide Mechanisms and models. Environ. Sci. Technol. 28,38—46. 

Schmitt, D., Taylor, H. E., Aiken, G. R., Roth, D. A., and Frimmel, F. H. (2002). Influence of natural organic matter on the adsorption of metal ions onto clay minerals. Environ. Sci. Technol. 36, 2932-2938. 

Peuravuori, J. and Pihlaja, K. (1997a) Isolation and characterization of natural organic matter from lake water comparison of isolation with solid adsorption and tangential membrane filtration. Environ. Int., 23, 441—451. 

FIGURE 7.9 Relative contribution to Pb adsorption by biogenic Mn oxide. Fe oxide and natural organic matter in a natural surface coating as a function of pH. Below pH 6.5, biogenic Mn oxide dominates Pb adsortion, while above pH 6.5, Pb adsorption to biogenic Mn oxide is second to that of Fe oxide. (See Wilson, A.R. et al., 2001.)... 

The ability to control NOM adsorption through modification of surface chemistry was demonstrated previously [20] the uptake of several model humic substances and natural organic matter isolated from surface waters decreased significantly with increasing surface acidity (as measured by NaOH neutralization). The uptake was partially restored by subsequent heat treatment of the oxidized surfaces (i.e. OX 9/70 HT650). For the wood-based carbons, the impact of surface treatment on adsorption of organic matter was surprisingly small or absent. Overall, the reactivity of carbon surfaces to DOM uptake depended on the raw material type, activation conditions and surface treatment. 

Sorption of VOCs involves the processes of adsorption and partitioning. Partitioning is the incorporation of the VOC into the natural organic matter associated with the solid and is analogous to the dissolution of an organic compound into an organic solvent. Adsorption is the formation of a chemical or physical bond between the VOC and the mineral surface of a solid particle (Rathbun, 1998). The equilibrium relation between aqueous and solid phase concentrations then is expressed as... 

The practical and fundamental interests in dye adsorption stem from three considerations (I) their ubiquity in industrial waste waters [499-511,395] (2) their use as surrogates for natural organic matter [512], and (3) their use for the determination of porous structure of adsorbents [451,513,514,346,515-520,512]. 

FIG. 23 Effect of pH on the adsorption isotherms for natural organic matter on a commercial activated carbon. (Adapted from Ref 566.)... 

In a recent review of technological alternatives for NOM removal, Jacangelo et al. [558] presented field data that illustrate wide variability in adsorption capacities of activated carbon in a single location (e.g., exhaustion periods between 41 and 182 days). They concluded that these results are evidence of the site-specific nature of [dissolved organic carbon] removal by [activated carbon] and that the concerns regarding reliability of treatment practices to meet the new [regulations] have a sound basis. Clearly, much fundamental work remains to be done to understand fully the complex nature of these adsorbent/adsorbate interactions and thus be able to optimize both the physical and the chemical accessibility of the carbon surface to natural organic matter. 

TABLE 34 Freundlich Isotherm Parameters for Adsorption of Dissolved Natural Organic Matter (DOM) in the Absenee of Oxygen... 

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