Adsorption organic pollutants

Keywords Lignocellulosic sorbent, adsorption, organic pollutant, chemical modification of cellulose, biosorbent... 

Adsorption. Adsorption (qv) is an effective means of lowering the concentration of dissolved organics in effluent. Activated carbon is the most widely used and effective adsorbent for dyes (4) and, it has been extensively studied in the waste treatment of the different classes of dyes, ie, acid, direct, basic, reactive, disperse, etc (5—22). Commercial activated carbon can be prepared from lignite and bituminous coal, wood, pulp mill residue, coconut shell, and blood and have a surface area ranging from 500—1400 m /g (23). The feasibiUty of adsorption on carbon for the removal of dissolved organic pollutants has been demonstrated by adsorption isotherms (24) (see Carbon, activated carbon). Several pilot-plant and commercial-scale systems using activated carbon adsorption columns have been developed (25—27). 

Karickhoff133 discusses in detail adsorption processes of organic pollutants in relation to K<)C. 

Wang, L.K. and Wang, M.H.S., Removal of organic pollutants by adsorptive bubble separation processes, 1974 Earth Environment arid Resources Conference Digest of Technical Papers, Vol. 1, IEEE Cat. No. 74 CH0876-3EQC, pp. 56-57, September 1974. 

SCRAM (28) is a TDE dynamic, numerical finite difference soil model, with a TDE flow module and a TDE solute module. It can handle moisture behavior, surface runoff, organic pollutant advection, dispersion, adsorption, and is designed to handle (i.e., no computer code has been developed) volatilization and degradation. This model may not have received great attention by users because of the large number of input data required. 

Kowalska M, Gtiler H, Cocke DL (1994) Interactions of clay minerals with organic pollutants. Sci Total Environ 141 223-240 Kukkadapu RK, Boyd SA (1995) Tetramethylphosphonium-smectite and tetramethylammonium-smectite as adsorbents of aromatic and chlorinated hydrocarbons - effect of water on adsorption efficiency. Clays Clay Miner 43 318-323... 

It is well known that complexation of trace elements by both inorganic and organic ligands plays an important role in their transport through natural waters, influencing their solubility and their adsorption on both bottom and suspended sediments. In many cases organic pollutants have been shown to complex with a wide variety of cations and, in particular, many of these pollutants have been shown to complex with iron (157). It is possible that there will be a similar complexation of... 

Keywords. Sorption, Interaction mechanisms, Organic pollutants, Solid phases, Adsorption, Partitioning, Humic substances, Humus, Organic matter... 

Fig. 1. Adsorption vs absorption mechanisms of organic pollutants in aqueous media...

Adsorption mechanisms represent probably the most important interaction phenomena exerted by solid surfaces on the environmental fate of organic pollutants [65, 127-130]. Adsorption controls the quantity of free organic components in solution and thus determines their persistence, mobility, and bioavailability. The extent of adsorption depends on the amount and properties of both solid phase-humic substances (SPHS) and organic pollutants. Once adsorbed on an SPHs >an organic pollutant may be easily desorbed, desorbed with difficulty, or not at all. Thus sorption phenomena may vary from complete reversibility to total irreversibility. 

Construction and use of adsorption isotherms from equilibrium sorption data has been employed by numerous researchers to describe adsorption of organic pollutants on a solid matrix [131-137]. An isotherm represents a relation between the amount of solute (i.e., the pollutant of interest) adsorbed per unit weight of solid adsorbent (i.e., soil, sediment) and the solute concentration in solution at equilibrium. 

The adsorption of a number of organic pollutants on various solid surfaces was found to fit the Langmuir-model isotherm [139,143-145]. 

Van der Waals forces, although very weak, operate in all adsorbent-adsorbate interactions, and result from short-range dipole-dipole, dipole-induced dipole, or induced dipole-induced dipole attractions. Although van der Waals interactions are forces acting universally, they assume particular importance in the adsorption of nonionic and non-polar molecules or portions of molecules on similar sites of the adsorbent molecule [17,159]. These forces are additive, and thus their contribution increases with the size of the molecule and with its capacity to adapt to the adsorbent surface. Van der Waals attractions have often been invoked in case of difficulties in explaining adsorption of an organic pollutant onto SPHS, but the experimental evidence has not always been convincing. 

Reversible physical adsorption of hydrophobic pollutants with dissolved-phase and solid-phase HS (i. e., DPm and SPm, respectively) is a well established and fundamental interaction affecting the equilibrium distribution and rate of an organic pollutant between soil/sediment, water, and air [82,181-184]. There has been - and still is - continuing literature discussion regarding the physical association of hydrophobic organic pollutants with sediment and soil involving a process of adsorption or partitioning [77,103,108,113,130,185-188]. 

The evidence presented in the literature on the dominance of a partition mechanism in the process of adsorption of a nonionic organic pollutant onto SOM does not mean, for instance, that the physical adsorption model based on weak chemical forces of interaction can be ignored or excluded [82,99,107,109, 114,115,183,192,204-218]. The following summary is a critical evaluation for reconsidering the universal applicability of the partitioning model to various nonionic compounds onto SP0M [82,84,92,103,113,130,182,184,185,187,193, 219,220,222-226] ... 

The molecular structure and conformation of an organic pollutant is a property which may affect adsorption onto a solid surface and/or partition into its organic lipid phase differently, thus hindering the expected correlation between KQM and K )W ... 

The humic/organic matter coatings of different solid phases (i. e., SPm /SP0M), such as soils, sediments, suspended solids, colloids, and biocolloids/biosolids, interact with organic pollutants in aqueous systems in various ways. Adsorption is an important interaction mode. The reversibility and/or irreversibility of the adsorption processes is of major importance. The question whether the bound residues of pollutants are to be considered definitely inactivated has been the focus of extensive research. This question was posed as follows. Have the adsorbed pollutants become common components incorporated into the humic polymer coating of solid phases (i. e., being absorbed), or are they only momentarily inactivated in reversibly bound forms thus representing a possible source of pollution by a time-delayed release of toxic units ... 

To interpret the kinetics experimental data of an organic pollutant(s) or leachate from complex organic mixtures, it is necessary to determine the adsorption/ desorption process steps in a given experimental system which govern the overall adsorption/desorption rate. For instance, the adsorption process of an organic compound by a porous adsorbent can be categorized as three consecutive steps ... 

Chiou CT. 1989. Partition and adsorption on soil and mobility of organic pollutants and pesticides. In GerstI Z, ed. Ecological studies, Vol. 73. Toxic organic chemical in porous media Second international workshop on behavior of pollutants in porous media. Bet Dagan, Israel, June 1987. 

A wide range of organic pollutants can be adsorbed by MFl, Y and mixtures of the two structure types. In the VOC application fixed beds are comparatively few with most VOC adsorption being done by rotary adsorbers such as are built and sold by Seibu Giken. A few words about rotary adsorption applications follow in Section 9.7. 

Bell, J.P. and Tsezos, M. Removal of hazardous organic pollutants by biomass adsorption, /. Water Pollut. Control Fed., 59(4) 191-198, 1987. 

Reinbold, K.A., Hassett, J.J., Means, J.C., and Banwart, W.E. Adsorption of energy-related organic pollutants a literature review. Office of Research and Development, U.S. EPA Report-600/3-79-086, 1979, 180 p. 

Sheindorf, C., Rebhun, M., and Sheintuch, M. Organic pollutants adsorption from multicomponent systems modeled by Freundlich type isotherm. Water Res., 16(3) 357-362, 1982. 

Liu C, Zachara JM, Smith SC, McKinley JP, Ainsworth CC (2003) Desorption kinetics of radiocesium from subsurface sediments at Hanford Site USA. Geochim Cosmochim Acta 67 2893-2912 Loffredo E, Senesi N (2006) Eate of anthropogenic organic pollutants in soils with emphasis on adsorption/desorption processes of endocrine disruptor compounds. Pure App Chem 78 947-961... 

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