Adsorption of Micropollutants on Activated Carbon - ACS Publications

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Adsorption of Micropollutants on Activated Carbon Massoud Pirbazari, Varadarajan Ravindran, Sau-Pong Wong, and Mario R. Stevens Department of Civil Engineering, University of Southern California, Los Angeles, CA 90089-0231

This chapter addresses the effect of humic substances (HS) on the activated-carbon adsorption of several contaminants, including trichloroethylene, chloroform, geosmin, and polychlorinated biphenyls. Complexation potentials of these compounds with HS were investigated to determine the extent of their association. Adsorption experiments performed included equilibrium, minicolumn, and high -pressure minicolumn studies. The ideal adsorbed solution theory (IAST) model was employed to predict adsorption equilibria of mixtures containing each pollutant and HS from their single-solute isotherms. The theoretical predictions obtained from the model were in good agreement with the experimental results. Furthermore, the reduction in adsorption capacity attributed to preloading of carbon with HS was substantial for chloroform, but marginal for polychlorinated biphenyls.

V^HARCOAL BEDS WERE REGARDED AS A PANACEA for purification of con

taminated ground and surface waters over 2000 years ago. A more sophis ticated version of charcoal adsorption that involves the use of activated carbon is widely recognized today as one of the fundamental technologies in water and wastewater treatment. It has proven effective in removing a broad spec trum of potentially hazardous contaminants. The presence of dissolved or ganic matter (DOM), a major portion of which is dissolved humic substances (DHS), complicates the design and operation of adsorption treatment proc esses because D O M may interact with activated carbon and organic con taminants. A n intensive study of such interactions, their associated mech anisms and transformations, and their effect on adsorption appears to be 0065-2393/89/0219-0549$08.50/0 © 1989 American Chemical Society

In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988.


550

AQUATIC H U M I C SUBSTANCES

necessary in order to develop mathematical models for effective appraisal of adsorption systems, from an engineering viewpoint. The formulation of mathematical models to describe adsorption proc esses for treating complex organic mixtures is one of the most challenging areas in the research and development of adsorption technology. Predictive mathematical models help in the design of fixed-bed adsorbers by estimating the pattern of adsorbate concentrations as a function of time or volume of influent treated. Models appropriately calibrated for specific influent and operating conditions can be effectively used for optimal design and operation of pilot-scale and eventually full-scale adsorbers. Predictions of such models depend on accurate characterization of the various physical phenomena af fecting adsorber performance (J). Combined film and particle diffusion models are of interest because they represent the two most common ratelimiting steps in the adsorptive mechanism, namely, film transfer coefficient and intraparticle mass transfer (2). The general approach to adsorber modeling and design involves the solution of differential equations with appropriate boundary conditions rep resenting the mass balance of solid and liquid phases, coupled with the relation that describes the equilibrium distribution of the adsorbate between the two phases, using a suitable numerical technique. Crittenden and Weber (3, 4) developed a model of this type that required several input variables, including kinetic parameters that represent film and intraparticle diffusivities, and isotherm constants that describe adsorption-phase equilibria. Adsorption models have recently attained such high levels of mathe matical sophistication that questions often arise about the analytical certainty of experimentally determined model inputs. Nevertheless, such adsorption models show substantial promise for reducing the gap between the design of bench-scale and field-scale adsorbers. They have deservedly become an integral aspect of engineering design. Adsorption modeling for organic micropollutants in the presence of D H S is complicated by a number of factors. Competition occurs for adsorption sites among the micropollutants and dissolved humic materials ( D H M ) . Fur thermore, complexation between the organic pollutants (OP) and D H S adds a new dimension to adsorption modeling, because competition may arise among the OP, D H S , and O P - D H S complexes. A l l equilibrium models focus on the competitive effect of various adsorbent species, but few models consider the effects of complexation. Study of the theoretical aspects of complexation between O P and D H S is therefore needed to obtain a realistic picture of its contribution to competitive adsorption.

Theoretical Background Humic Substances and Micropollutants in the Environment. The ubiquitous presence of D H S as the predominant naturally occurring



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PiRBAZARi E T AL.

Adsorption of Micropollutants on Activated Carbon

organic species i n most surface and ground waters is environmentally sig nificant. The complexation of several organic micropollutants with D H S largely controls their distribution in air, water, biota, suspended solids, and sediments. Complexation can also modify the mechanisms and kinetics of their phase transport and chemical reactions (5). For instance, rates of deg radation, volatilization, photolysis, transfer to sediments, and biological up take may change considerably when a pollutant is bound to D O M . Thus the extent of complexation between the pollutant and D H M would significantly affect the chemical interactions, distribution, and environmental transport of the pollutant. This aspect affects activated-carbon adsorber design, as the degree of complexation controls the equilibrium and kinetics of adsorbate transfer from the liquid phase to the adsorbent phase. Characteristics of Humic Substances. Aquatic humic substances (HS) constitute about 40-60% of the dissolved organic carbon (DOC). They are nonvolatile and have a molecular weight of 500-5000. Their elemental composition is approximately 50% carbon, 35-40% oxygen, 4-5% hydrogen, 1-2% nitrogen, and less than 1% sulfur and phosphorus. The important functional groups present are carboxylic acids, phenolic hydroxyls, carbonyls, and hydroxyls. Thurman (6) provided a good review of H S characteristics that compared the properties of aquatic and soil H S . Although it has not been proven that both types of H S are the same, they have similar general characteristics (7). They are polyelectrolytic, colored organic acids, with comparable molecular weights and similar elemental compositions and func tional groups (6). HS concentrations vary for different natural waters. Ground-water con centrations are generally low, 0.1-1.0 mg of C / L . In streams, rivers, and lakes the concentrations are much higher, generally 0.6-4.0 mg of C / L . Fulvic acid constitutes about 85-90% and humic acid 10-15% of nearly all surface and ground waters (6). Besides the carboxyl, hydroxyl, and carbonyl groups, humic substances contain lesser amounts of phenolic hydroxyl and trace amounts of carbohydrates and amino acids. In general, humic sub stances from rivers and streams originate from soil and plant matter; those in lakes are of both terrestrial and aquatic origins (S).

Adsorption of Pollutants in the Presence of Humic Substances. The adsorption system (target organic compound, D O M , and activated car bon) is rather complex because the contaminant can exist in one or more of at least four states (2): free form in aqueous solution, adsorbed state on activated carbon, i n a complex with D H M , or associated to a molecule of D H M adsorbed on carbon. Simultaneous existence of all four forms is highly possible, with the distribution of various species governed by mutual equi libria, as well as by the kinetics and degree of reversibility of the reactions.


551

552

AQUATIC HUMIC SUBSTANCES

Hence, in the present context, the extent of complexation and the factors indicating it are quite important. Factors Indicating the Degree of Complexation. Organic com pounds have several properties that determine their degree of complexation with D H S . The most important among these properties are the octanol-water partition coefficient (K ) and aqueous solubility (S). Both prop erties, to a certain extent, reflect the compound's polarity, hydrophobic nature, and affinity for association with D H M (9). In general, higher K or lower S signifies lower polarity, higher hydrophobicity, and therefore a larger potential for forming complexes with D H M . O n the basis of this principle, Carter and Suffet (5) stated that compounds with l o g K values of 4.0 and above could be classified as hydrophobic, and therefore should form a strong complex with D H M . However, those compounds with values less than 4.0 could be considered less hydrophobic and expected to form weak complexes or no complexes at all. Table I lists the l o g K and S values for several hydrophobic organic compounds (log K in the range of 4.0-8.0) classified as priority pollutants by the U.S. Environmental Protection Agency (10). A statistically significant linear relationship exists between the l o g K and l o g S values listed in T a b l e I ( l o g K = -0.542 log S + 8.163; correlation coefficient = -0.80). In the present scenario, the relationship between K and the extent of complexation represented by the binding or association constant, K , is significant. K is defined as the ratio of the mass of bound compound per unit mass of total dissolved humic acid (DHA) to the concentration of un bound compound in solution. Table II compares the l o g K and l o g K values for a number of hydrophobic compounds and also shows the range of degree of complexation for a D H A concentration range of 1-10 m g / L . A statistically significant linear relation can be observed between the two pa rameters listed in Table II (log K = 0.747 l o g K + 0.661; correlation coefficient = 0.86). This functional dependence can facilitate an a priori estimation of the extent of complexation. Nevertheless, although the correlations between l o g K and l o g S, and between l o g K and l o g K may be statistically significant, they are not necessarily practically meaningful. This and other factors that control complexation make such estimation more complicated.


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10

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10

c

Factors Determining the Degree of Complexation.

The extent

of binding of organic pollutants to D H M is determined by a number of factors, including the source, characteristics, molecular sizes, and concen trations of the D H M , as well as the nature and concentration of the pollutant (12), p H , metallic ion concentration, and ionic strength (9). Carter and Suffet (5) reported that D H A and sewage-effluent D O M tend to bind D D T most strongly, and that dissolved fulvic acids (DFA) showed considerably less


32.

PIRBAZARI ET AL.

Adsorption of Micropollutants on Activated Carbon 553

Table I. Octanol-Water Partition Coefficients, K^, and Aqueous Solubilities, S, for Several Hydrophobic Organic Compounds S x JO (ng/L) logw S No. log 10 K Compound 6.26 1.80 1 3.99 Hexachlorocyclopentadiene 2 4-Chlorophenyl phenyl ether 4.08 3.30 6.52 3 1,2,4-Trichlorobenzene 4.26 30.0 7.48 3.78 4 0.006 6.18 Hexachlorobenzene 7.15 14.0 5 5.01 Pentachlorophenol 6 Di-n-butyl phthalate (DBP) 5.20 13.0 7.11 7 Butylbenzyl phthalate 5.80 2.90 6.46 8 Acenaphthene 4.33 3.42 6.53 9 Acenaphthylene 4.07 3.93 6.59 10 4.18 1.98 6.30 Fluorene 4.86 11 0.073 4.45 Anthracene 5.42 0.26 12 Fluoranthene 5.33 6.11 1.29 13 4.46 Phenanthrene 3.95 14 0.009 Benz[a]anthracene 5.61 15 0.002 3.30 Chrysene 5.61 0.14 5.15 16 5.32 Pyrene 2.42 17 0.00026 7.23 Benzo[g/it]perylene 18 Benzo[a]pyrene 7.23 0.0038 3.58 19 Dibenz[a,h]anthracene 5.97 0.0005 2.70 20 DDD (ρ,ρ' isomer) 5.99 0.09 4.95 21 5.0 0.1 6.08 DDD (ο,ρ' isomer) 0.12 5.08 22 5.69 DDE (ρ,ρ' isomer) 5.15 23 0.14 DDE (ο,ρ' isomer) 5.78 24 0.025 4.40 6.19 DDT (ρ,ρ' isomer) 0.25 5.40 25 5.60 Endrin 7.33 21.3 4.14 26 δ-Hexachlorocyclohexane 27 Lindane (7-hexachlorocyclohexane) 3.72 6.60 6.82 28 PCB (Aroclor 1254) 6.03 0.024 4.38 29 6.74 6.83 4.12 2-Chloronaphthalene -6


ow

NOTE: DDD, dichlorodiphenyldichloroethane; DDE, dichlorodiphenyldichloroethylene; and DDT, dichlorodiphenyltrichloroethane. SOURCE: Data are from ref. 10.

Table II. Binding Constants, K , Octanol-Water Partition Coefficients, K^, and Binding Potential of Several Organic Compounds c

1

log

Compound Lindane DBP Anthracene PCB (Aroclor 1254) DDT (ρ,ρ' isomer)

K 3.72 4.91 4.45 6.05 6.19 JO

c

e

e

e

e

w

Percent Binding DOC = 1 rnglL DOC = 10 mg/L 1.09 0.11 4.76 0.50 22.48 2.82 10.45 53.85 21.88 73.68

logw K 3.04 3.70 4.46 5.07' 5.45

b c

d

e

e

e

NOTE: DBP, di-n-butyl phthalate; and DDT, dichlorodiphenyltrichloroethane. Percent binding, (10 X K X DOC) (10~ X K X DOC + Ι)" X 100. K is expressed in milliliters per gram. Data from ref. 10. Data from ref. 9. 'Data from ref. 11. 'Values determined in this study. e

6

c

1

c

b

c

c

rf



554

AQUATIC HUMIC SUBSTANCES

potential for complexation. These same investigators made similar obser vations for anthracene and di(2-ethylhexyl) phthalate ( D E H P ) . There have been a variety of unsuccessful attempts to investigate the characteristics of D H M that determine the differences i n the degree of binding, including measurements of carbon, ash, and iron content; spectroscopic techniques; pyrolysis gas chromatography; and molecular size estimates. The degree of complexation is highly system-specific and, with the limited data available, cannot be theoretically predicted for any type of D H M and OP. Actual experimental determinations of binding constants are therefore necessary (5). D H S chemical structures and the nature of binding between them and OP, quite important from the standpoint of understanding the various factors affecting complexation, will be discussed later. The effects of p H , metallic ion concentration (notably C a ) , ionic strength, and D H A concentration on the complexation of D D T (l,l'-(2,2,2trichloroethylidene)bis(4-chlorobenzene)) with D H A were reported by Carter and Suffet (9). Their observations were quite consistent with the previously established theories on the aqueous behavior of D H M . A number of researchers (12, 13) have observed that the size of the humic polymer is enhanced by an increase in hydrogen-ion or metallic-ion concentration. Thurman and Malcolm (7) observed that a decrease in p H or an increase in ionic strength causes a coiling effect in humic molecules, maldng them more prone to sorption on a number of surfaces. The charge on the humic polymer decreases when the hydrogen-ion or metal-ion concentration increases as a result of charge neutralization (14, 15). Similarly, as calcium concentration increases, the humic polymer becomes less hydrophilic and tends to bind more easily with hydrophobic organic compounds. The effect of increased ionic strength on binding may be attributed to the "salting out" of the hydrophobic organic compound. The chemical po tential of a nonionic compound dissolved in water is enhanced by increased ionic strength, and the compound tends to reduce its chemical potential by binding itself to the humic polymer (9). The effect of D H A concentration on the binding of organic substances has not been supported by any theory, although the binding constant, K , decreases with increasing D H A concen tration (9). In an analogous situation, O'Connor and Connolly (15) observed that the sorption coefficient of organic compounds to sediments containing D O M decreased as the total amount of sediment used was increased. 2 +

c

Mechanisms of Complexation. A number of mechanisms contrib ute to the bonding of organic compounds with H S . Such mechanisms include ion exchange and protonation, hydrogen bonding, van der Waals forces, coordination bonding through attached metal ion (ligand exchange), and hydrophobic bonding. Association of organic molecules to H S by ion exchange and protonation is largely restricted to compounds that either exist in cationic form or become


32.

Adsorption of Micropollutants

PiRBAZARi E T AL.

on Activated Carbon

555

positively charged through protonation (16). In the case of certain anionic organic substances, there is a possibility of anion exchange with positively charged areas on the humic molecules. F o r example, less basic organic substances such as s-triazines may become cationic through protonation and bind with H S molecules. The mechanism, as explained by Weber and co workers (17), depends on the acidic or basic strength of the compound (indicated by its p K value) and on the proton-supplying power of the H S . Anionic organic substances such as phenoxyalkanoic acids (PAA) may repulse the predominantly negatively charged humic molecules. Hydrogen bonding is an important mechanism for polar organic com pounds such as phenyl carbamates and substituted ureas (16), but it is limited to acid conditions where - C O O H groups are un-ionized. In the case of PAA such as 2,4-dichlorophenoxyacetic acid (2,4-D), van der Waals forces may contribute significantly to association with H S . Hydrophobic bonding may be important in the case of highly nonpolar compounds with low aqueous solubilities. The degree of binding depends primarily on the compound's affinity for H S and its hydrophobic nature. Weber and Weed (18) observed that humic molecules, by virtue of their aromatic structural framework and nonpolar functional groups, may contain both hydrophilic and hydrophobic parts. Highly nonpolar organic com pounds can be squeezed out of aqueous solutions because of their waterrepellent characteristics, and they can be adsorbed easily onto the hydro phobic sites of humic molecules (19).


a

Mathematical Modeling Adsorption Modeling for Micropollutants. There are several ap proaches for modeling adsorption data of organic compounds in the presence of D H S . In the first approach the adsorption data are modeled in terms of the target organic compounds alone. Compounds such as dissolved humic substances are treated not as components, but as system-specific background materials. The equilibrium parameters of the model for the specific target compounds are experimentally determined in the presence of the back ground materials (20, 21). A number of researchers have adopted a different theoretical approach that hinges on the mathematical treatment of all background organic sub stances as a single component. This background is represented by a lumped parameter such as total organic carbon (TOC) or D O C (2, 22, 23). Lumpedparameter characterization of background materials (and subsequent appli cation of multicomponent models for prediction of adsorption equilibria) is particularly advantageous from the viewpoint of water and wastewater ap plications because identification and quantification of all aquatic species pres ent can be a formidable task.



556


The third approach, which is a refinement of the second, includes the lumped-parameter characterization of the background substances. These substances are broken up into a number of hypothetical pseudospecies, whose individual adsorption equilibrium parameters are determined from lumped-parameter data, suitable mathematical curve-fitting techniques on ideal adsorbed solution theory (IAST) (22), or simplified competitive ad sorption model (SCAM) (24). These hypothesized parameters of pseudospecies can be used in the IAST or S C A M models for the approximate prediction of adsorption equilibria of specific compounds in the presence of background substances. Fettig and Sontheimer (25) employed this technique for predicting D F A adsorption isotherms. It can potentially be used for certain compounds in the presence of different types of D H S . A further extension of this idea has generated a new method in which several pseudocomponents are postulated for the unknown background sub stance. The isotherm parameters of these components are determined by using a weakly adsorbable tracer compound and observing the displacement of the multisolute isotherm from the single-solute isotherm (26, 27). A n offshoot of this procedure employs the concept of species grouping. Its re duced number of pseudospecies in the multicomponent system, character ized by average value of parameters, results in a considerable simplification of multicomponent equilibrium computations (28).

Equilibrium Modeling for the Adsorption of Micropollutants. The general approach we employed for the prediction of adsorption equilibria of various organic compounds in the presence of D H S is a straightforward application of the IAST model. Crittenden and coworkers (26, 27) used this theory, developed by Radke and Prausnitz (29), to predict the multicom ponent competitive interactions between several volatile organic compounds (VOC) from their single-solute isotherm parameters. The model assumes that the adsorbed phase forms an ideal solution and that there is no area change of the various components upon mixing at the spreading pressure of the mixture. The IAST model is based on the concept of a Gibbs dividing surface and an inert adsorbent. A two-dimensional planar surface is postu lated at the interface between the adsorbent phase and liquid phase. The adsorption of the solute onto the surface is considered analogous to the accumulation of excess concentration at the dividing surface. The thermo dynamic framework for the concept, including the application of the Gibbs-Duhem equation and the excess internal energies and entropies, is discussed in the next section.

Thermodynamic Aspects of IAST Model.

The thermodynamic

framework for the development of the IAST model is based on Gibbs free energy considerations for the interfacial surface, referred to as the Gibbs dividing surface, between a solid adsorbent phase and a liquid solution phase.


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Adsorption

of Micropollutants

on Activated

Carbon

557

The free energy change of the dividing surface, and its relationship with the molar composition of the components and the surface tension of the solution, are explained in detail by Atkins (30). The excess surface free energy, G , at equilibrium is given by s

Ν

G

= cry + ]Γ μ , η ^

s

(1)


J=I

where σ is the area of the dividing surface; y is the surface tension of the liquid; μ^ is the chemical potential of the component j; n is the number of moles of components j in the surface; and Ν is the number of components in solution. The relationship between the change in surface free energy correspond ing to change in surface tension is established by the Gibbs-Duhem equation js

Ν

Ν

dG = σ dy + y da + ^ n s

+ ^

ls

j=i

dn

js

(2)

j=i

The change in the Gibbs free energy of the surface at constant Γ, Ρ, σ, and rtj is as follows: Ν

dG = s

-S

s

dT + σ dy + 2 μ, dn

jtS

(3)

where Τ, P, and S represent the temperature, pressure, and entropy of the dividing surface, respectively. Comparison of equations 2 and 3 under iso thermal conditions (dT = 0), yields the result s

Ν

σ dy + 2 n dpj = 0

(4)

c

> ο

ΟΙ

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PiRBAZARi E T AL.

Adsorption of Micropollutants on Activated Carbon

5

7

7


References 1. Endicott, D. D.; Weber, W. J., Jr. Environ. Prog. 1985, 4(2), 105-111. 2. Smith, Ε. H.; Tseng, S. K.; Weber, W. J., Jr. Envir. Prog. 1987, 6(2), 18-25. 3. Crittenden, J. C.; Weber, W. J., Jr. J. Environ. Eng. Div. Am. Soc. Civ. Eng. 1978, 104(EE2), 185-197. 4. Crittenden, J. C.; Weber, W. J., Jr. J. Environ. Eng. Div. Am. Soc. Civ. Eng. 1978, 104(EE3), 433-443. 5. Carter, C. W.; Suffet, I. H. In Fate of Chemicals in the Environment; ACS Symposium Series 225; American Chemical Society: Washington, DC, 1983; pp 215-219. 6. Thurman, Ε. M . Organic Geochemistry of Natural Waters; Martin Nijhoff/Dr W. Junk: Dordrecht, Netherlands, 1985. 7. Thurman, Ε. M.; Malcolm, R. L. Environ. Sci. Technol. 1981, 15(4), 463-466. 8. Thurman, E. M.; Wershaw, R. L.; Malcolm, R. L.; Pickney, D. J. Org. Geochem. 1982 4, 27-35. 9. Carter, C. W.; Suffet, I. H. Environ. Sci. Technol. 1982, 16(11), 735-740. 10. Water Related Environmental Fate of 129 Priority Pollutants; U.S. Environ mental Protection Agency. Office of Wastewater Management. U.S. Government Printing Office: Washington, DC, 1979; ΕPA-440/479-0290. 11. Landrum, P. F.; Nihart, S. R.; Eadle, B. J.; Gardner, W. S. Environ. Sci. Technol. 1984, 18(3), 187-192. 12. Lee, M. C.; Snoeyink, V. L.; Crittenden, J. C. J. Am. Water Works Assoc. 1981 73(8), 440-446. 13. Ghosh, K.; Schnitzer, M. Soil Sci. 1980 129(5), 266-276. 14. Schnitzer, M.; Khan, S. V. Humic Substances in the Environment; Marcel Dek ker: New York, 1972. 15. O'Connor, D. J.; Connolly, J. P. Water Res. 1980 14(12), 1517-1523. 16. Stevenson, F. J. Humus Chemistry: Genesis, Composition, Reactions; Wiley: New York 1982. 17. Weber, J. B.; Weed, S. B.; Ward, T. M. Weed Sci. 1969, 17(4), 417-421. 18. Weber, J. B.; Weed, S. B. In Pesticides in Soil and Water; Guenzi, W. D., Ed.; American Society of Agronomy: Madison, WI, 1974; pp 223-256. 19. Physicochemical Processes for Water Quality Control; Weber, W. J., Jr., Ed.; John Wiley: New York, 1972; pp 199-259. 20. Pirbazari, M., Weber, W. J., Jr. J. Environ. Eng. 1984, 110(3), 656-669. 21. Smith, Ε. H.; Weber, W. J., Jr. Proceedings of 1985 Annual Conference; Amer ican Water Works Association: Washington, DC, 1985; pp 553-574. 22. Frick, B.,; Sontheimer, H. In Treatment of Water by Granular Activated Car bon; McGuire, M. J.; Suffet, I. H., Eds.; Advances in Chemistry 202; American Chemical Society: Washington, DC, 1983; pp 247-268. 23. Summers, R. S.; Roberts, P. V. In Treatment of Water by Granular Activated Carbon; McGuire, M. J.; Suffet, I. H., Eds.; Advances in Chemistry 202; Amer ican Chemical Society: Washington, DC, 1983; pp 503-524. 24. DiGiano, F. B.; Baldauf, G.; Frick, B.; Sontheimer, H. Chem. Eng. Sci. 1978, 33(12), 1667-1673. 25. Fettig,J.;Sontheimer, H. J. Environ. Eng. 1987, 113(4), 795-810. 26. Crittenden, J. C.; Luft, P.; Hand, D. W.; Oravitz, J. L.; Loper, S. W.; Arl, M. Environ. Sci. Technol. 1985 19(11), 1037-1043. 27. Crittenden, J. C.; Luft, P.; Hand, D. W. Water Res. 1985, 19(12), 1537-1548. 28. Calligaris, M. B.; Tien, C. Can. J. Chem. Eng. 1982, 60, 772-780. 29. Radke, C. J.; Prausnitz, J. M. AIChE J. 1972, 18, 761-768. 30. Atkins, P. W. Physical Chemistry; Oxford University Press: London, 1982.



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31. Wong, S. P.; Pirbazari, M . Proceedings of the 1987 Specialty Conference on Environmental Engineering, Orlando, FL; Dietz, J. D., Ed.; American Society of Civil Engineers: New York, 1987; pp 567-572. 32. Hutzinger, S.; Safe, S.; Zitko, V. The Chemistry of PCBs; Chemical Rubber Company: Akron, O H , 1974. 33. Alford-Stevens, A. L . ; Bellar, T. Α.; Eichelberger, J. W.; Budde, W. L. Anal. Chem. 1986, 58(9), 2014-2022. 34. Malcolm, R. L . ; McCarthy, P. Environ. Sci. Technol. 1986, 20(9), 904-911. 35. Pirbazari, M . ; Weber, W. J., Jr. In Chemistry in Water Reuse; Cooper, W. J., Ed.; Ann Arbor Science: Ann Arbor, 1981; pp 309-339. 36. Rosene, M . R.; Deithorne, R. T.; Lutchko, J. R.; Wagner, N . J. In Activated Carbon Adsorption of Organics from the Aqueous Phase; Suffet, I. H . ; McGuire, M . J., Eds.; Ann Arbor Science: Ann Arbor, 1980; Vol. 1, pp 309-316. 37. Bilello, L. J.; Beaudet, B. A. In Treatment of Water by Granular Activated Carbon; McGuire, M . J.; Suffet, I. H . , Eds.; Advances in Chemistry 202; Amer ican Chemical Society: Washington, D C , 1983; pp 213-246. 38. Lalezary, S.; Pirbazari, M.; McGuire, M . J., Krasner, S. W. J. Am. Waterworks Assoc. 1984 76(3), 83-87. 39. Environmental Engineering Program, University of Southern California—Los Angeles. Adsorption of Several Toxic and Carcinogenic Compounds from Drink ing Water; submitted to the Drinking Water Division, U.S. Environmental Protection Agency: Cincinnati, O H , 1987. 40. Stevens, M . R. Ph.D. Dissertation, University of Southern California—Los Angeles, 1987. 41. Weber, W. J., Jr.; Pirbazari, M.; Long, J. B.; Barton, D. A. In Activated Carbon Adsorption of Organics from the Aqueous Phase; Suffet, I. H . ; McGuire, M . J., Eds.; Ann Arbor Science: Ann Arbor, 1980; Vol. 1, pp 317-336. 42. Randkte, S. J.; Thiel, C. E . ; Liao, M . Y.; Yamaya, C. N . J. Am. Water Works Assoc. 1982 74(4), 192-202. 43. Pirbazari, M . Ph.D. Dissertation, University of Michigan, 1980. 44. Zimmer, G.; Sontheimer, H . Abstracts of Papers, 193rd National Meeting of the American Chemical Society, Denver, CO; American Chemical Society: Washington, D C , 1987; ENVR 119. RECEIVED

for review September 17, 1987.

ACCEPTED

for publication February 29,

1988.


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