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Title:Effects of Activated Carbon on Reactions of Free and Combined Chlorine With Phenols (Chlorination, Gac)
Author(s):Voudrias, Evangelos Alexandros
Department / Program:Civil Engineering
Discipline:Sanitary Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Sanitary and Municipal
Abstract:The use of prechlorination in drinking water treatment results in contact of free or combined chlorine with activated carbon, which is used to remove organic compounds from water. Free chlorine reacts with a group of phenols (phenol, guaiacol, catechol, 2,6-dimethoxyphenol, p-chlorophenol) in dilute aqueous solutions (10('-5)M), to produce mono-, di-, or trichloroderivatives. When free chlorine reacts with phenols adsorbed on granular activated carbon (GAC), however, many additional products are formed. GAC promotes reactions, such as hydroxylation, oxidation to quinones, chlorine substitution, carboxylation, and dimer formation.
Phenols react slowly with monochloramine in solution, giving low yields of chlorinated phenols. When monochloramine reacts with phenols adsorbed on GAC, however, principally hydroxy- and chlorohydroxybiphenyls are formed.
The formation of chlorohydroxybiphenyls (hydroxylated PCBs) (in vivo metabolites of PCBs) is particularly important, because of their potential toxicity. Such compounds are the main reaction products from chlorophenols, but they are also formed in smaller amounts from nonchlorinated phenols.
Furthermore, GAC becomes very reactive when it is preoxidized with free chlorine. Hydroxy- and chlorohydroxybiphenyls, respectively, are formed from phenol and 2,4-dichlorophenol adsorbed on preoxidized F-400 GAC, in the absence of chlorine.
The experimental data show that surface free radicals are produced from the oxidation of GAC with chlorine. Treatment with a free radical quencher, BHT, inhibits the promoting role of GAC. Some of the free radicals on the GAC surface are associated with oxygen-containing functional groups. Outgassing of GAC at high temperatures results in reduction of surface oxygen and free radical concentration, and ability of carbon to promote the surface reactions.
p-Benzoquinone and other products of the HOCl-phenol-GAC reaction can be displaced from the activated carbon column, by using an influent containing a strongly adsorbed compound (2,4-dichlorophenol). Computer simulations with the homogeneous surface diffusion model also show that there is a potential for desorption for some of these products.
Issue Date:1985
Description:253 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1985.
Other Identifier(s):(UMI)AAI8511687
Date Available in IDEALS:2015-05-13
Date Deposited:1985

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