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Naturally occuring matter (NOM), a heterogeneous mixture of complex organic compounds, is invariably present in all surface and ground waters. These materials act as substrate for the growth of bacteria in the distribution system. The disinfection of such water by chlorination produces disinfection by products consisting of several halogenated compounds which are toxic and carcinogenic. As gallic acid is the building block of most NOM, its adsorptive removal from water has been studied using activated carbon columns. The operating variables studied are the hydraulic loading rate (HLR), bed depth (Z), and the feed concentration (C o ). The breakthrough curves are S-shaped and the breakthrough time increases with increasing Z and decreases with increasing HLR and C o . The adsorption increases with increasing HLR and is maximum around HLR ¼ 8 m 3 /hr/m 2 . The column design parameters such as the critical bed depth and the depth of the mass transfer zone (MTZ) as calculated using the bed depth service time (BDST) approach are found to agree fairly closely with the experimental values. MTZ is smaller for the carbon cloth indicating its better adsorption characteristics. The adsorption column parameters such as the treated volume and the mass of the carbon required for a desired effluent concentration have been determined from the column data.

The adsorption isotherms of pyridine have been determined gravimetrically on different samples of granulated, fibrous and spherical activated carbons. Several chemical treatments such as oxidation, degassing and impregnation have been carried out on as-received activated carbon cloth (ACC) so as to modify the surface characteristics of the activated carbon. The porous and chemical structure of modified and unmodified activated carbons has been characterised by XRD, TGA-DTG, SEM and pore size distribution techniques. The adsorption increases on oxidation while decreases on degassing which can be correlated to increase and decrease in the concentration of surface oxygen groups. Loading with Ag ? and Cu 2? increases the adsorption of pyridine compared with the unloaded sample while loading with Cr 6? decreases the adsorption of these vapors. The adsorption-desorption branches of pyridine vapors on metal impregnated do not meet even at zero relative vapor pressure indicating the chemisorption or other specific interactions. The adsorption kinetics data has been examined using the linear driving force and empirical diffusion models. The initial decrease in isosteric enthalpy of adsorption for modified and unmodified ACC indicates the effect of surface heterogeneity and later increase indicates the influence of lateral interactions between adsorbate molecules. The results suggest that the adsorption of pyridine involves the physisorption as well as specific interactions with carbon oxygen functional groups and metal complexes present on the carbon surface.

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