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In the present study, adsorption of three metal ions Pb(II), Hg(II) and Cd(II) on carbon aerogel a new form of activated carbon has been investigated in mono- and multi-component (binary and tertiary) system. Batch experiments were also carried out for mono- and multi-component systems with varying metal ion concentration (mg/l) to investigate the competitive adsorption characteristics. Many adsorbents have been studied for their adsorption properties pertaining to mono-component solutions of metal ions. However, to treat wastewater with new materials, their performance needs to be ascertained in multi-component system. The scanning electron micrographs (SEM) and EDAX spectrum of carbon aerogel surfaces before and after the adsorbent was equilibrated with the metal ion solution clearly establishes the presence of the metal ions and some surface modifications can be observed on the carbon aerogel particles adsorption with (i) surface chemistry of the pellets on the surface of carbon aerogel and (ii) inside layers of the carbon aerogel. Applicability of the isotherm models namely Freundlich and Langmuir to predict the equilibrium uptake of Pb(II), Hg(II) and Cd(II) in mono-component, binary and tertiary system has also been tested. Langmuir and Freundlich models are found to generally represent the experimental though but not consistently.

The removal of Cd(II), Pb(II), Hg(II), Cu(II), Ni(II), Mn(II) and Zn(II) by carbon aerogel has been found to be concentration, pH, contact time, adsorbent dose and temperature dependent. The adsorption parameters were determined using both Langmuir and Freundlich isotherm models. Surface complexation and ion exchange are the major removal mechanisms involved. The adsorption isotherm studies clearly indicated that the adsorptive behaviour of metal ions on carbon aerogel satisfies not only the Langmuir assumptions but also the Freundlich assumptions, i.e. multilayer formation on the surface of the adsorbent with an exponential distribution of site energy. The applicability of the Lagergren kinetic model has also been investigated. Thermodynamic constant (K(ad)), standard free energy (DeltaG(0)), enthalpy (DeltaH(0)) and entropy (DeltaS(0)) were calculated for predicting the nature of adsorption. The results indicate the potential application of this method for effluent treatment in industries and also provide strong evidence to support the adsorption mechanism proposed.

Wastewaters discharged from the defence serviceable industries pose a serious environmental hazard due to their heavy metal load. The present study focused on optimizing the operational variables viz, hydraulic loading rate, bed height and feed concentration through bench scale study and using that for assessing the efficiency of pilot scale system with sulphur loaded carbon (AC-S) as the adsorbent in the removal of Pb (II). Static mode adsorption studies were also carried out for Pb (II) removal using treated (AC-S) and untreated carbon (AC). AC-S shows about 35 percent increase in maximum adsorption capacity over that on AC. The maximum adsorption capacity in the column mode for Pb (II) at the optimized conditions: bed height of 0.4 m, hydraulic loading rate of 7.5 m3h(-1)m(-2) and the feed concentration of 6 mg l(-1) for achieving 50% breakthrough concentration was found to be 2.89 mg g(-1). Adsorption mechanism involved during Pb (1) in the column has also been explored. Bohart-Adams model was used for modeling the bench scale data and predicting the adsorption behavior at pilot scale level.

The adsorption characteristics of nitro-organics such as trinitro-toluene (TNT), dinitro-toluene (DNT) and nitrobenzene (NB) on granular activated carbon (GAC) were studied to understand their dynamic adsorption behaviour for dilute aqueous solutions. A model was developed to predict the dynamics of the adsorption process and the effect of various design and operating parameters on adsorption characteristics. The model predictions would provide inputs to design of bench scale and pilot plant scale experiments. Section 2 of the paper describes the assumptions, predictions, development of the model and its validation with experimental data generated during bench scale and pilot plant trials. Section 3 presents the breakthrough characteristics obtained by conducting experimental runs for GAC of different surface areas from 650 to 1500 m(2)/g, hydraulic loading rates (HLR) ranging between 12 and 24 m(3)/h/m(2), feed concentrations from 50 to 130 mg/l and bed heights between 300 and 1000 mm for TNT, DNT and NB solutions. The effect of these independent parameters on the breakthrough time, adsorption capacity and the minimum concentration achieved in the effluent was studied and the results obtained are presented in this paper. These indicate that the adsorption capacity goes though a maximum when studied as a function of HLR and feed concentration. The adsorption capacity per unit surface area also shows a maximum around 1000 m(2)/g. The minimum bed height required for meeting environmental effluent discharge limit of 1 ppm was experimentally found to be about 800 mm. These results compare well with the predictions based on the model developed for column adsorption process. Data from these experimental runs and the model predictions have been used to optimise various parameters for the design of a pilot plant unit with 200 l per hour capacity.