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In our previous study [A.K. Sahu, V.C. Srivastava, I.D. Mall, D.H. Latye, Sep. Sci. Technol. 43 (5) (2008) 1239], commercial grade activated carbon (ACC) was used for adsorptive removal of furfural from aqueous solution using batch studies. In the present study, continuous fixed-bed adsorption was carried out in ACC packed bed for the removal of furfural from aqueous solution. The effects of important factors namely bed height (Z = 15–60 cm), influent concentration of furfural (Co = 50–200 mg/l), the flow rate (Q = 0.02–0.04 l/min) and column diameter (D = 2–4 cm) were studied. Capacity of the bed to adsorb furfural was found to increase with an increase in the value of Z, Co and D; and with decrease in the value of Q. Adams–Bohart, Bed-Depth Service-Time, Thomas, Yoon–Nelson, Clark and Wolborska models were applied to the experimental data for the prediction of the breakthrough point, and to determine the characteristic parameters of the column. Error analysis showed that the Yoon–Nelson model best described the experimental breakthrough curve, while Wolborska model showed good prediction of breakthrough curve for the relative concentration region up to 0.5.

This paper presents the physico-chemical characteristics of low-cost fertilizer plant waste carbon (WC) for the adsorption of different dyes. The particle size analysis showed an average particle size of 167.35 μm. Proximate and CHN analysis showed the presence of high amount of carbon in WC. Bulk density and heating value of WC were found to be 308.03 kg/m 3 and 22.3 MJ/kg, respectively. The pore size distribution results showed that the WC was predominantly mesoporous. The BET surface area was 357 m 2 /g. The average pore diameter by BET was 6.483 nm. The mesoporous surface area for adsorption was 96% of the total pore surface area. The polar groups present on the WC surface imparted considerable cation exchange capacity to it. WC was further used as an adsorbent for the removal of Auramine-O (AR), Congo red (CR), Orange-G (OG) and methyl violet (MV) dyes from aqueous solutions. Optimum initial pH (pH 0 ) was found to be 7.0. WC dose of 1 g/l was found to be optimum for the adsorption of all dyes at a concentration of 20 mg/l. The adsorption of dyes on WC was found to be gradual process and quasi-equilibrium reached in 5 h. The adsorption kinetics followed pseudo-second-order kinetics. The effective diffusion coefficient was of the order of 10 −12 m 2 /s. Error analysis showed that Redlich-Peterson (R-P) isotherm best represented the equilibrium adsorption data for all the dyes. Thermodynamics showed that the adsorption of CR on WC was most favourable in comparison to other dyes. The desorption study showed that the recovery of dyes and the regeneration of the WC using different solvents viz. water, acids and alkalies were not feasible. Spent WC can, however, be used as a fuel to recover its high energy content and the bottom ash obtained after its combustion/incineration can be blended with clay/cement–concrete mixture to make bricks and building blocks for its safe disposal. WC has been found to have high potential as an adsorbent for the removal of AR, CR, OG and MV dyes from aqueous solutions.

Present study deals with the adsorption of phenol on carbon rich bagasse fly ash (BFA) and activated carbon-commercial grade (ACC) and laboratory grade (ACL). BFA is a solid waste obtained from the particulate collection equipment attached to the flue gas line of the bagasse-fired boilers of cane sugar mills. Batch studies were performed to evaluate the influences of various experimental parameters like initial pH (pH0), contact time, adsorbent dose and initial concentration (C0) on the removal of phenol. C0 varied from 75 to 300 mg/l for the adsorption isotherm studies and the effect of temperature on adsorption. Optimum conditions for phenol removal were found to be pH0 ≈ 6.5, adsorbent dose ≈10 g/l of solution and equilibrium time ≈5 h. Adsorption of phenol followed pseudo-second order kinetics with the initial sorption rate for adsorption on ACL being the highest followed by those on BFA and ACC. The effective diffusion coefficient of phenol is of the order of 10−10 m2/s. Equilibrium isotherms for the adsorption of phenol on BFA, ACC and ACL were analysed by Freundlich, Langmuir, Temkin, Redlich–Peterson, Radke–Prausnitz and Toth isotherm models using non-linear regression technique. Redlich–Peterson isotherm was found to best represent the data for phenol adsorption on all the adsorbents. The change in entropy (ΔS°) and heat of adsorption (ΔH°) for phenol adsorption on BFA were estimated as 1.8 MJ/kg K and 0.5 MJ/kg, respectively. The high negative value of change in Gibbs free energy (ΔG°) indicates the feasible and spontaneous adsorption of phenol on BFA. The values of isosteric heat of adsorption varied with the surface loading of phenol.

Adsorption of malachite green (MG) was studied using three adsorbents namely, bagasse fly ash (BFA), a sugar industry waste, and activated carbons commercial grade (ACC) and laboratory grade (ACL). Batch adsorption studies were conducted to evaluate the effect of various parameters such as pH, adsorbent dose, contact time and initial MG concentration on the removal of MG. The initial pH of the dye solution strongly affected the chemistry of both the dye molecules and adsorbents in an aqueous solution. The effective pH was 7.0 for adsorption of MG by the three adsorbents. Equilibrium reached in about 4 h contact time. Optimum BFA, ACC and ACL dosages were found to be 1, 20 and 4 g l−1, respectively. The adsorption followed pseudo-second-order kinetics. Equilibrium adsorption data on BFA, ACC and ACL were analyzed by Freundlich, Langmuir, Dubnin–Radushkevich, Redlich–Peterson and Temkin isotherm equations using regression analysis. Non-linear error analysis showed that the Freundlich isotherm best-fits the equilibrium data for adsorptive removal of MG by BFA and ACC and Redlich–Peterson best follows the equilibrium data for ACL. Thermodynamic study showed that MG adsorption on BFA was comparable to that obtained with ACC or ACL.

The present study deals with the use of poly aluminium chloride (PAC) as a coagulant and bagasse fly ash (BFA), which is generated in sugar mills, as an adsorbent for the removal of chemical oxygen demand (COD) and colour of pulp and paper mill effluents. Under optimal conditions of pH 3 and initial PAC dosage of 3 g/l, about 80% COD removal and 90% colour removal were obtained. The optimal conditions for the adsorptive removal of COD and colour with BFA were pH 4 and BFA dosage of 2 g/l. Under these conditions, COD and colour removal were, respectively, 50 and 55%. Adsorptive removal of COD by BFA followed second-order kinetics. Intra-particle diffusion was found to be rate controlling. Freundlich and Langmuir adsorption isotherms were found to fit the equilibrium adsorption data with BFA. Two-stage treatment using PAC (3 g/l) as a coagulant in the first stage and BFA (2 g/l) as an adsorbent in the second stage gave the combined COD and colour removal of nearly 87 and 95%, respectively, for different effluents without any pH adjustment. Two-stage adsorptive treatment using BFA (2 g/l) in both the stages gave a combined COD and colour removal of about 70%. The sludge obtained can be dewatered by centri-clarifiers, dried, briquetted and incinerated to recover its energy content.