TREATMENT OF WASTEWATER FOR THE REMOVAL OF DYESTUFFS USING BIOMASS-DERIVED ADSORBENTS

Author: Okpe Emmanuel Chinonye
Department: Chemical Engineering
Affiliation: Nnamdi Azikiwe University Awka

The efficiency of activated carbons derived from PKS and KNS cost effective adsorbents for the removal of colour from industrial waste water effluents was studied. The chemical method of activation using zinc chloride (ZnCl2) was used to prepare the carbons obtained from Palm Kernel Shell (PKS) and Kola nut Shell (KNS) respectively. The dyes studied were Phenol Red and Orange G. The impregnated samples of carbons were left in an oven at 1100C for 24 hours. The dried samples were carbonized in muffle furnace for 1 hour at 5000C. Some physical properties of the carbons such as surface area, pH, moisture content, ash content, bulk density were determined. Both the activated and non-activated carbons were characterized using the Fourier Transform Infrared (FTIR) spectroscopy to determine the functional groups, and Scanning Electron Microscopy (SEM) to examine the surface morphology of the carbon. Preliminary adsorption studies were carried out to determine the significance of the parameters. The parameters shown to be more significant were adsorbent dosage, initial ion concentration and pH. Batch adsorption studies were carried out by studying the effects of pH, temperature, initial ion concentration, dosage and time on the adsorption process. The results of the adsorption studies showed that activated carbon produced from Kola nut Shell was a better adsorbent than that produced from Palm Kernel Shell. Langmuir, Freundlich, Temkin and Dubinin-Radushkekevich isotherms were used to describe the adsorption mechanism. The experimental data was found to fit very well to the Freundlich model. Kinetic models such as First-order, Pseudo first-order, Pseudo second-order, Elovich, Intra particle diffusion, Bhattacharya-Venkobachor and Power function models used to fit the experimental data. The results showed that the Pseudo second-order model best described the kinetics of the adsorption process. The calculated value of the amount adsorbed at equilibrium (qe) from the Pseudo second-order kinetic model was found to be in good agreement with the experimental value. Statistical analysis also confirmed these results. The Gibbs free energy change (ΔG) and the entropy change (ΔS) were negative. These indicate that the adsorption process was feasible and spontaneous. The enthalpy change (ΔH) of the adsorption process was negative showing that the process was exothermic. The adsorption process was optimized using the Central Composite Design (CCD) for three factors and the optimization results were analyzed using Design Expert 8.1.0 trial version. The optimum conditions for the adsorption of the dyes were 300C, 60 minutes, 0.30g of adsorbent, initial ion concentration of 100mg/l and pH 6.0 for Orange G adsorption and 300C, 60 minutes, 0.30g of adsorbent, initial ion concentration of 300 mg/l and pH 10 for Phenol Red adsorption which resulted in 93.93% and 89.95% removal for Orange G and Phenol Red respectively. Design considerations and equipment selection were also done.

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