USE OF ECO-FRIENDLY MODIFIED LIGNOCELLULOSIC MATERIAL FOR DETOXIFICATION OF METAL CONTAMINATED WATERS

Abstract

Biosorption is an upcoming technique that refers the use of non-conventional lignocellulosic materials for the detoxification of metal contaminated waters. Various byproducts resulted from agricultural practices have been investigated for this purpose. The present study explores the use of dead biomass generated from Sorghum biocolor L. termed as “Sorghum biomass” in its native as well as in modified form for the remediation of metal contaminated waters. The modification of Sorghum biomass was successfully carried out using commercial urea and thiourea as modifying agents under microwave irradiation. Divalent lead, cadmium and copper and trivalent chromium were chosen for the biosorption studies due to their hindrance to biological degradation and toxicity to life and environment. Sorghum biomass in its native state (SB) and modified states [urea modified (USB) and thiourea modified (TSB)] was characterized chemically and physically. The physical characteristics were performed using various analytical techniques like CHNS, FTIR, SEM, BET surface area and Bulk density. The chemical characteristics were explored using Bohem’s titration procedure and points of zero charge (pHpzc The use of SB, USB and TSB for selected metal ions detoxification was explored in batch mode. The effect of various process parameters like biosorbent dosage, contact ) determination. There was a strong evidence of the presence of functional groups like hydroxyl, carboxyl, amino, amido etc. that were responsible for metal ions binding to biosorbents surface. The increment in surface functionality was observed in USB and TSB. Chemical characteristics confirmed the surface alteration in terms of functional groups as a result of modification of SB by urea and thiourea. time, pH of medium, temperature and initial metal ions concentration was studied and optimized. The optimum removal of metal ions by SB, USB and TSB was found at slightly acidic pH. The data obtained was analyzed using renowned equilibrium models in order to provide insight in to mechanism of the process. The Langmuir model showed a better fit to equilibrium data as compared to other models. The maximum biosorption capacities of SB, USB and TSB for the studied metal ions binding were calculated using Langmuir equation. The values obtained in case of TSB were highest showing the efficacy of it relative to SB and USB. USB also showed significantly higher biosorption capacity values than SB. Kinetic modeling of the equilibrium data showed that the studied biosorption process was governed by pseudo-second order mechanism and boundary layer diffusion was the rate determining step. Thermodynamic studies were also performed which showed that biosorption of studied metal ions by SB, USB and TSB was endothermic and spontaneous. Desorption studies of metal loaded SB, USB and TSB were also carried out in acidic as well as basic medium. Acidic medium was found as the best desorbing medium for metal ions / biomass recovery. The results of our experimental studies indicated that a batch process can be used in an economic and eco-friendly way for metal ions detoxification on industrial scale. Modification was carried out without any solvent making the process more feasible. Both Sorghum biomass and modifying agents, urea and thiourea, are easily available. Hence urea and thiourea modified Sorghum biomass appears to be a good choice for detoxification of metal ions from industrial effluents.