Equilibrium modeling of cadmium biosorption from aqueous solution by compost.

One of the most serious environmental issues of the present century is metal contamination of the aqueous environment due to the release of metal-containing effluents into the water bodies. Cadmium (Cd) is one of the toxic heavy metals which is not biodegradable thereby causing high risks to animals, plants, and humans. In the present study, potential and feasibility of compost derived from fruits and vegetables for Cd biosorption from aqueous solution were investigated. The batch biosorption experiments were performed to evaluate the effects of Cd concentrations (5, 15, 30, and 60 mg/L), compost biomass (0.5, 1.0, and 1.5 g/100 mL), pH (4, 6, and 8), contact time (1, 4, and 19 h), and temperature (28 and 35 °C) on Cd sorption and removal by compost. The biosorption of Cd was found to be highly dependent on initial Cd concentration, sorbent biomass, pH, contact time, and temperature of aqueous solution. It was observed that Cd sorption by compost was rapid up to 4 h, and then it became slow and stable as the contact time shifted towards equilibrium state (19 h). At equilibrium, the Cd sorption (q = 0.33-5.43 mg/g compost) and removal (45-99%) were observed at pH 6 and temperature 28 °C depending upon Cd concentrations and sorbent biomass in aqueous solution. The equilibrium experimental data were fitted well with Langmuir adsorption isotherm model (q  = 6.35-7.14 mg/g compost, R  = 0.77-0.98). FTIR spectrum of the compost indicated the presence of hydroxyl and carboxyl groups, which might be involved in the biosorption of Cd through ion exchange and complexation mechanisms. The optimal environmental conditions (pH 6, sorbent biomass 0.5 g/100 mL, and temperature 28 °C) induced more Cd sorption on compost at equilibrium. Results show compost as a cost-effective adsorbent material having high potential for heavy metal remediation from aqueous solution.