Bioadsorption using compost: An alternative for removal of chromium (VI) from aqueous solutions

Abstract

The removal of Cr(VI) from aqueous solutions was studied using a compost generated from carnation flowers waste. The highest percentage of removal achieved (ca. 99 %) was obtained at pH 2.0, using a 10 mg L-1 of Cr(VI) solution, a dose of 10 g L-1 of compost, and with an equilibrium time of 3 hours. Under these conditions, the kinetics and adsorption isotherm were examined varying the initial Cr(VI) concentration from 15 to 200 mg L-1. The maximum sorption capacity at equilibrium (Qm), from the Langmuir model, was found to be 6.25 mg g-1. The evaluation of Cr(VI) removal at pH 2.0 showed a second order kinetics and showed that the process mechanism can be modeled by the "adsorption-coupled reduction" hypothesis. Also, the monitoring of Cr(VI) and total Cr in aqueous solutions showed that Cr(VI) and total Cr were removed from solution, and that part of the Cr(III) was retained on the compost. According to the results, the removal of Cr(VI) with the assayed compost can be explained by the following steps: (i) adsorption of Cr(VI) species onto compost, (ii) Cr(VI) reduction to Cr(III), and (iii) adsorption of part of Cr(III) on the compost. Thus, this study suggests that the carnation flower waste compost can be used as a remediation system for water contaminated with Cr(VI).