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The aim of the present study was to examine the performance of residue from extracted onion processing waste for the ability to remove Cr (VI) ions from aqueous solutions. The characterization of applied biosorbent was conducted by FT-IR analysis. Batch experiments were carried out and the effects of different adsorption process parameters were determined. Maximum removal efficiency of 98.29 ± 0.17 % was obtained at pH = 1.0, adsorbent dose 0.5 g·L-1, initial Cr (VI) concentration 50 mg·L-1, temperature 25.0 ± 0.5 oC, agitation speed 200 rpm and contact time of 30 min. The pseudo-second order model and Langmuir model provided the best fit to experimental kinetics and equilibrium isotherm data, respectively. Based on the values determined for the maximum adsorption capacity (qmax = 47.17 mg·g-1) the extracted onion processing waste could be applied as a low cost biosorbent for removal of Cr (VI) ions from polluted water.

The purpose of this paper is to tested carotenoid extracted tomato residue as a cheap biosorbent for its ability to remove Cu (II) ions from aqueous solution. Batch experiments were carried out to evaluate the effects of pH, agitation speed, biosorbent dosage, initial metal concentration and contact time. The maximum removal efficiency of 89.7 ± 0.14 % was reached at pH 6.0 by using of adsorbent dosage 4 g·L-1, initial metal concentration 40 mg·L-1, temperature 25 °C, agitation speed 200 rpm and contact time 60 min. Pseudo-first order and pseudo-second order models were applied to describe the obtained kinetic data. The pseudo-second order model provided the best fit for experimental data with coefficient of determination R2 = 0.999. Freundlich and Langmuir isotherm models were used to describe metal adsorption. Equilibrium data agreed well with Langmuir isotherm with R2 = 0.970