Nanoparticles Immobilized Watermelon Rinds Used in Bioreduction of Chromium (VI) from Industrial Effluent and Simulated Wastewater

Abstract

^{Presently, the trend in Cr (VI) Bioremediation is focused on seeking new low-cost biological materials that are readily available and have excellent bioremediation potentials. The bioremediation potentials of Cr (VI) to Cr (III) from industrial effluent and simulated wastewater via bioreduction using nanoparticles immobilized watermelon rinds (WMR) was investigated with respect to effects of process parameters such as concentration of anthocyanin, contact time, temperature, pH, and concentration of Cr (VI). The kinetics and thermodynamics of bioreduction process as well as half life (t1/2) and bioreduction ability of ARE-immobilized microparticles and nanospheres were investigated. Encapsulation Efficiency and Controlled Released Rate Constants kinetics were studied. Watermelon rinds (WMR) were extracted using the maceration method (70% methanol), encapsulation technique was used for the immobilization of WMR in the production of nanoparticles, and a batch process was used for the study. Results showed that bioreduction efficiency was influenced significantly by WMR concentration, as the optimum concentration of 0.1mg/ml was able to bioreduce 90% of Cr (VI) within a period of 20min, at a temperature of 250C and at pH 7.0. The kinetic data showed that pseudo-second order model best describes the reduction process. Thermodynamic studies showed the values for ΔHo, ΔGo,  Ea and ΔSo to be -6.50 (kJ/mol), -10.60 (kJ/mol), 0.007 (kJ/mol) and 0.02 (J/k/mol), respectively, indicating that the bioreduction process was exothermic, feasible and spontaneous. The results also showed that nanoparticles were produced, as evidenced by the dynamic light scattering spectrum. Encapsulation efficiency of 80.93% was obtained for the nanospheres with released transfer rate constants of 1.61 x 10-1 min-1. It can be concluded from the results that nanoparticles immobilized WMR was stable as it required little or no energy for the Bioreduction process. Hence, the stability of the bioactive material (WMR) was necessary for significant bioreduction of Cr (VI) to Cr (III).}