High-Efficiency Nanospheres from Watermelon Rinds for Enhanced Chromium(vi) Bioreduction in Simulated Wastewater and Industrial Effluents

The bioremediation potentials of Chromium from industrial effluent and simulated wastewater via bioreduction using nanoparticles immobilised watermelon rinds (WMR) were investigated with respect to the effects of process parameters such as concentration of WMR, contact time, temperature, and pH. The kinetics and thermodynamics of the bioreduction process, as well as half-life (t1/2) and bioreduction ability of WMR-immobilised nanoparticles. Encapsulation Efficiency and Controlled Release Rate Constants kinetics were studied. Watermelon rinds (WMR) were extracted using the maceration method (70% methanol), encapsulation technique was used for the immobilisation of WMR in the production of nanoparticles, and a batch process was used for the study. Characterisation of the nanoparticles was done using Scanning Electron Microscope (SEM) and Dynamic Light Scattering (DLS). Results showed that bioreduction efficiency was influenced significantly by WMR concentration, as the optimum concentration of 0.1mg/ml was able to reduce 90% of Cr (VI) within a period of 40min, at a temperature of 25 °C and at pH 7.0. The kinetic data showed that the pseudo-second order model best describes the reduction process. Thermodynamic studies showed the values for ΔHo, ΔGo, Ea and ΔSo to be -6500 (J), -10600 (J), 42.24(J/mol) and 25.02 (J/K), respectively, indicating that the bioreduction process was exothermic, feasible and spontaneous. The results also showed that nanoparticles were produced, as evidenced by the DLS 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 immobilised WMR were stable, as they 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).