Biosorbent residues of the traditionally fermented Ethiopian honey wine (Tej) for quantitative removal of heavy metals from contaminated waters: Adsorption kinetics, thermodynamics and equilibrium studies

The objective of this study was to investigate the adsorption capacity of environmentally available residue of fermented alcoholic beverage (Tej) as a novel adsorbent for the removal of Cd(II), Cu(II), Pb(II), and Zn(II) in a Single Metal System. The functional groups present on the surface of raw honey wine residue (HWR) were identified using the FT-IR before and after adsorption. The effects of several parameters, such as pH, dose, contact time, agitation speed, and initial metals concentration were also investigated and optimized in the batch mode. The maximum removal of Cd(II), Cu(II), Pb(II), and Zn(II) was attained at pH = 5 for Pb(II) and Zn(II), and pH = 4 for Cd(II) and Cu(II), adsorbent dose of 1 g, initial concentration of 50 mg l -1 , contact time of 180 min and agitation speed of 100 rpm. In kinetics studies of pseudo second-order reaction, the theoretical equilibrium capacity of the adsorbent was well fitted with the experimental equilibrium capacities, which resulted chemisorptions on each adsorbent. Based on the Langmuir adsorption isotherm, the maximum equilibrium adsorption capacity (Q o ) of each metal ion on honey wine residue were decreased in the order of: Pb(II) > Cu(II) > Zn(II) > Cd(II) at initial metal concentrations ranging from 20 to 200 mg l -1 . To predict the type of adsorption, thermodynamic parameters including standard free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were calculated. The negative values of ΔG° and positive value of ΔH° indicate that, the adsorption process of each metal was spontaneous and endothermic, respectively. Moreover, the adsorption capacities of each metal was found to increase when the temperature rose from 25 to 60 °C. Thus, the finding of this study suggests that the honey wine residue can be employed as an alternative low-cost novel adsorbent for the removal of Pb(II), Cd(II), Zn(II) and Cu(II) from wastewater.