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The response surface methodology was used to investigate the removal of Pb (II) from an aqueous solution using banana peel with varying operating parameters in a batch mode. The central composite design was used to study the interactive effects of the operating parameters (initial concentration, pH of the solution, adsorbent dosage and the particle size). The banana peel was characterized by FTIR which showed the functional groups, while SEM and EDS were used to study morphology and elemental composition. The optimum removal of Pb(II) was 98.146 % at initial concentration 100 mg/L, pH 5, adsorbent dosage 0.55 g and particle size 75 µm. The deviation between the experimental and the model predicted percentage removal was 5.17 %. The analysis of variance showed that the regression model was significant with a low probability and the correlation coefficient R 2 value of 0.9153. The results showed that the biosorption of Pb(II) was highly influenced by the pH and the adsorbent dosage, while the particle size had little effect on the biosorption process.

It is very rare to have the ions of only one metal ion in wastewater. Hence, the removal of copper and lead ions from aqueous solution in single and binary systems using natural banana peels was investigated in a batch mode. Banana peels were characterised using FTIR, which gave the functional groups present. The spectra of banana peels loaded with Pb(II) had a higher percentage transmittance after adsorption. The point of zero charge pH pzc of banana peel was found to be 4.83 which makes it suitable for the adsorption of cations. Kinetic and isotherm studies were carried out at a pH of 5.5, concentration range of 10-100 mg/ L, and adsorbent dosage range of 0.1-1 g. A pseudo-second order model is fitted to the kinetic data suggesting chemical adsorption. The Langmuir isotherm performed well with the experimental data which means adsorption occurred as a monolayer on the surface of banana peels. The maximum adsorption capacity of Pb(II) for Langmuir isotherm was 66.67 mg/g. This indicated that in the single system banana peels have more affinity for Pb(II) than for Cu(II). At higher concentrations, the experimental data for the isotherm study showed the effect of a competitive phenomenon which affected only Cu(II) in the binary system. Natural banana peels are efficient agricultural waste materials that can be used for the treatment of wastewater contaminated with copper and lead ions. ABOUT THE AUTHOR This research is part of a larger project funded by the South African National Research Foundation (NRF) and has been running for the past 3 years. Research activities seek to find sustainable and eco-friendly solutions for the removal of heavy metals commonly found in South African waters and detrimental to life. To this end, a selected number of readily available and low-cost biowaste adsorbents such as sugarcane bagasse, orange peel, eggshell, mango peel, banana peel etc, are being explored. The study covers their characterization, batch experiments to study the adsorption mechanisms and kinetics, as well as pilot-scale column studies for scale-up and design of household filters and industrial-scale adsorption columns. The designed equipment should be capable of handling multi-solute systems.

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Agricultural waste materials have been proven to be efficient for heavy metal sequestration from wastewater. In this paper, the interactive effects of initial concentration, adsorbent dosage, and particle size on the removal of copper and lead ions in a binary system onto orange peels were investigated using a central composite design. The pHpzc of orange peels was determined to be 3.85. The Fourier transform infrared (FTIR) and energy dispersive x-ray (EDX) revealed the functional groups and elemental composition present on the surface of the bio-sorbent, respectively, before and after adsorption. The ANOVA showed a good fit with a coefficient of determination (R2) of 0.973 and 0.993 for Cu and Pb, respectively. The bio-sorption of Cu and Pb increased with increasing adsorbent dosage while the percentage removal of Pb was consistently higher than Cu. The highest percentage removal of Cu and Pb gave 86.27% and 98.85%, respectively. The kinetic and isotherm studies showed that pseudo-second-order and Langmuir isotherm models fitted the experimental data suggesting chemisorption and monolayer adsorption, respectively. The treatment of wastewater is very essential to avoid water scarcity and to achieve the Sustainable Development Goals (SDGs). This study demonstrates the potential of utilizing orange peels as bio-sorbent for the treatment of wastewater containing Cu and Pb ions.