Theses and dissertations (Engineering and Built Environment)
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Item The biosorption of chromium and copper from AMD contaminated water using banana peels as a biomass adsorbent(2022-09-29) Mzimela, S'thembile; Musonge, Paul; Bakare, Babatunde F.The presence of heavy metals in water from industrial activities negatively affects human health. Metal accumulation in human bodies is toxic and can lead to carcinogenic effects when consumed for prolonged periods. There is no acceptable method for permanently removing heavy metals in water. As a result, water for human consumption and domestic use from various water sites contains harmful heavy metals. This study investigates the removal of hexavalent chromium (Cr6+) and copper (Cu 2+) from drinking water through the adsorption process using banana peels as biomass material. Banana peels were evaluated for their ability to remove heavy metals from water as a cheaper alternative resource to conventional adsorbents such as activated carbon. Cr6+ and Cu2+ are some of the most common heavy metals found in potable (drinking) water and they were chosen for this study amongst other heavy metals. Batch studies were conducted using water that was synthesized with the chosen metals. Parameters such as pH, agitation speed, biosorbent dose, initial metal concentration, and contact time were varied to determine their effect on biosorption. pH was varied between 2 and 7, agitation speed was varied between 100 and 200 rpm, dosage was varied between 1 and 6 grams, initial concentration was between 5 and 100 mg/L and contact time was also varied between 5 and 140 minutes. Each variable was done one factor at a time while keeping other values constant. The height of the column for column studies was studied between 5 and 30 cm at constant pH “4”, 5mg/L initial metal concentration and volumetric flowrate of 4mL/min. Results from the study showed that pH for both Cr6+ and Cu2+ was highest at pH “4” with % removal of 65% and 94%, respectively. Agitation speed had a high % removal at 180 rpm for Cr6+ (67%) and 160 and 180 rpm for Cu2+ (95%). Increase in biosorbent dose also increased biosorption efficiency from 17% to 95% for Cu2+ across the range, and from 58% to 65% for removing Cr6+ . In the study of initial metal concentration, banana peels performed better at lower metal concentrations for both metals. Highest % removal efficiency for Cr6+ was found at 5 mg/L at 64% and for Cu2+ at 10, 15 and 20 mg/L at 95%. Contact time between 5 and 140 minutes found that equilibrium was reached within 30 minutes for Cr6+ and within 50 minutes for Cu2+ . Adsorption equilibrium isotherms and kinetics were studied for both metals and found that the biosorption of Cr6+ followed the Freundlich isotherm and Langmuir isotherm models with R 2 of 0.99 and 0.95 respectively, and the process kinetics followed the pseudo-second-order kinetic reaction with R 2 of ~ 1. The biosorption of Cu2+ followed the Langmuir isotherm model with R 2 of 0.96 and Langmuir qm of 15.41 mg/g and the process kinetics followed the pseudo-first-order kinetic reaction as well as the intra-particle diffusion model with both R 2 of 0.98. Banana peels were characterized for their properties and the Fourier transform infrared (FTIR) spectroscopy identified the functional groups in the peels which were hydroxyls, carboxylic acids, alkanes, and amines. Most of the groups were active in the removal of Cr6+ and Cu2+. The scanning electron microscopy (SEM) identified the surface of the peels to be rough with uneven areas and the energy-dispersive x-ray spectroscopy (EDS) analysis identified the elements present in the peels which were carbon (C), oxygen (O), potassium (K), chloride (Cl) and silicon (Si). The x-ray diffraction (XRD) was used to identify the phase of the peels and it was found that the peels were amorphous with some crystallinity containing a crystal salt called sylvite. The Brunauer–Emmett–Teller (BET) analysis identified the pores of the banana peels to be mesoporous with a pore size of 2.9 nm, a surface area of 5.69 m2 /g, and a pore volume of 0.002605 cm3 /g. Column experiments in a fixed-bed column were studied for the removal of Cr6+ and the breakthrough time tb increased from 10 min at 5cm to 420 min at 30 cm. The mass transfer zone HB also increased from 0.206 at 5 cm to 7.426 at 30 cm. Other column performance indicators such as the adsorbent exhaustion rate (AER) and the number of volumes processed (NBV) showed that biosorption was efficient and dependent on bed height for better performance. The process favoured the Adams-Bohart model with R2 ranging between 0.94 to 0.98 and the Yoon-Nelson model with R2 ranging between 0.93 and 0.97. It can be concluded from this study that banana peels have the ability of removing Cu and Cr in potable water and has provided some insight for scaling-up of adsorption columns.Item Evaluating the performance of an eggshell-bagasse biosorption system in removing lead and cadmium from aqueous solutions(2021-02) Harripersadth, Charlene; Musonge, Paul; Isa, Yusuf MakarfiIn this research investigation, the simultaneous use of 2 biomaterials, sugarcane bagasse and eggshells, were applied as biosorbents in the treatment of metal laden effluent. Under the characterisation measurements investigated, it was found that carbon, calcium and oxygen atoms which constitute carboxylic and carbonate functional groups were prominent in eggshells, whereas for bagasse, it was carbon, hydrogen and oxygen atoms constituting hydroxyl and carbonyl groups. Batch studies were conducted to investigate the effect of fundamental process variables such as particle size (75 – 250 μm), initial metal ion concentration (40 – 240 mg/L), pH (2 – 7) and contact time (0 – 120 min). With respect to the equilibrium studies, the applicability of the Langmuir isotherm implied a monolayer formation of metal ions onto the surface of both biomaterials with the maximum amounts of Pb and Cd adsorbed based on 1 g of biosorbent being 277.8 and 13.62 mg/g for eggshells and 31.45 and 19.49 mg/g for bagasse, respectively. Moreover, kinetic modelling revealed that the process was well described by the pseudo – second order model for both Pb and Cd using eggshells and bagasse. Fixed bed studies were used to assess the dynamic adsorption behaviour of the eggshell – bagasse system using a lab – scale adsorption column of 2.3 cm in diameter and 30 cm in height. The effect of bed depth (4 – 12 cm) on 5 adsorbents (eggshells, bagasse, adsorbent A, adsorbent B and adsorbent C) in the removal of Pb were investigated. Adsorbents A, B and C were a combination of both eggshells and bagasse with adsorbent A constituting 75wt % bagasse and 25wt % eggshells, adsorbent B constituting 50wt % bagasse and 50wt % eggshells and adsorbent C constituting 25wt % bagasse and 75wt % eggshells. The column experiments highlighted an improvement in bed performance with an increase in bed depth resulting in greater mass transfer zones, breakthrough times and larger quantities of effluents treated. Two kinetic models (Thomas and Yoon–Nelson) were used to interpret the breakthrough curves where the data showed good fits to both models used. In determining the efficacy of the eggshell – bagasse biosorption system, adsorbent C was found to be most proficient in the removal of Pb with eggshells, adsorbent B, adsorbent A and bagasse following suit. The results from this investigation strongly suggest the plausible reuse of agricultural waste materials in the treatment of contaminated effluent through the biosorption process.