School of Engineering and Technology

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Biosorbents for the removal of synthetic organics and emerging pollutants: Opportunities and challenges for developing countries
(Environmental Development, 2016-05-23) Chaukura, Nhamo; Gwenzi, Willis; Tavengwa, Nikita; Manyuchi, Musaida Mercy
Contamination of aquatic systems by synthetic organic contaminants and emerging pollutants poses significant public and environmental health risks in developing countries. These contaminants mainly originate from textile, agrochemical, and pharmaceutical industries. The removal of such contaminants is problematic in developing countries because advanced water treatment methods are still lacking in developing countries due to their high costs. The application of biosorption for removal of organic contaminants in developing countries is attractive for three reasons; (1) large quantities of biomaterials for use as biosorbents are readily available; (2) lack of advanced water and wastewater treatment systems for removal of organic contaminants; and (3) the technology is relatively cheap compared to advanced methods (e.g. membrane filtration) often used in developed countries. Overall, this has the potential to remove organic contaminants from aqueous systems while simultaneously reducing the public health and environmental impacts associated with the disposal of such biowastes. However, large-scale application of biosorption faces potential challenges including lack of funding, poor mechanical properties of biosorbants, complex adsorption mechanisms involved, and poor regeneration capacity. In addition, spent biosorbents present an environmental risk and their disposal is problematic due to the potential of contaminating surface and ground water. Possible disposal methods for spent biosorbent include use as a filler in road surfacing, as a soil amendment, and in phytoremediation cells where the organics are absorbed and broken down by plants. Overall, biosorption is a potentially viable alternative, but further research on its ability to remove pollutants from multi-component systems, its regeneration capacity, and plant design parameters is required before the benefits of the technology are realised in developing countries.
Competitive sorption of Cd2+ and Pb2+ from a binary aqueous solution by poly (methyl methacrylate)-grafted montmorillonite clay nanocomposite
(Applied Water Science, 2016-03-24) Tavengwa, Bunhu; Tichagwa, Lilian; Chaukura, Nhamo
Poly(methyl methacrylate)-grafted montmorillonite (PMMAgMMT) clay and sodium-exchanged montmorillonite (NaMMT) clay were prepared through in situ graft polymerisation and used to remove Cd2+ and Pb2+ from synthetic wastewater. The modification of adsorbent materials was confirmed by fourier transform infra-red spectroscopy (FTIR), thermogravimetric analysis (TGA) and X-ray powder diffraction (XRD) techniques. BET surface area measurements showed NaMMT had a higher surface area than PMMAgMMT. Batch experiments were used to assess the simultaneous uptake of Cd2+ and Pb2+ from a synthetic binary solution. Pb2+ was preferentially sorbed, exhibiting greater affinity for the sorbents compared to Cd2+ as shown by its relatively higher uptake onto the sorbents than Cd2+. The maximum sorption capacities for NaMMT and PMMAgMMT were 18.73 and 19.27 mg/g for Cd2+, and 30.03 and 34.25 mg/g for Pb2+, respectively. The sorption data obeyed the Langmuir model and the pseudo-second order kinetic model with R 2 of at least 0.9800 for both models. The sorbents could also be regenerated up to three cycles without a significant loss in the sorption capacity. FTIR measurements showed the presence of metal–oxygen bonds after sorption, confirming the occurrence of adsorption as one of the heavy metal removal processes. The work demonstrated the potential of using low-cost nanoscale composite material for the removal of Cd2+ and Pb2+ from aqueous solution.
Preparation and Characterization of Polymer-Grafted Montmorillonite-Lignocellulose Nanocomposites by In Situ Intercalative Polymerization
(Journal of Applied Chemistry, 2016-07-11) Bunhu, Tavengwa; Chaukura, Nhamo; Tichagwa, Lilian
Lignocellulose-clay nanocomposites were synthesized using an in situ intercalative polymerization method at 60∘ C and a pressure of 1 atm. The ratio of the montmorillonite clay to the lignocellulose ranged from 1 : 9 to 1 : 1 (MMT clay to lignocelluloses, wt%). The adsorbent materials were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and X-ray powder diffraction (XRD). FTIR results showed that the polymers were covalently attached to the nanoclay and the lignocellulose in the nanocomposites. Both TEM and XRD analysis showed that the morphology of the materials ranged from phase-separated to intercalated nanocomposite adsorbents. Improved thermal stability, attributable to the presence of nanoclay, was observed for all the nanocomposites. The nanocomposite materials prepared can potentially be used as adsorbents for the removal of pollutants in water treatment and purification.