M.Tech. / The removal and recovery of heavy metals from effluents has been a subject of significant importance due the negative impact these toxic metals have on human health and the environment as a result of water and soil pollution. Precipitation is the mostly widely used wastewater treatment method because it is the most economical and easier to implement and operate on a large scale. However, traditional precipitation methods using lime, sulfides or hydroxides recover metals in the form of a sludge which is not reusable and has to be disposed in landfills creating a potential environmental hazard and resulting in loss of valuable minerals. The current focus in effluent treatment is now on the recovery and re-use of these heavy metals rather than removal and disposal. This study investigated the use of hydrazine as a reducing agent to remove and recover Ni2+, Cu2+, Co2+ and Fe2+ from effluent by reduction crystallization. In this process chemically reduced aqueous metal ions were plated on to a base substrate (nickel powder) with no electrical current required for deposition. A feasibility study was carried out to test the efficiency and find the optimum operating conditions for this method and generate an understanding of the chemical and particulate process occurring. The results obtained indicate that hydrazine is an effective reducing agent for removal and crystallization of Ni2+, Cu2+, Co2+ and Fe2+/ Fe3+ into their elemental states with nickel powder as a seeding material. Over 99 % of metals were removed from the effluent in all the systems (Ni-only, Ni-Cu, Ni-Fe and Ni-Fe). Breakage, aggregation and molecular growth were identified as the predominant mechanisms occurring during the reduction crystallization process in Ni-only, Ni-Cu, Ni- Co systems and there was evidence of nucleation in Ni-Fe solution. These finding were confirmed by analysing the scanning electron micrographs of the powder obtained. A nearly spherical structure powder with wide distribution in particle size and evidence of fragmentation was obtained in all the experimental runs. vii The residual concentrations obtained were far below the required limit for effluent discharge into sewer where 20 mg/L Ni, 20 mg/L Cu and 20 mg/L Fe and the total metal concentration of 50 mg/L for Fe, Cr, Cu, Ni, Zn and Cd is stipulated. Reduction crystallization using hydrazine as a reducing agent can be utilized for controlling environmental pollution and eliminating hazardous metals from the environment.

This thesis presents an alternative approach for pre-concentrating heavy metals in aqueous environments using electro spun polymer nanofiber sorbents. The conditions for electrospinning polyethersulfone, polystyrene, polysulfone and polyamide-6 were optimized. The morphologies and porosities of the electrospun nanofibers were studied using SEM and BET nitrogen gas adsorptions. The nanofibers had mesoporous morphologies with specific surface areas up to 58 m2/g. The electro spun nanofiber sorbents were characterized in terms of their tunability for both uptake and release of heavy metals. The usability of the sorbent was also assessed. The sorbents showed fast adsorption kinetics for heavy metals « 20 min for As, Cu, Ni and Pb) in different aqueous environments. The adsorption characteristics of the sorbents best fitted the Freundlich isotherm and followed the first order kinetics. The efficiencies of adsorption and desorption of heavy metals on both imidazolyl-functionalized polystyrene and amino-functionalized polysulfone sorbents were more than 95% up to the fifth cycle of usage. Reusability improved dramatically (up to 10 runs of usage) when mechanically stable amino-functionalized nylon-6 electro spun nanofibers were used. The capacity of the amino-functionalized nylon-6 sorbent to pre-concentrate heavy metals compared very favourably with those of aqua regia and HN03+H202 digestions especially in less complex matrices. Due to their highly porous nature, the electro spun nanofibers exhibited high adsorption capacities (up to 50 mg/g) for heavy metal ions. The loading capacities achieved with the imidazolyl-functionalized sorbent were higher than those for amino-functionalized mesoporous silica and biomass-based sorbents. The electro spun nanofiber sorbents presents an efficient and cost effective alternative for preconcentrating heavy metals in aqueous environments.

M.Sc. / The addition of lignocellulosic fibres to thermoplastic polymers is known to increase the toughness of the polymers but it compromises the tensile strength. On the other hand, inorganic fillers like TiO2 are known to improve the tensile strength of polymers. These plant fibres have been used as adsorbents of metal pollutants in water. Best results were obtained when such materials were ground to fine powder but due to low density, the fibres float and form aggregates in water. Being highly biodegradable in nature makes plant fibres unsuitable for water treatment over lengthy periods of time. They cannot be used as standalone materials. Mixing these adsorbents with polymers, which cannot only act as support for the adsorbents but also disperse the fibres within it thus preventing leaching, is a cause for concern. This study was aimed at fabricating plant fibre-polymer composites that will have improved mechanical and thermal properties. These composites were to be tested for their ability to be used as metal ion adsorbents. The composites were fabricated using a melt-mix compounding method. Two thermoplastic polymers, EVA and PCL were each mixed with either lignin or SCB and TiO2 in different ratios. A rheomex mixer coupled with a single screw extruder which was attached to a sheet die was used to synthesise the composites. TGA and DSC were used for thermal propagation while the mechanical properties were investigated using an instron. Metal ion adsorption measurements were analysed using an atomic absorption spectrometer (AAS). These adsorbents were used to remove Cr(VI), Cr(III) and Pb(II), varying different environmental parameters like pH, concentration, time and adsorbent at constant temperature. The reinforcing effect of both lignin and SCB resulted to poor thermal and mechanical properties. This was shown by a decrease in onset degradation temperature and the tensile and toughness of the composites compared to the neat polymers. The incorporation of TiO2 on SCB-EVA composites, however, improved the mechanical strength and resulted in a thermally stable composite compared to counterpart composites without TiO2. This observation was surpassed at high filler loading as the addition of TiO2 resulted in a decrease of the properties. For the tensile strength, neat EVA recorded 11.35 MPa while 2% TiO2-EVA registered 12.49 MPa for example. For the same composite, the onset degradation temperature for EVA was 353 oC but shifted to 368 oC after the addition of TiO2. At higher filler loading, no effect was observed when adding TiO2.

No description available.

M. Tech. Chemistry. / Objectives of this study was to assess the levels of heavy metals in bovine meat, hair, sediment, peat and water from the study areas using ICP-MS and internal standard calibration.The specific objectives are to: collect hair and meat of impala and cattle, sediment, peat, soil and water samples; digest samples; determine the level of some of the following heavy metals Cd, Cr, Cu, Hg, Mn, Pb, Sr, U, V depending on the background information on the above samples; compare the levels of Hg in sediment and peat using ICP-MS and Zeeman mercury spectrometer; determine the limit of detection of trace elements in different matrices using ICP-MS; establish correlations among concentrations of heavy metals in specified samples.

Excessive release of metals and metalloids into the environment is a major global environmental concern and there is need for environmentally friendly and cost effective methods for their removal. The present study investigated the adsorptive removal of zinc, lead, copper and nickel ions from synthetic aqueous solutions and various metals from three acid mine drainage (AMD) sites using chicken eggshells. Process parameters including the initial metal concentration were evaluated and the optimum conditions obtained were pH 7, adsorbent dose of 7 g and contact time of 360 minutes (for the removal of 100ppm metal ions). Under these conditions the percentage adsorptions were; 97% for lead, 95% for copper, 94% for nickel and 80% for zinc. Aluminium, iron, potassium, nickel and zinc ions all had percentage adsorptions above 75% in AMD Sample 1. Potassium had a 98.78% adsorption while magnesium, strontium and zinc had 72.33; 68.75 and 53.07% adsorption respectively in Sample 2. Arsenic, chromium, copper, iron, antimony and tellurium ions were above 75% for Sample 3. The study demonstrated the efficacy of chicken eggshells and presents it as a viable low-cost adsorbent for bioremediation. / Environmental Science / M. Sc. (Environmental Science)

Listeria monocytogenes is a zoonotic foodborne pathogen, transmissible from the natural agricultural environment to animals and humans. In recent years, the pig production industry has experienced a series of monetary losses as a result of the L. monocytogenes outbreak which threatened the economy of South Africa. This outbreak also had a detrimental effect on the health system of the country. In South Africa however, there is limited information regarding the genomic diversity of L. monocytogenes. Therefore, an overview of the genomic diversity of L. monocytogenes strains circulating at different levels of the pork production chain needs to be determined so as to be able to identify routes of contamination of the pathogen and thus improve meat safety. This study was aimed to determine the antimicrobial resistance patterns and population structure of L. monocytogenes isolated from pig farms in South Africa. Based on wholegenome sequence analysis, 77 isolates of L. monocytogenes were differentiated into four molecular serogroups with IIa (45.5%) being the most prevalent followed by IIc (26.0%), IVb (22.1%) and IIb (6.5%). Overall, 11 clonal complexes (CCs) were identified in this study, with the predominance being observed from; CC204 (23.4%), CC1 (19.5%) and CC2 (16.9%). Genetic elements associated with biocide, antimicrobial and heavy metal resistance were noted in 24.7 %, 48% and 11.7% of the isolates, respectively. Listeria pathogenicity island 1 and 3 that harbored clusters of virulence genes were present in 38.8% of the isolates. Five different plasmids were found in 68.9% of the isolates. This study has given baseline data on the genomic diversity of L. monocytogenes strains that are associated with biocides, heavy metal and antibiotics resistance genes. The data again demonstrated the genotypes of L. monocytogenes that are prone to contaminate the farm environment and possibly cause diseases in animals and humans. / Life and Consumer Sciences / M. Sc. (Life Sciences)