Submitted by Jorge Silva (jorgelmsilva@ufrrj.br) on 2017-06-23T17:57:14Z No. of bitstreams: 1 2016 - Camila Domingos dos Anjos.pdf: 1678010 bytes, checksum: fc61bea8918fef450e39c7005d074af1 (MD5) / Made available in DSpace on 2017-06-23T17:57:14Z (GMT). No. of bitstreams: 1 2016 - Camila Domingos dos Anjos.pdf: 1678010 bytes, checksum: fc61bea8918fef450e39c7005d074af1 (MD5) Previous issue date: 2016-04-25 / CAPES / The present dissertation seeks to analyse the initiatives of coercion to convert the hindu widows and bailadeiras (dancing girls) in Goa, between 1597 to 1606. We will research the pretentions of royal and ecclesiastical agents to convert and integrate the bailadeiras to a Christian project of colonization, from the decrees issued in the five provincial councils of Goa (made in the chronological cut above), of the legislation contained in the ?Book of the Father of the Christians?, from the royal determinations and from the viceroys of the State of India. We will investigate how the interdependence of the political and religious power favored the issuance of decrees that aimed at homogenizing the local societies, precisely the bailadeiras and the hindu widows from a Christian discipline. / A presente disserta??o busca analisar as iniciativas de coer??o ? convers?o de vi?vas hindus e bailadeiras em Goa, entre 1567 a 1606. Pesquisaremos as pretens?es dos agentes r?gios e eclesi?sticos em converter e integrar as bailadeiras a um projeto crist?o de coloniza??o, a partir dos decretos emitidos nos cinco conc?lios provinciais de Goa (realizados no recorte cronol?gico supracitado), da legisla??o contida no ?Livro do Pai dos Crist?os?, das determina??es r?gias e dos vice-reis do Estado da ?ndia. Investigaremos assim, como a interdepend?ncia do poder pol?tico e religioso favoreceu a emiss?o de decretos que visavam homogeneizar as sociedades locais, precisamente bailadeiras e as vi?vas hindus, a partir de uma disciplina crist?.

Heavy metals are released into the environment either by natural processes or by anthropogenic activities. Industries such as leather tanning, textiles, metallurgical, electroplating and mining activities discharge the chromium along with other heavy metals, which causes water pollution and environmental degradation. There are many conventional methods to overcome this problem such as chemical precipitation, ion exchange, reverse osmosis, etc but, these methods have certain drawbacks like generation of secondary sludge, inefficient removal of metal ions of low concentration, high cost etc. To overcome these limitations by conventional methods, an environmental friendly method, namely bioremediation has been adopted. Bioremediation uses microorganisms, biodegradable industrial wastes, or plants to mitigate this problem. In this investigation, bacterial strains have been isolated from the soil and water samples collected from a chromite mine in Karnataka. The capability of these bacterial strains have been assessed to remediate Cr (VI) in batch experiments in order to achieve the prescribed standards of regulatory agencies, and to elucidate the mechanisms of bioremediation of Cr (VI). Additionally, using these bacterial strains, biosensors have been developed to detect Cr (VI) ions in the solution by electroanalytical techniques. The major objectives of this research investigation are: a) Isolation, characterization and identification of bacterial strains from water and soil samples obtained from a chromite mine in Karnataka. b) To study the ability of three isolated bacterial strains namely Arthrobacter sp, Exiguobacterium sp. and Micrococcus sp. to remediate Cr (VI) during growth in media, amended with different concentrations of Cr (VI) c) Delineation of the probable mechanisms of bioremediation of Cr (VI) by three bacterial strains with the aid of proteomic and metabolomic studies d) Optimization of factors influencing the bioremoval of Cr (VI) using the isolated bacterial strains as biosorbents in batch experiments. c) Elucidation of mechanisms of bioremoval of Cr (VI) at the microbe – metal interface for all three bacterial strains, adopting characterization techniques like FTIR, XPS, SEM – EDS and zeta potential measurements. d) Micrococcus sp. was chosen for the fabrication of biomodified carbon paste electrode (CPE) to sense the Cr (VI) ions using voltammetric techniques, namely cyclic voltammetry (CV) and differential pulse cathodic stripping voltammetry (DPCSV). The salient findings of this research work are highlighted as follows: Firstly, bioremediation experiments were carried out using the bacterial strains isolated from soil and water samples collected from the chromite mines of Mysore Minerals Limited, Hassan district, Karnataka, India. Initially, the characterisation of the isolated bacterial strains were carried out with respect to their biochemical aspects, antibiotic susceptibility, morphology using scanning electron microscopy and cell wall nature by Gram’s staining. The identification of the three isolated bacterial strains were accomplished by 16S rRNA method and the three bacterial strains have been identified as Arthrobacter sp., Exiguobacterium sp. and Micrococcus sp.. The experiments were conducted to assess the potential of the isolated bacterial strains namely, Arthrobacter sp., Exiguobacterium sp. and Micrococcus sp., for the remediation at two different concentrations of 10 mg/L and 30 mg/L of Cr (VI) ions, during cell growth i.e. using metabolically active cells of bacteria. It was found that the three bacterial strains could bioreduce toxic Cr (VI) to the less toxic Cr (III) form, by 95% to 99%, within a time span of 12 h to 120 h. In the experiment with sulphate as the competitive ion in the growing mode of the bacterial strains Arthrobacter sp., Exiguobacterium sp. and Micrococcus sp., the percentage bioreduction of Cr (VI) to Cr (III) was not hampered. Scanning electron microscopic studies on the bacterial cells of Arthrobacter sp., Exiguobacterium sp. and Micrococcus sp., before and after interaction with Cr (VI) showed the morphological changes after interaction with Cr (VI), as an adaptive strategy to counter the toxic effect of Cr (VI). Further, to elucidate the mechanisms of bioreduction of Cr (VI) to Cr (III) by the three bacterial strains, the proteins and metabolites were isolated from the pristine bacterial cells and Cr (VI) interacted bacterial cells. The proteins were isolated from different parts of the cells and assessed for the differential expression of proteins under Cr (VI) stress. It was found that, seven differentially expressed protein bands were observed on SDS PAGE profile of Arthrobacter sp. interacted with Cr (VI), from the soluble protein isolated from the crude extract, devoid of cell membrane. A single band of differentially expressed protein was observed in the extracellular secretion in Exiguobacterium sp. and in the case of Micrococcus sp. four differentially expressed proteins were observed in the membrane fraction of proteins. The mass spectrometry data of the differentially expressed proteins were used to identify the probable protein candidates using MASCOT search in NCBIr database. It was found that some of these proteins were a class of transport proteins and a few belong to the reactive oxygen species scavengers. These findings suggested that the bioreduction of Cr (VI) to Cr (III) involved the efflux mechanism and ROS scavenger production, to resist the toxicity of Cr (VI). The metabolite concentration profile was studied for the all three bacterial cells in the absence and presence of Cr (VI) using NMR spectroscopy. The results of this study showed an increase and decrease in the concentration of various metabolite components after interaction with Cr (VI), and this was observed in all the three bacterial strains. Some of the metabolites identified using Chenomx 8.1 metabolite library, were found to be osmoprotectants like betaine, proline etc, which combat the stress of Cr (VI). Therefore, the overall bioremediation of Cr (VI) by metabolically active bacterial cells is through bioreduction of toxic Cr (VI) to the less toxic Cr (III) form and the resistance mechanisms to overcome the toxic effect of Cr (VI) is by the efflux mechanism, production of osmoprotectants and expression of ROS scavengers. In the third part of investigation, the bioremoval of Cr (VI) ions in batch experiments using metabolically inactive cells as biosorbents, for all the three bacterial strains, were studied. The bioremediation efficiency of each bacterial strain was evaluated, considering the various parameters like effect of contact time of bacterial cells with the Cr (VI) ions, pH of Cr ion solution, biomass loading and initial concentration of Cr (VI) ion. The Cr (VI) biosorption efficiency obtained for the bacterial strains Arthrobacter sp., Exiguobacterium sp. and Micrococcus sp. was found to be 93 %, 85 % and 100 % respectively. Apart from the biosorption of Cr (VI) by bacterial cells, the residual Cr was found to be in the form of Cr (III) ions. Therefore, complete bioremoval of Cr (VI) ions could be achieved as a combined process of biosorption and bioreduction, for all three bacterial strains, meeting the acceptable limits prescribed for Cr (VI) ion for drinking water, by regulatory agencies i.e. 0.05 mg/L of Cr (VI) ions. The biosorption of Cr ions by all the three bacterial strains were found to follow a typical Langmurian behaviour. The bioremediation process by the bacterial strains was also evaluated using suitable kinetic models and the results indicated that the bioremoval of Cr (VI) by Arthrobacter sp., Exiguobacterium sp. and Micrococcus sp. followed pseudo second order kinetics. The next aim was to ascertain the mechanism of bioremoval of Cr (VI) ions by the metabolically inactive cells. For this, different characterisation techniques were adopted that aided in the elucidation of reactions occurring at the interface of bacterial cell surface and Cr solution. The nature of interacting forces in bioremoval process was found out by desorption studies, and it was observed that only partial desorption of Cr ions was achieved from the biosorbed bacterial cells. This was further confirmed, by calculation of Gibbs free energy and the values were found to be in the range of – 25 to -32 kJ/mol, thus indicating that the process of bioremoval of Cr (VI) ions by the bacterial cells, is by chemisorption process. The variation in the charge of the bacterial cell surface, before and after interaction with chromium ions, was studied by performing zeta potential measurements as a function of pH. The surface charge of the bacterial cells alone was found to be negatively charged over a wide range of pH. Subsequent to interaction of the bacterial cells with the negatively charged oxyanions of Cr (VI) ions, the surface charge was observed to be less electronegative, which further confirmed the binding of the positively charged Cr (III) ions, formed via bioreduction on the bacterial cell surface. FTIR spectral studies revealed the functional groups involved, in bioremoval of Cr ions, present on bacterial cell surface. The functional group facilitating the bioremoval of Cr ions are –NH, -COOH and phosphate. EDS studies confirmed the Cr peak for the bacterial cells interacted with Cr ions. The oxidation state of Cr ion bound to the bacterial cell surface was determined with the help of XPS analysis. It was interesting to observe the Cr (III) peaks along with their Cr (VI) peaks. These studies provided evidence in support of the bioreduction of Cr (VI) to Cr (III) and biosorption of bioreduced Cr (III) ions onto the surface of bacterial cells, apart from the fraction present in bulk solution. The next objective was to assess the potential of Micrococcus sp. as sensor for the detection of Cr (VI) ions, using electroanalytical techniques such as, cyclic voltammetery (CV) and differential pulse cathodic stripping voltammetry (DPCSV). For this, Carbon Paste Electrode (CPE) was coated with the bacterial strain namely, Micrococcus sp and the modified electrode was used as the working electrode in a three electrode system. The developed biomodified electrode showed an approximately 3-fold increase in the sensing of Cr (VI) ion in comparison with the unmodified electrode CPE, which is attributed to the binding of Cr (VI) ions to functional groups present on the bacterial cell surface. The lower limit of detection obtained for Cr (VI) ions using CV was found to be 1 x10-4 M. The lower limit of detection was improved to 1 x 10-9 M of Cr (VI) using DPCSV.

Memoria para optar al Título Profesional de Ingeniero Forestal

In South Africa, the ferrochromium industry produces approximately 100,000 t bag house filter dust and slurry, while the stainless steel industry produces 24,000 t of dust annually [17,39]. The toxic substances in these wastes potentially pose a threat to the environment and human health, especially Cr (VI) due to its toxic, carcinogenic, highly soluble and strongly oxidizing properties. Therefore, the existence and treatment of wastes from stainless steel and ferrochrome production remain a challenge and an issue of concern. The increase of environmental legislation globally and the trend towards sustainable development are drives for alternatives to landfill. In the present thesis, the characteristics, formation mechanisms, leachability and stabilisation of the Cr (VI)-containing electric furnace dust and filter cake were investigated using various techniques such as XRD, XRF, TG/DTA, XPS, SEM-EDS, FT-IR, Raman spectrometer and UV/Vis spectrometer. The electric furnace dust and filter cake are very fine particles. Stainless steel dust forms by the entrainment of charge materials, evaporation or volatilisation of elements and ejection of slag and metal by spitting or the bursting of gas bubbles. It was found that ferrochrome dust is formed by the ejection of slag and metals droplets from the electrode hole, the entrainment of charge materials, vaporisation as well as the formation and precipitation of compounds from vaporised species in the off-gas duct. Filter cake contains crystal phases (CaF2 and CaSO4 ) and metal rich amorphous phases. It is formed due to super saturation and precipitation. Leaching experiments on the wastes showed that Cr (VI) rapidly leaches out by distilled water. Bricks were produced by mixing wastes (stainless steel plant dust, ferrochrome dust and filter cake) and clay. The optimum sinter parameter was found to be 1100oC and 5 hours for a 50wt% SPD-50wt% AS mixture in the brick. The leachability of Cr(VI) is strongly influenced by the mass%CaO/mass%SiO2 ratio and alkali metal oxides content in the wastes. The emission factors from the stabilised wastes (SPD, FCD1, FCD2 and FC) are similar to those reported for the cement industry. Semi-dynamic leaching tests indicated that the predominant leaching mechanisms of chromium species are initial surface wash-off followed by matrix diffusion. / Thesis (PhD (Metallurgical Engineering))--University of Pretoria, 2007. / Materials Science and Metallurgical Engineering / unrestricted

Des nanocristaux (NC) de CdSe et CdS ont été élaborés par grossissement thermique à partir de précurseurs organométalliques, de type thiophénolates de cadmium, synthétisés préalablement par voie sol-gel. Le protocole de synthèse des précurseurs a été validé par le contrôle de leurs compositions et de leur stabilité par spectrométrie de masse (SM) ESI-FTICR. La mise en place d'un protocole original avec croissance thermique par paliers à des T° de réaction plus basses que celles habituellement employées a permis d'obtenir des NC de tailles inférieures à celles couramment obtenues (< 2nm) durant un temps de réaction n'excédant pas 200 min. Les NC ont été caractérisés conjointement par plusieurs techniques physiques et physico-chimiques. Leur forme sphérique, leurs diamètres moyens (~ 2-3,5 nm) et leurs distributions de taille (8-19 %) ont été déterminés par TEM. Leur nature cristalline de type würtzite a été vérifiée par DRX. Une estimation supplémentaire des tailles moyennes, en accord avec les résultats de TEM, a été obtenue par DRX et SM MALDI-TOF. La spectrométrie optique à T° ambiante a mis en évidence l'évolution des propriétés d'absorption et de photoluminescence des NC en fonction de la T° de prélèvement, en particulier le glissement de l'énergie de transition fondamentale sous l'effet du confinement quantique. L'ensemble des résultats s'inscrit dans la correspondance empirique énergie excitonique-taille du NC communément admise et valide le protocole d'élaboration des NC adopté. L'analyse théorique des spectres optiques en approximation de la fonction enveloppe a montré les limites de validité de cette approche aux très petites tailles de NC / CdSe and CdS nanocrystals (NC) were produced by thermally growing cadmium thiophenolates organometallic precursors. These precursors were previously synthesized by a sol-gel reaction. The synthesis protocol has been validated by the study of their composition and stability by ESI-FTICR mass spectrometry. An innovative thermal growth method has been used by applying a temperature ramp with extraction of NC at fixed values. This approach is different of usual methods described in the literature as the NC sampling is done at lower temperatures ensuring the elaboration of smaller particles (< 2 nm) during shorter reaction time (< 200 min). The NC were characterized by combined physical and physical-chemical techniques. Spherical shape, average size (~2-3,5 nm) and size distribution (8-19 %) were determined by TEM. DRX confirmed the würtzite structure of the synthesized NC. Additional data of average size were obtained by DRX and MALDI-TOF mass spectrometry confirming those obtained by TEM. Room temperature optical spectrometry has demonstrated the evolution of the absorption and the photoluminescence as a function of the extraction temperature, more particularly, the fundamental transition of energy shifts due to the quantum confinement effect. These results are consistent with the empirical correspondence 'excitonic energy/NC size' universally recognized. Finally, the theoretical study of the different optical spectra shows the limit of the envelope-function approximation for very small size particles

Uppsatsen intresserar sig för icke-vita svenskar som trots sitt svenska medborgarskap upplever att de inte alltid kan eller får känna sig som svenskar. Utgångspunkten är att det i Sverige råder en vithetsnorm som för icke-vita svenskar får konsekvenser som rasism, exkludering och utanförskap. För att få en förståelse för mekanismerna bakom dessa konsekvenser används istället för en övergripande teori flertalet centrala begrepp och teoretiska utgångspunkter som alla ses utifrån ett postkolonialt perspektiv. För att undersöka detta har det genomförts sju kvalitativa intervjuer med icke-vita svenskar. De har intervjuats om hur de upplever och tolkar rasism. Vidare har uppsatsen sökt svar på huruvida respondenterna har omedvetna eller medvetna strategier för att bemöta den rasism de utsätts för. Det har sedan gjorts en jämförelse för att se om erfarenheterna skiljer sig åt beroende på om respondenterna är uppväxta i Sverige eller inte. Resultatet visar att alla respondenter oavsett grupp upplever rasism och får sin svenskhet ifrågasatt. De största skillnaderna mellan grupperna ligger i vilka strategier respondenterna använder sig av för att hantera den rasism de möter. Gruppen med respondenter som är uppväxt i Sverige väljer i högre grad att konfrontera den rasism de utsätts för medan gruppen som inte växt upp i Sverige i högre grad väljer att hitta strategier för att handskas med eller undkomma den. / The thesis is interested in the non-white Swedes who, despite their Swedish citizenship feel that they are not always able or allowed to feel like Swedes. The starting point is that in Sweden there is a whiteness standard witch for non-white Swedes have consequences in form of racism, exclusion and alienation. To get an understanding of the mechanisms behind these effects the writers instead of a general theory use several key concepts and theoretical points all seen from a postcolonial perspective. Seven interviews were held with non-white Swedes who was interviewed on how they perceive and interpret racism. Furthermore, the paper sought answers on whether respondents have been unconscious or conscious strategies to manage or respond to racism. It has since been made a comparison to see if it differs depending on whether respondents grew up in Sweden or not. The result shows that all respondents, regardless of group, experience racism and get their Swedishness questioned. The biggest differences between the two groups lies in how respondents choose to deal with the racism they encounter. The group of respondents who grew up in Sweden chooses to confront the racism they face while the group of respondents who didn’t grow up in Sweden are more inclined to deal with or escape it.

Syftet med studien är att undersöka hur samerna respektive den nordamerikanska ursprungsbefolkningen framställs i samtida historieläroböcker för gymnasiets senare historiekurser. Det som undersökts är hur de två ursprungsfolkens historia och kulturmöten framställs i relation till vad som står i Gy11:s läroplan. Den använda metoden är Norman Faircloughs kritiska diskursanalys integrerat med Homi Bhabhas postkoloniala teori. Faircloughs metod belyser maktförhållanden i texten och Bhabhas teori klarlägger hur dessa maktförhållanden ter sig. Resultatet visar att det förekommer maktdiskurser i samtliga undersökta läroböcker. I vissa av böckerna finns ett tydligt ”vi och dem” perspektiv, där de två ursprungsfolken framställs som ”dem”. När urfolken väl nämns i läroböckerna nämns de kort och utan vidare problematisering, vilket gör att eleverna inte ges den kunskap om ursprungsfolk som läroplanen uttrycker. Dessutom nämns de alltid i relation eller åtskillnad från nationalstaten, aldrig enskilt. Resultatet överensstämmer med tidigare forskning inom området, vilket tyder på att varken samernas eller den nordamerikanska ursprungsbefolkningen ges något vidare utrymme i den svenska historieskrivningen på gymnasiet.

M. Tech (Department of Chemistry, Faculty of Applied and Computer Sciences) Vaal University of Technology. / Macadamia activated carbon (MAC) was impregnated with different concentrations of nitric acid and heated under reflux to improve the structural characteristics of the adsorbent for both considerable reduction and enhanced removal of Cr(VI). The chemical oxidation of ACs increased the surface oxygenated functional groups. Adsorption of Cr(VI) was carried out by varying parameters such as contact time, pH, concentration, and adsorbent dosage. The optimum operating conditions for the adsorption of Cr(VI) were pH 1, contact time 240 min, adsorbent dosage 10.67 g/L and Cr(VI) concentration 100 mg/L. The results showed that the Macadamia–based AC could be used efficiently for the treatment of chromium-containing solutions as a low-cost alternative compared to commercial AC and other adsorbent reported. The results showed that treated MAC performed better than untreated MAC, signifying the effect of secondary treatment on the enhanced removal of pollutants. Comparable to the application of ACs is the development of imprinting technologies for selective metal ion remediation in environmental samples. The combination of ion imprinting effects and functionalized carbon adsorbents produce materials which effectively remove and selectively recognize the target analyte. Macadamia activated carbon (MAC) was chemically pre-treated with nitric acid to generate carboxyl groups on the surface. The carboxylated MAC was then reacted with triethylenetetramine, N,N’-diisopropylcarbodiimide and CrCl3.6H2O to produce MACN20-imprinted sorbents (MACN20-IIP). MACN20-non imprinted (MACN20-NIP) counterparts were prepared, but Cr3+ was excluded in the synthesis. Alteration of surface structural characteristics and characterization of prepared adsorbents as confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis, Brunauer–Emmett–Teller and scanning electron microscopy. MACN20-IIP and MACN20-NIP adsorbents were evaluated for their Cr3+ uptake from aqueous solution in batch format. Maximum conditions were achieved at pH 5, 50 mg/L Cr(III) initial concentration and 33.33 g/L of adsorbent dosage. Presence of co-ions slightly diminished the removal of Cr(III) by MAC-IIP adsorbents. Application of the MACN20-IIP and MACN20-NIP on spiked acid mine drainage artificial sample led to collapse in the removal efficiency of MACN20-NIP while MACN20-IIP still showed good removal efficiencies. These results demonstrated that surface imprinting led to better adsorption rates and capacity. The data was better described by the Freundlich multilayer adsorption and pseudo-second order kinetic rate model. The combination of both the carbon sorbent and the surface-mediated IIPs effectively improved total chromium remediation in aqueous systems.

M. Tech (Department of Chemistry, Faculty of Applied and Computer Sciences) Vaal University of Technology. / Agricultural waste such as Macadamia nutshells are currently receiving more attention for removal of hexavalent chromium (Cr(VI)). However, they have low adsorption capabilities when used in their raw form. In this study, the efficiency of using Macadamia nutshell powder modified with different concentrations of hydrogen peroxide, grafted with 1,5’-diphenylcarbizide (DPC) for the removal of hexavalent chromium from aqueous solution was explored. The effects of various parameters controlling adsorption of Cr(VI) onto Macadamia adsorbents such as initial concentration, contact time, adsorbent concentration and pH were investigated. The optimal operating parameters for Macadamia nutshells treated with hydrogen peroxide (MHP) adsorbents were determined to be 75 mg/L, 3 h, 0.1 g and pH 1. The optimal operating parameters for Macadamia nutshells treated with hydrogen peroxide and grafted with 1,5’-diphenylcarbizide (MHPD) were determined to be 150 mg/L, 1 h, 0.1 g and pH 3. Fourier transform infrared (FTIR) spectroscopy of the adsorbents revealed that treated MHP showed amino groups attached to the adsorbents. Thermogravimetric analysis (TGA) revealed that the grafted material lowered the thermal stability from 180◦C to 300◦C due to volatile nature of DPC. The surface of the MHPD materials was rough due to grafting. The results showed that the 1,5’-diphenylcarbazide treatment improved the removal efficiency of Cr(VI).

An indigenous mixed culture of bacteria collected from a Wastewater Treatment Plant (Brits, North West Province, South Africa), biocatalytically reduced Cr(VI) in the presence of As(III). Both the reduced chromium (Cr(III)) and the oxidised arsenic (As(V)) readily form amorphous hydroxides that can be easily separated or precipitated from the aqueous phase as part of the treatment process. Treatment of Cr(VI) and As(III) before disposal of wastewater is critical since both compounds are known to be carcinogenic and mutagenic at very low concentrations, and acutely toxic at high concentrations. Batch experiments were conducted to evaluate the rate of Cr(VI) reduction under anaerobic condition in the presence of its co-contaminant As(III) typically found in the groundwater and mining effluent. Results showed near complete Cr(VI) reduction under initial Cr(VI) concentrations up to 70 mg/L in a batch amended with 20 mg/L As(III). However, increasing Cr(VI) concentrations up to 100 mg/L resulted in the inhibition of Cr(VI) reduction activity. Further investigation was conducted in a batch reactor amended with 70 mg/L Cr(VI) concentration at different As(III) concentrations ranging from 5-70 mg/L to evaluate the effect of varying As(III) concentration on Cr(VI) reduction efficiency. Results showed that Cr(VI) reduction efficiency increased as As(III) concentrations increased from 5-40 mg/L. However, further increase in As(III) concentration up to 50 mg/L resulted in incomplete Cr(VI) reduction and decrease in Cr(VI) reduction efficiency. These results suggest that the rate of Cr(VI) reduction depends on the redox reaction of As(III) and As(V) with Cr(VI). Moreover, the inhibitory effect observed at high Cr(VI) and As(III) concentration may also be attributed to the dual toxicity effect of Cr(VI) and As(III) on microbial cell. From the above batch kinetic studies lethal concentration of Cr(VI) and As(III) for these strains was evaluated and established. Initial evaluation of the bacteria using 16S rRNA partial sequence method showed that cells in the mixed culture comprised predominantly of the Gram-positive species: Staphylococcus sp., Enterobacter sp., and Bacillus sp. The biokinetic parameters of these strains were estimated using a non-competitive inhibition model with a computer programme for simulation of the Aquatic System “AQUASIM 2.0”. Microbial reduction of Cr(VI) in the presence of As(III) was further investigated in continuous-flow bioreactors (biofilm reactor) under varying Cr(VI) loading rates. The reactor achieved Cr(VI) removal efficiency of more than 96 % in the first three phases of continuous operation at lower Cr(VI) concentration ranging from 20-50 mg/L. However, 20 % decrease in Cr(VI) removal efficiency was observed as Cr(VI) concentration increase up to 100 mg/L. The reactor was able to recover from Cr(VI) and As(III) overloading phase after establishing the resilient nature of the microorganism. Similarly to the batch reactor studies the overall performance of the reactor also demonstrated that the presence of As(III) greatly enhance Cr(VI) reduction in a bioreactor. This was evident by near complete removal of Cr(VI) concentration up to 50 mg/L. The basic mass balance expressions on Cr(VI) along with the non-competitive inhibition model were used to estimate the biokinetic parameters in the continuous flow bioreactor system. Cr(VI) reduction efficiency along the longitudinal column was also evaluated in this study. Results showed that Cr(VI) efficiency increased as Cr(VI) concentration travels along the longitudinal column. Other important factors such as oxygen and pH during biological Cr(VI) reduction in the presence of As(III) oxidation were also evaluated. / Dissertation (MEng)--University of Pretoria, 2014. / tm2015 / Chemical Engineering / MEng / Unrestricted